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.

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.

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.

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.

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., Jones, 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.

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.

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.

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.

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.

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.

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.

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.

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 95^th 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: Jones, 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.

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.

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.

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.

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.

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.

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 2^nd 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.

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.

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.

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.

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.

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 (δ¹⁸O_b). One such uncertain variable key in the analysis of δ¹⁸O_b is the isotopic composition of paleo-seawater (δ¹⁸O_sw). 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 δ¹⁸O_b 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 δ¹⁸O_b-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.

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.

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 20^th 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.

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.

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.

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.

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.

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.

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 40^oC 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.

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.

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.

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 (δ¹⁸O_CF) 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 δ¹³C_CF, 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.

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 U^K₃₇ 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.

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.

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.

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.

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.