Waterbelt states are an alternative scenario for Snowball Earth, where a narrow strip of ocean remains ice-free at the equator, providing a robust solution for the survival of life. Recent studies have shown that waterbelt states can be stabilised by subtropical low-level clouds, because they weaken the ice-albedo feedback created by the expanding sea ice beneath the clouds. Thick subtropical clouds are therefore needed to stabilise the waterbelt state.

However, clouds also have the opposite effect over the open ocean equatorward of the ice margin. Here they provide a destabilising cloud feedback that supports the ice-albedo feedback in favour of a Snowball Earth. When sea ice enters the subtropics, this effect becomes particularly strong, as the vertical structure and the phase partitioning of tropical clouds begin to change. As a result, tropical clouds can ultimately determine the stability of the waterbelt state.

Here we show a preliminary analysis of simulations with two versions of the atmospheric ICON model using the same setup, a slab-ocean aquaplanet with a thermodynamic sea-ice model and over a broad range of atmospheric CO₂ concentrations. While waterbelt states are easily found in ICON-A, they are absent in ICON-ESM due to a difference in tropical clouds. The tropical cloud feedback will be analysed by means of cloud controlling factors, and simulations with the cloud locking method will be employed to demonstrate the critical role of tropical cloud feedback for waterbelt states. 

How to cite: Hörner, J. and Voigt, A.: Tropical cloud feedback in near-Snowball Earth waterbelt states, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6305, https://doi.org/10.5194/egusphere-egu24-6305, 2024.

The temporal synchronism between large igneous provinces (LIP) emplacements and mass extinction all along the Phanerozoic reveals a possible link between the two. The release of huge amount of gases during the LIP emplacement is considered to cause major climate and environmental perturbations possibly leading to a biodiversity crisis. However no clear correlation can be drawn between LIP’s properties i.e. the LIP size, the amount of gas released, etc… and the mass extinction severity.

Our primary focus was on investigating the consequences of the Siberian traps emplacement which is considered to be responsible of the end-Permian mass extinction. This biodiversity crisis lead to the disappearance of 90% of the marine species and 75% of the terrestrial species. The Siberian volcanism has produced 3 to 5 millions km³ of magma over a period not exceeding 1 Myr according to U-Pb dating. This volcanism is accompanied by the release of huge amount of gases within the atmosphere, notably CO₂ and SO₂.
These gases have two sources : the magmatic degassing and the thermogenic degassing generated by the intrusion of magmas in carbonate-rich or evaporite-rich sediments deposited within the Siberian basin. We propose to explicitly model volcanism by considering both short-term and long-term scale processes along the entire LIP emplacement with different scenarios to mimic the sequence of volcanic and thermogenic gas emissions. For this purpose, we employed the biogeochemical model GEOCLIM to simulate the changes of the ocean in term of temperature and pH caused by the LIP emplacement. This approach enables a detailed exploration of the impact of LIP emplacement on the climate and geochemical cycles.

How to cite: Pierron, A., Le Hir, G., Fluteau, F., Goddéris, Y., and Maffre, P.: Modelling the consequences of the Siberian traps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16065, https://doi.org/10.5194/egusphere-egu24-16065, 2024.

Changes in climate feedback processes drive fluctuations in equilibrium climate sensitivity (ECS), the measure of global warming associated with a doubling of atmospheric CO₂. Warming in different past climates resulted in various responses in ECS that can be explored to further understand how distinct feedbacks and forcings control CO₂-induced warming. Previous studies generally agree that ECS increases with increases in the CO₂ background state. We investigate this further through simulations of different time slices from ~100 million years ago to present, all run with the same model version. We will use Community Earth System Model (CESM1.2) simulations to study Earth’s response to an increase in CO₂ radiative forcing under past greenhouse and icehouse climates. We compare time slices that have differences in geography, vegetation, and ice, which affect feedbacks that drive ECS. We will use slab ocean model and fully-coupled CESM1.2 simulations of the late Cretaceous, early Eocene, late Oligocene, mid Miocene, and preindustrial (PI) all at modern orbital parameters, with greenhouse climate simulations at 840 ppm and 1680 ppm CO₂ and icehouse climate simulations at 280 ppm and 560 ppm CO₂, in order to compare changes in temperature resulting from changes in albedo, ocean heat flux, and nonlinearities in atmospheric water vapor and cloud feedbacks. We will compare simulations of greenhouse and icehouse climates, past climates to the PI climate, and our CESM1.2 simulations to previously published simulations run on other earth system models, like the Hadley Centre Coupled Model, to study the degree of model-dependence in ECS. Analyzing ECS in past climates, with a control on model version, and comparing differences in climate feedbacks will help constrain the sensitivity of ECS to boundary conditions and the range of ECS through Earth’s history. 

How to cite: Campbell, J. and Poulsen, C. J.: Changes in equilibrium climate sensitivity and associated feedbacks through past greenhouse and icehouse climate simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12923, https://doi.org/10.5194/egusphere-egu24-12923, 2024.

Deep-time climate simulations typically disregard tidal dynamics while trying to reconstruct the paleoclimate. Tidally induced mixing is a dominant part of vertical mixing in the deep ocean, which is key for maintaining ocean stratification and influences the strength of the Meridional Ocean Circulation (MOC). We add this missing tidal mixing component to the Community Earth System Model (CESM) and try to reconstruct the mid-Cretaceous (~90Ma) climate, which is known for its warm, equable climate and low meridional temperature gradient. In the next step, as an improvement over the default tidal mixing scheme, an energetically consistent internal wave model IDEMIX is used in CESM to get the vertical diffusivity coefficients in simulating the mid-Cretaceous climate. 

Initially, 90Ma simulations were performed in the conventional method with enhanced constant background diffusivity coefficients for the default vertical mixing scheme and then with the tidal mixing component enabled. Preliminary results from the simulations with tidal mixing show that there is a considerable reduction in the global ocean mean temperature and a change in the strength of MOC in the deep ocean when compared to the simulations without the tidal mixing component. We will be also presenting results from additional experiments that are being performed with the internal wave model IDEMIX as the tidal mixing parameterization in the model. IDEMIX is forced by the dissipated barotropic tidal energy, which is modelled from the mid-Cretaceous bathymetry. With the IDEMIX parameterization, we expect more realistic results for ocean circulation hoping to reduce the disagreements between proxy data and model simulations.

How to cite: Kattamuri, S., Paul, A., Pollmann, F., Green, M., and Schulz, M.: Modelling the Ocean Circulation during the mid-Cretaceous using an Energetically Consistent Internal Wave Model in the Community Earth System Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11330, https://doi.org/10.5194/egusphere-egu24-11330, 2024.

Diapycnal mixing in the ocean interior is largely fueled by internal tides. Mixing schemes that represent the breaking of internal tides are now routinely included in ocean and earth system models applied to the modern and future. However, this is more rarely the case in climate simulations of deep-time intervals of the Earth, for which estimates of the energy dissipated by the tides are not always available. Here, we present and analyze two IPSL-CM5A2 earth system model simulations of the Early Eocene made under the framework of DeepMIP. One simulation includes mixing by locally dissipating internal tides, while the other does not. We show how the inclusion of tidal mixing alters the shape of the deep ocean circulation, and thereby of large-scale biogeochemical patterns, in particular dioxygen distributions. In our simulations, the absence of tidal mixing leads to a deep North Atlantic basin mostly disconnected from the global ocean circulation, which promotes the development of a basin-scale pool of oxygen-deficient waters, at the limit of complete anoxia. The absence of large-scale anoxic records in the deep ocean posterior to the Cretaceous anoxic events suggests that such an ocean state most likely did not occur at any time across the Paleogene. This highlights how crucial it is for climate models applied to the deep-time to integrate the spatial variability of tidally-driven mixing as well as the potential of using biogeochemical models to exclude aberrant dynamical model states for which direct proxies do not exist.

How to cite: Ladant, J.-B., Millot-Weil, J., de Lavergne, C., Green, J. A. M., Nguyen, S., and Donnadieu, Y.: Impacts of tidally driven internal mixing in the Early Eocene Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19857, https://doi.org/10.5194/egusphere-egu24-19857, 2024.

The El Niño-Southern Oscillation (ENSO) influences the world through its teleconnection. Forced by global warming and rising atmospheric CO2 levels, the evolution of ENSO is still under debate. ENSO records in deep-time greenhouse climates can enhance the understanding of ENSO and its teleconnection under global warming.

This research analyzes Earth System Model (ESM) outputs of Late Cretaceous to show ENSO teleconnection between North Pacific and Mediterranean Climate region of North America (MCNA) under greenhouse gas and paleogeographic forcing. ESM outputs show 2.1-3.2-year ENSO-band cycles in both sea surface temperature (SST) and precipitation in MCNA, which are consistent with records from high-resolution sedimentary archives. The simulated ENSO teleconnection to Late Cretaceous MCNA is more influenced by the Subtropical High than the Aleutian Low. This is thought to be related to paleogeographic forcing, where a closed polar-ward seaway results in a warmer sub-polar Pacific and a more robust Aleutian Low over it. Consequently, under the remote forcing of ENSO, the Subtropical High shifts the Westerlies longitudinally, leading to alterations in both moisture and thermal transportation, which in turn changes the winter precipitation of MCNA.

This study reveals that ENSO teleconnections remain robust under Late Cretaceous greenhouse climates, and in comparison with today, forcing from the subtropics played a more significant role in affecting the evolution of North American climate.

How to cite: Qin, J., Gao, Y., Du, X., and Wang, C.: North Pacific ENSO Teleconnection to Mediterranean Climates of North America in Late Cretaceous Greenhouse, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7232, https://doi.org/10.5194/egusphere-egu24-7232, 2024.

Tropical precipitation is profoundly influenced by continental evolution across geological time scales. However, the effects of Australia’s drift on warm pool precipitation remains poorly understood. Using a fully coupled climate model with realistic geography, our results reveal a significant amplification of the seasonal migrations of warm pool precipitation in longitude and latitude due to the equatorward drift of Australia. Notably, the observed feature aligns with paleoclimate simulations over the past 40 million years, highlighting the dominant role of Australia’s drift in comparison to the other continental drifts. This study provides insight into how Australia’s drift has shaped the characteristics of warm pool precipitation over the geological timescales.

How to cite: Yin, Z. and Nie, J.: Australia’s drift as a pacemaker for the seasonal variability of warm pool precipitation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7113, https://doi.org/10.5194/egusphere-egu24-7113, 2024.

The Eocene-Oligocene Transition is marked by a sudden δ¹⁸O excursion occurring in two distinct phases: a precursor event at 34.15±0.04 Ma and the Earliest Oligocene oxygen Isotope Step at 33.65±0.04 Ma. These events signal a shift from the warm Late-Eocene greenhouse climate to cooler conditions, with temperature decreases of 3-5 °C, and the emergence of the first continent-wide Antarctic Ice Sheet (AIS). Despite clear evidence from proxy data, general circulation models (GCMs) struggle to replicate this Antarctic transition accurately, failing to capture the shift from warm, ice-free to cold, glaciated conditions. Even with unrealistically low pCO₂ levels, Late-Eocene Antarctic summers in GCMs remain too warm and moist for snow or ice to survive. This study evaluates CESM1.0.5 simulations conducted by Baatsen et al. (2020), using a 38 Ma geo- and topographical reconstruction, considering different radiative (4 pre-industrial carbon levels (PIC) and 2 PIC) and orbital (present-day insolation and low Antarctic summer insolation) forcings. The climate is found to be highly seasonal, characterised by hot and wet summers and cold and dry winters. While reduced radiative and summer insolation forcing weaken this seasonality, the persistent atmospheric circulation still impedes ice sheet growth by limiting summer snow survival. For that reason, a new simulation is conducted with regional, moderately-sized ice sheets imposed on the continent, in order to investigate their stability and their influence on the atmospheric circulation. These ice sheets demonstrate self-sustaining and even expansion potential under 2 PIC and low summer insolation conditions. However, correlating resulting temperature and precipitation patterns with proxy data proves challenging, given the absence of terrestrial proxies. Extended simulations with coupled GCM-ISM models are therefore recommended, allowing for more dynamic atmosphere-ice-ocean-vegetation feedback mechanisms and dynamic radiative and orbital forcing.

How to cite: Vermeulen, D., Baatsen, M., and von der Heydt, A.: Response of Late-Eocene warmth to incipient glaciation on Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5826, https://doi.org/10.5194/egusphere-egu24-5826, 2024.

The Late Eocene is a period of global cooling and high-latitude tectonic changes culminating in the Eocene Oligocene Transition (34 Ma ago), one of the major climatic shifts of the Cenozoic. Across the Late Eocene, the Earth went from a largely ice-free greenhouse during the early Eocene climatic optimum to an icehouse with the ice sheet inception over Antarctica. This long-term cooling happened simultaneously with a decrease in the atmospheric content in carbon dioxide whose causes are still unclear.

During the same period, marine gateways surrounding Antarctica (Drake Passage and Tasman Gateway) opened and deepened and Atlantic-Artic gateways changed configurations, thereby allowing the onset of oceanic currents such as the circumpolar current isolating Antarctica.

Here, we investigate how coupled changes in the configuration of these gateways may impact oceanic circulation and carbon cycle using climate simulations performed with the IPSL-CM5A2 model, an Earth System Model equipped with the biogeochemical model PISCES. Our reference simulation uses the paleogeography from Poblete et al (2021), based on the paleobathymetry of Straume et al (2020). Several sensitivity experiments with different gateway configurations are then presented and discussed, with specific focus on global ocean circulation changes and implications for the carbon cycle.

How to cite: Fabre, E., Ladant, J.-B., Donnadieu, Y., and Sepulchre, P.: Impact of marine gateways on oceanic circulation and carbon cycle in the Late Eocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10538, https://doi.org/10.5194/egusphere-egu24-10538, 2024.

The Cenozoic era reflects a discernible global cooling trend attributed to the prolonged decrease in atmospheric pCO₂. Various theories have been proposed to elucidate the mechanisms behind this reduction, with a focus on the substantial carbon exchange between the atmosphere and the global ocean. However, the carbon storage dynamics in the abyssal ocean during the geological past remain enigmatic. Employing a state-of-the-art ocean-biogeochemical model and leveraging recently published paleoceanographic records, this study unveils distinct basin-scale carbon storage patterns in the Pacific and Atlantic in a hypothetical no-Tibetan-Plateau scenario. Through sensitivity experiments, our findings suggest that orographic forcing, specifically the absence of the Tibetan Plateau, may have triggered a significant carbon transition from the Atlantic to the Pacific. This transition appears to be driven by a substantial reorganization of deep ocean overturning circulation. Importantly, this observed phenomenon could be a contributing factor to the long-term reduction in atmospheric pCO₂.

How to cite: Du, J. and Tian, J.: Dramatic transition of abyssal oceanic carbon reservoir driven by deep ocean overturning circulation during the Cenozoic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2334, https://doi.org/10.5194/egusphere-egu24-2334, 2024.

The modern thermohaline circulation in the Atlantic Ocean plays a crucial role in shaping the climates of Europe and North America. It also significantly influences ocean carbon storage and biological productivity through processes such as deep ocean ventilation and nutrient advection. A pivotal element of this intricate circulation system is the deep convection in the North Atlantic, which is essential for the Atlantic meridional overturning circulation. Paleogeographic studies based on data from the Cenozoic era propose that the establishment of this ocean conveyor belt occurred between the Middle Eocene (approximately 48 to 38 million years ago) and the Late Miocene (around 11 to 5 million years ago). This period witnessed significant climate fluctuations, notably exemplified by the Eocene-Oligocene transition (34 million years ago), marked by a sudden global temperature cooling and the emergence of the Antarctic Ice Sheet (AIS). Did these changes have a significant impact on the stability of the North Atlantic Ocean? To address this question, we investigate the mechanisms behind the initiation of deep water in the North Atlantic during the Eocene to Miocene transition, using the Earth System model IPSL-CM5A2. Our Eocene simulation indicates an absence of convective instabilities in the North Atlantic, whereas deep convection is evident in our Miocene simulation, enabling the presence of a proto-Atlantic Meridional Overturning Circulation (AMOC) cell. In order to investigate the processes triggering North Atlantic Deep Water (NADW) initiation under Miocene conditions, we conducted sensitivity tests involving a reduction in atmospheric CO2 concentration from 1,120 ppmv to 560 ppmv and the introduction of AIS for Eocene conditions. Our findings reveal that halving the CO2 concentration and initiating AIS during the Eocene is insufficient to destabilize the water column in the North Atlantic and instigate the formation of NADW. The Eocene paleogeography emerges as a key factor, contributing to an inflow of fresh water into the Atlantic Ocean, resulting in low surface water density. This process reinforces stratification, hindering the onset of convection.

How to cite: Pineau, E., Donnadieu, Y., Maffre, P., Lique, C., Huck, T., and Ladant, J.-B.: Emergence of North Atlantic Deep Water during the Cenozoic: A Tale of Geological and Climatic Forcings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11160, https://doi.org/10.5194/egusphere-egu24-11160, 2024.

Maintaining global freshwater conservation in climate models is crucial for accurately simulating Earth's hydrological cycle. This property particularly deserves specific attention in the deep-time paleoclimate simulations for the different geographies that changes the river route to the ocean. Changes in the volume of runoff directly exert significant impact on the ocean circulation. Large uncertainties in paleo-topography causes the uncertainties in runoff, but the latter receives less attention in the model simulations. To investigate the effects of the uncertainties on the model simulations, climate simulations of the Pre-Industrial (PI) and the Middle Miocene Climatic Optimum (MMCO) are compared by two sets of experiments —— freshwater conservative and non-conservative experiments that with sufficient and insufficient runoff import to the ocean model, respectively. Responses of the differences between the MMCO and the PI to the runoff changes are investigated. For the mean state, large qualitive and quantitative differences appear in the North Atlantic. Compared to the non-conservative experiments, the conservative experiments show the reduced salinity in the North Atlantic and collapsed Atlantic Meridional Overturning Circulation (AMOC), in contrast to the high salinity distribution and much strong AMOC in the non-conservative experiments. These differences lead to the discrepancies in volume transport through the oceanic seaway, as well as contribute to the temperature, sea ice and surface albedo changes in different amplitude in the North Atlantic. Although the climatic variabilities are affected by the runoff changes, enhanced Atlantic Multidecadal Oscillation (AMO) and reduced El Niño–Southern Oscillation (ENSO) are simulated in the MMCO regardless of the quality of freshwater conservation. Besides, the MMCO simulations show that the intensity of the Asian monsoon is greater in the South Asia and lower in the East Asia compared to PI. The study suggests that runoff changes have great effect on the climate change in the North Atlantic and need extra attention in the paleoclimate study.

How to cite: Wei, J.: Effects of Runoff Changes on the Climate Simulations of the Middle Miocene Climate Optimum, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7590, https://doi.org/10.5194/egusphere-egu24-7590, 2024.

During the Miocene epoch (~23-5 Ma), the Earth experienced a notably warmer climate, with global surface temperatures ranging approximately 4°C to 8°C higher than pre-industrial levels, accompanied by atmospheric CO₂ concentrations in the range of 400-800 ppm. Throughout this period, tropical ocean gateways underwent constriction or closure, while high-latitude gateways expanded. These developments likely played a pivotal role in shaping the modern ocean circulation structure, with strong bipolar hemispheric overturning in the Atlantic, although the precise mechanisms remain poorly understood. This study explores Miocene ocean circulation through an opportunistic climate model intercomparison (MioMIP1), encompassing 14 simulations that use different paleogeographies, CO₂ levels, and vegetation distributions. A consistent feature across all models is the fresher-than-modern Arctic and a resulting increased freshwater export to the North Atlantic. Consequently, the Atlantic Meridional Overturning Circulation (AMOC) appears markedly weaker than its modern counterpart in all simulations, ranging from approximately 1 to 16 Sv. However, there is no discernible correlation between the transport of Arctic freshwater to the Atlantic and the strength of the AMOC across the simulations. Similarly, contrary to earlier suggestions, our analysis reveals that neither Panama nor the Tethys gateway exerts a consistent impact on circulation across the simulations. This implies that the influence of these three straits on circulation dynamics also depends on other factors such as background palaeogeography, CO₂ levels, vegetation, or model physics and requires further study. In three out of the 13 simulations, deep overturning in the North Pacific (PMOC) is observed, ranging from approximately 5 to 10 Sv. Notably, in the North Atlantic, the simulations with a higher salinity have a stronger AMOC, and although this is not observed as distinctly in the North Pacific, the simulations with a PMOC exhibit a reduced salinity contrast between the North Pacific and North Atlantic and highlight the salinity feedback in play. A proto-AMOC appears to be developing in most of the simulations, albeit weak. This indicates that while the AMOC began to take shape during the Miocene, it likely attained its modern strength during the late Miocene.

How to cite: Naik, T., de Boer, A., Coxall, H., Burls, N., Bradshaw, C., Donnadieu, Y., Farnsworth, A., Frigola, A., Herold, N., Huber, M., Karami, P., Knorr, G., LeGrande, A., Lunt, D., Prange, M., and Zhang, Y.: Opportunistic Model Intercomparison of the Miocene Ocean Circulation – MioMIP1, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-988, https://doi.org/10.5194/egusphere-egu24-988, 2024.

The Indo-Pacific warm pool plays a crucial role in regulating heat and water vapor exchange between low and high latitudes. Since the late Miocene epoch, the tectonic evolution of the Indonesian seaway, particularly its gradual closure, has controlled the development of the Indo-Pacific warm pool, leading to altered current patterns between the western Pacific and eastern Indian Oceans. Reconstructed palaeoceanographic records along with numerical simulation experiments have revealed that during the Pliocene period, there was a shift in water source for Indonesian throughflow from high temperature and high salinity South Equatorial Pacific waters to low temperature and low salinity North Equatorial Pacific waters. The closure of the Indonesian Seaway may have shifted the atmospheric convective center from the east Indian Ocean to the West Pacific Ocean, leading to the gradual strengthening of the Western Pacific Warm Pool while reducing surface temperatures and subsurface salinity in the eastern Indian Ocean. The synchronous evolution between the Indonesian Seaway closure and the throughflow not only impacts arid climates in northwest Australia and East Africa but also reduces heat transport towards higher latitudes in the Northern Hemisphere. Previous studies have indicated that changes in meridional heat transport caused by the closure of the Indonesian seaway may contribute to the formation of the Arctic ice sheet; however, further study of the influence of this process and the degree of influence is still weak.

Here, we analyzed the Mg/Ca ratio of surface and subsurface foraminifera shells of ODP (Ocean Drilling Program) sites 807 and 762 in the western Equatorial Pacific and Eastern Indian Ocean, and reconstructed changes in Sea Surface Temperature (SST) and Thermocline Water Temperature (TWT) between 6-3.8Ma. It was observed that ODP site 807 experienced a rise in surface water temperature from 5.2 to 4.9Ma, while ODP site 762 witnessed a drop in surface seawater temperature during this period. Additionally, both sites exhibited a deepening thermocline between 5-4.5Ma. These findings indicate that there was a contraction of the Indonesian seaway during 5.2-4.9Ma, leading to warm water accumulation within the Western Pacific Warm Pool, which subsequently increased surface water temperature in this region while decreasing it in the eastern Indian Ocean, thereby strengthening the Western Pacific Warm Pool. We performed a group of numerical simulation sensitivity experiments on the opening and closing of the Indonesian Seaway. The results showed that when the Indonesian Seaway is closed, the sea surface temperature of the Pacific Ocean and the Indian Ocean will both increase. However, for the subsurface layer, the temperature of the subsurface water in the Pacific Ocean increased, while that of the Indian Ocean decreased. At the same time, the West Pacific Warm Pool strengthening caused by the closure of the Indonesian Seaway was observed clearly.

Keywords： Indonesian Seaway, Indonesian Throughflow, Indo-Pacific Warm Pool, Mg/Ca ratio.

How to cite: Ding, Y., Tian, J., and Wei, J.: Upper ocean temperature change caused by the closing of the Indonesian Seaway from the late Miocene to early Pliocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4920, https://doi.org/10.5194/egusphere-egu24-4920, 2024.

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 (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 (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 (Hill, 2015). Nevertheless, this geographic change has so far not been well considered in the Pliocene Modelling Intercomparison Project (Dowsett et al., 2016; 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. We demonstrate that the sea surface temperatures were warmer than pre-industrial values and Nordic Seas had warmed significantly. Our results hint that a subaerial Barents-Kara Sea might contribute to the data-model SST mismatch during the mid-Pliocene.

References:

Dowsett, H., Dolan, A., Rowley, D., Moucha, R., Forte, A. M., Mitrovica, J. X., . . . Haywood, A. (2016). The PRISM4 (mid-Piacenzian) paleoenvironmental reconstruction. Climate of the Past, 12(7), 1519-1538. doi:10.5194/cp-12-1519-2016

Dowsett, H. J., Foley, K. M., Stoll, D. K., Chandler, M. A., Sohl, L. E., Bentsen, M., . . . Zhang, Z. S. (2013). Sea Surface Temperature of the mid-Piacenzian Ocean: A Data-Model Comparison. Scientific Reports, 3. doi:ARTN 2013 10.1038/srep02013

Haywood, A. M., Dowsett, H. J., & Dolan, A. M. (2016). Integrating geological archives and climate models for the mid-Pliocene warm period. Nature Communications, 7. doi:ARTN 1064610.1038/ncomms10646

Haywood, A. M., Dowsett, H. J., Dolan, A. M., Rowley, D., Abe-Ouchi, A., Otto-Bliesner, B., . . . Salzmann, U. (2016). The Pliocene Model Intercomparison Project (PlioMIP) Phase 2: scientific objectives and experimental design. Climate of the Past, 12(3), 663-675. doi:10.5194/cp-12-663-2016

Hill, D. J. (2015). The non-analogue nature of Pliocene temperature gradients. Earth and Planetary Science Letters, 425, 232-241. doi:10.1016/j.epsl.2015.05.044

Lien, O. 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. Quaternary Science Reviews, 282. doi:ARTN 10743310.1016/j.quascirev.2022.107433

McClymont, E. L., Ford, H. L., Ho, S. L., Tindall, J. C., Haywood, A. M., Alonso-Garcia, M., . . . Zhang, Z. S. (2020). Lessons from a high-CO₂ world: an ocean view from ∼ 3 million years ago. Climate of the Past, 16(4), 1599-1615. doi:10.5194/cp-16-1599-2020

How to cite: Li, S., Zhang, X., Sun, Y., Lien, Ø., Hjelsturn, B., Stepanek, C., Gowan, E., and Yu, Y.: Global impacts of a subaerial Barents Sea on the mid-Pliocene climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4363, https://doi.org/10.5194/egusphere-egu24-4363, 2024.

The tectonically induced closure/constriction of the Central American Seaway (CAS) and Indonesian Seaway (Indo) during the early to mid-Pliocene has been associated with many climatic events, such as the onset of Northern Hemisphere glaciation, the intensification of the Atlantic meridional overturning circulation (AMOC) and Australian aridification. However, studies on how the closure/constriction of tropical seaways affects the tropical climate system are still sparse and not systematic. Previous studies have linked the constriction of Indo to the aridification over East Africa and discussed the role of CAS closure in affecting the moisture supply over South America, but the underlying mechanism and combined effect of both tropical seaways are not well studied. In this study, we evaluate the impacts of tropical seaways' closure/constriction and distinguish the relative roles of CAS and Indo on climate in tropical Africa and South America using the NorESM-L Atmosphere-Ocean General Circulation Model (AOGCM) and a dynamic vegetation model (LPJ-GUESS). Our results show that the closure of the CAS leads mainly to aridification in northeastern Brazil, resulting in an expansion of tropical xerophytic shrubland and savanna in this region. The narrowing of the Indo mainly leads to enhanced aridification in eastern tropical Africa and reduces the extent of tropical forests in eastern and northern tropical Africa, which is generally consistent with the data. The closure/narrowing of the two tropical seaways results in a superposition of the individual seaway's effect, particularly over the northeastern Brazil region, which exhibits enhanced aridification compared to the closure of the individual CAS. The seaways’ changes are shown to be pivotal for the evolution of climate and vegetation over East Africa and northeastern South America to contemporary conditions.

How to cite: Tan, N., Li, H., Zhang, Z., Wu, H., Ramstein, G., Sun, Y., He, Z., Su, B., Zhang, Z., and Guo, Z.: Influence of Tropical Seaways on the Climate and Vegetation in Tropical Africa and South America , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4931, https://doi.org/10.5194/egusphere-egu24-4931, 2024.

The Langhian (15.98 - 13.82 Ma) was a stage of the mid-Miocene characterized by higher atmospheric CO₂ concentrations than modern days and substantially warmer surface temperatures. The mid-Miocene has garnered growing attention as a potential analog for future climate change. Several climate models have assessed the influence of CO₂ and geography on the Miocene warmth. In this study, we simulated the Langhian using a new unpublished paleogeography. This configuration notably features shallower and narrower access to the Arctic Ocean than has been previously documented. Despite CO₂ concentrations equivalent to three times the pre-industrial levels (840 ppm) and the absence of ice sheets, we observe persistent sea ice in the Arctic Ocean and cooling of the Northern Atlantic Ocean. This cooling is related to the collapse of the Atlantic meridional ocean circulation. Conversely, a robust Pacific meridional ocean circulation emerges, which is less frequently observed in Miocene simulations. We investigate the reasons behind such behavior, by notably widening and deepening the Fram Strait; forcing a fixed, warmer vegetation; using a more recent atmospheric model with improvement to the physics. These adjustments underscore the critical role of geography in achieving an accurate simulation of the Miocene and facilitating more precise data-model comparisons.

How to cite: Renoult, M. and de Boer, A.: Sensitivity of mid-Miocene simulations to different continental configurations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9688, https://doi.org/10.5194/egusphere-egu24-9688, 2024.

How to cite: Kravette, N., Feng, R., and Dvorak, M.: Exploring Radiative Forcing from Pliocene Boundary Conditions and CO2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11853, https://doi.org/10.5194/egusphere-egu24-11853, 2024.