The intensification of the hydrological cycle, driven by global warming is expected to amplify extreme weather events and associated erosion. These hydrological shifts are likely to disrupt soil stability, accelerate organic carbon mineralization, and alter terrestrial ecosystems, all of which have potential implications for carbon cycle dynamics. Such terrestrial carbon cycle feedback mechanisms remain poorly constrained. While relatively slow compared to present-day carbon cycle change, the millennial scale onset of the Paleocene-Eocene Thermal Maximum (PETM, ~56 million years ago) was similarly associated with a massive input of 13C-depleted carbon into the ocean-atmosphere system that is recorded by a negative carbon isotope excursion (CIE) in sedimentary components. The PETM marks a global temperature increase of ~5 °C and is characterized by significant associated hydrological disturbances, erosion, and vegetation changes; the precise timing, impact and spatial scale of these processes are still being debated. Here, we show vegetation shifts at the Norwegian Margin during the CIE onset interval at centennial scale resolution. Furthermore, we show terrestrial disturbances during the CIE onset are synchronous along several continental margins globally based on organic microfossil assemblages and reworked soils (clay minerals and organic matter). These observations signal changes in terrestrial biomass, intensified oxidation of soils and weathering of fossil organic carbon, potentially acting as a positive carbon cycle feedback mechanism. Carbon cycle model simulations indicate that these shifts in terrestrial carbon storage and fluxes may have appreciably contributed to the CIE and climate change, highlighting the importance of constraining the response of terrestrial biosphere feedback mechanisms to changing weather and climate.
How to cite: Nelissen, M., Willard, D., Bowen, G., Hollaar, T., Sluijs, A., Frieling, J., and Brinkhuis, H.: Increased terrestrial ecosystem disturbances during the onset of the PETM and associated carbon cycle perturbations , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20536, https://doi.org/10.5194/egusphere-egu25-20536, 2025.
Inorganic carbonate proxies measured on planktic foraminifera, such as δ18O and Mg/Ca, suggest that the early Eocene Climatic Optimum (EECO; ~50 Ma) was a period characterised by extremely warm global ocean temperatures (Hollis et al., 2019). However, significant inter-proxy offsets in reconstructed absolute temperatures exist and stem from differing sensitivities to diagenesis, uncertainties of past seawater composition, and variations in the water depth recorded by different proxy archives. Here we present clumped isotope-derived upper ocean temperature reconstructions measured on coccoliths, from a suite of globally distributed sites for an interval (50.7 Ma–50.4 Ma) representative of peak EECO conditions. Coccolith clumped isotope-derived temperatures are independent of the seawater carbonate chemistry and are species-independent (Clark et al., 2024), which allows for reliable past temperature reconstructions. We compare our results to HADCM3 and GFPL annual time series model simulations with multiple CO2 levels from the recent DeepMIP model compilation (Steinig et al., 2024). Since we consider variability across “deep” time to be minimal, we identify the depths and months our coccoliths most likely calcified at for each site, to allow for better comparison to the annual time series model simulation. This is especially important since modern coccoliths calcify at different depths across different ocean basins (Clark et al., 2024; Mejia et al., 2023).
Using the well-constrained coccolith calibration (Clark et al., 2024), we find that coccolith clumped isotope-derived temperatures generally agree well with previous surface ocean temperature reconstructions from other inorganic carbonate proxies (Hollis et al., 2019). During the EECO, we also find a similar magnitude of variability in coccolith calcification depths as observed in the modern ocean. This suggests that coccolith calcite records upper ocean temperature signals rather than solely sea surface temperature. Furthermore, the variability in overlap between the model and coccolith clumped temperatures across an annual year, in particular for the mid latitudes, further confirm that coccolith calcite captures upper ocean temperature signals largely during coccolithophore blooming months. Our coccolith clumped isotope-derived temperature data confirms the relatively flat latitudinal gradients and warm high latitudes found by other temperature proxies during the EECO, highlighting the potential of coccolith clumped isotopes as an useful tool for reconstructing past upper ocean temperatures during past warm climates.
Hollis et al., 2019, https://doi.org/10.5194/gmd-12-3149-2019 ; Mejia et al., 2023, https://doi.org/10.1016/j.epsl.2023.118313 ; Clark et al., 2024, https://doi.org/10.22541/essoar.173042174.40363194/v1 ; Steinig et al., 2024, https://doi.org/10.1038/s41597-024-03773-4
How to cite: Clark, A., Jaggi, M., Bernasconi, S., Taylor, V., Meckler, N., Liu, X., Huber, M., and Stoll, H.: Proxy-model comparison of EECO upper ocean temperatures using coccolith clumped isotope thermometry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11152, https://doi.org/10.5194/egusphere-egu25-11152, 2025.
Seasonality and extreme weather events are important aspects of Earth’s climate system. Yet few climate archives provide continuous records at suitably high-resolution (i.e. daily) and long duration (i.e. decades) to study these features in the geologic past. (Sub)tropical marine giant clams (Tridacna) are ideal for this purpose because they grow quickly (mm-cm/year) and live for up to 100 years. Their aragonitic shells capture multi-annual climate to multi-day weather patterns of tropical reefs.
We present a late Miocene multi-proxy environmental record from the Makassar Strait (East Borneo, Indonesia), which includes oxygen and carbon isotope data at sub-monthly to seasonal resolution, growth rates at daily resolution as well as elemental ratios (B, Na, Mg, Sr, Ba to Ca) at sub-daily resolution. Using our Daydacna Python script we used the daily elemental cycles from LA-ICPMS analyses to create an internal age model, which revealed a growth span of ~57 years (20,916 ± 1,220 days (2 SD)).
Our high-resolution data reveal multi-annual, seasonal and daily cycles, along with evidence of extreme weather events. We suggest that the multi-annual cycles (about three years) may indicate a global ENSO-like climate pattern in the late Miocene, while annual cycles reflect local changes in water inflow to the reef influencing seawater isotopic composition, temperature and nutrients. Seasonal changes, likely tied to the movement of the Intertropical Convergence Zone (ITCZ), reduced light and primary productivity during rainy, cloudy periods, affecting the clam’s growth. Short-term extreme weather events (e.g. storms, heavy rainfall) indicated by few days-long El/Ca peaks, potentially resulted in reduced sea surface temperatures and likely disturbed the clam’s growth as a result of increased runoff and turbidity. Moreover, dual clumped isotope measurements confirm that the clam grew in equilibrium with seawater and provide a sea surface temperature independent of seawater-δ18O of 27.9°C ± 2.4°C as well as a seawater δ18O value of -0.43 ± 0.50‰ for this late Miocene reef.
How to cite: Arndt, I., Bernecker, M., Erhardt, T., Evans, D., Fiebig, J., Fursman, M., Kniest, J., Renema, W., Schlidt, V., Staudigel, P., Voigt, S., and Müller, W.: Late Miocene giant clam records 57 years of multi-annual, seasonal and daily weather patterns from the Indonesian Throughflow, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20544, https://doi.org/10.5194/egusphere-egu25-20544, 2025.
The Indian Ocean Dipole (IOD) is a distinct east-west temperature gradient in the Indian Ocean, similar to the El Niño Southern Oscillation in the Pacific. Here, positive IOD (+IOD) events bring warm eastern and cool western sea surface temperatures, and vice versa for negative IOD (-IOD). This temperature seesaw brings increased seasonal rainfall to northeastern Africa while western Australia faces severe droughts during +IOD events. Conversely, -IOD states result in more droughts in Africa and increased precipitation in Australia. In addition to these immediate climatic impacts, possible IOD-driven teleconnections may impact the Australasian Monsoon system, as they (appear to) modulate summer monsoon precipitation over India, Southeast Asia, and possibly Australia.
However, despite its nature as a key climate driver in the Indian Ocean today, little data exists on changes in large-scale IOD patterns in the geologic past, especially in our past understanding of its role in ENSO dynamics. For instance, on glacial-interglacial timescales, sea level-driven exposure of the West Australian Shelf affects Pacific heat transport into the western region of the IOD. These changes were further exacerbated by the ongoing restriction and reorganization of the Indonesian Gateway since 5 Ma ago and the related changes in Pliocene to recent ENSO dynamics.
To disentangle the impact of IOD patterns in the Plio-Pleistocene climatic patterns in the Indo-Pacific region, we present new X-ray fluorescence core scanning data from Ocean Drilling Project (ODP) Site 763 between 2 – 5 Ma ago. These data provide new insights into Australian climate dynamics, which we could then relate to Indo-Pacific Warm Pool (IPWP) changes and the establishment of Late Pliocene to Pleistocene pIOD mean states. Changes in IOD and IPWP sea surface temperature patterns were constructed using a selected set of latitudinal temperature gradients through the equatorial Indo-Pacific. Temperature gradients were calculated using published SST reconstructions based on mixed layer planktonic foraminifer (Trilobatus sacculifer) Mg/Ca records from ODP Site 806 (West Pacific Warm Pool), ODP Site 763 (eastern Indian Ocean) and ODP Site 709 (western Indian Ocean).
Comparison of these data for the first time, reveals the close interconnectivity of tropical climate and oceanographic changes over the study interval. These include Plio-Pleistocene Australian and African hydroclimate trajectories and the contemporary monsoonal precipitation over Southeast Asia. We further pinpoint shifts in the Indian Ocean climate system corresponding to the tectonic restriction of the Indonesian Gateway (3.6 Ma), the Pliocene M2 glacial event (3.3 Ma), and the intensification of Northern Hemisphere glaciation (2.9- 2.7 Ma).
Our results provide insight into the importance of permanent shifts in the Indian Ocean Walker Circulation mean states for near-future climate scenarios. Our recorded IOD mean state shifts highlight the need for further detailed studies to better understand past IOD changes and their associated paleoclimatic impact in the region.
How to cite: Auer, G., Drury, A. J., Christensen, B., Bialik, O. M., and De Vleeschowuer, D.: Plio-Pleistocene Indian Ocean Dipole dynamics and their impact on paleoclimate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12659, https://doi.org/10.5194/egusphere-egu25-12659, 2025.
Climate condition of the Plio-Pleistocene is characterized by global cooling and intensification of the Northern Hemisphere Icesheet. During this time period, sea surface temperatures (SSTs) both at mid and high latitudes showed long-term cooling, whereas SST at the western Pacific warm pool (WPWP) showed only minor cooling, resulting in a gradual increase of latitudinal SST gradient. However, SST reconstruction at the WPWP is controversial because the SST trends from different proxies are not consistent. The long-term continuous planktonic foraminiferal Mg/Ca-based SST record in WPWP has been only available from ODP Site 806 with Trilobatus sacculifer, whose calcification depth is slightly deeper than Globigerinoides ruber. Here, we conducted Mg/Ca-based temperature reconstruction using two mixed layer species of planktonic foraminifera, G. ruber and T. trilobus, at IODP Site U1488 for the last 4 Myr. The reconstructed temperature of T. trilobus shows consistent results with previously published one by T. sacculifer at ODP 806, whereas that of G. ruber showed slightly warmer SST and different pattern from T. trilobus. The temperature difference between two species decreased between 2.0 and 1.5 Ma, which coincides with decrease in SSTs in the subarctic, subantarctic, and east Pacific upwelling regions. Because of the limited seasonality in the WPWP, the temperature difference of these species at a single site probably reflects differences in their habitat depth. Our results suggest that the upper ocean stratification in the WPWP has been closely related to the meridional and zonal SST gradients, which are associated with the Northern Hemisphere Glaciation.
How to cite: Sagawa, T., Kubota, Y., and Rosenthal, Y.: Sea surface temperature reconstructions using Mg/Ca of two mixed layer foraminifera species in the western Pacific warm pool for the last 4 Myr, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3938, https://doi.org/10.5194/egusphere-egu25-3938, 2025.
Extended salt deposits, indicative of pronounced aridity, are preserved in a 220,000-year sediment core from the Dead Sea in the eastern Mediterranean Levant. These arid intervals occur in the warm interglacial periods of Marine Isotope Stages (MIS) 7, 5, and in the Holocene, and coincide with maxima in the Northern Hemisphere fall precession cycle. Similar salt layers are also present during the current and penultimate deglaciations. In insolation-driven climate model simulations, the North Atlantic latitudinal surface temperature gradient intensifies in the subsequent winter when boreal fall precession reaches a maximum. A lag that is due to the inherent delay in the upper ocean response. The enhanced surface temperature gradient leads to a shift the North Atlantic eddy-driven jet stream poleward, a decrease in polar sea-level pressure and an increase subtropical sea-level pressure. A weakening in the Mediterranean winter storm track occurs and a reduction in the rainfall over the Basin. Abrupt subpolar cooling events during recent and penultimate deglaciations—driven by ice sheet melt—similarly amplify the North Atlantic latitudinal surface temperature gradient, eliciting a comparable atmospheric response and similar rainfall reductions in the eastern Mediterranean. The late Quaternary palaeohydrology of the Dead Sea thus highlights an important North Atlantic ocean-atmosphere interaction that drives eastern Mediterranean droughts. A similar link exists between the changes in the North Atlantic Basin and the eastern Mediterranean rainfall trend in recent history and helps understand CMIP6 inter-model differences in their projected eastern Mediterranean drying.
How to cite: Kushnir, Y., Stein, M., Biasutti, M., Kiro, Y., Goldsmith, Y., and Goldstein, S.: Paleoclimate Evidence of Significant Eastern Mediterranean Aridity During Interglacial Periods: Implications for the Projected Drying Trend, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5280, https://doi.org/10.5194/egusphere-egu25-5280, 2025.
While it is accepted that the tropical hydrological cycle has intensified during past interglacial periods due to changes in insolation, greenhouse gases, and ice volume, variations in the intensity and spatial distribution of rainfall in the South Asian monsoon domain, as well as the respective influence of these forcings during past warm periods, remain uncertain. Here, we present a pollen record from the Bay of Bengal (IODP Site U1446, located off the Mahanadi river exit, outside the influence of the Bengal fan) that allows reconstruction of vegetation changes in the core monsoon zone of India during two warm periods, the current and last interglacial periods. We compare the data with numerical model simulations (HadCM3 and LOVECLIM1.3) to assess the influence of different forcing mechanisms on the response of summer monsoon rainfall during past interglacials characterized by different levels of warming (Clément et al., 2024). We also present a pollen record from cores (SO93) taken at 16°N from the Ganges-Brahmaputra-Meghna (G-B-M) river-fed Bengal fan, covering the current interglacial period.
Results from IODP Site U1446 show tropical forest expansion between 11.7-5 ka and 127-120 ka, defining two Indian humid periods, with the last interglacial showing the strongest monsoon activity, consistent with salinity reconstructions. During the last five millennia of both interglacial periods, moist tropical forest largely declined in favor of savanna marking a significant decrease in summer monsoon rainfall. Although the pollen assemblages from sites SO93 and U1446 show substantial differences in Holocene vegetation cover between the basins, the maximum expansion of the evergreen component of the tropical forest is recorded contemporaneously in both sequences. This suggests a similar Holocene evolution of the summer monsoon from central to northern India. The model-data comparison highlights boreal summer insolation as the primary driver of vegetation dynamics and monsoon intensity during interglacial periods, with CO2 and ice-sheets having a limited effect. These results also show that vegetation remains unaffected by pre-industrial CO2 variations above 250 ppmv, a threshold value that characterizes most interglacials of the last million years.
Clément, C., Martinez, P., Yin, Q., Clemens, S., Thirumalai, K., Prasad, S., Anupama, K., Su, Q., Lyu, A., Grémare, A., Desprat, S., 2024. Greening of India and revival of the South Asian summer monsoon in a warmer world. Commun. Earth Environ. 5, 685.
How to cite: Desprat, S., Zorzi, C., Clément, C., Yin, Q., Galy, A., Clemens, S., Thirumalai, K., Prasad, S., Anupama, K., Su, Q., Lyu, A., Grémare, A., Galy, V., France-Lanord, C., and Martinez, P.: Records of vegetation and South Asian summer monsoon dynamics in the Bay of Bengal during the current and last interglacial periods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9895, https://doi.org/10.5194/egusphere-egu25-9895, 2025.
Foraminifera-bound nitrogen isotopes (FB-δ15N) are a powerful tool for reconstructing past oxygen-deficient zones (ODZs). FB-δ15N record the strong isotopic fractionation associated with bacterial water column denitrification that occurs in oxygen-deficient environments, typically characterised by dissolved oxygen concentrations of less than ~5 µM. We applied this oxygen-sensitive proxy across multiple ocean basins during the Miocene, focusing on the Miocene Climatic Optimum (MCO) and Middle Miocene Climate Transition (MMCT), to study the expansions and contractions of tropical ODZs as a response to past global climate change.
Our multi-basin analysis indicates nuanced oxygen dynamics, including evidence of a persistent proto-ODZ in the Arabian Sea since ≥19.8 Ma. By integrating FB-δ15N with foraminiferal calcite trace element data (I/Ca, Mn/Ca), we generated the first temporal and spatial record of MMCT deoxygenation in the Arabian Sea. Combining these new data with regional palaeoceanographic proxies, we assess the roles of global climate, regional monsoonal activity, and tectonics in driving Arabian Sea hypoxia, recognising that the contributions of these factors varied in magnitude and timing.
In comparison, new preliminary data from the Atlantic and Pacific Oceans suggest synchronised yet regionally distinct ODZ responses during the MCO and subsequent cooling. Our high-resolution reconstructions of Pacific Ocean deoxygenation following the MMCT cooling indicate glacial/interglacial variations and provide critical new insights into potential marine oxygen deficient zone trajectories under future climate scenarios.
How to cite: Auderset, A., Hess, A. V., Petrick, B., Rosenthal, Y., Sigman, D. M., and Martínez-García, A.: Tracing Ocean Oxygen Dynamics Through Time: A Miocene Perspective, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-740, https://doi.org/10.5194/egusphere-egu25-740, 2025.
In this study, we analyze the outputs of the Deep-Time Model Intercomparison Project (DeepMIP) for
the Early Eocene, focusing on the representation of the southwestern Indian Ocean gyre and investigating
the sources of inter-model variability. Specifically, we address three key aspects : (1) biases associated with
resolution through a comparison of realistic reanalyses with PI (pre-industrial) simulations, (2) the impact of
paleogeography by comparing PI with x1 (Early Eocene simulations under the same CO2 concentration as PI),
and (3) the sensitivity of paleo simulations to increased CO2 through a comparison of x1 and x3 scenarios.
(1) Our findings reveal that biases in the current representation of circulation in the southwestern Indian
Ocean particularly those linked to coarse resolution—persist across the seven DeepMIP models when compared
to realistic reanalyses such as GLORYS (ocean) and ERA5 (atmosphere). While certain patterns, like the
position of fronts, are well captured by the models, others, including stratification, western boundary currents,
and Agulhas leakage, display significant inter-model variability.
(2) Next, we evaluate the present-day/paleo sensitivity of these models by comparing PI and Early Eocene
(47–56 Ma) outputs under identical CO2 concentrations (x1). Consistent with existing literature, all seven
models exhibit a weaker wind stress curl and the absence of the ACC (Agulhas Circumpolar Current). Especially
at depth, temperatures in the region are generally 0.5°C to 4°C higher (except in COSMOS), and north-south
temperature gradients are weaker. On average, the frontal positions are located 5° farther south in the Early
Eocene. The first baroclinic Rossby deformation radius shows limited changes relative to the inter-model spread.
(3) Finally, we investigate the sensitivity of Early Eocene simulations to increased CO2 levels by comparing
x1 and x3 scenarios. Across all models, higher CO2 concentrations lead to slightly weaker wind stress and
transport. Water temperatures increase by 4–8°C, depending on the model, and the Rossby deformation radius
decreases slightly at mid-to-low latitudes.
How to cite: Le Hir, T.: Deep MIP Early Eocene Indian Gyre comparison , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-573, https://doi.org/10.5194/egusphere-egu25-573, 2025.
The largest Cenozoic hyperthermal, the Paleocene-Eocene Thermal Maximum (PETM, 56 Ma) was associated with about 5 K global surface warming and an estimated total carbon release of several thousand Pg. The PETM is widely considered the best analog for present/future carbon release. Over the next few centuries, with unabated emissions of anthropogenic carbon dioxide (CO2), a total of several thousand Pg C may enter the atmosphere, causing CO2 concentrations to rise sharply, global temperature to warm by several degrees, and surface ocean pH to decline substantially. A carbon release of this magnitude is unprecedented during at least the past 66 million years and the outcome accordingly difficult to predict. In this regard, the geological record provides foresight to how the Earth system will respond in the future. Here, I analyze the long-term legacy of massive carbon release into the Earth's surface reservoirs, comparing the Anthropocene with the PETM and evaluating the PETM's potential as a case study for present and future anthropogenic carbon emissions. I will examine climate forcing and response, chronology, and time scales of CO2 neutralization that determine the atmospheric lifetime of CO2 in response to carbon release. I compare forcings in terms of carbon release rate, i.e., the duration of carbon release during the Anthropocene vs. PETM and the ensuing effects on climate and ocean chemistry. Importantly, I will examine proxies used to reconstruct changes in atmospheric CO2 and hence carbon input during the PETM. The analysis provides new insight into the pitfalls associated with pH and pCO2 proxies, and reconciles previous inconsistencies between carbon input, climate change, and sedimentary response. I will also discuss the conundrum that the observed duration of the PETM appears to be much longer than predicted by models that use first order assumptions. Understanding the long duration of the PETM is critical for predicting the long-term consequences of anthropogenic carbon release.
How to cite: Zeebe, R.: The Paleocene-Eocene Thermal Maximum as a Future Analog: New Insight into pCO2 reconstructions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7526, https://doi.org/10.5194/egusphere-egu25-7526, 2025.
The mid-Piacenzian Warm Period (mPWP), specifically Marine Isotope Stage KM5c, has been the focus of many palaeoclimate studies due to its potential analogy to the future climate. The similar to modern continental configuration, higher CO2 concentrations of 400ppm, and similar to modern orbit provides the opportunity to examine the world in a warmer climate with relevance to our future.
To date, the majority of studies have focussed on changes to the mean state, however, changes to higher frequency climate variability are crucial to assess to understand both the potential for the mPWP to be used as an analogue for extremes, and to understand the distribution of data that may be recorded in the palaeo record. Here, we use data from the Pliocene Model Intercomparison Project Phase 2 and move beyond the mean state to shorter temporal scales. This aims to improve our understanding of the change in extreme events in the mPWP and the drivers of these changes.
We start broad, looking at the mean state and examining changes to the Northern Hemisphere jet stream and find that in boreal winter months, the jet stream exhibits a poleward shifted state, with a dipole pattern in the speed of the winds, in the mPWP compared with the pre-industrial control. We then move beyond the mean state analysis to consider the variability of the speed and position of the northern hemisphere jet stream in the mPWP and how these changes relate to extreme events.
To further understand the mechanisms behind these changes in the jet stream we present new forcing factorisation simulations using Hadley Centre Coupled Model version 3 (HadCM3) which aim to understand the different contributions of ice sheets, orography, and CO2 forcings to jet stream behaviour.
How to cite: Buchan, A., Tindall, J., Hunter, S., Dolan, A., Haywood, A., and Hill, D.: Moving beyond the mean state: Jet stream variability in the Pliocene, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6059, https://doi.org/10.5194/egusphere-egu25-6059, 2025.
Although the Pliocene is a well-studied epoch, key sources of uncertainty remain that add significant complexity to our understanding of climate at the time. From a climate/earth system modelling perspective palaeogeography is a key source of uncertainty, especially in terms of the veracity of specified model boundary conditions. Small variations in prescribed conditions can potentially lead to different local, regional and even global simulated climate states.
Here we explore this uncertainty within the experimental framework of the 3rd phase of the Pliocene Model Intercomparison Project (PlioMIP3). Building on the foundations of PlioMIP1 and 2, PlioMIP3 outlines three experiments within the Core and Core-Extension experimental design that are capable of directly addressing some of the key sources of palaeogeographic uncertainty in models, and which are potentially relevant to our understanding of both the Early and Late Pliocene. We use the Hadley Centre Coupled Climate Model Version 3 to perform the PlioMIP3 Core and Core-Extension experiments integrated for 4000 years. This includes the control simulation for the Late Pliocene, an alternative Late Pliocene simulation incorporating minimum land/sea mask changes from present-day, as well as an additional experiment that opens the Central American Seaway, and which is used as a single possible realisation of the Early Pliocene.
We compare and contrast climate states within the Late Pliocene and between the Eary and Late Pliocene. Palaeogeographic uncertainty within the Late Pliocene is shown to have a significant enough impact on climate conditions to influence outcomes of localised data/model comparison, but it does very little to influence model results in terms of large-scale features of climate, or the simulated global annual mean temperature. In contrast, the Central American Seaway being open in the Early Pliocene simulation leads to significant variations in the simulated climate state, and even in the global annual mean temperature with identical greenhouse gas forcing as the Late Pliocene.
This underlines the importance of continued research to better understand palaeogeographic evolution through the Pliocene, which adds new detail to the complex tapestry of what we understand to be ‘Pliocene’ climate.
How to cite: Haywood, A., Tindall, J., Hunter, S., and Dolan, A.: The influence of palaeogeographic uncertainty on the simulation of Pliocene climate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5699, https://doi.org/10.5194/egusphere-egu25-5699, 2025.
Understanding the drivers of past warming climates is fundamental to reconstructing Earth’s climate history and refining projections of future climate change. Cenozoic warming intervals, including the mid-Pliocene (3–3.3 Ma), mid-Miocene (11.6–16 Ma), and early Eocene (47–56 Ma), provide analogs for present-day warming, featuring similar boundary conditions but substantially warmer climates. These intervals illustrate how variations in CO₂, ice sheets, vegetation, geography, and topography influenced global climates through radiative forcing and feedback mechanisms, offering essential insights into the climate dynamics following an intermediate warming pathway.
Despite extensive research on these intervals, the role of radiative forcings from changing boundary conditions remains poorly constrained. Here, focusing on the mid-Pliocene, we leverage three generations of the Community Earth System Model (CCSM4, CESM1.2, CESM2) to quantify radiative forcing and decompose the contributions of CO₂, vegetation and ice sheets, and topography and geography. Using published CESM radiative kernels, we diagnose radiative adjustments in atmospheric temperature, water vapor, surface albedo, and cloud properties, with a particular focus on cloud forcing and its interactions due to their critical role in modulating radiative adjustments and subsequent feedbacks.
Effective radiative forcing (ERF) is calculated as the difference in net top-of-atmosphere radiative fluxes between pre-industrial control and warming interval simulations, with prescribed sea surface temperatures specific to each interval. The simulations incorporate CO₂ levels, ice and vegetation, and geographic and topographic conditions representative of each period.
Our results show that CO₂ contributes approximately 60% of total forcing, with the strongest impacts in the tropics and Arctic. Cloud-related adjustments exhibit significant variability, with the net cloud adjustment even reversing its sign in with different radiative perturbations--emphasizing the complex interplay between radiative adjustments and the role of clouds in shaping climate responses across Cenozoic warming intervals.
We suggest that constraining radiative forcing from different perturbations of the past warm intervals is essential for understanding and decomposing drivers of past climate warmth and reducing inter-model variability in climate simulations.
How to cite: Kravette, N. and Feng, R.: Constraining effective radiative forcing and adjustments driving past warm intervals, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13363, https://doi.org/10.5194/egusphere-egu25-13363, 2025.
A warmer atmosphere holds more water vapor supporting an amplified hydrological cycle with both more intense precipitation events and droughts. Yet future climate projections are uncertain when it comes to predicting climatological changes in regional hydroclimate, particularly for subtropical and Mediterranean climates. Past warm climates in Earth's history offer an opportunity to learn how regional hydroclimate responds to global warming. Here we review insights from several studies that model and reconstruct hydroclimate during the warm climates of the Pliocene, Miocene and Eocene. A common finding is the importance of correctly predicting warming patterns and their impact on large-scale circulation, leading to circulation driven changes in climatological moisture convergence. Most notably, climate models that simulate the largest reduction in equator-to-pole temperature gradients are characterized by a reduction in subtropical moisture divergence, leading to an increase in mean annual precipitation and better agreement with proxy reconstructions.
How to cite: Burls, N.: Hydroclimate insights from the warm Pliocene, Miocene, and Eocene , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5463, https://doi.org/10.5194/egusphere-egu25-5463, 2025.
Paleoclimate data play a crucial role in validating advanced coupled climate models by offering insights into past climate transitions, which can inform our understanding of potential future conditions that may diverge significantly from today's climate. By examining past warm periods, we can assess the performance of climate models during interglacials and potential future warmer climates. This talk will highlight how integrating paleoclimate records with climate model simulations helps bridge knowledge gaps, focusing on the impact of ocean circulation, extreme weather events, and spatio-temporal dynamics in a warming world. Focus will be on interglacial sea surface temperatures, The higher the resolution, the higher is the spatial heterogeneity. Additionally, our Earth system model now incorporates an interactive cryosphere component, enabling us to simulate changes in both Antarctica and the Northern Hemisphere effectively. Theses feedbacks are essential for previous interglacials and the future.
As a second related aspect, current Earth system models are limited in their ability to accurately capture climate variability across different temporal scales, particularly underestimating temperature trends, multidecadal to centennial fluctuations. In this study, we show that high-resolution climate simulations with explicitly resolved sub-mesoscale ocean eddies, reveal increased long-term variability in the tropics, while simultaneously reducing interannual variability. This shift in spectral power, from dominance by interannual to multidecadal timescales, has significant implications for understanding past climate variability, refining future climate projections, and enhancing the detection of anthropogenic climate change.
How to cite: Lohmann, G., Ackermann, L., Shi, X., Gou, R., and Ma, Y.: Interglacials as test bed for climate change and variability in climate models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20469, https://doi.org/10.5194/egusphere-egu25-20469, 2025.
Posters on site: Thu, 1 May, 14:00–15:45 | Hall X5
Following the publication of the IPCC's Fifth Assessment Report in 2013, there has been mounting evidence indicating that the social and ecological impacts of global warming are increasingly contingent on seasonal extremes, such as peak summer temperatures, rather than trends in annual averages. This phenomenon is especially evident in the tropics, where extreme events have become a major threat to ecosystems. However, there remains a paucity of data concerning the present and future rates of change in means and extremes. This dearth of knowledge can be attributed to two key factors: firstly, the paucity of high-resolution data from bygone warm climates that could serve as analogues; and secondly, the absence of sophisticated data analysis methodologies.
The SEARCH project (Seasonal Extremes and Rates of Change in Past Warm Climates: Insights from Advanced Statistical Estimations on High-Resolution Coral Proxy Records) has been developed to enhance our understanding of past climates through the utilization of a database comprising high-resolution coral proxy records, complemented by the application of sophisticated simulation techniques from the domain of statistical science. The SEARCH database contains approximately 50 existing and newly acquired (bi-)monthly resolved coral proxy records from the following periods: (a) the Anthropocene, (b) the Medieval Climate Anomaly-Medieval Warm Period, (c) the Holocene Thermal Maximum, (d) the Last Interglacial, and (e) the Mid-Pliocene Warm Period.
We explain the methodological foundations of the project: proxy calibration, nonparametric kernel estimation of the first derivative of the climate proxy series and linear regression. It is important to note that these methods take into account the typical peculiarities of palaeoclimate time series, including non-Gaussian distributions, autocorrelation, uneven spacing, and uncertain timescales.
The primary outcome of our analyses indicates that the warming rates during the Anthropocene, which approximate 0.14 ± 0.04 °C per decade, appear to be relatively indistinguishable from the rates documented in other warm periods. We proffer an explanation for this observation and propose refinements to the analytical methodology.
This work has been funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), project number 468589022 (SEARCH), within the SPP 2299, project number 441832482
How to cite: Mudelsee, M. and Felis, T.: Rates of change in past warm periods, Part 3, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21556, https://doi.org/10.5194/egusphere-egu25-21556, 2025.
The Mediterranean is widely recognized as a climate change hotspot. The Last Interglacial (~127 ka; LIG) and mid-Holocene (~6 ka; MH), characterized by increased boreal summer insolation and decreased winter insolation, provide valuable opportunities to investigate the Mediterranean climate’s response to global-scale forcings. In agreement with proxy data, multi-model simulations from the Paleoclimate Model Intercomparison Project Phase 4 (PMIP4) show that the Mediterranean experienced wetter conditions during the LIG and MH compared to the pre-industrial period. The simulated wetting is most pronounced in late winter and early spring (February to April), when the circulation anomalies are akin to a negative phase of the North Atlantic Oscillation and the North Atlantic storm tracks shift southward. Standalone atmospheric experiments emphasize the critical role of cooling and suppressed convection over the Indian Ocean, which modulate the North Atlantic climate through atmospheric teleconnections. This physical link between Mediterranean wetting and Indian Ocean drying is consistently reproduced across the inter-model spread during the LIG and might also be one factor in the spread of future climate projections in the Mediterranean.
How to cite: He, L., Biasutti, M., and Kushnir, Y.: Interglacial Mediterranean wetting driven by suppressed Indian Ocean convections, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2341, https://doi.org/10.5194/egusphere-egu25-2341, 2025.
The Westerly Jet, locating northern boundary of the Hadley Circulation, plays a critical role in contributing mid-latitude climate by facilitating heat and moisture transport through its meandering path. Previous proxy records and numerical simulations have shown that the Jet’s path was altered in response to the repeated reduction events of the Atlantic Meridional Overturning Circulation (AMOC) during the Last Glacial period, through the modulation of Hadley Cell intensity and latitudinal position (e.g. Nagashima et al., 2011; Lee et al. 2011). Considering the possible future AMOC reduction following the global warming (Rahmstorf 2004), it is critically important to investigate the Jet's response to AMOC reduction during the warmer interglacial periods to enhance our understanding of future mid-latitude climate dynamics.
Recently, increasing evidence revealed AMOC reductions occurred even during interglacial periods, including MIS 1, 5e, 7e, 9e, and 11c (e.g. Galaasen et al. 2020). In this study, we reconstructed the Westerly Jet path over East Asia during MIS 5e and 11c through a provenance analysis of Asian dust in Japan Sea sediments (MD01-2407, KR02–06 D-GC-6, and KR07-12 PC-5, PC-8). This reconstruction utilized the electron spin resonance intensity of quartz, following Nagashima et al. (2007, 2011, 2013). Our findings, combined with previously published data (Nagashima et al., 2013), revealed southward shifts of the Westerly Jet in response to AMOC reductions during the warmer interglacial periods recorded in the North Atlantic. Given the strong relationship between changes in the Westerly Jet's path over East Asia and variations in East Asian summer monsoon precipitation, particularly its northwest-southeast spatial distribution within China, the observed southward shifts in the Westerly Jet provide important insights into potential precipitation changes in monsoon regions due to the forthcoming AMOC weakening in the near future.
How to cite: Nagashima, K., Hasegawa, H., Okada, K., and Toyoda, S.: Westerly Jet southward shifts in response to Atlantic Meridional Overturning Circulation reductions during past interglacial periods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14361, https://doi.org/10.5194/egusphere-egu25-14361, 2025.
The Holocene epoch offers insights into past climate variability and associated environmental changes in the Arctic region, with implications for future scenarios. We present a multi-proxy study of Nuup Kangerlua (the fjord by Nuuk), southwest Greenland, covering the past ~10,500 years. Using sediment cores and a one-year sediment trap deployment, we reconstruct environmental changes, focusing on ice-sheet dynamics, oceanography, and productivity. Following the fjord deglaciation (~10-8 ka BP), the fjord was characterised by cold, low-productivity conditions with significant ice-rafted debris, transitioning to warmer, more productive conditions by ~7.5 ka BP. The mid-to-late Holocene (6.5–3 ka BP) experienced an exceptional oceanographic regime with indication of entrainment of Subpolar Mode Water (Atlantic origin) at the time of minimum extent of the Greenland Ice Sheet. At this time, dinoflagellate cyst assemblages reveal shifts from heterotrophic dominance to autotrophic taxa, signaling increased light availability and stratification. Biogeochemical proxies (TOC, δ13C, and biogenic silica) corroborate heightened productivity during this period. Contrasts with modern conditions suggest that sustained warming could alter fjord hydrography, potentially enhancing Atlantic-derived inflows. Our study provides new knowledge on the fjord's sensitivity to climate variability and it offers baselines for understanding the interplay between the Greenland ice sheet, fjord systems, and broader oceanographic processes under changing climatic conditions.
How to cite: Ribeiro, S., Kvorning, A., Pearce, C., Seidenkrantz, M.-S., Kuijpers, A., Simpson, G., Larsen, N. K., Meire, L., and Heikkilä, M.: Holocene climate and environmental change in Nuup Kangerlua, southwest Greenland , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18353, https://doi.org/10.5194/egusphere-egu25-18353, 2025.
The Eocene-Oligocene Transition (EOT) (~34.4–33.7 Ma) is not only known for its drastic shift from greenhouse to icehouse climate, but also for a dynamic ocean gateway configuration. The Southern Ocean gateways are expected to open during this period, while the Arctic Ocean likely remains largely isolated, resulting in distinct ocean circulation patterns.
Using the AWI-Earth System Model (AWI-ESM) coupled to the Parallel Ice Sheet Model (PISM), we explore the ocean dynamics under an ocean straight configuration markedly different from today’s, providing a detailed depiction of global climate during the EOT. Low-latitudinal seaways, which are absent in the present continental configuration, and opening Southern gateways change the global ocean circulation fundamentally. This also has profound impacts on the continental climate, such as the formation of deserts.
With a targeted study of the Southern Ocean, we show that deep Southern gateways alone are insufficient to allow an Antarctic Circumpolar Current (ACC). Whether the Antarctic glacial inception came before or after the onset of the ACC is broadly debated. Here we observe, the onset of the ACC is not a necessary condition for East Antarctic glaciation. Instead of the ACC, a large Weddel-Australian gyre dominates the Southern Ocean. This gyre creates mixing and deep water formation and thus influences an Atlantic Ocean that faces very different boundary conditions than today.
This study enhances our understanding of Southern Ocean dynamics prior to the establishment of a strong ACC and underscores the critical role of oceanic gateway configurations in assessing their impact on regional and global climate.
How to cite: Knahl, H., Hochmuth, K., Niu, L., Ackermann, L., Lohmann, G., Klages, J., Golledge, N., and Krebs-Kanzow, U.: How gateways shape the world – An ocean perspective on the Eocene-Oligocene-Transition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-954, https://doi.org/10.5194/egusphere-egu25-954, 2025.
The Maritime Continent (MC) plays a critical role in regulating global atmospheric and oceanic circulation. This study explores the impact of MC topography on both regional and remote climate under preindustrial (PI) and mid-Pliocene warm period (mPWP) conditions using a lately tuned version of the HadCM3 climate model. Simulations are conducted by varying the topography of the northern MC (MCn) and southern MC (MCs), following the Pliocene Model Intercomparison Project (PlioMIP) Phase 2 experimental framework.
Results indicate that changes in the MCn topography during the mPWP, compared to PI conditions, lead to cooling in the northwestern Pacific, while variations of the MCs results in cooling over the eastern Indian Ocean. The MC topography variation has a large impact on the net hydrological flux (precipitation minus evaporation) over the MC and Indian Ocean, with both MCn and MCs leading to a decrease near the Timor passage region and an increase over the northern Indian Ocean. Compared to the PI, there is a westward movement of the Walker Circulation in the mPWP, and the MCs topography contributes to this westward movement. Although MC topographical changes have a limited effect on the total volume transport of the Indonesian Throughflow (ITF), variations in MCs topography substantially affect the ITF structure above 200 meters, and variations in MCn topography affect the ITF structure at depths around 1000 meters.
While the overall contribution of MC topography to global temperature changes is relatively small compared to the combination of other mPWP boundary conditions (CO2, ice sheets, soil, vegetation, lakes, and changes in topography of other regions), it plays a critical role in shaping the ITF and influencing both local and remote climate systems.
How to cite: Ren, X., Lunt, D., and Hendy, E.: The Impacts of Maritime Continent Topography in the Preindustrial and the Pliocene Warm Period Using HadCM3, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7133, https://doi.org/10.5194/egusphere-egu25-7133, 2025.
The Middle Miocene Climatic Optimum (MMCO, ∼16.9 - 14.7 Ma), is marked by lower δ18O values in bulk and benthic suggesting a warming and/or reduction in land ice. CO2, due to its climatic influence, is suspected to be a key driver of this temperature shift. However, the climate and CO2 during the MMCO was highly variable in some records. The limited number of high-resolution temperature and CO2 reconstructions for this interval makes it difficult to characterize the temperature and CO2 change across the MMCO onset. pCO2 levels can be estimated using the fractionation factor (εp) of coccolithophores when they photosynthesize and produce alkenones as their biomass. We present a high-resolution record of sea surface temperature (SST) and εp values for 16 to 19.7 Ma, derived from alkenones at IODP Site 1168 in the Southern Ocean, providing insights into the onset of the MMCO. The data reveals an increase in temperature of approximately 4°C, from 23°C to 27°C, across the MMCO δ18O shift. There is a modest positive correlation observed between SST and bulk δ18O values. In addition, δ18Osw trends, calculated from alkenone temperature and coccolith δ18O, indicate freshening between period 16.5 to 17.5 Ma, consistent with the expected retreat of the Antarctic ice sheet during the MMCO. Orbital scale temperature variations of 2 degrees can be observed. Further analysis of εp values will help reconstruct the contribution of CO2 to this climatic transition.
How to cite: Jonk, L., Wijker, R., Jaggi, M., Ziegler, M., and Stoll, H.: Southern ocean temperatures and CO2 across the onset of the Middle Miocene Climatic Optimum, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12153, https://doi.org/10.5194/egusphere-egu25-12153, 2025.
The Early Eocene Climatic Optimum (EECO; ~53–49 Ma) represents the prolonged interval with the highest temperatures and CO₂ levels of the Cenozoic with superimposed transient peak warming events (hyperthermals). The geological record provides a long-term perspective to current observations of marine ecosystem response to global warming. The EECO interval offers the opportunity to evaluate how global climatic shifts have influenced the resilience of planktic foraminifera, a key component of marine ecosystem.
Planktic foraminifera morphologic traits, including shifts in coiling direction - the ability to grow their chambers either clockwise (dextral) or counterclockwise (sinistral) - serve as highly sensitive indicators of environmental changes. This underscores their pivotal role in the study of past climate conditions. Previous studies highlighted a permanent decline in the symbiont-bearing Morozovella abundance and diversity near the EECO onset and a coiling shift from dextral to sinistral during the K/X event in the Atlantic Ocean.
Here, we extend the coiling direction record to tropical Pacific (Shatsky Rise, Sites 1209–1210), southern Pacific (Tasman Sea, Site U1510), and Indian Ocean locations (Exmouth Plateau, Hole 762C). Our results reveal that the switch to sinistral coiling in Morozovella occurred at all the studied sites thus it appears globally recorded within the last ~200 kyrs after the K/X event. This evidence emphasizes the utility of this coiling shift as a valuable biostratigraphic tool. The Morozovella species-specific analysis discloses that the dominant M. aragonensis and M. crater significantly contributed to the coiling switch in the Atlantic, tropical Pacific, and Indian Oceans. Regardless sinistral and dextral Morozovella forms indicate cryptic speciation or morphotypes within the same species, our record implies that this interval favoured sinistral forms, so that he morozovellid decline in abundance can be largely read as the decline of dextral morphotypes. Notably, Acarinina exhibits no coiling preference.
Stable isotope analysis on dextral and sinistral Acarinina and Morozovella morphotypes can shed light on the intricate ecological dynamics of planktic foraminifera during the EECO. Sinistral Morozovella have lower δ 13C values across the EECO with respect to the pre-EECO interval, with both dextral and sinistral Acarinina showing even lower values. This suggests that Acarinina occupied a deeper habitat within the mixed layer and/or had reduced symbiotic activity. This ecological strategy may have ensured the Acarinina success, allowing it to thrive during the EECO, but only partially advantaged the sinistral morozovellids forms, which survived with respect to dextral morphotypes but only in small abundance.
Within the first ~600 kyr of the EECO, morozovellids declined in abundance and changed their coiling direction. The scenario recorded in this research delineates on how planktic foraminifera adapted—or struggled— in response to extreme warmth, a crucial result for a future climatic perspective.
How to cite: Filippi, G., Sigismondi, S., Wade, B., and Luciani, V.: Global Coiling Shifts in Morozovella and Ecological Resilience of Acarinina during the EECO, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18070, https://doi.org/10.5194/egusphere-egu25-18070, 2025.
The Middle Eocene Climatic Optimum (MECO), occurring around 40 million years ago, is marked by a gradual decline in marine bulk and benthic carbonate δ18O values by approximately 1‰ over a span of ~400,000 years. This is typically interpreted as a global temperature increase of 3–6 °C, followed by a rapid return to pre-event conditions. The MECO event is garnering increasing scientific interest, as it serves as a natural experiment for the temperatures and pCO2 levels Earth could reach by the end of this century if anthropogenic greenhouse gas emissions are not reduced. The MECO's δ13C signal, along with biotic and paleoceanographic changes, exhibits significant geographic variability, leaving many aspects of the event unresolved. Specifically, the biotic response remains poorly understood. This study addresses this gap by focusing on planktic foraminifera, which are sensitive to oceanic physical and chemical conditions and can provide insights into marine ecosystem resilience to global warming. We analyzed Ocean Drilling Program Sites 1051, 1263, and 702, spanning different latitudes across the Atlantic Ocean. These sites provide robust age models and stable isotope data. Our results show a marked turnover in planktic foraminiferal assemblages during the MECO, mainly driven by increased surface-water temperatures affecting pelagic food webs. The warming prompted a southward migration of warm-water taxa at Site 702, also observed in calcareous nannofossils. Notably, the warm-water taxon Large Acarinina (>150 μm) showed a significant, permanent decline within ~250,000 years during the late MECO stage at Sites 1051 and 702, well before its evolutionary disappearance at the Bartonian-Priabonian boundary. This decline was also observed in the Tethys. We hypothesize that changes in microalgal symbionts may have contributed to this decline. Additionally, a drop in Chiloguembelina abundance suggests increased oxygenation in its ecological niche, the oxygen-deficient zone (ODZ). While the foraminiferal assemblages exhibited some plasticity through community shifts and latitudinal migration, they did not recover their pre-disturbance diversity, indicating low stability and a lack of resilience during the MECO.
How to cite: Sigismondi, S., Luciani, V., Alegret, L., and Thomas, W.: Impact of the Middle Eocene Climatic Optimum on Planktic Foraminiferal Resilience in the Atlantic Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17458, https://doi.org/10.5194/egusphere-egu25-17458, 2025.
