GC10

GC10-Pliocene
The warm Pliocene: Bridging the geological data and modelling communities
Orals
| Wed, 24 Aug, 09:30–21:00 (BST)|Room Headingley Suite, Thu, 25 Aug, 09:00–21:00 (BST)|Room Headingley Suite, Fri, 26 Aug, 09:00–15:00 (BST)|Room Headingley Suite
Posters
| Attendance Wed, 24 Aug, 14:30–16:00 (BST)|Poster area Session A, Attendance Thu, 25 Aug, 10:30–11:30 (BST)|Virtual poster area Session B, Attendance Thu, 25 Aug, 15:30–17:00 (BST)|Poster area Session C

Orals: Wed, 24 Aug | Room Headingley Suite

Chairperson: Aisling Dolan
09:30–10:00
Session 1: Overview of the Pliocene
10:00–10:15
10:15–10:30
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GC10-Pliocene-52
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invited
Erin McClymont, Sze Ling Ho, Heather Ford, Sarah White, Jeroen Groenveld, Clara Bolton, Kau Thirumalai, Georgia Grant, Molly Patterson, Montserrat Alonso-Garcia, and Babette Hoogakker

The Pliocene epoch (~2.6-5.3 million years ago) is one of the best resolved examples of a climate state in long-term equilibrium with current or predicted near-future atmospheric CO2 concentrations, characterised by a globally warmer climate, reduced continental ice volume, and reduced ocean/atmosphere circulation intensity compared to today. Towards the end of the Pliocene, there was a marked increase in glaciation in the northern hemisphere and atmospheric CO2 concentrations declined.

The Past Global Changes (PAGES) PlioVAR working group aimed to co-ordinate a synthesis of terrestrial and marine data to characterise spatial and temporal variability of Pliocene climate, underpinned by high quality data sets supported by robust stratigraphies. Here we present some of the main findings of this synthesis effort, including new assessments of ocean temperatures during the KM5c interglacial, and recent work assessing orbital-scale climate variability across the late Pliocene-early Pleistocene northern hemisphere ice-sheet growth. We outline our approaches to integrating multi-proxy data recording ocean temperatures, d18O and sea-level variability from a globally distributed suite of marine sediment cores. We explore regional expressions of environmental change across this transition, identifying asynchronous trends and patterns in climate changes. We consider how these results might inform our understanding of past climate forcings and feedbacks during both warm intervals of the past and the development of larger ice sheets in the northern hemisphere.

How to cite: McClymont, E., Ho, S. L., Ford, H., White, S., Groenveld, J., Bolton, C., Thirumalai, K., Grant, G., Patterson, M., Alonso-Garcia, M., and Hoogakker, B.: Assessing late Pliocene climate variability over glacial-interglacial timescales (PlioVAR), The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-52, https://doi.org/10.5194/egusphere-gc10-pliocene-52, 2022.

10:30–10:45
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GC10-Pliocene-64
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invited
Alan Haywood

Since 2008 PlioMIP participants have fundamentally transformed our understanding of Pliocene climates and environments. In this presentation we will review some of the most significant highlights and milestones of PlioMIP, including our changing appreciation of large-scale climate features, meridional and zonal temperature gradients, atmospheric and oceanic circulation, polar amplification, and monsoon behaviour. We will examine recent studies that have sought to better understand climate and environmental feedbacks in a warmer world, as well as quantifying Climate Sensitivity. These achievements will be placed into the broader context of Pliocene climate and environmental literature in order to help identify significant scientific challenges and opportunities which remain to be explored.

How to cite: Haywood, A.: Scientific Outcomes of the Pliocene Model Intercomparison Project: An Overview , The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-64, https://doi.org/10.5194/egusphere-gc10-pliocene-64, 2022.

10:45–11:00
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GC10-Pliocene-24
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invited
Harry Dowsett

The evolution of PlioMIP  (Pliocene Model Intercomparison Project) marine data-model comparisons (DMC) is closely coupled with the historical development of PRISM (Pliocene Research, Interpretation and Synoptic Mapping) paleoenvironmental reconstructions. Chronology, correlation, mode of reconstruction, availability and type of proxy estimates, boundary condition choices, and model development, have all played significant roles in refining DMC. A brief history of the collaboration between disciplines provides insight into the comparison of proxy-based sea surface temperature estimates with model results. In particular, I stress the importance of large-scale gradients and regional indicators of climate over locality-based comparisons. Lessons learned from both the data and modeling communities may offer guidance for future PlioMIP3 DMC efforts.

How to cite: Dowsett, H.: Late Pliocene sea–surface temperature data–model comparisons: A historical perspective., The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-24, https://doi.org/10.5194/egusphere-gc10-pliocene-24, 2022.

Break (11:00–11:30)
Chairperson: Heather L. Ford
Session 2: Global Reconstructions and Ice Processes
11:30–11:45
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GC10-Pliocene-67
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invited
Dan Lunt, Alan Haywood, and Darrell Kaufman

In the most recent IPCC assessment report (AR6), lines of evidence associated with paleoclimate were distributed throughout the report.  The Pliocene played a key role in Chapter 2 in terms of providing a benchmark against which recent and future changes could be measured, and in Chapter 7 in terms of model-data comparison and constraining climate sensitivity, in Chapter 9 in terms of sea level change, and also appeared in multiple other chapters.  Here, I will summarise some of these contributions, and also look forward to ways in which the Pliocene community can contribute to AR7.

How to cite: Lunt, D., Haywood, A., and Kaufman, D.: The Pliocene in the IPCC: AR6 and thoughts on AR7I, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-67, https://doi.org/10.5194/egusphere-gc10-pliocene-67, 2022.

11:45–12:00
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GC10-Pliocene-16
James Annan, Julia Hargreaves, and Thorsten Mauritsen

We present a new reconstruction of global climatological temperature fields for the mid-Pliocene Warm Period.

The method combines globally complete modelled temperature fields, with sparse proxy-based estimates of local temperature anomalies. We use the full set of PlioMIP and PlioMIP2 model simulations, and the proxy-based SST estimates of of Haywood et al 2020 (time slice at MIS KM5c, 3.2Ma) to ensure the best possible global coverage. 

We perform some initial filtering of the model simulations to remove duplicates and closely related models. We then de-bias the ensemble (relative to the proxy data) and show via sensitivity tests that this can be an essential step in the process. Specifically, any bias in the prior ensemble leads to a significant bias (which may take roughly 70-80% of its initial magnitude) in the posterior estimate. Thus we recommend that this step is taken in similar reconstructions unless the researcher is confident that the bias in the prior ensemble is low relative to likely bias in interpretation of proxy data.

The assimilation method is a localised Ensemble Kalman Filter, which ensures spatially coherent fields that both respect the physical principles embodied in the models, and are also tied closely to observational estimates. This method takes the processed ensemble of models to represent our prior uncertainty, and updates it with observational estimates arising from the proxy data. Thus, in areas where proxy data are sparse and/or highly uncertain, our result is still described by the spread of model results. However, accurate proxy data can improve the estimate over a local region. Our reconstruction has a global mean surface air temperature anomaly of + 4.7 +- 1C relative to the pre-industrial climate.

How to cite: Annan, J., Hargreaves, J., and Mauritsen, T.: A new global climate reconstruction for the mid-Pliocene Warm Period., The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-16, https://doi.org/10.5194/egusphere-gc10-pliocene-16, 2022.

12:00–12:15
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GC10-Pliocene-48
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ECS
james o'neill, Tamsin Edwards, and Lauren Gregoire

Reconstructions of warm Pliocene sea level imply a large but uncertain contribution from the Antarctic ice sheet. Their high end implies collapse of the West Antarctic ice sheet, and mass loss from East Antarctic subglacial basins. Previous work has suggested that extensive East Antarctic retreat is facilitated by the marine ice cliff instability – where loss of ice shelves and mechanical failure of unbuttressed cliffs drives retreat. We explored the Antarctic ice sheet under warm Pliocene climate using BISICLES, a relatively higher-order physics ice sheet model, capable of simulating grounding line and ice stream dynamics at relatively high resolution. We used perturbed parameter ensemble experiments to explore uncertainty in Pliocene Antarctic retreat, without the marine ice cliff instability. We simulated the most dynamic regions of the ice sheet at relatively high resolution, down to 4 km in ice streams and at the grounding line . To explore uncertainties in basal sliding, surface mass balance processes, bedrock-ice sheet interactions and ice shelf basal melt sensitivity to ocean forcing, we ran a 120-member Latin Hypercube perturbed parameter ensemble. Climate forcing was based on results from four different PlioMIP2 climate models, which the ensemble was evenly divided across. This allowed us to explore the role of climate model choice in simulated Pliocene Antarctic configuration. Additional experiments explored parametric uncertainty under a modern climate, and initial condition uncertainty. We compared ensemble results to a reconstructed Pliocene sea level range, as well as geochemical provenance based reconstructions of grounding line retreat into the Wilkes subglacial basin (East Antarctica) – which some ensemble members successfully reproduced. We simulated a large Antarctic sea level contribution range, which was wider than the reconstructed Pliocene sea level contribution range. Moreover, simulated sea level contribution was highly sensitive to a perturbed basal sliding parameter. We show that our modelling framework can simulate the magnitude and location of Pliocene Antarctic mass loss consistent with proxy-based reconstructions under some modelling choices, however uncertainties remain in the representation of basal sliding.

How to cite: o'neill, J., Edwards, T., and Gregoire, L.: Modelling the Antarctic ice sheet under warm Pliocene climates, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-48, https://doi.org/10.5194/egusphere-gc10-pliocene-48, 2022.

12:15–12:30
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GC10-Pliocene-51
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ECS
Javier Blasco, Ilaria Tabone, Daniel Moreno, Jan Swierczek-Jereczek, Antonio Juarez-Martinez, Sergio Perez-Montero, Alexander Robinson, Jorge Alvarez-Solas, and Marisa Montoya

Due to anthropogenic global warming since the pre-industrial era, sea level has been rising along with global temperature. This sea-level rise is due to thermal expansion of the ocean and melting of mountain glaciers and continental ice sheets, mainly Greenland (GrIS) and Antarctica (AIS). The latter are the potential largest contributors as they store a total amount of 63 meters of sea-level rise in the form of ice. Modelling studies agree that these ice sheets will melt more in the future, however results differ due to associated uncertainty in representing several physical processes, as well as in assessing warming projections. Past warm scenarios can help to elucidate this uncertainty as we can obtain information, such as the sea-level standings, the ice extension from continental ice sheets and infer global temperatures from proxy records. The mid-Pliocene warm period (3.3-3.0 million years ago) offers an ideal benchmark, as it is the most recent period with CO2 levels comparable to the present-day (PD; 350-450 ppmv), although showing global mean temperatures 2.5-4.0 degrees higher. The inferred sea-level reconstructions from that period estimate a sea level standing of 15-20 meters higher than PD. Whereas the modern GrIS was starting to form, the AIS was restricted to its eastern region due to warm oceanic temperatures. The Pliocene Model Intercomparison Project, Phase 2 (PlioMIP2) has brought together various climate outputs from different general circulation models to elucidate the pliocene climate conditions. Here we force a higher-order ice sheet model with these climatic outputs at a high spatial resolution. Our aim is to investigate how polar continental ice sheets respond to these different climatic fields and to infer tipping values that can lead these ice sheets to drastically change their topographic shape.

How to cite: Blasco, J., Tabone, I., Moreno, D., Swierczek-Jereczek, J., Juarez-Martinez, A., Perez-Montero, S., Robinson, A., Alvarez-Solas, J., and Montoya, M.: The Antarctic and Greenland Ice Sheet configuration at the warm Pliocene, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-51, https://doi.org/10.5194/egusphere-gc10-pliocene-51, 2022.

Lunch (12:30-13:30)
Chairperson: Lina Perez
Session 3: Global Reconstructions and Hydroclimate I
13:30–13:45
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GC10-Pliocene-13
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ECS
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invited
Ran Feng and Tripti Bhattacharya and the PlioMIP2 colleagues

Despite tectonic conditions and atmospheric CO2 levels (pCO2) similar to those of present-day, geological reconstructions from the mid-Pliocene (3.3-3.0 Ma) document high lake levels in the Sahel and mesic conditions in subtropical Eurasia, suggesting drastic reorganizations of subtropical terrestrial hydroclimate during this interval. Here, using a compilation of proxy data and multi-model paleoclimate simulations, we show that the mid-Pliocene hydroclimate state is not driven by direct CO2 radiative forcing but by a loss of northern high-latitude ice sheets and continental greening. These ice sheet and vegetation changes are long-term Earth system feedbacks to elevated pCO2. Further, the moist conditions in the Sahel and subtropical Eurasia during the mid-Pliocene are a product of enhanced tropospheric humidity and a stationary wave response to the surface warming pattern, which varies strongly with land cover changes. These findings highlight the potential for amplified terrestrial hydroclimate responses over long timescales to a sustained CO2 forcing.

How to cite: Feng, R. and Bhattacharya, T. and the PlioMIP2 colleagues: Past terrestrial hydroclimate sensitivity controlled by Earth System Feedbacks, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-13, https://doi.org/10.5194/egusphere-gc10-pliocene-13, 2022.

13:45–14:00
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GC10-Pliocene-57
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ECS
Monika Markowska, Hubert B. Vonhof, Huw Groucutt, Michael D. Petraglia, Denis Scholz, Michael Weber, Axel Gerdes, Ashley N. Martin, and Gerald Haug

The global development and modern distribution of arid zones in subtropical regions (drylands) are likely associated with the global cooling marking the dawn of the Quaternary (~2.6 Ma). This coincides with global shifts in ocean circulation patterns, the intensification of the Walker-Hadley circulation, declining atmospheric CO2, the initiation of glacial–interglacial cycles and the intensification of Northern Hemisphere glaciation, the combination of which has led to the current global distribution of non-polar deserts at ~30° latitude. Although modern drylands represent Earth’s largest terrestrial biome, covering ~46% of global land surfaces and supporting a global population of ~3 billion people, it is currently unclear how drylands will change under future climate change scenarios.

 

Speleothems, preserved in arid-zone caves, are particularly useful terrestrial climate archives as they act as underground rain gauges, which require a minimum of ~300 mm a-1 precipitation, pedogenesis and vegetation cover to form. Moreover, they can be accurately and precisely dated and are subsequently a valuable tool in identifying past large-scale hydrological and vegetation changes in ancient drylands. Here, we present new data from speleothems during past ‘warm periods’ from the Arabian hyper-arid zone. We apply a novel technique of extracting speleothem fluid inclusions waters to reconstruct the isotopic composition (d18O and d2H) of ‘fossil rainwater’ preserved in the speleothem fabric pristinely over millions of years. Speleothem evidence suggests that during the last 7 million years, the Sahara-Arabian desert experienced numerous intermittent humid phases, typically occurring with periods of low global ice-volume and warmer global temperatures. We further explore tropical push-pull mechanisms driving heating of the deep tropics and subsequent expansion of the tropical zone and synchronicity of humid phases regionally. These results have significant implications for understanding the drivers of dryland aridity in non-polar deserts globally. 

How to cite: Markowska, M., Vonhof, H. B., Groucutt, H., Petraglia, M. D., Scholz, D., Weber, M., Gerdes, A., Martin, A. N., and Haug, G.: Terrestrial hydroclimate reconstructions of ‘fossil rainwater’ from Arabian arid-zone speleothems , The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-57, https://doi.org/10.5194/egusphere-gc10-pliocene-57, 2022.

14:00–14:15
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GC10-Pliocene-50
Anya Crocker, Amy Jewell, Bryce Mitsunaga, Solana Buchanan, Thomas Westerhold, Ursula Röhl, James Russell, Timothy Herbert, and Paul Wilson

The Sahel region is one of the most vulnerable regions on Earth to anthropogenically-driven climate change, but also one of the least equipped to deal with the consequences. Predictions of precipitation levels over the forthcoming centuries diverge, not only in magnitude, but also in the sign of change. One key aspect of this uncertainty comes from the role of Atlantic Ocean sea surface temperatures (SST), which are known to exert a strong control over precipitation in the Sahel and are implicated in both the major drought of the late 20th century and extreme droughts associated with the Heinrich events of the last glacial. To better understand how Sahelian hydroclimate may respond to SST variability in a warmer world, we turn to the Pliocene epoch, when atmospheric CO2 levels were comparable to present.

 

We studied sediments from Ocean Drilling Project Site 659, which is situated in the subtropical North Atlantic beneath the major modern summer Saharan dust plume. Our dust accumulation and X-ray fluorescence core scan data indicate that there were major shifts between highly arid conditions and humid intervals with vegetated or “Green Sahara” conditions over much of northern Africa, driven by both solar insolation and glacial-interglacial variability. We also report three unusually long Plio-Pliocene humid intervals (each lasting ca. 100 kyr), characterised by very low dust emissions, that we term “Green Sahara Megaperiods (GSMPs)”. All three of these GSMPs occur at times when insolation variability was weak resulting in values close to the long-term mean. This observation strongly suggests that factors other than insolation drove the sustained humidity of GSMPs. We present paired alkenone SST estimates and multi-species planktonic foramaniferal isotope records from 3.5–2.3 Myr ago to explore the extent to which the GSMPs were accompanied by intervals of extended warmth in the surface waters of the North Atlantic Ocean.

How to cite: Crocker, A., Jewell, A., Mitsunaga, B., Buchanan, S., Westerhold, T., Röhl, U., Russell, J., Herbert, T., and Wilson, P.: Green Sahara (Mega)periods during the Pliocene: What was the role of North Atlantic Ocean temperature?, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-50, https://doi.org/10.5194/egusphere-gc10-pliocene-50, 2022.

14:15–14:30
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GC10-Pliocene-3
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ECS
Scott Knapp, Natalie Burls, Sylvia Dee, Ran Feng, Sarah Feakins, and Tripti Bhattacharya

The Pliocene epoch offers insights into future climate change, with near-modern atmospheric pCO2 and global mean surface temperature estimated to be 3-4°C above pre-industrial. The discrepancy in the hydrological response seen between simulations of future global warming and early Pliocene simulations is hypothesized to result from reduced SST gradients in the early Pliocene. However, the interpretation of Pliocene SST proxies is still debated, generating uncertainty about the reduced gradient scenario. One avenue toward reducing uncertainty in Pliocene warming patterns is to establish the degree of dynamical consistency between Pliocene SST reconstructions and hydrological cycle reconstructions. To this end, hydrological cycle reconstructions are needed in regions where water isotopic signals are predicted to be uniquely sensitive to Pliocene SST gradient changes. Here, we seek to identify these regions using an isotope-enabled GCM, iCAM5, to model the distribution of water isotopes in precipitation in response to four climatological SST and sea-ice fields representing modern, abrupt 4xCO­­2, late Pliocene and early Pliocene climates. We identify two regions with distinct precipitation isotope fingerprints resulting from early Pliocene SST gradients. The first region, the Indo-Pacific warm pool, is characterized by isotopic enrichment due to weakened convection and a reduced amount effect. The second region, the Sahel, is characterized by isotopic depletion due to more intense and widespread precipitation. A model-proxy comparison with available precipitation proxies in Africa provides promising initial results. However, additional proxy reconstructions are needed in both target regions to provide robust tests of dynamical consistency with current early Pliocene SST reconstructions.

How to cite: Knapp, S., Burls, N., Dee, S., Feng, R., Feakins, S., and Bhattacharya, T.: Isotopic Fingerprints of Early Pliocene-like Sea Surface Temperature Gradients, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-3, https://doi.org/10.5194/egusphere-gc10-pliocene-3, 2022.

Poster session A (14:30–16:00)
Chairperson: Lauren Burton
Session 4: Global Reconstructions and Hydroclimate II
16:00–16:15
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GC10-Pliocene-37
Alexey Fedorov

Debates continue on various aspects of the Pliocene climate, and Pliocene warmth in general, but there are several characteristics of this climate state on which we seem to agree, including the reduced equatorial (east-west) and reduced meridional SST gradients in the Pacific ocean relative to the modern. The actual magnitude of these reductions (in the range of 1 to 4oC) is however strongly debated, as it depends on the way the gradients are defined, particular calibrations used to estimate temperature, and specific time intervals considered. In contrast to the equatorial Pacific SST gradient, the pH gradient was probably stronger during the Pliocene, and biological productivity in the eastern equatorial Pacific was higher. In the subtropics, coastal upwelling regions were much warmer (up to 10oC). Subtropical land regions were wetter and had extensive lake systems and lush  vegetation. Arctic inland annual-mean temperatures were much warmer (by 10-20oC). The subarctic North Pacific may have sustained deep water formation leading to an active Pacific meridional overturning circulation (PMOC) at least during parts of the Pliocene, with more evidence becoming available recently. The early Pliocene was probably 1-2oC warmer, and some of these effects were more pronounced, compared to the mid-Pliocene. The Pliocene climate had atmospheric CO2 concentrations around 400ppm (with a large uncertainty and slightly higher concentrations during the early Pliocene). Several of the Pliocene climatic features appear to be consistent with each other, such as warmer coastal upwelling regions and stronger precipitation in the subtropics. Other features seem to contradict, as the reduced equatorial SST gradient, and hence a weaker Walker circulation and equatorial upwelling, versus increased productivity in the eastern equatorial Pacific. The question then arises whether these climate features are independent or closely linked and therefore have to be explained together. Here, I attempt to combine these disparate features into one holistic picture of the Pliocene climate that puts all these elements in a consistent framework, based on changes in both atmospheric and oceanic circulations, and incorporating models and data.

How to cite: Fedorov, A.: A holistic view of the Pliocene climate, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-37, https://doi.org/10.5194/egusphere-gc10-pliocene-37, 2022.

16:15–16:30
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GC10-Pliocene-55
Tim Herbert, Rocio Caballero-Gill, and Harry Dowsett

As we move beyond assessing Pliocene temperature patterns over broad time intervals (e.g. Piacenzian Warm Period), interesting questions arise as to the variability of temperatures on orbital time scales.   Did the absence of large northern hemisphere ice-albedo feedbacks lead to greatly reduced temperature variations in comparison to the Pleistocene? And would temperature variations be heterogenous regionally,  reflecting the influence of  local insolation anomalies, in contrast to the globally coordinated Pleistocene changes in temperature? We report here orbitally resolved late Pliocene (3.6-2.6 Ma) SST measurements in all ocean basins using the alkenone method.  Sites were selected based on high quality stable isotope data and/or paleomagnetic age control.  SST time series demonstrate that, to first order, ocean surface temperature changes fluctuated synchronously between high and low latitudes, and between the hemispheres.  An obliquity-related signal dominates, but  time series analysis indicates a substantial contribution from precession as well.  In the absence of a strong ice-albedo feedback in the late Pliocene, the evidence thus suggests a dominant role for greenhouse gas forcing of orbital-scale changes in temperature.

How to cite: Herbert, T., Caballero-Gill, R., and Dowsett, H.: Global Synchrony Of Late Pliocene Sea Surface Temperature Variations, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-55, https://doi.org/10.5194/egusphere-gc10-pliocene-55, 2022.

16:30–16:45
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GC10-Pliocene-9
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invited
Tripti Bhattacharya and Ran Feng

Geologic evidence suggests drastic reorganizations of subtropical terrestrial hydroclimate during past warm intervals, including the mid-Piacenzian Warm Period (MP, 3.3 to 3.0 Ma). These changes, which involved mesic conditions on subtropical continents, are at first glance at odds with theory that predicts subtropical drying in a warmer world. The mechanisms and precise patterns of regional hydroclimate during the MP remain unclear. In this talk, I show that compound specific isotopic analyses of lipid biomarkers can be used to constrain the drivers of Pliocene subtropical hydroclimate, with special focus
on ongoing in western North America and other Mediterranean regions. Our results show that regional SST patterns play a key role in determining Pliocene subtropical hydroclimate. Moreover, we are able to identify similarities between Pliocene hydroclimate and current patterns of hydroclimate variability and change in subtropical regions, suggesting that the Pliocene can serve as an analog for understanding hydroclimate responses to anthropogenic warming.

How to cite: Bhattacharya, T. and Feng, R.: Molecular perspectiveson Pliocene subtropical hydroclimate, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-9, https://doi.org/10.5194/egusphere-gc10-pliocene-9, 2022.

Break (16:45–17:00)
17:00–18:00
Our ECR activity is an informal, friendly space for ECRs to meet and discuss their research. We will break out into small themed groups where you will have the opportunity to briefly introduce yourself and your work, and then mingle with other ECRs.
19:00–21:00

Orals: Thu, 25 Aug | Room Headingley Suite

Chairperson: Erin McClymont
Planning for the Future
Session 5: Regional Reconstructions and Future Directions
09:00–09:15
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GC10-Pliocene-25
Hannah Donald, George Swann, and Gavin Foster

The intensification of Northern Hemisphere glaciation (iNHG) at 2.73 Ma is associated in the subarctic Pacific Ocean with an abrupt drop in opal mass accumulation rates and the development of a halocline stratification. Uncertainty, however, remains around the extent to which these changes: 1) altered carbon dynamics in the water column; and 2) contributed to a reduction in atmospheric pCO2 over this period. These issues can be resolved by applying the boron isotope (δ11B) proxy to quantify past changes in the pH and pCO2 of ambient seawater. By analysing δ11B in diatom frustules, we document a surface water increase of 0.3 to 0.5 pH units in the subarctic Pacific Ocean over the iNHG. This confirms that the development of the halocline at 2.73 Ma both reorganised the vertical water column structure and limited CO2 outgassing from the ocean interior. In conjunction with other external and internal processes, including changes in the Southern Ocean, these events would have contributed to a lowering of atmospheric pCO2 and the long-term expansion of ice sheets across the Northern Hemisphere.

This research demonstrates the potential for diatom δ11B measurements to be used to reconstruct changes in pCO2, particularly in high-latitude settings where diatom frustules are readily preserved and dominate the sediment record. Such analyses have the potential to complement δ11B measurements in foraminifera and so provide further insights into the carbon dynamics of the “warm Pliocene” and other periods of interest.

How to cite: Donald, H., Swann, G., and Foster, G.: Carbon dynamics in the subarctic Pacific Ocean - diatom δ11B insights into the past, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-25, https://doi.org/10.5194/egusphere-gc10-pliocene-25, 2022.

09:15–09:30
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GC10-Pliocene-5
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ECS
Jinrong Gan, Kate Littler, Pallavi Anand, Melanie J. Leng, and Marci M. Robinson

The Indian summer monsoon (ISM) is a critical component of the overarching Asian monsoon system, which dominates seasonal rainfall patterns over the region. The underlying mechanisms controlling monsoon variability include internal forcings (e.g., ice volume, ocean circulation) and external forcings (e.g., solar insolation), operating over a range of time scales from tectonic to decadal. While there is now considerable data from regions dominated by the SE Asian monsoon, there remains a significant data gap for the regions affected by the Indian monsoon, particularly prior to the late Pleistocene. Many unknowns remain regarding the response of ISM to past changes in global climate, such as during the intensification of Northern Hemisphere glaciation in the late Pliocene (~2.5–3.5 Ma). Key questions centre on the role of external vs. internal forcing at controlling both long-term and orbital-scale monsoon variability, and whether wind and rainfall responses were coupled during these transitions. 
Here, we present a high resolution (~4 kyr), benthic oxygen isotope age model spanning from ~2.4 to 4.0 Ma for IODP Site U1448 in the Andaman Sea. This record allows us to interrogate (X-ray fluorescence) bulk elemental data from the same core to reconstruct past ISM behaviour across this enigmatic interval. Trends in elemental ratios representing terrestrial runoff and marine productivity (linked to ISM strength) show both long-term evolution in response to changing boundary conditions, and the influence of orbital forcing. Additionally, high resolution benthic carbon isotope data allows us to track changes in both water mass and marine productivity associated with orbital-scale variability in this region. Comparison of this data with comparable data from IODP Site U1445 in the NW Bay of Bengal allow us to examine spatial and temporal trends in ISM strength during the Pliocene, and identify changing loci of dominant precipitation across this region with time.

How to cite: Gan, J., Littler, K., Anand, P., J. Leng, M., and M. Robinson, M.: Orbital scale variability and evolution of the Indian Monsoon during the Pliocene: new data from the Andaman Sea, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-5, https://doi.org/10.5194/egusphere-gc10-pliocene-5, 2022.

09:30–09:45
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GC10-Pliocene-10
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ECS
Xin Ren, Erica Hendy, and Dan Lunt

The Maritime Continent (MC) forms the western boundary of the tropical Pacific Ocean, and relatively small changes in this region could impact the climate locally and remotely. In the mid-Pliocene (3.264 Ma and 3.025 Ma BP), atmospheric CO2 concentrations were ∼ 400 ppm, and the subaerial Sunda and Sahul shelves made the land-sea distribution of the MC different to today. These two effects, combined with other forcings, are therefore expected to have driven a substantial climate signal in MC region. By using the results the Pliocene Model Intercomparison Project phase 2 (PlioMIP2) we study the mean climatic features of the MC in the mid-Pliocene, and the changes in Indonesian Throughflow (ITF). Results show a warmer and wetter climate of the MC and lower sea surface salinity. Another feature is enhanced easterlies over the western tropical Pacific Ocean which may result from the westward shift of the Pacific Walker Circulation and the intensified Southern Hemisphere Subtropical High pressure system. Furthermore, we quantify the volume transfer through the ITF; although the ITF may be expected to be hindered by the subaerial shelves, 7 out of 9 models show an increased volume transport.
In order to avoid undue influence from closely-related models, we introduce a new metric - the multi-cluster mean (MCM), based on cluster analysis of the individual models. We compare the MCM to the more traditional multi-model mean (MMM) and individual models by quantifying the discrepancy between model results and reconstructed proxy data. The result shows that the MCM can reproduce sea surface temperature better than more than half of the PlioMIP2 models in both the pre-industrial experiment and the mid-Pliocene experiment. The clusters include spatial signals that are not captured by the MMM, so the MCM  provides us with a new way to illustrate the results from multiple models.

How to cite: Ren, X., Hendy, E., and Lunt, D.: The hydrological cycle of the Maritime Continent in the mid-Pliocene: results from PlioMIP2, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-10, https://doi.org/10.5194/egusphere-gc10-pliocene-10, 2022.

09:45–10:00
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GC10-Pliocene-12
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ECS
Gabriel M. Pontes and the PlioMIP and invited authors

One of the most remarkable features of the mid-Pliocene climate is the polar amplified warming, which occurred at a higher magnitude in the Northern than that in Southern Hemisphere. In this study, we use the PlioMIP models, including phases one and two, to investigate how the differing rates of warming between Hemispheres affect the Southern Hemisphere climate. Through energetic constraints for the position of the Inter-Tropical Convergence Zone (ITCZ), we find that there is a consistent northward shift of the ITCZ in the mid-Pliocene, which is accompanied by intensified low-level wind circulation in the tropical and subtropical Southern Hemisphere. We show that these changes in the atmospheric circulation drive weakened South American Monsoon and South Atlantic and Pacific Convergence Zones. Additionally, we find that the mean state changes create unfavorable conditions to the development of the main tropical modes of SST variability in the Pacific and Atlantic oceans. More precisely, a northward ITCZ shift and intensified southeasterly trades winds in the equatorial Pacific reduce the probability of occurrence of extreme El-Niño events in the eastern Pacific. In the Atlantic Ocean, the ITCZ shift weakens the northeasterly trades along the African coast reducing the activity of the Atlantic Meridional Mode. Thus, the PlioMIP simulations allowed us to identify key mechanisms for important climate features under a warmer scenario.

How to cite: Pontes, G. M. and the PlioMIP and invited authors: PlioMIP models shed light on key Southern Hemisphere processes, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-12, https://doi.org/10.5194/egusphere-gc10-pliocene-12, 2022.

10:00–10:15
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GC10-Pliocene-66
Heather L. Ford

For decades the mid-Pliocene warm period has been a data-model comparison target (PlioMIP, PlioVAR, PRISM). During the mid-Pliocene warm period (~3.2 Ma), global temperatures are estimated to be ~2.3°C warmer than today and atmospheric CO2 is estimated at ~350-400. However, as modern atmospheric concentrations rise above 410 ppm, it is increasingly necessary to expand our efforts to other periods of sustained warmth. There is community interest in expanding into the Miocene (~23.03 to 5.33 Ma) when atmospheric CO2 was ~600 ppm. Additionally, the ice sheet expansion and cooling of the mid-Miocene Climate Transition presents another opportunity to study threshold climate changes and forcing mechanisms, much like the Northern Hemisphere Glaciation during the Pliocene, a PlioVAR scientific objective.  Launching the MioPlioVAR Working Group will provide a framework for sharing best practices in community-wide engagement, database building and data-model comparison.

The MioPlioVAR Working Group has three main goals. The first is to maintain the existing PlioVAR database and expand to the Miocene by synthesizing climate records and including age model quality metadata. This will help identify the Miocene target for data-model comparison (likely the Miocene Climate Optimum) and identify gaps in our current Miocene paleoclimate records (temporal resolution, spatial coverage, proxy confidence). The second is to explore new data-model comparison studies to characterize climate variability including transient model simulations and coupled models with biogeochemistry. The third is to compare the long-term evolution of Pliocene and Miocene climate and consider forcing mechanisms like tectonic gateways or CO2.

How to cite: Ford, H. L.: Expanding PlioVAR to PlioMioVAR, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-66, https://doi.org/10.5194/egusphere-gc10-pliocene-66, 2022.

10:15–10:30
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GC10-Pliocene-61
Alan Haywood, Lauren Burton, Aisling Dolan, Harry Dowsett, Tamara Fletcher, Daniel Hill, Stephen Hunter, and Julia Tindall

The Pliocene Model Intercomparison Project (PlioMIP) is one of the most successful MIPs in palaeoclimatology. Over two phases since 2008, PlioMIP has co-ordinated the experimental design and publication strategy of the community, which has included an increasing number of climate models and modelling groups from around the world. It has engaged with the palaeo-data community in order to foster new data synthesis, supporting the construction of new model boundary conditions as well as to facilitate new data/model comparisons.

Given the long implementation period for a new phase it is necessary to define the broad parameters of PlioMIP3 now. Here we present different potential components of a new science plan. This incorporates feedback gained from PlioMIP participants following the online PlioMIP2 showcase event in 2021.

PlioMIP3 will continue to have balanced scientific portfolio across both Pliocene for Pliocene and Pliocene for Future agendas. It will continue to carefully consider the competing demands of the overall effort required to complete experiments, and to be a part of the project, versus having the ability to introduce new and existing elements to enhance scientific exploration and understanding of the Pliocene.

We propose the retention of the PlioMIP2 core experiment (Eoi400), but an extension to Core requirements to include either (or both) an experiment focussed on the Early Pliocene, or an alternative Eoi400 simulation. These additions will (a) allow an intercomparison of Early and Late Pliocene warm intervals and help build research connections and synergies with the MioMIP project, and (b) through removal of some of the largest palaeogeographic differences introduced between the PlioMIP2 and 1 (the closure of the Bering Strait and Canadian Archipelago and the exposure of the Sahul and Sunda Shelves), create a time slice simulation for 3.205 Ma (MIS KM5c) with minimal palaeogeographic variations from the modern. This will enhance the palaeo to future scientific connection, and enable an exploration of the significance of palaeogeographic uncertainties on climate simulations.

In addition, we propose a number of optional experiments across 2 tiers of additional activity that incorporate simulations designed to enhance our understanding of Climate Sensitivity, as well as incorporating the radiative forcing potentially stemming from non-CO2 greenhouse gases. For the first time, we have introduced orbital sensitivity experiments into the science plan examining both Northern Hemisphere minimum and maximum insolation forcing, as well as a specific simulation using dynamic vegetation models. Finally, we have proposed an experiment designed to examine the potential significance of East Antarctic Ice Sheet boundary condition uncertainty, which would help inform a new phase of the Pliocene Ice Sheet Model Intercomparison Project.  

How to cite: Haywood, A., Burton, L., Dolan, A., Dowsett, H., Fletcher, T., Hill, D., Hunter, S., and Tindall, J.: PlioMIP3 A Science Programme Proposal to the Community, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-61, https://doi.org/10.5194/egusphere-gc10-pliocene-61, 2022.

Virtual poster session B (10:30–11:30), Break (11:30–11:45)
11:45–12:00
12:00–12:30
Lunch (12:30–13:30)
13:30–15:00
15:00–15:30
Poster session C (15:30–17:00)
17:15–18:15
19:00–21:00

Orals: Fri, 26 Aug | Room Headingley Suite

Chairperson: Bette L. Otto-Bliesner
Session 6: Ocean Circulation and Carbon Dynamics
09:00–09:15
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GC10-Pliocene-43
Kexin Wang, Huayu Lu, Fang Lei, Carmala Garzione, and Jingjing Wang

Pliocene warmth has been used as one of the best analogues for future anthropogenic warming. How East Asian hydroclimate respond to the increased temperature during the Pliocene is still elusive. Here, we present a combined element and isotopic geochemistry study of a Red Clay and loess-paleosol sequence covering the period 4-2 Ma on the southern Chinese Loess Plateau (CLP). The Na/K ratio and CIA values indicate increased weathering intensity during the late Pliocene. Meanwhile, the stable carbon isotopic compositions of pedogenic carbonate (δ13Ccarb) show relatively negative values which are explained as enhanced soil respiration flux (SRF) along with increased vegetation density. We propose that the increased East Asian Summer Monsoon (EASM) precipitation is a primary control of increased weathering intensity and vegetation density during the late Pliocene. An overall higher SRF across the CLP during the mid-Pliocene, compared with the Holocene and the Last Glacial Maximum, suggests there was a northwestward shift of the EASM rain belt and vegetation under warmer climate. In combination of modeling result from CESM 2, we support the hypothesis that global warming has driven the increasing of the EASM-derived rainfall, through the north migration of the intertropical convergence zone (ITCZ) and the monsoon precipitation belt during the Pliocene warmth.

How to cite: Wang, K., Lu, H., Lei, F., Garzione, C., and Wang, J.: A combined geochemistry study of late Pliocene Red Clay deposits from southern Chinese Loess Plateau and their paleoclimate implications, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-43, https://doi.org/10.5194/egusphere-gc10-pliocene-43, 2022.

09:15–09:30
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GC10-Pliocene-22
Antje Voelker, Xiaolei Pang, Liping Zhou, Nils Andersen, and Henning Kuhnert

The early Pliocene, with atmospheric CO2 concentrations at levels similar to today, is seen as a case study for Earth’s future climate evolution. During this period the progressive closing of the Central American Seaway led to increased poleward heat and salt transport within the Atlantic with North Atlantic Deep Water (NADW) becoming warmer and saltier and resulting in an enhanced Atlantic Meridional Overturning Circulation (AMOC). To evaluate the stability of the Pliocene AMOC, we are producing centennial-scale surface and deep-water records for IODP Site U1313 (41°N, 33°W, 3412m) for the interval from 3.3 to 4.4 Ma. This site is ideally located to monitor past AMOC changes with North Atlantic Drift waters at the surface and NADW, exported by the deep western boundary current, in the deep. Surface water variations are reconstructed based on the stable isotope data of the planktonic foraminifer genus Globigerinoides sp. and on Mg/Ca derived temperatures during the late Pliocene, whereas deep-water changes are revealed by the stable isotope records of the benthic foraminifer genus Cibicidoides. Besides the interglacial/glacial cycles, higher frequency oscillations are recorded in the foraminiferal records. Varying surface water conditions, especially during Late Pliocene interglacial periods, are observed and we will use the pending Mg/Ca temperature data to assess if they are linked to salinity changes. The high-frequency oscillations are related to precession forcing, especially its harmonics in the 5.5 kyr and 11 kyr ranges. The benthic δ13C values indicate nearly continuous NADW presence and confirm a strong AMOC throughout the studied interval, also during most of the glacial periods. During the early Pliocene, glacial stage Gi 6 had a stronger impact on the AMOC than Gi 2 and Gi 4. Overall, the AMOC was strong throughout, but experienced high frequency oscillations at a level similar to the middle Pleistocene interglacial periods.

How to cite: Voelker, A., Pang, X., Zhou, L., Andersen, N., and Kuhnert, H.: Early to Late Pliocene climate change at mid-latitudinal North Atlantic Site U1313, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-22, https://doi.org/10.5194/egusphere-gc10-pliocene-22, 2022.

09:30–09:45
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GC10-Pliocene-19
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ECS
Lina C. Pérez-Angel, Julio Sepúlveda, Peter Molnar, Hector Mora-Páez, Ángelica Parrado, Katie Eaman, Catalina González-Arango, Katie Snell, Camilo Montes, and Nadia Dildar

We provide a Plio-Quaternary quantitative temperature record based on the distribution of bacterial membrane lipids; branched glycerol dialkyl glycerol tetraethers (brGDGTs) preserved in lake sediment of the Funza-II core in the Sabana de Bogotá (2500 m.a.s.l.), Eastern Cordillera of Colombia (~4°N). Using a refined age model based on 4 new zircon U-Pb dates from ash layers that place the base of the core at around ~4 Ma, we show that Pliocene temperatures were ~2.2 ± 2.0°C warmer than Mid-Late Pleistocene temperatures. If the Pliocene eastern tropical Pacific were as warm as it becomes during major El Niño events today, the teleconnection to the Eastern Cordillera of Colombia could account for a warmer Pliocene than present-day climate by 2°C, without a pantropical change in temperature. These temperature estimates are the only terrestrial tropical record within 5° of the equator for Pliocene time.

How to cite: Pérez-Angel, L. C., Sepúlveda, J., Molnar, P., Mora-Páez, H., Parrado, Á., Eaman, K., González-Arango, C., Snell, K., Montes, C., and Dildar, N.: A Pliocene-Pleistocene temperature reconstruction from the tropical Andes of Colombia , The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-19, https://doi.org/10.5194/egusphere-gc10-pliocene-19, 2022.

09:45–10:00
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GC10-Pliocene-15
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ECS
Martin Renoult, Navjit Sagoo, and Thorsten Mauritsen

In recent years, simulations of the Paleoclimate Modelling Intercomparison Project (PMIP) of the cold Last Glacial Maximum (LGM) and the warm mid-Pliocene have been used to constrain the equilibrium climate sensitivity (ECS) in an emergent constraint framework. The constraint on ECS arising from Pliocene temperatures is surprisingly robust, as opposed to that based on LGM temperatures. Nevertheless, observational uncertainties on proxy data from the Pliocene are large, in particular at high latitudes. We analyse the sensitivity of the Pliocene-based emergent constraint on ECS to different reconstructions as to verify if the well-constrained ECS is sensitive to the proxy data. We also investigate the boundary conditions of the Pliocene to identify key structural elements which may weaken the emergent constraint relationship. We show that the wider range of ECS in models simulating the Pliocene, as well as numerous sensitivity experiments, is a great advantage for the emergent constraint approach.

How to cite: Renoult, M., Sagoo, N., and Mauritsen, T.: Exploring climate sensitivity from Pliocene temperatures, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-15, https://doi.org/10.5194/egusphere-gc10-pliocene-15, 2022.

10:00–10:15
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GC10-Pliocene-21
Gerrit Lohmann, Gregor Knorr, Akil Hossain, and Christian Stepanek

During the Cenozoic Era hothouse climate transformed to a state that allowed establishment of extensive ice-sheets. The transformation towards an overall cooler climate encompassed periods of relatively steady change of global temperatures which were interrupted by short-term aberrations of relatively rapid cooling or warming. Global climate cooling culminated in the glacial-interglacial cycles that characterize the Quaternary until today. Various drivers have been found to contribute to this complex process of climate cooling - among these drawdown of carbon dioxide, reorganized ocean circulation related to ocean gateway evolution, varying amplitude and geographic location of deep water upwelling and formation processes, and internal feedbacks related to changes in environmental and land surface conditions in particular at high latitudes and on the continents.

The fact that carbon dioxide as the most important current driver of climate change is not always proportionally linked to past changes in global temperatures underlines the importance of mechanisms beyond greenhouse gas drawdown that contributed to Cenozoic climate cooling. Several questions remain regarding mechanisms and drivers of climate evolution as reconstructed from Cenozoic proxy recorders: How can a low meridional temperature gradient be maintained at carbon dioxide concentrations that are in line with reconstructions and inference on relatively modest tropical tempatures? Which mechanisms contributed to extremely high deep sea temperatures that are not commonly reproduced by simulations of Cenozoic climate?

Here we propose that during the Miocene and the Pliocene enhanced vertical mixing in the ocean may provide potential explanations to some of these enigmas. We employ the global general circulation model COSMOS, which contributed to PlioMIP, MioMIP, and DeepMIP, and study the impact of variations in vertical mixing in the ocean on large-scale climate patterns, meridional temperature gradient, and deep sea ocean temperatures. We find that both carbon dioxide and enhanced vertical mixing cause increased radiative feedback by reducing effective emissivity and surface albedo. For the Miocene, enhanced oceanic heat uptake due to invigorated vertical mixing causes intense warming of the deep ocean (5-10°C) and of the Arctic (>12°C). For the Pliocene we find that the impact of radiative forcing and enhanced vertical mixing is less relevant. This hints to a dependency of carbon dioxide and mixing sensitivity to background climate and ocean dynamics.

While our work is focused on climate modelling we highlight that consideration of enhanced vertical mixing leads in our Miocene and Pliocene climate simulations to large-scale climate patterns that are in better agreement with specific aspects of proxy-based inference on past warm climates. To further corroborate our results we must compare our simulations with reconstructions of thermocline depth and seasonality - lower seasonality in reconstructions would be in line with higher heat capacity as facilitated by enhanced vertical mixing.

How to cite: Lohmann, G., Knorr, G., Hossain, A., and Stepanek, C.: A comparison of effects of carbon dioxide and ocean mixing on Miocene and Pliocene temperature gradients, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-21, https://doi.org/10.5194/egusphere-gc10-pliocene-21, 2022.

10:15–10:30
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GC10-Pliocene-29
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ECS
George William Harrison, Ken Johnson, and Willem Renema

Since the Pliocene Climate Optimum is frequently referenced as a parallel to future conditions, studying the trajectories of Pliocene coral reefs might give insights into the future of Anthropocene reefs. The Coral Triangle and surrounding areas in North Australia are the biodiversity hotspots for Anthropocene reef associated taxa so we assembled a database of all published reef-containing cores from the Miocene, Pliocene, and Pleistocene of the Coral Triangle and North Australia regions and analyzed it for shifts in reef occurrences over time. In the Pliocene, the Coral Triangle and North Australia regions had half as many reefs as they did in the Miocene or Pleistocene. This decline cannot have been driven by temperature since the Miocene was warmer than the Pliocene but likely resulted from local tectonics and possibly fluctuating CO2 levels. This study also provides a comprehensive stage-level dataset of Pliocene coral reef locations in the Coral Triangle and North Australia which could be combined with models of reef-promoting conditions in the Anthropocene to test models of Pliocene climate.

How to cite: Harrison, G. W., Johnson, K., and Renema, W.: Pliocene Reef Gap in the Indo-Pacific, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-29, https://doi.org/10.5194/egusphere-gc10-pliocene-29, 2022.

Break (10:30–10:45)
10:45–11:00
11:00–12:30
Lunch (12:30–13:15)
Chairpersons: Alan Haywood, Heather L. Ford
13:15–13:45
Session 7: Group Discussion and Next Steps
13:45–14:30
14:30–15:00

Posters: Wed, 24 Aug, 14:30–16:00 | Poster area Session A

PA1
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GC10-Pliocene-6
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ECS
Mary Grace Albright, Ran Feng, Jiang Zhu, Bette Otto-Bliesner, Hui Li, and Tripti Bhattacharya

The North American Southwest (SW NA) has recently experienced periods of extreme drought, largely due to an increased intensity in evaporation. Yet, there remains large uncertainty in the predicted future changes of precipitation over this region. As a result, the future of SW NA hydroclimate remains uncertain.  The North American Monsoon (NAM) is an atmospheric circulation feature of SW NA hydroclimate that is generated by interactions between topography and moisture surge from the Gulf of California and the Gulf of Mexico.  Previous research has shown a weakened NAM in response to elevated levels of atmospheric CO2. Consistent with this result, PlioMIP2 simulations also show reductions in precipitation throughout this region. However, when analyzing proxy paleoclimate reconstructions during the Pliocene, various records suggest wetter conditions during that time.  We use the mid-Pliocene (3.3 – 3.0 Millions of years ago) as an analog for ongoing climate change because this interval featured topography, geography, and biome assemblages similar to today, but a warmer global mean temperature by 2 - 4 °C compared to pre-industrial, and a sustained 400 ppm CO2.  Here we are testing whether a high resolution simulation (25 km) can better capture the NAM and provide different sensitivity to boundary conditions compared to low resolution (100 km) simulations, using the same Community Earth System Model.  Our pre-industrial simulations with high elevation in the Sierra Madre Occidental mountain range display a more realistic distribution of the NAM rainbelt and its dependency on topography. In the Pliocene simulations, despite that the lowered mountain range reduces precipitation in the NAM region, an increase in summer precipitation is seen in the high resolution run on the eastern side of the mountains and along the gulf of Mexico. Ongoing work will explore the sources for this resolution dependency, and will quantify contributions of mesoscale systems, such as tropical and extratropical cyclones, to precipitation in the monsoon region.  

How to cite: Albright, M. G., Feng, R., Zhu, J., Otto-Bliesner, B., Li, H., and Bhattacharya, T.: Mid-Pliocene North American Monsoon in Weather Resolving Coupled Simulations, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-6, https://doi.org/10.5194/egusphere-gc10-pliocene-6, 2022.

PA2
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GC10-Pliocene-60
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ECS
Lauren Burton, Alan Haywood, Julia Tindall, Aisling Dolan, and Daniel Hill and the PlioMIP Participants

Understanding the dominant climate forcings in the Pliocene is crucial to assessing the usefulness of the Pliocene as an analogue for future climate. Previous research has shown the dominance of CO2 forcing in driving Pliocene surface air temperature change but little is understood about the drivers of other climate parameters.

We implement a novel, simple linear factorisation method to seven models in the PlioMIP2 ensemble to assess the relative influence of CO2 forcing in the Pliocene. Outputs are termed “FCO2” and reflect the relative influence of CO2, where 1 represents wholly dominant CO2 forcing.

CO2 forcing is found to be the dominant driver of surface air temperature change in six of the seven models (global mean FCO2 of ensemble = 0.56), and five of the seven models for sea surface temperature (global mean FCO2 of ensemble = 0.56). FCO2 varies latitudinally for both, with CO2 forcing less dominant at high latitudes.

FCO2 shows the most variation between models for precipitation change (individual model global mean FCO2 range = 0.30-0.69), though CO2 remains the most dominant driver in the ensemble (global mean FCO2 = 0.51). Spatial change in precipitation is predominantly driven by changes in orography and ice sheets in individual models.

The accuracy of our FCO2 method is evidenced by comparison to an energy balance analysis, which also adds nuance to the results and highlights feedbacks that arise from CO2 forcing.

Our results go some way to better understanding the drivers of Pliocene climate and have implications for the interpretation of proxy data and data-model comparison, which is to be investigated further. Our results could also be expanded to include additional climate parameters, such as surface pressure.

That CO2 forcing is the dominant driver of surface air temperature, sea surface temperature and precipitation change suggests that the Pliocene is a relevant climate analogue for the future, but attention must also be paid to the significant effect of non-CO2 forcing in the Pliocene, the equivalent of which is not expected to be seen for hundreds or thousands of years in the future.

How to cite: Burton, L., Haywood, A., Tindall, J., Dolan, A., and Hill, D. and the PlioMIP Participants: On the climatic influence of CO2 forcing in the Pliocene, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-60, https://doi.org/10.5194/egusphere-gc10-pliocene-60, 2022.

PA3
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GC10-Pliocene-26
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ECS
Julia Weiffenbach, Michiel Baatsen, Henk Dijkstra, and Anna von der Heydt and the PlioMIP2 model community

Sea surface temperature (SST) proxies of the mid-Pliocene warm period (3.264-3.025 Ma) indicate amplified warming over the North Atlantic with respect to the pre-industrial period, which may be linked to an intensified Atlantic Meridional Overturning Circulation (AMOC) in the mid-Pliocene. Earlier results from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) show that all models in the PlioMIP2 ensemble simulate a stronger AMOC in the mid-Pliocene than in the pre-industrial. However, no consistent relationship has been found between the stronger mid-Pliocene AMOC and either the Atlantic northward ocean heat transport (OHT) or average North Atlantic SSTs.

In this study, we look further into the drivers and consequences of a stronger AMOC in mid-Pliocene compared to pre-industrial simulations in PlioMIP2. We find that all model simulations with a closed Bering Strait and Canadian Archipelago show reduced freshwater transport from the Arctic Ocean into the North Atlantic. The resulting increase in salinity in the subpolar North Atlantic and Labrador Sea drives the stronger AMOC in the mid-Pliocene. To investigate the ensemble’s variable response of the total Atlantic OHT to the stronger AMOC, we separate the Atlantic OHT into two components associated with either the overturning circulation or the wind-driven gyre circulation. While the ensemble mean of the overturning component is increased significantly in magnitude in the mid-Pliocene, it is partly compensated by a reduction of the gyre component in the northern subtropical gyre region. This reduction originates from a zonal asymmetry in mid-Pliocene warming in the subtropical North Atlantic, rather than through changes in atmospheric forcing of the gyre. Our results indicate that these components should be considered separately to gain a more complete understanding of the Atlantic OHT response to a stronger mid-Pliocene AMOC. In addition, we show that the AMOC exerts a stronger influence on North Atlantic SSTs in the mid-Pliocene than in the pre-industrial, providing a possible explanation for the improved agreement of the PlioMIP2 ensemble mean SSTs with reconstructions in the North Atlantic.

How to cite: Weiffenbach, J., Baatsen, M., Dijkstra, H., and von der Heydt, A. and the PlioMIP2 model community: Dynamics associated with a stronger mid-Pliocene Atlantic Meridional Overturning Circulation in PlioMIP2, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-26, https://doi.org/10.5194/egusphere-gc10-pliocene-26, 2022.

PA4
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GC10-Pliocene-39
Xu Zhang, Yong Sun, Yongqiang Yu, Øyvind Lien, Berit Hjelstuen, Christian Stepanek, Evan Gowan, Daniel Hill, Shengqian Chen, and Siqi Li

A long-standing challenge for mid-Pliocene climate simulations is large underestimation of simulated surface warming in the Nordic Seas in comparison to sea surface temperature (SST) proxy records (e.g. Dowsett et al., 2013; McClymont et al., 2020). Previous modelling studies have proposed that geographic changes in the Barents-Kara Sea are of great importance for surface temperature change in the Nordic Seas (e.g., Hill, 2015). That is, changing the Barents Sea from a marine to a subaerial setting can give rise to evident warming in the Nordic Seas. Nevertheless, this geographic change has so far not been well considered in the Pliocene Modelling Intercomparison Project (Haywood et al., 2016 a,b), potentially due to the lack of quantitative reconstruction of this paleogeographic change. Recently, Lien et al. (2022) provided such reconstruction, which enables a test of the impact of a subaerial Barents Sea on mid-Pliocene climate. Based on iCESM1.2, we accordingly conducted sensitivity experiments where we changed bathymetry in the eastern Nordic Sea and topography in the Barents-Kara Sea region in a setup of otherwise unaltered PRISM4 mid-Pliocene boundary conditions (Dowsett et al., 20016). Our results hint that a subaerial Barents-Kara Sea might contribute to a reduction of the data-model SST mismatch during the mid-Pliocene.

References:

Dowsett, H., Foley, K., Stoll, D., et al., 2013. Sea Surface Temperature of the Mid-Piacenzian Ocean: A Data-Model Comparison: Science Reports, vol. 3. https://doi.org/10.1038/srep02013.

Dowsett, H., Dolan, A., Rowley, D., Moucha, R., Forte, A. M., Mitrovica, J. X., Pound, M., Salzmann, U., Robinson, M., Chandler, M., Foley, K., and Haywood, A., 2016. The PRISM4 (mid-Piacenzian) paleoenvironmental reconstruction, Clim. Past, 12, 1519–1538, https://doi.org/10.5194/cp-12-1519-2016.

Haywood, A.M., Dowsett, H.J., Dolan, A.M., 2016a. Integrating geological archives and climate models for the mid-Pliocene warm period. Nat. Commun. 7, 10646. https://doi.org/10.1038/ncomms10646.

Haywood, A.M., Dowsett, H.J., Dolan, A.M., Rowley, D., Abe-Ouchi, A., Otto-Bliesner, B., Chandler, M.A., Hunter, S.J., Lunt, D.J., Pound, M., Salzmann, U.,2016b. The Pliocene model Intercomparison project (PlioMIP) phase 2: scientific objectives and experimental design. Clim. Past 12, 663e675. https://doi.org/10.5194/cp-12-663-2016.

Hill, D.J., 2015. The non-analogue nature of Pliocene temperature gradients. Earth Planet Sci. Lett. 425, 232e241. https://doi.org/10.1016/j.epsl.2015.05.044

Lien, Ø. F.,  Hjelstuen, B. O.; Zhang, X.; Sejrup H. P., 2022. Late Plio-Pleistocene evolution of the Eurasian Ice Sheets inferred from sediment input along the northeastern Atlantic continental margin. Quat. Sci. Rev. 282, 107433. https://doi.org/10.1016/j.quascirev.2022.107433

McClymont, E. L., Ford, H. L., Ho, S. L., Tindall, J. C., Haywood, A. M., Alonso-Garcia, M., Bailey, I., Berke, M. A., Littler, K., Patterson, M. O., Petrick, B., Peterse, F., Ravelo, A. C., Risebrobakken, B., De Schepper, S., Swann, G. E. A., Thirumalai, K., Tierney, J. E., van der Weijst, C., White, S., Abe-Ouchi, A., Baatsen, M. L. J., Brady, E. C., Chan, W.-L., Chandan, D., Feng, R., Guo, C., von der Heydt, A. S., Hunter, S., Li, X., Lohmann, G., Nisancioglu, K. H., Otto-Bliesner, B. L., Peltier, W. R., Stepanek, C., and Zhang, Z., 2020: Lessons from a high-CO2 world: an ocean view from ∼ 3 million years ago, Clim. Past, 16, 1599–1615, https://doi.org/10.5194/cp-16-1599-2020.

How to cite: Zhang, X., Sun, Y., Yu, Y., Lien, Ø., Hjelstuen, B., Stepanek, C., Gowan, E., Hill, D., Chen, S., and Li, S.: Global impacts of a subaerial Barents Sea on the mid-Pliocene climate, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-39, https://doi.org/10.5194/egusphere-gc10-pliocene-39, 2022.

PA5
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GC10-Pliocene-46
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ECS
Ruby Barrett, Jamie D. Wilson, Chloe Todd, Marci M. Robinson, and Daniela N. Schmidt

During the Pliocene the planktic ecosystem, for the first time in its evolutionary history, experienced a separation of the tropical seaways. At the same time, low latitude planktic foraminifers reached sizes not seen for millions of years. We set out to examine whether the closure of the Central American Seaway (CAS) led to the reorganisation of the planktic food web and enabled this growth. As many plankton are not well preserved in the fossil record, we applied a trait-based ecosystem model for plankton – ForamEcoGEnIE – to an open and closed CAS Pliocene environment. ForamEcoGEnIE is an extension of the size-structured 3-D plankton ecosystem model, “EcoGEnIE” that includes non-spinose planktic foraminifers as a new functional group based on the costs and benefits of key traits (e.g. growth, grazing, calcification). We test whether the planktic food web and planktic foraminiferal physiology responded to this change in paleogeography by quantifying changes in plankton biomass and size. In large regions of the ocean, we observe no change in phytoplankton, zooplankton, or foraminiferal biomass in response to a closed CAS. However, we note an increase in biomass at the eastern equatorial Pacific and a decrease in the North Atlantic in response to the closure of the CAS. ForamEcoGEnIE predicts an increase in non-spinose foraminiferal body size at the eastern equatorial Pacific and a small decrease in the North Atlantic. We attribute the Pacific response to increased upwelling due to the closure of the CAS and in the North Atlantic we suggest the reduction in biomass and size is linked with the reorganisation of surface ocean currents. As much of the ocean shows no response, we tentatively conclude that the closure of the CAS did not induce a major reorganisation of the planktic ecosystem. 

How to cite: Barrett, R., Wilson, J. D., Todd, C., Robinson, M. M., and Schmidt, D. N.: Did the closure of the Central American Seaway induce a major reorganisation of the planktic ecosystem?, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-46, https://doi.org/10.5194/egusphere-gc10-pliocene-46, 2022.

PA6
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GC10-Pliocene-62
Aisling Dolan, Stephen Hunter, Alan Haywood, and Harry Dowsett

Following the first Pliocene Model Intercomparison Project (PlioMIP), data-model comparisons showed that regionally there were significant discrepancies between predictions of climate. Uncertainties in the prescribed climate model forcings and in proxy data were shown to limit our ability to truly evaluate the models. In part this uncertainty was due to the proxy reconstructions being based on a time slab (of ~300,000 years). Haywood et al (2013) identified a time slice within the Piacenzian that presented a target for modellers and the data community for reconstructing a mid-Pliocene climate and environment. This time slice centred on 3.205 Ma (3.204–3.207 Ma) is a warm interval characterized by a negative benthic oxygen isotope excursion (0.21–0.23‰) centred on marine isotope stage KM5c (KM5.3). It occurred during a period of orbital forcing that was very similar to present day. This time slice became the key target for the second Pliocene Modelling Intercomparison Project (PlioMIP2) and data reconstructions led by the USGS PRISM Group and the PAGES PlioVAR group. 

As part of the planning for PlioMIP3, the community is considering whether a simulation in the Early Pliocene (5.3 – 3.6 Ma) would be a useful target for modelling groups. To this end, we show plausible time slices during the Early Pliocene that have similar to modern orbital forcing.  As derived from the astronomical solution (Laskar et al 2004), we use the annual insolation pattern at the top of the atmosphere to determine which time slices have the most similar to modern orbital configuration.  We consider 10 different solutions between 3.6 and 5.0 Ma alongside the Lisiecki and Raymo (2004) and Ahn et al (2017) benthic oxygen isotope records and the record of magnetic reversals (Gradstein et al (2020)).  We identify two negative isotope excursions that could provide a target for proxy data collection to compare to a PlioMIP3 Early Pliocene simulation.   

How to cite: Dolan, A., Hunter, S., Haywood, A., and Dowsett, H.: On the identification of an Early Pliocene time slice target for data-model comparison, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-62, https://doi.org/10.5194/egusphere-gc10-pliocene-62, 2022.

PA7
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GC10-Pliocene-63
Daniel Hill and Aisling Dolan

The large glacial period that immediately precedes the mid-Pliocene Warm Period (mPWP) is a ~0.6‰ benthic oxygen isotope shift at 3.3Ma, known as M2. The excursion is roughly equivalent to 60m of sea level drop or 40msle (metres sea level equivalent) more ice than today. However, there is significant uncertainty in both these values and the potential locations of any large volumes of ice. Previous modelling studies have either used Last Glacial Cycle analogues for the M2 ice sheets or failed to reproduce the large Northern Hemisphere ice sheets implied by global ice volume proxies.

 

Here we present new climate and ice sheet models simulating the M2 glacial period, by lowering Pliocene atmospheric carbon dioxide concentrations and selecting specific Pliocene orbital forcing. These climates are sufficiently cold to produce ice sheets in North America and northern Europe within our modelling framework. The largest components of these ice masses are centred over regions with significant landscape differences between Pliocene and present day, including the Hudson Bay, Canadian Archipelago and Barents Sea. This suggests that the M2 glacial may have had very different initiation locations to the most recent glacial cycles and that Pliocene palaeogeographic changes may be key to understanding the M2 glacial.

How to cite: Hill, D. and Dolan, A.: Northern Hemisphere ice sheets during the M2 Pliocene glacial, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-63, https://doi.org/10.5194/egusphere-gc10-pliocene-63, 2022.

PA8
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GC10-Pliocene-2
Elizabeth Okoyeh and Chibuzo Ahaneku

The impact of climate variability in Niger Delta Basin is enormous and poses unimaginable negative effects on the land and water environment of the area. The significant increase in temperature of 0.190C, high degree of variation in the on-set and cessation of rainfall resulting in substantial variation in annual rainfall amount of 2000mm has left negative imprint in the environment of the area. The increase in temperature and rainfall amount occasioned by variation in climatic condition of the Pliocene to recent results in hydroenvironmental extreme events of flooding, gully erosion and landslide with deterioration of water quality/quantity and degradation of the land. Over 580 active gully erosion sites have been identified in different parts of the basin with depth of about 75m and width of more than 20m in some places. The dimensions of the gullies increase with each rainy season silting surface water bodies and exposing shallow aquifers. The impacts of climate variability exacerbate water scarcity and development of bad land with implications on food security and public health in the area.  These are common triggers of communal conflict resulting in loss of live, properties and means of livelihood. The influence of variability in climate system is gender sensitive with significant effect on women and children in the rural area. The impact of the uncertainty of the climate system from Pliocene is aggravated by geogenic as well as anthropogenic activities in the basin to affect sustainable development. Varieties of plant and animal species and wildlife have been terminally-lost; by which all losses affecting parts of the Tropics of African countries are trending fast to an emerging regional biotic extinction within the Pliocene age. Integrated approach in Pliocene related research is recommended for better understanding of the climate system for the actualization of global sustainable development. 

How to cite: Okoyeh, E. and Ahaneku, C.: Hydroenvironmental impacts of Pliocene climate variability in parts of Niger Delta basin, Nigeria, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-2, https://doi.org/10.5194/egusphere-gc10-pliocene-2, 2022.

PA9
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GC10-Pliocene-7
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ECS
Warm Pliocene- as archived in Himalayan Landforms
(withdrawn)
Anjali Kumari and Sarabjeet Singh
PA10
|
GC10-Pliocene-18
Friso de Graaf, Heather Ford, and Natalie Burls

Modern ocean circulation is driven by formation of deep waters in the North Atlantic and Southern Oceans. Despite the cold temperatures at high latitudes, the North Pacific exhibits no modern deep-water formation, due to the strong halocline in the subpolar North Pacific Ocean. However, modelling results suggest the halocline was weak during the Pliocene, allowing the formation of North Pacific Deep Water (NPDW). Here we compare the oxygen isotopes from benthic foraminifera at two sites in the Northwest Pacific Ocean, ODP Sites 1208 (3346 m) and 1209 (2387 m) to understand how NPDW varied over the Plio-Pleistocene (3.3 to 2.6 Ma). While in the modern the water that occupies the deep Pacific is homogenous, during the Pliocene there was a ~0.5 per mill gradient at times between sites 1208 and 1209, with, surprisingly, more positive δ18O values observed at the shallower 1209. The disparity in oxygen isotopes suggests different water masses over the two sites over the Plio-Pleistocene. Oxygen isotopes of foraminifera record temperature and the δ18O of seawater which loosely correlates with salinity in the modern surface oceans, with more positive δ18O values generally representing more saline, colder, and therefore more dense waters. High latitude processes like sea ice formation could result in a decoupling of salinity from δ18O of seawater. We suggest that the divergences in oxygen isotopes are the result of Site 1208 being bathed in southern-sourced waters, while Site 1209 is bathed in deep waters formed in the North Pacific. Modelling results suggest NPDW is a warm, saline water mass. That the divergence in δ18O values between the two sites is not constant throughout this period suggests that the strength of NPDW export may have fluctuated over this interval. Future work includes Mg/Ca analyses at Site 1209 to compare with the existing record at 1208 to examine the temperature and δ18O of seawater differences between these sites.

How to cite: de Graaf, F., Ford, H., and Burls, N.: North Pacific Deep Water Formation Termination over the Northern Hemisphere Glaciation, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-18, https://doi.org/10.5194/egusphere-gc10-pliocene-18, 2022.

PA11
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GC10-Pliocene-33
Sarah Feakins

Dual measurements of the carbon and hydrogen isotopic composition of plant wax, provide a powerful means to gather parallel evidence on vegetation and climate change. Following the Miocene expansion of C4 grasslands in the tropics, both C3 and C4 plant types are present on the tropical landscape. Carbon isotopes in plants can reveal the history of vegetation during the Pliocene. Hydrogen isotopes in plants record that of precipitation isotopes, tracing rainout processes associated with large scale atmospheric circulation patterns. Drilling by the International Ocean Discovery Program and earlier scientific ocean drilling has recovered Pliocene age sediments, around the margins of Africa and South Asia, capturing plant waxes that blow off or are washed off the continents by fluvial transport. Multiple drill cores have published plant wax C and H isotopic reconstructions available, that I synthesize here to explore the regional expression of Pliocene vegetation and climate. This effort seeks to address the IODP Science Plan: how does climate respond to elevated CO2 (challenge 1), what drives past precipitation change (challenge 3) and vegetation response (challenge 7)? It contributes to the flagship initiative of the IODP 2050 Science Framework to ground-truth climate models, focused on the critical aspect of assessing precipitation patterns on land across elevated CO2 to validate model reconstructions of past hydrological change and thus to constrain confidence in future predictions. To achieve the model connection, the hydrogen isotope data are summarized for comparison to isotope-enabled climate model output, including General Circulation Climate model experiments for the 3.2 Ma focus of the Pliocene Model Intercomparison Project (PlioMIP) and 5-4 Ma timeslice – see  presentation by Knapp et al., (this conference).

How to cite: Feakins, S.: Plant wax reconstructions of Pliocene vegetation and hydroclimate – from scientific ocean drilling, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-33, https://doi.org/10.5194/egusphere-gc10-pliocene-33, 2022.

PA12
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GC10-Pliocene-36
Benjamin Petrick, Lars Reuning, Gerald Auer, Alexandra Auderset, Nicolas Duprey, Alfredo Martienz-Garcia, Yige Zhang, Lorenz Schwark, and Miriam Pfeiffer

The Queensland Plateau in the Coral Sea has one of the best constrained geologic histories of coral reef expansion and demise since the early Miocene. The development coral reefs in the past is not well understood with a number of theories proposed for their loss and expansion. Coral reefs were first established in the Early Miocene in the Coral Sea. In the Late Miocene, between 11 and 7 Ma, the reef area on the Queensland Plateau declined by ~50% leading to a partial drowning and a change in platform geometry from a reef rimmed platform to a carbonate ramp. The modern atoll reefs were reestablished around 3.6 Ma although the Great Barrier Reef only developed around 0.7-0.6 Ma. The loss of the reefs has often been tied to the expansion cool nutrient rich waters in the Coral Sea during the Late Miocene. This model has been used to explain the loss and expansion of corals in other parts of the globe. However, there have been questions about the planktonic δ18O based Sea Surface Temperature (SST) records on which they are based and how accurately they reflect SSTs. Here we show new TEX86 SST data from the Queensland Plateau from ODP site 811 showing temperature changes from the Late Miocene to 1 Ma. Our data shows instead of cooler SSTs during the Late Miocene in fact SSTs were warmer than the modern Coral Sea and at the upper end of the modern coral window. Therefore, it is unlikely that cooler SSTs during the Late Miocene caused the loss of corals on the Queensland Plateau. Instead, the loss seems to have been driven by the restricted growth combined with high SST driven lower growth rate and increases in subsidence at the same time among other drivers.  We also will discuss changes in the latitudinal extent of the warm pool during the late Pliocene and what caused the re-expansion of corals during this period of time.  Given the modern debate about the future of coral reefs under current climate predictive scenarios it is worth pointing out that a similar series of changes is occurring in the modern ocean.

How to cite: Petrick, B., Reuning, L., Auer, G., Auderset, A., Duprey, N., Martienz-Garcia, A., Zhang, Y., Schwark, L., and Pfeiffer, M.: The influence of SST on the loss and development of coral reefs in the Coral Sea from the Miocene to Pliocene, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-36, https://doi.org/10.5194/egusphere-gc10-pliocene-36, 2022.

PA13
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GC10-Pliocene-41
Nicolas Waldmann, John Greenlee, Silas Dean, Christine Hall, Ankit Yadav, Olajide Oladipo, Lisa Park-Boush, and Isla Castañeda

The Pliocene (5.33-2.58 Ma) was the last significant sustained warm period in Earth climate history. Atmospheric carbon dioxide and global temperatures during this interval are comparable to those estimated for our planet’s future climate trajectory. Considering a similar to current continental and oceanic positioning, it is possible to assume similar oceanic and atmospheric circulation patterns, and hence reliable climate archives dated to this interval may serve as a good analogue for providing a base of comparison to the future climate conditions of our planet. Current data on the Pliocene mostly focus on marine sediments with terrestrial data arriving from loess and paleosol records. Yet, there is a lack of information from continental lacustrine formations, especially from the Eastern Mediterranean. The Erk’-el-Ahmar Formation (3.15-4.5 Ma) is exposed in the central Jordan Valley and includes a ~150 m succession of mostly lacustrine deposits (clay, silt, very find sand, and carbonate layers), with excellent preservation of freshwater mollusk shells, ostracod bivalves, micromammal bone fragments, and even a mammoth tusk. This study aims to reconstruct the paleoenvironmental conditions in the region during this time interval using a multi-proxy approach that includes physical parameters (grain size distribution, magnetic susceptibility), chemical compositional data (X-ray fluorescence and total organic carbon/inorganic carbon), with preliminary results of ostracod and biomarker data from three push-cores (60 m) and the formation’s outcrop.

Our results show major fluctuations in the lake hypsometry, as evidenced by the different parameters, which are suggested to reflect the local hydro-climate conditions. An orbital-scale dry-wet climate cyclicity is well identified in the sedimentary record, which probably influenced the lake depth and structure, redox conditions, sedimentary provenance, and the habitat for faunal species. The sediment cores capture transitions between continuous deep to shallow lacustrine environments, with potential short intermittent events (perhaps seismic or climate-induced), indicating the sustainability of this perennial water body. Results from this study provide an important understanding of the hydrological conditions that may have dominated the region during a warmer climate phase, challenging previous estimations on the governing mechanisms for climate variability in the region, such as humidity provenance.

How to cite: Waldmann, N., Greenlee, J., Dean, S., Hall, C., Yadav, A., Oladipo, O., Park-Boush, L., and Castañeda, I.: Pliocene environmental changes in the Levantine Corridor (Near East): insights from a new multi-proxy study from a lacustrine record in the central Jordan Valley, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-41, https://doi.org/10.5194/egusphere-gc10-pliocene-41, 2022.

PA14
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GC10-Pliocene-45
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ECS
Chloe Todd, Ruby Barrett, Heather Birch, Daniel Hill, Jamie Wilson, Marci Robinson, and Daniela Schmidt

Size is fundamentally important in individual planktic foraminifers as it determines the number of offspring and hence reproductive success. Over evolutionary timescales, individuals tend to increase in size, altering the average size of assemblages; in the last million years, individuals were larger than at any other time in the geological record. This pattern is specifically driven by size increases in tropical and subtropical taxa in the Plio-Pleistocene. Here we use a taxon-free approach to assess what facilitated this novelty and to quantify the response of planktic foraminifers to both long and short time-scale environmental changes. We focus on the Pliocene, a time interval characterized by the closure of the Central American Seaway (CAS) and the short glaciation at marine isotope stage (MIS) M2. We measured size in foraminiferal assemblages using automated microscopy across 24 globally distributed PRISM locations, from subpolar to tropical environments. The 95th percentile was calculated on the maximum diameter measurements of 1.28 million specimens. Although there is a slight decrease in the average size of the assemblage in the high latitudes from the Early to Late Pliocene, with minimal changes in the tropics, results indicate little to no effect on foraminiferal size across MIS M2. The results show an unexpected stability and resilience against the reorganization of the tropical oceans associated with the closure of the CAS.

How to cite: Todd, C., Barrett, R., Birch, H., Hill, D., Wilson, J., Robinson, M., and Schmidt, D.: Role of the closure of the Central American Seaway in gigantism of planktic foraminifers, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-45, https://doi.org/10.5194/egusphere-gc10-pliocene-45, 2022.

PA15
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GC10-Pliocene-59
|
ECS
Tamara Fletcher, Julia Tindall, and Alan Haywood

Cloud has profound impacts on climate, thus accurate cloud simulation is critical for accurate climate modelling. As the greatest source of uncertainty in such models, cloud drives discrepancies in the prediction of future climate. Cloud simulations are validated against recent observations; however, these records do not capture the climate space we are entering this century, limiting our ability to test model accuracy under near future conditions.

The best analogue for the 21st Century climate trajectory comes from the Pliocene. Reconstructions of Pliocene cloud regimes would provide critical validation data for climate model performance with respect to cloud. However, despite the wealth ways to reconstruct other climate variables, no method has been developed for reconstructing cloud in the distant past.

The aim of my current work is to develop proxies capable of reconstructing past cloud, with the ultimate goal of establishing a global cloud database for the Pliocene. I will be presenting preliminary results that demonstrate the relationship between vegetation and large-scale patterns in cloud – a first step to a novel terrestrial cloud proxy.

How to cite: Fletcher, T., Tindall, J., and Haywood, A.: Palaeocloud for the Pliocene, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-59, https://doi.org/10.5194/egusphere-gc10-pliocene-59, 2022.

Posters: Thu, 25 Aug, 10:30–11:30 | Virtual poster area Session B

VPB1
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GC10-Pliocene-1
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ECS
Sarah Roffe, Francois Engelbrecht, and Marion Bamford

The mid-Pliocene warm period (mPWP; 3.264-3.025 Ma) was characterised by near-modern geography and atmospheric carbon dioxide concentrations (~400 ppmv). With temperatures ~3°C warmer than the pre-Industrial era, it is often considered an analogue for near-future climate change. While many paleoenvironmental reconstructions suggest wetter conditions across southern Africa, projections for the mPWP and future suggest drier conditions associated with warmer climate states. Southern Africa’s mPWP proxy record is, however, limited and to date no detailed study exists for the region using Pliocene Model Intercomparison Project (PlioMIP) model outputs. Thus, to further understand southern African climate during the mPWP and to add constraints to future warmer world scenarios for the subcontinent, we use outputs from 17 models participating in the second PlioMIP phase to explore changes in annual and seasonal rainfall and associated atmospheric circulation patterns during the mPWP, compared to pre-Industrial period simulations. Although patterns of change are diverse, robust signals are evident. An annual rainfall decline, of approximately -0.5 mm/day, is quantified for most regions. Overall, drier conditions of a similar magnitude for the summer (October-March) and winter (April-September) periods contribute to this change, but the winter period shows more consistent drying. Relatively strong consistency across individual models for the pattern of intensification and expansion of the subtropical high-pressure belt suggests increased subsidence is a dominant driver behind the drying evident. General poleward tendencies of large-scale atmospheric circulation belts cause a poleward shift in the subcontinent's rainfall zones, resulting in a farther (reduced) southwestern (northeastern) extent of the summer (winter) rainfall zone (SRZ and WRZ). Projections reveal reduced seasonality for WRZ regions due to relatively stable summer rainfall and substantially reduced winter rainfall, while a relatively large early (late) summer rainfall decline (increase) for October-December (January-March) for SRZ regions re-organises the summer wet-season to be more concentrated in the late summer period.

How to cite: Roffe, S., Engelbrecht, F., and Bamford, M.: Southern African rainfall regimes in a warmer world: Insight from PlioMIP2 mid-Pliocene Warm Period (3.264-3.025 Ma) simulations, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-1, https://doi.org/10.5194/egusphere-gc10-pliocene-1, 2022.

VPB2
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GC10-Pliocene-11
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ECS
Hanzhi Zhang, Huayu Lu, Jing He, Wanting Xie, Hanlin Wang, Honhyan Zhang, Daniel Breecker, Anna Bird, Thomas Stevens, Junsheng Nie, and Gaojun Li

The formation of the unique landscape of Chinese Loess Plateau (CLP) is debated because of uncertainties on dust provenance and transport pathways. We present a detailed quantitative estimation of dust source contributions of the CLP, based on more than 37,100 detrital zircon U-Pb ages, combined with mineral assemblages and isotope analyses. Our results reveal that the CLP was stepwise formed by ~8 Ma, and is mainly composed of material from Northeastern Qinghai-Tibet Plateau (NQTP), with increased dust contributions from NQTP occurring at ~2.5 Ma and ~1.2 Ma, and the CLP was formally established. We infer that these changes were driven by stepwise global cooling, which induced aridification and enhanced silt production in glaciated high mountains, the NQTP, as well as dust ablation in the expanded arid regions. We propose that the global cooling, rather than regional tectonic deformation, was the main driver of the formation and evolution of the CLP.

How to cite: Zhang, H., Lu, H., He, J., Xie, W., Wang, H., Zhang, H., Breecker, D., Bird, A., Stevens, T., Nie, J., and Li, G.: Large-number detrital zircon U-Pb ages reveal global cooling caused formation of Chinese Loess Plateau during Late Miocene, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-11, https://doi.org/10.5194/egusphere-gc10-pliocene-11, 2022.

VPB3
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GC10-Pliocene-20
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ECS
Ke Zhang, Yong Sun, and Xu Zhang

The mid-Pliocene (Plio; 3Ma) which has been proved to be one of the most similar paleoclimate periods for the future climate. In this study, we conduct dynamic analysis on the large-scale features of tropical Hadley and Walker cells changes by examining the PlioMIP2 simulations. It was shown that a generally weakening of Hadley circulation strength (especially for the Northern Hadley cell) and widening of Hadley cells edges are captured by most of PlioMIP2 models. In addition, the Walker cell over the Pacific Ocean in responses to mid-Pliocene warming shows a significant westward shift compared to the pre-industrial conditions. Nevertheless, our analysis also shows evident inter-model spread of the Hadley and Walker cells changes.

How to cite: Zhang, K., Sun, Y., and Zhang, X.: Large-scale features of the tropical atmospheric circulation changes during the mid-Pliocene: results from the PlioMIP2, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-20, https://doi.org/10.5194/egusphere-gc10-pliocene-20, 2022.

VPB4
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GC10-Pliocene-23
Huayu Lu, Mark Dekkers, Xiaoqiang Li, Feng Cheng, Ran Zhang, Yichao Wang, Hanlin Wang, Jef Vandenberghe, and Chengsen Li
  • Pliocene climate is regarded as an analogue of future global warming (Burke et al, 2018; IPCC, 2021). How was the Pliocene precipitation in the monsoonal East Asia is not well known, although the Pliocene eolian silt ‘Red Clay’ deposit sequences have been investigated (Gallagher et al., 2021; Wang et al., 2022.). The poor preservation of floral and fauna fossils, and low sedimentation rate of the Red Clay makes it inappropriate to use as proxies that quantitatively reconstructing the Pliocene paleoclimate. In this study, a thick lacustrine deposit sequence at the Taigu-Yushe Basin (TYB) in central China is investigated, in order to semi-quantitatively reconstruct the East Asian monsoon precipitation variations during the Pliocene and early Pleistocene. These lacustrine sediments are rich in fossils. The thick lacustrine deposit sequences are dated by paleomagnetic stratigraphy analysis and correlated with the loess-paleosol time-series. The results show that the TYB lake deposit was accumulated during circa 4.0 -1.5 Ma. The Xiaobai Formation, which indicates a humid climate, was formed during 4.0-2.4 Ma. The pollen assemblage of the lake deposits and fluvial sediments reveals a dry climate after 2.4 Ma. Our proxy analyses show the precipitation during the middle Pliocene was 30% more than the present. This sedimentary record unravels the strengthened East Asian monsoon circulation which transported more vapor to the monsoon marginal during the Pliocene warmth.

How to cite: Lu, H., Dekkers, M., Li, X., Cheng, F., Zhang, R., Wang, Y., Wang, H., Vandenberghe, J., and Li, C.: A Pliocene palaeoclimate record from Taigu-Yushe Basin, central China , The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-23, https://doi.org/10.5194/egusphere-gc10-pliocene-23, 2022.

VPB5
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GC10-Pliocene-27
Charles Williams, Alistair Sellar, Xin Ren, Alan Haywood, Peter Hopcroft, Stephen Hunter, William Roberts, Robin Smith, Emma Stone, Julia Tindall, and Daniel Lunt

Here we present the experimental design and results from a new mid-Pliocene simulation using the latest version of the UK’s physical climate model, HadGEM3-GC31-LL, conducted under the auspices of CMIP6/PMIP4/PlioMIP2.  Although two other paleoclimate simulations have been recently run using this model, they both focused on more recent periods within the Quaternary and therefore this is the first time this version of the UK model has been run this far back in time.  The mid-Pliocene Warm Period, ~3 Ma, is of particular interest because it represents a time period when the Earth was in equilibrium with CO2 concentrations roughly equivalent to those of today, providing a possible analogue for current and future climate change.

 

The implementation of the Pliocene boundary conditions is firstly described in detail, based on the PRISM4 dataset, including CO2, ozone, orography, ice mask, lakes, vegetation fractions and vegetation functional types.  These were incrementally added into the model, to change from a preindustrial setup to a Pliocene setup. 

 

The results of the simulation are then presented, which are firstly compared with the model’s pre-industrial simulation, secondly with previous versions of the same model and with available proxy data, and thirdly with all other models included in PlioMIP2.  Firstly, the comparison with preindustrial suggests that the Pliocene simulation is consistent with current understanding and existing work, showing warmer and wetter conditions, and with the greatest warming occurring over high latitude and polar regionsthe.  The global mean surface air temperature anomaly at the end of the Pliocene simulation is 5.1°C, which is the 2nd highest of all models included in PlioMIP2 and is consistent with the fact that HadGEM3-GC31-LL has one of the highest Effective Climate Sensitivities of all CMIP6 models.  Secondly, the comparison with previous generation models and with proxy data suggests a clear increase in global sea surface temperatures as the model has undergone development.  Up to a certain level of warming, this results in a better agreement with available proxy data, and the “sweet spot” appears to be the previous CMIP5 generation of the model, HadGEM2-AO.  The most recent simulation presented here, however, appears to show poorer agreement with the proxy data compared with HadGEM2, and may be overly sensitive to the Pliocene boundary conditions resulting in a climate that is too warm.  Thirdly, the comparison with other models from PlioMIP2 further supports this conclusion, with HadGEM3-GC31-LL being one of the warmest and wettest models in all of PlioMIP2 and, if all the models are ordered according to agreement with proxy data, HadGEM3-GC31-LL ranks approximately halfway among them.  A caveat to these results is the relatively short run length of the simulation, meaning the model is not in full equilibrium.  Given the computational cost of the model it was not possible to run for longer; a Gregory plot analysis indicates that had it been allowed to come to full equilibrium, the final global mean surface temperature could have been approximately 1.5°C higher.   

How to cite: Williams, C., Sellar, A., Ren, X., Haywood, A., Hopcroft, P., Hunter, S., Roberts, W., Smith, R., Stone, E., Tindall, J., and Lunt, D.: Simulation of the mid-Pliocene Warm Period using HadGEM3:experimental design and results from model–model andmodel–data comparison, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-27, https://doi.org/10.5194/egusphere-gc10-pliocene-27, 2022.

VPB6
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GC10-Pliocene-34
Mark Chandler, Linda Sohl, Jeffrey Jonas, and Larissa Nazarenko

The Mid-Pliocene Warm Period (MPWP) ca. 3.2 Ma provides an opportunity to explore an equilibrium climate state under pCO2 and solar insolation conditions similar to those that may govern near-term future climate as per the IPCC’s SSP1 “Sustainability” scenario, which limits warming to +3.0 °C by the year 2100. Here we discuss mid-Pliocene simulations using the NASA-GISS-E2.1 coupled ocean-atmosphere model conducted for the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). We include our results using both modern and mid-Pliocene paleogeography, in accordance with PlioMIP2 protocols and provide comparisons to the results from PlioMIP1.

The PlioMIP2 simulations do not result in a significant change in global mean surface air temperature or global mean sea surface temperature compared to PlioMIP1. Global mean warming was +2.2 °C in PlioMIP1 and is slightly lower at +2.1 °C in PlioMIP2. However, there are notable contrasts in how temperatures respond regionally and the northern and southern high latitude temperature changes in PlioMIP2 show a marked contrast with PlioMIP2 producing less warming in the Arctic and more warming in the Southern Ocean compared to PlioMIP1. There is significant improvement in the simulation of Pliocene SSTs in PlioMIP2 in the region south of the Labrador Sea, where the PlioMIP1 simulation was anomalously cool. However, the region of greatest warming in the North Atlantic moves too far north, thus the SST warming in the Greenland Sea is only half what was seen in PlioMIP1 simulations weakening correlations to proxy data at key core sites in that region.

The GISS GCM has the strongest AMOC amongst the PlioMIP2 GCMs at 33 Sv, as was the case in the PlioMIP1 study, but the GISS model also has the largest increase in Pliocene AMOC strength compared to its preindustrial control run indicating that the intense overturning in GISS PlioMIP2 Pliocene simulations is, at least in part, due to changes in the response of the CMIP5 vs CMIP6 versions of the GCM. Similarly strong AMOC changes are found in the preindustrial control run comparisons of the GISS ModelE CMIP5 vs CMIP6 runs. As with other models in the PlioMIP2 study, the effect of AMOC on ocean heat transports is limited. Regardless, the increased sensitivity in the Pliocene in our model is impacted by changes in the freshwater flux and salinity distribution resulting from the PlioMIP2 paleogeographic changes, specifically the effects of closing the Bering Strait and the straits of the Canadian Archipelago connecting the Arctic Ocean to the Labrador Sea. Overall it is difficult to evaluate the impact of these substantial boundary condition changes in the Arctic gateways versus the effects of changes in model physics between CMIP5 and CMIP6, so additional simulations may be required to separate these factors. As with nearly all the PlioMIP models, the GISS ModelE continues to point to the potentially large impacts of CO2 on climate – and generally shows that the long-term sensitivity to increasing CO2 could be world altering.

How to cite: Chandler, M., Sohl, L., Jonas, J., and Nazarenko, L.: The PlioMIP2 Mid-Pliocene Climate Simulations Using the NASA-GISS ModelE, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-34, https://doi.org/10.5194/egusphere-gc10-pliocene-34, 2022.

VPB7
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GC10-Pliocene-42
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ECS
Xiaofang Huang, Shiling Yang, Alan Haywood, Julia Tindall, Dabang Jiang, Yongda wang, Minmin Sun, and Shihao Zhang

Warming-induced topographic changes of the East Antarctic Ice Sheet (EAIS) could have significant influence on the climate. However, how large changes in the EAIS height could theoretically affect global climate have yet to be studied. Here, the influence of possible height changes of the EAIS on climate is investigated through numerical climate modeling, using the Pliocene as a test case. As expected, the investigation reveals that the reduction of ice sheet height leads to a warmer and wetter East Antarctica. However, unintuitively, both the surface air temperature and the sea surface temperature decrease over the rest of the globe. These temperature changes result from the higher air pressure over Antarctica and the corresponding lower air pressure over extra-Antarctic regions with the reduction of EAIS height. This topography effect is further confirmed by energy balance analyses. These findings could provide insights into future climate change caused by warming-induced height reduction of the Antarctic ice sheet.

How to cite: Huang, X., Yang, S., Haywood, A., Tindall, J., Jiang, D., wang, Y., Sun, M., and Zhang, S.: The effect of the Antarctic ice sheet height changes on global climate: A case study of the mid-Pliocene, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-42, https://doi.org/10.5194/egusphere-gc10-pliocene-42, 2022.

VPB8
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GC10-Pliocene-53
William Lukens, David Fox, Emily Beverly, and John Kingston

The Pliocene Epoch is a high priority for understanding climatic and geomorphic responses to rising CO2 levels, yet the majority of paleoclimate records from this interval are from marine basins. Paleosols (fossil soils) preserve in situ archives of terrestrial paleoclimate, paleovegetation, and surface processes. This presentation showcases ongoing efforts to leverage paleosols from Pliocene deposits in North America and eastern Africa to develop quantitative estimates of mean annual precipitation (MAP), temperature (MAT) and paleovegetation (C3 vs. C4 biomass). We use a previously published random-forest recursive partitioning model (RF-MAP) that reconstructs MAP values using 10 major and minor elemental oxides from paleosol B horizons as input variables and is applicable on most soil types in most climate regimes. Our work in the Meade Basin of Kansas, USA, shows evidence of expanding and contracting wetlands during the Pliocene, with paleosols consisting of Vertisols to Aridisols depending on geomorphic position. Average paleoprecipitation totals appear to be near the semi-arid to subhumid boundary (~500 mm, similar to modern values) and remain steady across the Pliocene through early Pleistocene. Pliocene deposits of the Baringo Basin of central Kenya consists of orbitally-controlled lacustrine-alluvial cycles. Paleosols tend to be Vertisols in lowland marsh to alluvial plain settings, however localized Andisols and Inceptisols are also present. Our continuing efforts include analyses of pedogenic carbonate formation temperatures from clumped isotopes (Δ47) development of paleovegetation records from δ13C analyses on pedogenic carbonates and organic matter, and application of the RF-MAP model on Baringo Basin paleosols.  

How to cite: Lukens, W., Fox, D., Beverly, E., and Kingston, J.: Terrestrial paleoclimate and paleoenvironments from the Pliocene: case studies from the Meade Basin, Kansas, USA and the Baringo Basin, Kenya, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-53, https://doi.org/10.5194/egusphere-gc10-pliocene-53, 2022.

VPB9
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GC10-Pliocene-54
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ECS
Ana Lopes, Montserrat Alonso-García, Emília Salgueiro, Teresa Rodrigues, Mária Padilha, Antje Voelker, and Fátima Abrantes

Sensitive areas, like those of the upwelling systems, which are responsible for high ecological diversity, fisheries resources and air-sea CO2 exchanges are threatened by climate warming, and therefore, it is crucial to understand how they behaved in past warm climates. The Iberian margin upwelling system corresponds to the northern branch of the Canary Eastern Boundary Upwelling System. At the present, seasonal upwelling of cold and nutrient-rich waters makes the margin highly productive, being responsible for the high ecological biodiversity richness in the area. Despite of its enormous ecological and social importance, the knowledge on how the upwelling system worked in the past is still limited, particularly for periods older than 900 ka. 

In this work, we focused on the reconstruction of surface water conditions during the Late Pliocene, a period characterized by warm temperatures and high atmospheric CO2 concentration and considered as a unique analogue for future climate conditions. We studied sediments from IODP Site U1391 (37°21.5′N; 9°24.6′W, 1085 m water depth), recovered at the Southwest Iberian margin during Expedition 339, which provided for the first time, an almost continuous marine record of the SW Iberian margin dating back to the Pliocene. Surface water conditions have been reconstructed using planktonic foraminifer faunas and lipid biomarker concentrations across Marine Isotope Stages (MIS) G12 to G3 (2.84 to 2.66 Ma). The planktonic foraminifer results are being compared to the alkenone derived sea-surface temperature (SST), and the total alkenone concentration (reflecting coccolithophore productivity) records of Site U1391 in order to get a comprehensive interpretation of changes in sea surface productivity, seasonality and ecological diversity.

 

How to cite: Lopes, A., Alonso-García, M., Salgueiro, E., Rodrigues, T., Padilha, M., Voelker, A., and Abrantes, F.: Late Pliocene surface ocean conditions at the SW Iberian margin, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-54, https://doi.org/10.5194/egusphere-gc10-pliocene-54, 2022.

VPB10
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GC10-Pliocene-56
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ECS
Elena Domínguez Valdés, Ilja Kocken, Tobias Agterhuis, Inigo Müller, Noa Bode, Dirk Kroon, Lucas Lourens, and Martin Ziegler

The deep ocean comprises a large and relatively stable heat reservoir in the climate system. Hence deep sea temperature (DST) records constitute an important pillar of knowledge in the study of past climate states. Furthermore, a promising link exists between DSTs and global mean surface temperatures (GMSTs) [1]. DST reconstructions are nevertheless hampered by idealistic assumptions surrounding the interpretation of widely-used proxies like the ratio of oxygen isotopes on benthic foraminifera (δ18Ob). One such uncertain variable key in the analysis of δ18Ob is the isotopic composition of paleo-seawater (δ18Osw). Deconvolving this signal into temperature and ice-volume components across the last 5 Ma is non-trivial. Attempts to resolve it have often relied on independent temperature constraints from foraminiferal Mg/Ca ratios that also involve added uncertainties regarding variations in ocean chemistry through time, as well as the need for species-specific calibrations.

Carbonate clumped isotope thermometry (Δ47) can aid in overcoming these limitations since it is based on thermodynamic principles that govern the abundance of 13C-18O bonds within the crystal lattice, therefore granting it independence from estimations surrounding the composition of the precipitating fluid [2]. Recent clumped isotope DST records of the Eocene [3] and the Miocene [4] reveal significantly warmer ocean temperatures than traditionally accepted [5], suggesting a re-evaluation of the interpretation of δ18Ob records in the geological past.

Here we present Δ47-based DST constraints of the last 5 Ma obtained from benthic foraminifera of ODP Site 1264 in the South Atlantic Ocean. Reconstructions covering the Pliocene-Pleistocene transition shed light on the global climatic change that followed the mid-Pliocene warm period and culminated in full glaciation of the Northern Hemisphere. In particular, our Pliocene DST data lies in closer agreement with recent GMSTs estimations [6] than δ18Ob-based DST would imply.

 

[1] Valdes, P. J., et al. (2021). Climate of the Past, 17(4), 1483-1506.

[2] Eiler, J.M. (2007), Earth Planet. Sci. Lett. 262, 309-327.

[3] Agterhuis, T., et al. (2022), Commun Earth Environ 3, 39

[4] Modestou, S. E., et al. (2020) Paleoceanography and Paleoclimatology 35, e2020PA003927.

[5] Westerhold, T., et al. (2020), Science, 369, 1383–1387

[6] McClymont, E. L., et al. (2020) Climate of the Past, 16(4), 1599-1615.

How to cite: Domínguez Valdés, E., Kocken, I., Agterhuis, T., Müller, I., Bode, N., Kroon, D., Lourens, L., and Ziegler, M.: South Atlantic deep-sea temperature evolution across the Pliocene-Pleistocene from clumped isotope thermometry, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-56, https://doi.org/10.5194/egusphere-gc10-pliocene-56, 2022.

VPB11
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GC10-Pliocene-65
Viacheslav Khon, Babette Hoogakker, Birgit Schneider, Joachim Segschneider, and Wonsun Park

The world’s largest oxygen minimum zone (OMZ) resides in the eastern tropical Pacific where a poor oceanic ventilation and high biological production are both favourable for ocean oxygen deficiency in this area. The modern continental configuration with the Panamanian isthmus prevents the Pacific-Atlantic water mass exchange, shaping the climate and marine biogeochemistry features in this region. Therefore, a tectonic transition from the open to closed Central American Seaway (CAS) during the middle Miocene to middle Pliocene (~16-3 Ma BP) can be considered as a key time interval for the development of the tropical Pacific OMZ. This study aims at investigating an impact of the Pliocene CAS closure on a large-scale ocean circulation and its role for emergence of the modern tropical Pacific OMZ. To this end, we employ the global climate model KCM in combination with biogeochemical model PISCES.

According to our experiments, the Pliocene CAS closure has led to a termination of fresh-water supply from the Pacific to the North Atlantic and therefore to intensification of Atlantic Meridional Overturning Circulation. This result is supported by many previous modelling studies. It was also found that the open CAS is associated with large-scale eastward subsurface flow in the eastern tropical Pacific thereby enhancing water mass ventilation in this area. This, in turn, leads to an increase in marine oxygen concentration in the eastern tropical Pacific during the Miocene.

A biological production is another important factor affecting the OMZ maintenance. Here we show that the CAS opening is associated with the export of nutrients from the Pacific towards the Atlantic. This, in turn, leads to a reduced net primary production (NPP) in the eastern tropical Pacific and, therefore, to lower oxygen consumption in this region. Both altered NPP and ocean ventilation contribute effectively to the OMZ development in the eastern tropical Pacific for the modern continental configuration.

How to cite: Khon, V., Hoogakker, B., Schneider, B., Segschneider, J., and Park, W.: Evolution of the tropical Pacific oxygen minimum zone during the Miocene-Pliocene from model simulations: A role of the Panama Isthmus closure , The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-65, https://doi.org/10.5194/egusphere-gc10-pliocene-65, 2022.

VPB12
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GC10-Pliocene-40
Natalie Burls, Alexey Fedorov, Ulla Heede, Madison Shankle, Matthew Thomas, Wei Liu, Donald Penman, Heather Ford, Peter Jacobs, Noah Planavsky, and Pincelli Hull

Several oceanic and atmospheric mechanisms have been put forward to describe the response of the tropical Pacific to global warming. Still uncertainties persist in their interaction and relative importance, with projections varying substantially across climate models. When we turn to the last time in Earth’s history that atmospheric CO2 estimates exceed 400 ppm, the Pliocene, several apparent paradoxes appear, clouding our view of the tropical Pacific during the Pliocene and its utility as a potential analogue for future warming. However, when proper consideration is given to the timescales associated with the oceanic and atmospheric mechanisms that support tropical Pacific climate variability, several of these apparent paradoxes can be resolved. The first apparent paradox is between the reduced east-west SST gradient (weaker Walker Circulation) mean state reconstructions for the Pliocene and the strengthening of the east-west SST gradient during 20th century warming. This paradox can be resolved by considering the transient versus equilibrium processes involved in the response to global warming. The second apparent paradox is evidence for ENSO during the Pliocene even while the mean state resembled more El Nino-like (i.e., El Padre) conditions. This apparent paradox is resolved by the relative importance of coupled feedbacks, other than the thermocline feedback, generating inter-annual variability in the Pliocene. Thirdly, an apparent paradox between the reduced Pliocene east-west SST gradient, indicative of reduced wind-driven upwelling, and evidence of enhanced biological productivity in the east Pacific where productivity is typically driven by upwelling. This apparent paradox can be reconciled by evidence for older, more acidic, and nutrient-rich water reaching the equatorial Pacific by way of a Pacific meridional overturning circulation during the Pliocene, providing a mechanism for enhanced productivity existing alongside a reduced east-west SST gradient.

How to cite: Burls, N., Fedorov, A., Heede, U., Shankle, M., Thomas, M., Liu, W., Penman, D., Ford, H., Jacobs, P., Planavsky, N., and Hull, P.: How will the tropical Pacific respond to global warming? The importance of timescale when considering apparent paleo-paradoxes , The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-40, https://doi.org/10.5194/egusphere-gc10-pliocene-40, 2022.

Posters: Thu, 25 Aug, 15:30–17:00 | Poster area Session C

PC1
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GC10-Pliocene-8
Edward Gasson, Carrie Lear, Amy Sparkes, Ruthie Halberstadt, Rob DeConto, Matt Trevers, Tony Payne, and David Pollard

Despite a major effort to constrain peak sea level during the mid-Pliocene warm period, uncertainties remain large. This interval is of interest because of the analogous CO2 concentration to present day and because of the potential retreat of a large portion of the Antarctic Ice Sheet. The usefulness of this period to constrain ice sheet model physics is limited by these large uncertainties on peak sea level. Here we discuss efforts to produce a new record of the amplitude of sea level change from interglacial to glacial periods during the early and mid-Pliocene, which have lower uncertainties than peak sea level. We combine this effort with new climate and ice sheet model simulations of the glacial to interglacial cycle for ice sheets in both hemispheres. We discuss how this work will constrain the magnitude of Antarctic Ice Sheet retreat during warm intervals of the mid-Pliocene and how we use these constraints to discriminate between different ice sheet model physics.

How to cite: Gasson, E., Lear, C., Sparkes, A., Halberstadt, R., DeConto, R., Trevers, M., Payne, T., and Pollard, D.: Constraining the amplitude of Antarctic Ice Sheet change during warm intervals of the Pliocene , The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-8, https://doi.org/10.5194/egusphere-gc10-pliocene-8, 2022.

PC2
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GC10-Pliocene-14
Bette L. Otto-Bliesner, Jiang Zhu, Jessica Tierney, Ran Feng, Clay Tabor, Jesse Nusbaumer, Andrew Walters, Esther Brady, and Chijun Sun

In this poster, I will present plans to complete a PlioMIP2 simulation at high resolution (HR) in the fully-coupled Community Earth System Model (CESM). This simulation is part of the NCAR Accelerated Scientific Discovery PaleoWeather project and also includes HR simulations of the Early Eocene Climatic Optimum, with CO2 reconstructed to be much higher than today’s, and the Last Glacial Maximum with much lower CO2. CESM is being configured with a resolution of 0.25° for the atmosphere and land, and 0.1° for the ocean and sea ice.

This set of fully-coupled paleo-HR climate simulations for past greenhouse and icehouse climates will study the drivers that govern the characteristics of extreme weather events in both atmosphere and ocean under altered climate states. Potential applications include diagnosing changes in atmospheric synoptic features like mesoscale convective systems, tropical cyclones, monsoons, and atmospheric rivers, of coastal upwelling zones, and for their impacts on past regional precipitation patterns. In addition, the paleo-HR simulations will better resolve the landscape of topographies and coasts.  Both are critical for accurate comparison with the paleoclimate record since most of the terrestrial and marine paleo-observations come from basins surrounded by mountains and near-shore locations.

The paleo-HR simulations will complement the preindustrial, historical and RCP8.5 future simulations available from the iHESP project (https://ihesp.tamu.edu/), resulting in HR simulations to investigate the dynamics that connect past and future climate changes.

How to cite: Otto-Bliesner, B. L., Zhu, J., Tierney, J., Feng, R., Tabor, C., Nusbaumer, J., Walters, A., Brady, E., and Sun, C.: Modeling the Mid-Pliocene at High Resolution, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-14, https://doi.org/10.5194/egusphere-gc10-pliocene-14, 2022.

PC3
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GC10-Pliocene-28
Ning Cao, Katherine Power, and Qiong Zhang

A distinct multi-centennial climate variability signal is apparent in the EC-Earth3 model 2000-year pre-industrial control simulation. This variability arises primarily in the North Atlantic basin and appears to be closely associated with Atlantic Meridional Overturning Circulation (AMOC). It is mainly modulated by the ocean heat transport and freshwater exchange between the Arctic Ocean and the North Atlantic. When a stronger AMOC occurs, it is coherent with anomalous anticyclonic surface currents in the Arctic and cyclonic surface currents in Greenland, Iceland, Norwegian Seas and Labrador Seas. The increased heat in the subpolar gyre region strengthens the oceanic surface evaporation, resulting in a saltier deep convection region and hence strengthens the deep-water formation. Meanwhile, stronger AMOC transports more ocean heat into the Arctic and melts the sea-ice, causing more freshwater to enter the Arctic. The AMOC strength and freshwater accumulation in the Arctic both reach their peaks in about 50 years. Then, in the following 50 years, the freshwater in Arctic slowly pours into the Greenland-Iceland-Labrador Seas, weakens the subpolar gyre, inhibits deep-water formation and eventually weakens the AMOC. Finally, the oscillation shifts to the opposite phase. These physical processes sustain a 160-200 year variability of AMOC, which is considered as the main driver of the multi-centennial climate variability signal in our simulation.

 

In high CO2 forced climates, here simulated with climate sensitivity experiments with alternate CO2 levels of 400 and 560 ppm respectively, the multi-centennial variability of AMOC is present but has a suppressed amplitude. AMOC variability under 400 ppm CO2 forcing shows a similar frequency band as that in the pre-industrial simulation, with enhanced Arctic-Atlantic salinity anomaly exchange. Under 560 ppm CO2 forcing, the AMOC variability shows a lower frequency band. Here, alongside the Arctic-Atlantic salinity exchange, there are also salinity anomalies propagating from the south Atlantic to the north Atlantic. This leads to a longer maintaining of meridional inter-basin exchanges in the entire Atlantic and Arctic. The decrease of Arctic sea-ice under stronger radiative forcing will cause more freshwater to enter the North Atlantic, slow down the deep-water flow, and thus suppress the AMOC strength. Meanwhile the mechanism that sustains AMOC variability, which was inferred from the pre-industrial simulation, will also change as less sea ice in the North Atlantic and Arctic lead to a more well mixed Arctic-Atlantic salinity anomaly exchange.

These experiments indicate that the dynamics of the meridional inter-basin exchange in the north Atlantic and its influence on the salinity are essential components to the centennial climate variability and should be considered when assessing future North Atlantic climate.

How to cite: Cao, N., Power, K., and Zhang, Q.: Suppressed multi-centennial climate variability in EC-Earth3 high CO2 simulations, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-28, https://doi.org/10.5194/egusphere-gc10-pliocene-28, 2022.

PC4
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GC10-Pliocene-30
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ECS
Arthur Oldeman, Michiel Baatsen, Anna von der Heydt, Aarnout van Delden, and Henk Dijkstra

The Pliocene is often considered the ‘best analog’ for near future climate (e.g. Burke et al, 2018). This notion is mainly based on similar atmospheric CO2 concentration and surface temperatures. However, a ‘best’ analog does not necessarily imply a good analog. We therefore pose the question; to what extent can we treat the mid-Pliocene climate as an analog for a warm future?

We focus on atmospheric dynamics and variability in the Northern Hemisphere winter, for two main reasons: 1. Climate projections are not agreeing on the changes in atmospheric variability we can expect in the future, and 2. The mid-Pliocene exhibits the largest geographical differences to the present-day in the Northern Hemisphere, compared to the Southern Hemisphere. We use the results of simulations from a global coupled climate model, CCSM4-Utrecht, that is a part of PlioMIP2. From a pre-industrial reference simulation (E280), we consider a CO2 doubling experiment at 560ppm (E560), and a mid-Pliocene boundary conditions experiment at 280ppm (Eoi280).

We consider the mean sea-level pressure using 200 years of January-mean data. In response to the mid-Pliocene boundary conditions, we find a large increase in the mean along with a decrease standard deviation over the North Pacific Ocean. This is accompanied with a weakened subtropical jet over the western North Pacific, as well as increased occurrence of a split jet condition over the eastern North Pacific. We connect all these findings to a reduction in the potential vorticity gradient over the western North Pacific. This causes the jet to weaken over the western North Pacific and allows a regime shift towards more anticyclonic wave breaking in the eastern North Pacific. We do not see tendencies towards similar behavior in the CO2 doubling experiment. This suggests that the mid-Pliocene is not a good analog for a warm future climate when considering Northern hemisphere winter atmospheric dynamics.

How to cite: Oldeman, A., Baatsen, M., von der Heydt, A., van Delden, A., and Dijkstra, H.: Mid-Pliocene not a good analog for future warm climate when regarding atmospheric dynamics in Northern Hemisphere winter , The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-30, https://doi.org/10.5194/egusphere-gc10-pliocene-30, 2022.

PC5
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GC10-Pliocene-31
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ECS
Jordan Abell and Matthew Osman

The midlatitude jet streams, frequently referred to as ‘the westerlies’, are an important facet of the climate system that critically impact global hydroclimate, ocean circulation, and aerosol distributions. Recent observations hint at changes in both the position and intensity of the westerlies due to ongoing anthropogenic climate change.  However, the historical significance of these shifts, as well as the magnitude and implications of projected future westerly changes, remains highly uncertain given the short time span of modern observations. Here we use output from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) to evaluate changes in the position, intensity, and variability of the westerlies during the mid-Pliocene (~3.3 to 3.0 Ma), a warm period in Earth’s history that is considered an analogue for climate expected in the coming decades to century. We focus on comparing the Pliocene results to output from corresponding Pre-industrial simulations for three societally relevant ocean basins: the North Atlantic, the North Pacific, and the Southern Ocean. For the annual mean, we find considerable cross-model disagreement, amounting to near-negligible multi-model mean (n = 17) shifts of ≤1˚ and <0.5 m s-1 in the position and intensity of the westerlies, respectively, during the Pliocene. While these are considerably smaller than those indicated by prior (PlioMIP1) results, we show that annual averaging obscures a much larger seasonal divergence in Pliocene westerly wind variability, which appears broadly consistent across models and oceans basins. This divergence is especially evident in the North Atlantic westerlies, which show a poleward migration and intensification of nearly 2˚ and ~1 m s-1, respectively, during boreal winter, and an equatorward shift and diminishing of ~4˚ and ~1 m s-1 during boreal summer. To better contextualize and further validate these findings, ongoing efforts are now comparing the PlioMIP2 results to available paleoclimate dust flux, precipitation, and sea-surface temperature records that are potentially relevant for characterizing the Pliocene westerlies.

How to cite: Abell, J. and Osman, M.: Were Winds Weird in a Warmer World? A Data-Model Comparison of the Pliocene Westerlies, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-31, https://doi.org/10.5194/egusphere-gc10-pliocene-31, 2022.

PC7
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GC10-Pliocene-58
Julia Tindall and Alan Haywood

The Pliocene Model Intercomparison Project (PlioMIP; phases 1 and 2) has provided a wealth of model output relating to a climate with CO2 ~400ppmv.  However much of the analysis of this dataset has focussed on temporally averaged diagnostics. 

Here we look at the contribution of the HadCM3 model to PlioMIP2 in more detail.  We consider daily precipitation, the maximum daily temperature, and the minimum daily temperature, and use these to derive indices of extreme weather and climate.    

We show that the area of land where the maximum daily temperature exceeds 40oC at some point during the year was greatly expanded in the Pliocene compared to the preindustrial.  We also show that, at many locations, most days in the year have daily temperatures that are above the warm extreme threshold for that calendar day in the preindustrial.  Correspondingly very few Pliocene temperatures are below the preindustrial cold extreme threshold.

These Pliocene extreme climate diagnostics can be compared with future extreme climate diagnostics to provide additional information about the analogous nature of the Pliocene climate.

How to cite: Tindall, J. and Haywood, A.: Palaeo perspectives on climate extremes:  What can the Pliocene tell us?, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-58, https://doi.org/10.5194/egusphere-gc10-pliocene-58, 2022.

PC8
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GC10-Pliocene-4
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ECS
Amila Sandaruwan Ratnayake

Sedimentary profiles in Sri Lanka capture evidence for the regional and global-scale long-term climatic transition (e.g. K-Pg boundary mass extinction, Late Paleocene Thermal Maximum, Eocene–Oligocene climate transition, the growth of the Antarctic ice sheets) during its northward voyage from Gondwana to Asia. However, a glacial-interglacial climatic transition is not studied yet in Sri Lanka, and is poorly resolved in the Indian Ocean. Consequently, this ongoing research project is aimed to (i) reconstruct glacial-interglacial sea-level changes and (ii) identify its teleconnection to the Antarctic ice sheet dynamics. Sri Lanka has few recorded seismically driven tectonic activities and a low tidal range (about 0.5 m) making it suited for interglacial sea-level studies. The continental shelf along the south and southwest coasts of Sri Lanka is narrow and it is among the steepest continental slope in the world. However, several sea cliffs along the northwest and southeast coasts of Sri Lanka can be used to reconstruct interglacial sea-level changes in the central Indian Ocean. Here, several sedimentary profiles (i.e. deepwater Mannar Basin  and sea cliffs at Point Kudrimalai in the Wilpattu National Park,  Bundala and Patirajavela cliffs, and Ussangoda cliff) were examined to identify stratigraphic variations. Results show that carbonate burial drastically increased (average = 40.2%) in the Mannar Basin sediments from the Late Paleocene (close to the Paleocene–Eocene boundary). This observation can be linked to the movement of the Indian plate (including Sri Lanka) northward into equatorial latitudes and/or the growth of the Antarctic ice sheets by the sharp decline of atmospheric CO2 concentration. The Miocene limestone in the northwest of Sri Lanka has also suggested the global cooling trend. Nevertheless, sea cliffs along the northwest and southeast coasts of Sri Lanka provide sufficient sedimentological evidence for the interglacial highstands. The Uranium–Thorium ages of marine shells in near-coast sites in India are dated to ca. 124.0–112.0 ka. It suggests that sea-level rose about 6–9 m to the present level during the Eemian interglacial period. The association of cross-bedded sandstone with calcrete in the upper beds shows a terrestrial dune environment after a relative sea-level fall during the glacial period. Consequently, the preliminary stratigraphic observations concluded that sea cliffs in Sri Lanka can be identified as promising sites to study teleconnection between glacial-interglacial sea-level changes in the Indian Ocean and the melting history of Antarctic ice sheets.

How to cite: Ratnayake, A. S.: Stratigraphical evidence for glacial-interglacial sea-level changes in the Indian Ocean: Projection to the Antarctic ice sheet dynamics, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-4, https://doi.org/10.5194/egusphere-gc10-pliocene-4, 2022.

PC9
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GC10-Pliocene-17
Heather L. Ford, Natalie J. Burls, Peter Jacobs, Alexandra Jahn, Rocio P. Caballero-Gill, David A. Hodell, and Alexey Fedorov

Geologic intervals of sustained warmth such as the mid-Pliocene warm period can inform our understanding of future climate change, including the long-term consequences of oceanic uptake of anthropogenic carbon. Here we generate carbon isotope records and synthesize existing records to reconstruct the position of water masses and determine circulation patterns in the deep Pacific Ocean. We show that the mid-depth carbon isotope gradient in the North Pacific was reversed during the mid-Pliocene in comparison to today, which implies water flowed from north to south and deep-water formation likely formed in the subarctic North Pacific Deep Water. An isotopically enabled climate model that simulates this North Pacific Deep Water reproduces a similar carbon isotope pattern. Modelled levels of dissolved inorganic carbon (DIC) content in the North Pacific decreases slightly,  though the amount of carbon stored in the ocean actually increases by 1.6% relative to modern due to an increase in DIC in the surface ocean. Although the modelled Pliocene ocean maintains a carbon budget similar to the present, the change in deep ocean circulation configuration causes pronounced downstream changes in biogeochemistry.

How to cite: Ford, H. L., Burls, N. J., Jacobs, P., Jahn, A., Caballero-Gill, R. P., Hodell, D. A., and Fedorov, A.: Sustained mid-Pliocene warmth led to deep water formation in the North Pacific, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-17, https://doi.org/10.5194/egusphere-gc10-pliocene-17, 2022.

PC11
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GC10-Pliocene-35
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ECS
Deborah Tangunan, Ian Hall, Luc Beaufort, Paul Halloran, Aidan Starr, and Alexandra Nederbragt

The mid-Piacenzian or mid-Pliocene Warm Period (mPWP; 3.264-3.025Ma) is the most recent period of sustained global warmth, which stands in contrast to the more variable and progressively cooler Pleistocene glacial-interglacial climate which followed. Global temperatures were 3˚C higher than the pre-industrial level, with atmospheric carbon dioxide (pCO2) reaching up to 410ppmv, making the mPWP the nearest past analogue for future warm climate. Thus, proxy reconstructions that can accurately capture biological response to past and projected pCO2 are crucial in understanding future climate scenarios.

Here we present initial high-resolution climatic variability and carbon cycling records from oxygen and carbon isotopes, assemblage, and morphometry of coccoliths – calcium carbonate exoskeletons produced by marine phytoplankton coccolithophores – from sediments collected during the IODP Expedition 361 at the Mozambique Channel (U1476; 15°49.25′S, 41°46.12′E; 2166m water depth), spanning 2.96 and 3.40Ma at 0.5 to 3.7kyr resolution. Previous studies show that the modern surface waters above Site U1476 are in air-sea exchange CO2 equilibrium, making Site U1476 an ideal location for pCO2 reconstructions. We also explore the expressions of coccolith isotopic vital effects from size-separated fractions that have been linked to cell size, growth rate, and calcification degree, providing empirical correlation with aqueous CO2 concentrationsand ultimately, with pCO2 levels.

Preliminary results show strong precession-related 23-kyr cyclicities prior to M2 glaciation. These cycles are associated with negative coccolith fraction δ18O (δ18OCF) excursions coinciding with increasing upper ocean primary productivity resulting from a more vigorous Mozambique Channel Throughflow, forced by precession minima and northern hemisphere summer insolation maxima. A change in orbital configuration in upper ocean temperature and stratification records, from precession to obliquity, occurs after M2, with an overall climate background of 100-kyr glacial-interglacial cycles in upper ocean primary production, indicating commencement of the longer-term 100-kyr cooling trend observed through the Pleistocene. Periodicities at the eccentricity band, often linked to Pliocene ice volume, are shown in the δ13CCF, supporting prior findings on tight coupling between ice volume and carbon cycle changes, analogous to those recorded during the late Pleistocene.

How to cite: Tangunan, D., Hall, I., Beaufort, L., Halloran, P., Starr, A., and Nederbragt, A.: Climate and carbon cycling across the mid-Pliocene Warm Period, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-35, https://doi.org/10.5194/egusphere-gc10-pliocene-35, 2022.

PC12
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GC10-Pliocene-38
Coralie Zorzi and Anne de Vernal

Evolution of the temperature contrast in the subarctic gyre is fundamental to better constrain the scheme of the Plio-Pleistocene climate-ocean-ice transition in the northern North Pacific region. The growth of glaciers in Alaska during the early Pliocene is in disagreement with the hypothesis suggesting that development of permanent continental ice in the circum-North Pacific is associated to onset of the modern halocline at 2.7 Ma. Hence, development of warm surface conditions in eastern Pacific during the early Pliocene has been proposed as key mechanism fostering regional evaporation. These assumptions are sustained by model experiments simulating a strong W-E contrast in subarctic Pacific during the Pliocene (Burls et al., 2017) and a reduction of the surface gradient at 2.7 Ma (Haug et al., 2005). However, evolution of the zonal subarctic temperature gradient remains unclear in geological records. In the view to fill this gap, we investigated the dinocyst assemblages at Ocean Drilling Program (ODP) Site 882 located in western subarctic gyre, which were be compared with the Plio-Pleistocene palynostratigraphy previously performed in the Gulf of Alaska.

Prior 4.2 Ma, dinocyst assemblages at ODP Site 882 are characterized by cold and cool-tolerant species such as Pyxidinopsis braboi and Filisphaera filifera with occasional occurrence of thermophilic species reflecting cold sea-surface water conditions. This observation is in line with UK37 SST analysed at the study site but contrasts with the highest percentages of thermophilic dinocysts, including Ataxiodinium zevenboomii, Impagidinium velorum and Impagidinium patulum, recorded in the Gulf of Alaska. Hence, our results documented for the first time a strong temperature contrast in the subarctic Pacific gyre with warmer conditions in the East than in the West as previously simulated by the models (Bursl et al., 2017). However, reduction of the zonal temperature contrast was reported at 4.2 Ma, well before the development of the halocline at 2.7 Ma, by the increase of Impagidinium detroitense and Habibacysta tectata over the subarctic gyre. Despite uncertainties regarding the ecology of these two extinct taxa, we tentatively interpreted this change as the development of cool but saline conditions in the subarctic Pacific. Our study acknowledges that a better understanding of the mechanisms driving major climate changes is reinforced by integrating approach combining proxy data and climate models.

How to cite: Zorzi, C. and de Vernal, A.: Evolution of East-West contrast in the subarctic Pacific gyre during the Plio-Pleistocene based on new palynological evidences at ODP Site 882, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-38, https://doi.org/10.5194/egusphere-gc10-pliocene-38, 2022.

PC13
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GC10-Pliocene-44
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ECS
Emmeline Gray, Pallavi Anand, Marcus Badger, Clara Bolton, Melanie Leng, and Masafumi Murayama

The Indian Summer Monsoon (ISM) brings seasonal winds and rains to the Indian subcontinent.  The winds cause surface ocean mixing in the southern Bay of Bengal (BoB), bringing nutrients to the surface that fuel ocean productivity and export of carbon to the sea floor. To improve the understanding of the role of monsoon winds in low-latitude surface ocean productivity and carbon export, the Plio-Pleistocene interval is ideal because boundary conditions were evolving.  We aim to reconstruct variability in surface ocean and export productivity across the late-Pliocene and early-Pleistocene in response to ISM wind-driven mixing in the southern BoB.

Here we analyse sediments from IODP Site U1443  (Exp. 353) from ~1.9-2.8 million years ago.  A new benthic oxygen isotope (δ18O) stratigraphy (at ~3-thousand-year resolution) and age model tied to the global benthic δ18O stack are presented.  We utilise these sediments to obtain bulk sediment X-ray fluorescence (XRF) core scanning elemental data and coccolithophore assemblages to infer changes in summer monsoon runoff and surface ocean productivity influenced by monsoon wind strength. We use % Florisphaera profunda (coccolithophore assemblage) along with bulk sediment XRF Br as productivity indicators and a “terrigenous” bulk sediment XRF elemental composition stack as a wind strength and runoff indicator.  We observe increased productivity during glacials (MIS 96, 98, 100), coinciding with increased terrigenous input.  This observation is coherent with previous low-latitude productivity records from the equatorial Pacific. However, in contrast to equatorial Pacific productivity records, influenced by obliquity, our southern BoB records show robust surface productivity (% F. profunda) and summer monsoon runoff (terrigenous stack) peaks in both the obliquity and precession bands. We will discuss linkages between monsoon wind and runoff across the Plio-Pleistocene in context with other monsoon records.

How to cite: Gray, E., Anand, P., Badger, M., Bolton, C., Leng, M., and Murayama, M.: Plio-Pleistocene productivity reconstructions in the Indian Monsoon region, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-44, https://doi.org/10.5194/egusphere-gc10-pliocene-44, 2022.

PC14
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GC10-Pliocene-47
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ECS
Kai Zhang, Tereza Kunkelova, Paul A. Wilson, Chuang Xuan, and Anya J. Crocker

Past hydroclimate change in Africa and the Arabian Peninsula plays a vital role in early human evolution and dispersal. Although arid today, North Africa and the Arabian Peninsula experienced periodic humid intervals, during which strengthened rainfall driven by astronomical forcing (chiefly eccentricity-modulated precessional cycles) transformed the Saharo-Arabian desert into a vegetated landscape cross-cut by rivers and lakes. The relationship between hydroclimate variability and hominid evolution is strongly debated and continuous palaeoclimate reconstructions are required to provide a context for understanding evolutionary outcomes on land. However, there are major discrepancies between different types of proxy data and between these reconstructions and those generated by numerical models as to the spatial and temporal occurrence of humid events and to the seasonality of the rainfall responsible. Two major contributing problems concern (i) the incontinuous nature of palaeo records from terrestrial archives (palaeolake sediments and stalagmites) and (ii) the challenges of attribution associated with records from marine sediment cores. Here, we report geochemical and stable isotope data from the Arabian Sea to reconstruct past environmental changes in a multi-proxy approach, which will help us to understand the relationship between palaeoclimate change and hominid evolution, reveal how the West Asian monsoon responded to a period of increased global warmth and furthermore, provide a reliable data set for model simulations in the future.

How to cite: Zhang, K., Kunkelova, T., Wilson, P. A., Xuan, C., and Crocker, A. J.: What don't we understand about past rainfall changes in Africa and Arabia during the Pliocene?, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-47, https://doi.org/10.5194/egusphere-gc10-pliocene-47, 2022.

PC15
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GC10-Pliocene-68
Ellen Berntell, Qiong Zhang, and Qiang Li

The mid-Pliocene warm period (mPWP; ∼ 3.2 million years ago) is seen as the most recent time period characterized by a warm climate state, with similar to modern geography and ∼ 400 ppmv atmospheric CO2 concentration, and is therefore often considered an interesting analogue for near-future climate projections. Paleoenvironmental reconstructions indicate higher surface temperatures, decreasing tropical deserts, and a more humid climate in West Africa characterized by a strengthened West African Monsoon (WAM). Using model results from the second phase of the Pliocene Modelling Intercomparison Project (PlioMIP2) ensemble, we analyze changes of the WAM rainfall during the mPWP by comparing them with the control simulations for the pre-industrial period. The ensemble shows a robust increase in the summer rainfall over West Africa and the Sahara region, with an average increase of 2.5mm/d, contrasted by a rainfall decrease over the equatorial Atlantic. An anomalous warming of the Sahara and deepening of the Saharan Heat Low, seen in >90% of the models, leads to a strengthening of the WAM and an increased monsoonal flow into the continent. A similar warming of the Sahara is seen in future projections using both phase 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). Though previous studies of future projections indicate a west–east drying–wetting contrast over the Sahel, PlioMIP2 simulations indicate a uniform rainfall increase in that region in warm climates characterized by increasing greenhouse gas forcing. We note that this effect will further depend on the long-term response of the vegetation to the CO2 forcing. 

How to cite: Berntell, E., Zhang, Q., and Li, Q.: Mid-Pliocene West African Monsoon rainfall as simulated in the PlioMIP2 ensemble , The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-68, https://doi.org/10.5194/egusphere-gc10-pliocene-68, 2022.

PC16
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GC10-Pliocene-32
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ECS
Theodor Mayer, Ran Feng, Tripti Bhattacharya, Erin McClymont, Heather Ford, and Sze Ling Ho

Ocean-atmosphere coupled models predict pronounced weakening of the Pacific Walker Circulation (PWC) with increasing CO2 concentration associated with the enhanced tropospheric stability and reduced convective mass overturning. However, instrumental observations from the past few decades are inconsistent and do not support a clear weakening of the Walker circulation. The detection of the role of increasing CO2 is in part impeded by substantial internal variability and anthropogenic aerosol forcings. Here we explore the possibility of using a paleoclimatic analogue to understand the contemporary PWC sensitivity to CO2 changes. We focus on the interval from mid-Piacenzian (MP, 3.3 – 3.0 Ma) to early Pleistocene (~2.4 Ma). The MP had elevated CO2 concentrations (~400ppm) and geography, topology, and vegetation similar to today. Following the MP, global CO2 and temperature decreased, leading to the intensification of the Northern hemisphere glaciation. We seek to identify potential proxy constraints on model simulated PWC sensitivity to CO2 forcing by focusing on changes in the hydroclimatology during this time interval. We developed several sets of isotope-tracking enabled CESM version 1.2 simulations, which utilize pre-Industrial and mid-Piacenzian boundary conditions, different CO2 levels, and water tagging of several key oceanographic regions to track the life cycles of various water species (H216O, H218O and HD16O). Preliminary results show that Pliocene boundary conditions have little impact on the relationship between the CO2 forcing and the intensity of PWC. The precipitation δD contrast between the eastern and western tropical Pacific is linked to varying rates of moisture convergence change, and scales well with the PWC strength, suggesting high potential for developing PWC strengths proxy with precipitation isotopic records from both sides of the tropical Pacific. Our ongoing work will further identify physical processes responsible for the simulated precipitation isotopic signals: i.e., whether they reflect changes in the moisture source, moisture transport, or moist convection at the destination. Furthermore, coupled simulations are being carried out to understand seawater isotopic signatures of PWC related precipitation changes, and contributions from changing ocean dynamics to PWC changes during this interval.

How to cite: Mayer, T., Feng, R., Bhattacharya, T., McClymont, E., Ford, H., and Ling Ho, S.: Water isotopic imprints of Pacific Walker Circulation responses to CO2 decline during the late Pliocene and early Pleistocene, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-32, https://doi.org/10.5194/egusphere-gc10-pliocene-32, 2022.