The study of deep-time (pre-Quatrenary) climate evolution is important not only for understanding Earth’s habitable history but also for providing insights to present and future changes of the Earth system. To investigate deep-time climate, several international modelling intercomparsion projects, for example DeepMIP, MioMIP, PlioMIP, have been initiated. All these MIPs pay attention to the Cenozoic climate. However, relatively fewer modelling studies simulate climate in deeper time before the Cenozoic. This session invites works on deep-time climate simulations and reconstructions over the tectonic time scales, including, but not limited to, idealized and comprehensive model simulations, geological, geochemical, and paleontological reconstructions. We wish this session could integrate our knowledge of deep-time climate and environment evolution in the spirit of an integrated Earth system.
vPICO presentations: Thu, 29 Apr
Nearly A century ago the pioneering book published in 1924 “Die Klimate der geologischen Vorzeit “ explained by plate motion the evolution of vegetation revealed in sedimentary records. Nevertheless, they did not invoke climate changes. In the second part of the 20th century the intricate relationship between tectonics, long-term carbon cycle and climate was depicted by James G. C. Walker (1981). Since these major steps, climate modeling of the Earth system kept on improving and including more and more components and processes to enable the investigation of deep time periods using general circulation model that can account for atmosphere and ocean dynamics. Here we illustrate long but drastic climate changes clearly related with tectonics, through three different examples:
1) The crucial role of paleogeography (continental distribution) to explain the drawdown of atmospheric carbon dioxide and the huge glaciation associated that occured during the Neoproterozoic period.
2) The shrinkage of large epicontinental Paratethys that covered a large part of Eastern Europe and Western Asia and its impact on both monsoonal systems (African and Asian) since 40 Ma.
3) The large impact of mountain range uplifts since Eocene both in Asia (Tibetan Plateau and Himalaya) and in Africa (buildup of the rift), on atmosphere and ocean dynamics.
These studies not only allow for testing the ability of Earth system models to capture long term changes of Earth climate, but they pinpoint the pivotal role tectonics played in shaping the long-term evolution of atmospheric CO2 and monsoon patterns.
How to cite: Zhang, Z. and Ramstein, G.: Some illustrations of large tectonically driven climate changes in Earth history, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15737, https://doi.org/10.5194/egusphere-egu21-15737, 2021.
The climate of the Cretaceous and Eocene (146-34 Million years ago) was exceptionally warm. Crocodiles and Palm trees, which cannot withstand a few nights of subfreezing temperatures, could be found in the waters of Greenland and in the middle of present day Canada, where current winter temperatures can drop to -40C. State-of-the-art climate general circulation models cannot reproduce the exceptionally warm continental winter temperature during these periods even with very high atmospheric CO2 concentrations. One wonders whether these models are missing some significant feedback that may also affect their future global warming projections. We present two cloud feedbacks that may have contributed to such past warming, and that are found to be part of the atmospheric response to future warm climate projections, explaining the lapse-rate feedback in future Arctic climate change scenarios and the projected appearance of tropical-like deep convection during winter in the Arctic.
Recent studies (Cronin and Tziperman 2015; Cronin, Li and Tziperman, 2017), using Lagrangian single column atmospheric models, have proposed that in warmer climates low clouds would form as maritime air masses advect into Northern Hemisphere high-latitude continental interiors during winter (DJF). The greenhouse effect due to these low clouds could reduce surface radiative cooling and suppress Arctic air formation events, explaining the warm winter high-latitude continental interiors during past warm climates, and the positive lapse-rate feedback in future Arctic climate change scenarios. A 3D atmospheric general circulation model (Hu, Cronin and Tziperman, 2018) confirms these finding by simulating different warming scenarios under prescribed CO2 and sea surface temperature (SST) conditions. Winter 2-meter temperatures on extreme cold days is found to increase about 50\% faster than the winter mean temperatures and the prescribed SST. Low cloud fraction and surface longwave (LW) cloud radiative forcing also increase in both the winter mean state and on extreme cold days, consistent with the Lagrangian air-mass studies.
Air parcels experiencing extreme cold events in the present climate often arrive from Siberia and pass over the Arctic. An ice-free Arctic (during past of future warm climates) allows air parcels can accumulate moisture and therefore experience the formation of low clouds and thus the suppression of Arctic air formation. An ice free Arctic may be triggered due to the convective cloud feedback of (Abbot and Tziperman 2008, 2009; Abbot et al. 2009; Arnold et al. 2014) in which tropical-like deep atmospheric convection is triggered at high-latitudes during winter time. The radiative effects of the high tropospheric clouds associated with the atmospheric convection act to keep the surface warm, and this in turn maintains the convection active. Finally, it will be shown that the proposed cloud feedback is at work also in effectively all models run under the extended RCP 8.5 scenario, and that this may aid in the elimination of both summer and winter sea ice from the Arctic in these simulations, acting together with other related Arctic feedbacks (Hankel and Tziperman 2021, submitted).
How to cite: Tziperman, E.: Arctic winter warming due to cloud feedbacks in warm climates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8354, https://doi.org/10.5194/egusphere-egu21-8354, 2021.
CO2 is the most important greenhouse gas in the Earth’s atmosphere and has fluctuated considerably over geological time. However, proxies for past CO2 concentrations have large uncertainties and are mostly limited to Devonian and younger times. Consequently, CO2 modelling plays a key role in reconstructing past climate fluctuations. Facing the limitations with the current CO2 models, we aim to refine two important forcings for CO2 levels over the Phanerozoic, namely carbon degassing and silicate weathering.
Silicate weathering and carbonate deposition is widely recognized as a primary sink of carbon on geological timescales and is largely influenced by changes in climate, which in turn is linked to changes in paleogeography. The role of paleogeography on silicate weathering fluxes has been the focus of several studies in recent years. Their aims were mostly to constrain climatic parameters such as temperature and precipitation affecting weathering rates through time. However, constraining the availability of exposed land is crucial in assessing the theoretical amount of weathering on geological time scales. Associated with changes in climatic zones, the fluctuation of sea-level is critical for defining the amount of land exposed to weathering. The current reconstructions used inmodels tend to overestimate the amount of exposed land to weathering at periods with high sea levels. Through the construction of continental flooding maps, we constrain the effective land area undergoing silicate weathering for the past 520 million years. Our maps not only reflect sea-level fluctuations but also contain climate-sensitive indicators such as coal (since the Early Devonian) and evaporites to evaluate climate gradients and potential weatherablity through time. This is particularly important after the Pangea supercontinent formed but also for some time after its break-up.
Whilst silicate weathering is an important CO2 sink, volcanic carbon degassing is a major source but one of the least constrained climate forcing parameters. There is no clear consensus on the history of degassing through geological time as there are no direct proxies for reconstructing carbon degassing, but various proxy methods have been postulated. We propose new estimates of plate tectonic degassing for the Phanerozoic using both subduction flux from full-plate models and zircon age distribution from arcs (arc-activity) as proxies.
The effect of revised modelling parameters for weathering and degassing was tested in the well-known long-term models GEOCARBSULF and COPSE. They revealed the high influence of degassing on CO2 levels using those models, highlighting the need for enhanced research in this direction. The use of arc-activity as a proxy for carbon degassing leads to interesting responses in the Mesozoic and brings model estimates closer to CO2 proxy values. However, from simulations using simultaneously the revised input parameters (i.e weathering and degassing) large model-proxy discrepancies remain and notably for the Triassic and Jurassic.
How to cite: M. Marcilly, C., Torsvik, T. H., Domeier, M., and Royer, D. L.: Revising key parameters for long-term carbon cycle models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2794, https://doi.org/10.5194/egusphere-egu21-2794, 2021.
In the equatorial regions on Earth today, the seasonal cycle of the monthly mean surface air temperature is <10°C. However, deep (>1 m) sand wedges were found near the paleoequator in the Marinoan glaciogenic deposits at ~635 million years ago, indicating a large seasonal cycle (probably >30°C). Such observations have been used to argue that the Earth had a very high obliquity (>54°) during that time, leading to the proposal of high-obliquity hypothesis. Although the hypothesis was criticized for not being able to find a mechanism for the Earth to return to a low-obliquity state, there was no other explanation for the observed large equatorial seasonal cycle. Through numerical simulations, we show that the equatorial seasonal cycle could reach >30°C at various continental locations if the oceans are completely frozen over, as would have been the case for a snowball Earth, or could reach ~20°C if the oceans are not completely frozen over, as would have been the case for a waterbelt Earth or slushball Earth. It is pointed out that the eccentricity is important for the equatorial seasonal cycle especially when the climate is cold and dry. These large equatorial seasonal cycle above are obtained at the maximum eccentricity of the Earth orbit, i.e., 0.0679, and will be approximately 10°C smaller if the present-day eccentricity is used. For these seasonal cycles, theoretical calculations show that the deep sand wedges form readily in a snowball Earth while hardly form in a waterbelt Earth. Therefore, our results remove a loophole of the (hard) snowball Earth hypothesis, while make the waterbelt Earth and high-obliquity Earth hypotheses much less appealing.
How to cite: Liu, Y.: Large Equatorial Seasonal Cycle during Marinoan Snowball Earth, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10559, https://doi.org/10.5194/egusphere-egu21-10559, 2021.
On present-day Earth, dust emissions are restricted only to a few desert regions mainly due to the distribution of land vegetation. The atmospheric dust loading is thus relatively small and has a slight cooling effect on the surface climate. For the Precambrian (before ~540 Ma), however, dust emission might be much more widespread since land vegetation was absent. Here, our simulations using an Earth system model (CESM1.2.2) demonstrate that the global dust emission during that time might be an order of magnitude larger than that of the present day, and could have cooled the global climate by ~10 °C. Similarly, the dust deposition in the ocean, an important source of nutrition for the marine ecosystem, was also increased by a factor of ~10. Therefore, dust was a critical component of the early Earth system, and should always be considered when studying the climate and biogeochemistry of the Precambrian.
How to cite: Liu, P., Liu, Y., Peng, Y., Lamarque, J.-F., Wang, M., and Hu, Y.: Large influence of dust on the Precambrian climate , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10524, https://doi.org/10.5194/egusphere-egu21-10524, 2021.
The Permo–Triassic Boundary (PTB) marks a time of profound climatic change. Near the PTB (~252 Ma), the largest known mass extinction occurred with more than 90% of marine species and 70% of terrestrial species became extinct. The mass extinction is linked to a massive warming event at the PTB, where tropical regions became too hot for survival ofspecies. The increase in atmospheric CO2 during the Permian and the PTB is mainly attributed to the decrease of chemically weatherable fresh silicate rock due to orogenesis, and the CO2 released in the atmosphere from the Siberian Traps. In this study, we use the UK Met Office fully coupled HadCM3L General Circulation Model (GCM) to perform Permo-Triassic climate simulations with different atmospheric CO2 values that encompass most of the estimates of atmospheric CO2 concentration during this time, to provide more insights about the climate changes during the end Permian – early Triassic. Specifically, we focus on: a) the spatial extension of dry conditions/lethally hot temperatures under different CO2 conditions, b) the seasonal surface temperature difference and precipitation changes at higher latitudes and c) the effects of increased atmospheric CO2 on the large-scale wind and monsoonal circulation.
How to cite: Zoura, D., Hill, D. J., Hunter, S. J., Haywood, A. M., and Wignall, P. B.: The effects of CO2 increase and its link to the mass extincton at the Permo-Triassic boundary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8367, https://doi.org/10.5194/egusphere-egu21-8367, 2021.
The evolution of continents over the past 250 million year is remarked by the breakup of the Pangea supercontinent. The changes of continents must have important influences on regional and global monsoon systems because monsoons are primarily a result of land-sea thermal contrast.
To study how the monsoon system had been evolved with continent changes over the past 250 million years, we carried out a series of climate simulations, using the Community Earth System Model (CESM). Changes in continents, mountain building, solar radiation, and carbon dioxide (CO2) are all considered in the simulations. In the present talk, we will present our preliminary simulation results of how the mega-monsoon associated with the supercontinent Pangea evolved into the six regional monsoons at the present over the past 250 million years. We will also demonstrate ocean circulation changes with different continent distributions, such as ENSO, and its influences on regional monsoons. Monsoon impacts on land-surface processes and the associated carbon-cycle will be also presented.
How to cite: Hu, Y., Guo, J., Li, X., Lan, J., Lin, Q., Han, J., Zhang, J., Liu, Y., and Yang, J.: Evolution of the monsoon system over the past 250 million years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1459, https://doi.org/10.5194/egusphere-egu21-1459, 2021.
For modern Earth, the annual-mean equatorial atmosphere is flowing from east to west or called easterly winds. This is mainly due to the deceleration effect of the seasonal cross-equatorial flows of the Hadley cells, against the acceleration effect of equatorial Rossby and Kelvin waves excited from tropical convection and latent heating release. In this work, we examine the evolution of equatorial winds during the past 250 million years (Ma) using the global Earth system model CESM1.2.2. Three climatic factors different from the modern Earth, solar constant, atmospheric CO2 concentration, and land-sea configuration, are considered in the simulations. We find that the equatorial winds in the upper troposphere change the sign to westerly flows or called atmospheric superrotation in certain eras. The strength of the superrotation is comparable to the magnitude of the present easterly winds, several meters per second, not strong. This phenomenon occurs when the waves are relatively stronger and/or the Hadley cells are relatively weaker, which in turn are due to the changes in the three factors.
How to cite: Lan, J., Yang, J., and Hu, Y.: Weak Equatorial Superrotation During the Past 250 Million years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1503, https://doi.org/10.5194/egusphere-egu21-1503, 2021.
The tropical rainfall, which contributes on about half of global rainfall, is manifested as a quasi-global rain belt called the intertropical convergence zone (ITCZ). This study examines the linkage between continental configurations and the annual mean latitude of ITCZ over the tectonic timescale. Over the past 250Ma, the break of supercontinent Pangea led to dramatic changes of continental mass distribution driven by tectonic dynamics. With a series of slicewise general climate model (GCM, CESM1.0) simulations over the past 250Ma, we investigate how is the latitude of ITCZ changes over time and how do the continental configurations set the latitude of ITCZ. With an energetic framework of the ITCZ latitude, we examined the contributions of the hemispheric asymmetry of radiation budget and ocean heat transport on the ITCZ latitude, and further demonstrate that those factors are largely driven by the continental configurations.
How to cite: Nie, J., Han, J., and hu, Y.: Migrations of tropical rain belt driven by tectonic dynamics over the past 250 Ma, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2018, https://doi.org/10.5194/egusphere-egu21-2018, 2021.
Dust in the atmosphere can affect climate by directly absorbing and scattering solar radiation. In present day, most of dust is emitted from the dry regions over North Africa and Arabian Peninsula, it has been shown that they impact on global mean surface temperature, African monsoon, number of tropical cyclones over the Atlantic Ocean, ENSO variability and the strength of Atlantic meridional ocean circulation (AMOC). During the Mesozoic, the continental configuration was very different from the present, the supercontinent Pangea gradually broke up and Atlantic Ocean formed during this time period. On a different continental configuration, the area and location of dry regions may be very different, so the dust emission and atmospheric dust loading is different too. In this work, we use the global Earth system model CESM1.2.2 to examine the influence of dust on climate during the Mesozoic. Specifically, we simulate the dust and climate at two time slices, 250 million years ago (Ma) and 80 Ma. Results show that the atmospheric dust loading in both periods was much higher than that of present day. Such dust induced significant cooling of the surface climate, especially over polar regions.
How to cite: Lin, Q. and Liu, Y.: Influence of Dust on Climate during the Mesozoic , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6803, https://doi.org/10.5194/egusphere-egu21-6803, 2021.
A set of deep-time climate simulations each 10Ma years from 250Ma to PI are conducted by using the NCAR-CESM1.2, for understanding the evolution of the ocean monsoon regions driven by tectonic dynamics over the past 250 million years and exploring its variation mechanisms. In recent years, scientists have proposed the concept of a global monsoon system, which includes not only typical monsoon regions (such as the African monsoon region and South Asian monsoon region), but also the atypical Northwest Pacific Ocean monsoon region. Research on the ocean monsoon is very limited, especially in the field of paleoclimate. The results in this paper show that the horizontal gradients of the thickness of the ocean mixed layer may be more important for the formation of the ocean monsoon than land-sea thermal contrast, which is confirmed by the aquaplanet simulations with various gradients of the ocean mixed-layer thickness. Near the Pacific monsoon region in the northern hemisphere, the thickness of the ocean mixed layer has obvious meridional and zonal gradients, which will correspond to the meridional and zonal thermal contrasts. In addition, there are obvious seasonal reversals in the gradients of the ocean mixed-layer thickness in summer and winter, and the corresponding longitudinal and zonal thermal contrast produce seasonal reversals. Over the past 250 million years, the thickness of the ocean mixed layer on the east side of the Pacific Ocean Basin in the Northern Hemisphere has deepened, and the corresponding ocean monsoon area on the east side of the Pacific Ocean has decreased. The changes in the thickness of the ocean mixed layer are closely related to the changes in the surface wind field. Examining the changes in the atmospheric circulations, we find that the Pacific subtropical high strengthens and extends from east to the west bank of the ocean basin, where the atmospheric low-level anticyclonic circulation causes the ocean surface layer to converge and sink and thus causes the ocean mixed layer to deepen. The changes in the Pacific subtropical high are related to changes in the continental monsoon region. Since the 170Ma, the Pangea supercontinent splits up, causing the supercontinent's inland water vapor to increase, the land monsoon area to increase, and the ocean monsoon area to decrease. According to the "monsoon-desert mechanism" of Rodwell and Hoskins, we can understand the relationship between the strengthening of land monsoon condensation heating and the formation of subtropical high over the western ocean.
How to cite: Han, J., Hu, Y., and Liu, Y.: Evolution of the ocean monsoon regions over the past 250 million years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3690, https://doi.org/10.5194/egusphere-egu21-3690, 2021.
The Pacific-North American (PNA) teleconnection is one of the most crucial climate modes in the current climate. It is well known that the PNA is related to the ENSO variability, and it has a significant influence on North American climate. Whereas, the traditional physical mechanisms about the PNA is probably not applicable for the deep-time paleoclimate. During the past 250 million years, climate variabilities are strongly structured by the evolution of land-sea distribution, CO2 forcing, and solar radiation. In this work, we use the Community Earth System Model (CESM) version 1.2.2 to investigate the changes of PNA every 10 million years. The deep-time simulation provides a new way to understand the nature of PNA and the related physical mechanisms. We found that the spatial distribution of the PNA-like mode is closely related to the land-sea distribution. And the combination effect from atmospheric circulation and the thermal condition is proved to be important to modulate the evolution of PNA.
How to cite: Li, Z. and Hu, Y.: The evolution of Pacific-North American teleconnection during the past 250 million years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10751, https://doi.org/10.5194/egusphere-egu21-10751, 2021.
The Tibetan Plateau has a significant impact on the Asian climate due to its high topography. However, its uplift history, especially the uplift of the Gangdese Mountains in its early stage, is under intense debate. Most quantitative reconstructions are done for the Cenozoic only, impeding our understanding of the geodynamic and paleoenvironmental evolution during the Cretaceous. How high would the Gangdese Mountains be then, and what effects would they have on Asian climate? In order to explore these two questions, here we model the impacts of the Gangdese Mountains on the Asian climate during the Late Cretaceous by employing the Community Earth System Model version 1.2.2. It is found that the extent of dry land in East Asia is sensitive to the altitude of the Gangdese Mountains; it expands eastwards and southwards with the rise of the mountain range, which is due to the fact that the Gangdese Mountains can significantly reduce the precipitation over the low- to mid-latitude Asia. We then attempt to constrain their paleoaltitude using the available climate indicators in the sediments. The aridity index is further calculated for this region, and its comparison with the climate records suggests that Gangdese Mountains should be higher than 1 km but lower than 3 km during the Late Cretaceous, most likely ~2 km.
How to cite: Zhang, J., Liu, Y., Fang, X., Zhang, T., Zhu, C., and Wang, C.: Elevation of the Gangdese Mountains and Their Simulated Impacts on Asian Climate during the Late Cretaceous, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2606, https://doi.org/10.5194/egusphere-egu21-2606, 2021.
How to cite: Zhu, C.: East‐Central Asian Climate Evolved With the Northward Migration of the High Proto‐Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1878, https://doi.org/10.5194/egusphere-egu21-1878, 2021.
The Oligocene-Miocene boundary climatic reorganization linked to the northward advance of the East Asian monsoon in subtropical China is a potentially important but poorly constrained atmospheric CO2 consumption process. Here, we performed a first-order estimate of the difference in CO2 consumption induced by silicate chemical weathering and organic carbon burial in subtropical China related to this monsoon advance. Our results show that an increase in CO2 consumption by silicate weathering varies between ~1% and 15% of the current global continental silicate sink with an ~60% contribution of Mg-silicate weathering but a negligible increase in the global organic carbon burial (<3.5%) since the late Oligocene. The results highlight the significant role of weathering of the Mg-rich upper continental crust in East China that would also contribute significantly to the rise in the Mg content of the ocean. Our study thus suggests that the uplift of the Himalaya-Tibetan Plateau can lead to indirect modification of the global carbon and magnesium cycles by changing the regional hydrological cycle in areas of East Asia that are tectonically less active in addition to the well studied direct impact of high erosion-induced atmospheric CO2 consumption along the orogenic belt in South Asia.
How to cite: Yang, Y., Galy, A., Fang, X., France-Lanord, C., Wan, S., Yang, R., Zhang, J., Zhang, R., Yang, S., Miao, Y., Liu, Y., and Ye, C.: Cenozoic advance of the East Asian monsoon promoted weathering of the magnesium-rich southern China upper crust and its significance for global geochemical cycles of carbon and magnesium, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5262, https://doi.org/10.5194/egusphere-egu21-5262, 2021.
Previous climate modeling studies suggest that the surface uplift of the Himalaya–Tibetan plateau (TP) is a crucial parameter for the onset and intensification of the East Asian monsoon during the Cenozoic. Most of these studies have only considered the Himalaya–TP in its present location between ∼26°N and ∼40°N despite numerous recent geophysical studies that reconstruct the Himalaya–TP 10° or more of latitude to the south during the early Paleogene. We have designed a series of climate simulations to explore the sensitivity of East Asian climate to the latitude of the Himalaya–TP. Our simulations suggest that the East Asian climate strongly depends on the latitude of the Himalaya–TP. Surface uplift of a proto-Himalaya–TP in the subtropics intensifies aridity throughout inland Asia north of ∼40°N and enhances precipitation over East Asia. In contrast, the rise of a proto-Himalaya–TP in the tropics only slightly intensifies aridity in inland Asia north of ∼40°N, and slightly increases precipitation in East Asia. Importantly, this climate
sensitivity to the latitudinal position of the Himalaya–TP is non-linear, particularly for precipitation across East Asia.
How to cite: Zhang, R., Jiang, D., Ramstein, G., Zhang, Z., Lippert, P. C., and Yu, E.: Changes in Tibetan Plateau latitude as an important factor for understanding East Asian climate since the Eocene: A modeling study , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10479, https://doi.org/10.5194/egusphere-egu21-10479, 2021.
Fluctuations in the Pacific Walker circulation (PWC), a zonally-oriented overturning cell across the tropical Pacific, can cause widespread climatic and biogeochemical perturbations. It remains unknown how the PWC developed during the Cenozoic era, with its substantial changes in greenhouse gases and continental positions. Through a suite of coupled model simulations on tectonic timescales, we demonstrate that the PWC was ~38º broader and ~5% more intense during the Early Eocene relative to present. As the climate cooled from the Early Eocene to the Late Miocene, the width of the PWC shrank, accompanied by an increase in intensity that was tied to the enhanced Pacific zonal temperature gradient. However, the locations of the western and eastern branches behave differently from the Early Eocene to the Late Miocene, with the western edge remained steady with time due to the relatively stable geography of the western tropical Pacific; the eastern edge migrates westward with time as the South American continent moves northwest. A transition occurs in the PWC between the Late Miocene and Late Pliocene, manifested by an eastward shift (both the western and eastern edges migrate eastward by >12º) and weakening (by ~22%), which we show here is linked with the closure of the tropical seaways. Moreover, our results suggest that rising CO2 favors a weaker PWC under the same land-sea configurations, a robust feature across the large spread of Cenozoic climates considered here, supporting a weakening of the PWC in a warmer future.
How to cite: Yan, Q.: Large shift of the Pacific Walker Circulation across the Cenozoic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10454, https://doi.org/10.5194/egusphere-egu21-10454, 2021.
How to cite: Lunt, D. and the DeepMIP team: DeepMIP: Model intercomparison of early Eocene climatic optimum (EECO) large-scale climate features and comparison with proxy data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4744, https://doi.org/10.5194/egusphere-egu21-4744, 2021.
The early Eocene greenhouse represents the warmest interval of the Cenozoic and therefore provides a unique opportunity to understand how the climate system operates under elevated atmospheric CO2 levels similar to those projected for the end of the 21st century. Early Eocene geological records indicate a large increase in global mean surface temperatures compared to present day (by ~14°C) and a greatly reduced meridional temperature gradient (by ~30% in SST). However, reproducing these large-scale climate features at reasonable CO2 levels still poses a challenge for current climate models. Recent modelling studies indicate an important role for shortwave (SW) cloud feedbacks to drive increases in climate sensitivity with global warming, which helps to close the gap between simulated and reconstructed Eocene global warmth and temperature gradient. Nevertheless, the presence of such state-dependent feedbacks and their relative strengths in other models remain unclear.
In this study, we perform a systematic investigation of the simulated surface warming and the underlying mechanisms in the recently published DeepMIP ensemble. The DeepMIP early Eocene simulations use identical paleogeographic boundary conditions and include six models with suitable output: CESM1.2_CAM5, GFDL_CM2.1, HadCM3B_M2.1aN, IPSLCM5A2, MIROC4m and NorESM1_F. We advance previous energy balance analysis by applying the approximate partial radiative perturbation (APRP) technique to quantify the individual contributions of surface albedo, cloud and non-cloud atmospheric changes to the simulated Eocene top-of-the-atmosphere SW flux anomalies. We further compare the strength of these planetary albedo feedbacks to changes in the longwave atmospheric emissivity and meridional heat transport in the warm Eocene climate. Particular focus lies in the sensitivity of the feedback strengths to increasing global mean temperatures in experiments at a range of atmospheric CO2 concentrations between x1 to x9 preindustrial levels.
Preliminary results indicate that all models that provide data for at least 3 different CO2 levels show an increase of the equilibrium climate sensitivity at higher global mean temperatures. This is associated with an increase of the overall strength of the positive SW cloud feedback with warming in those models. This nonlinear behavior seems to be related to both a reduction and optical thinning of low-level clouds, albeit with intermodel differences in the relative importance of the two mechanisms. We further show that our new APRP results can differ significantly from previous estimates based on cloud radiative forcing alone, especially in high-latitude areas with large surface albedo changes. We also find large intermodel variability and state-dependence in meridional heat transport modulated by changes in the atmospheric latent heat transport. Ongoing work focuses on the spatial patterns of the climate feedbacks and the implications for the simulated meridional temperature gradients.
How to cite: Steinig, S., Zhu, J., and Feng, R. and the DeepMIP team: Drivers of (non-)linear Eocene surface warming in the DeepMIP ensemble, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14127, https://doi.org/10.5194/egusphere-egu21-14127, 2021.
The Eocene – Oligocene Transition (~33.7 million years ago), marks the largest step transformation within the Cenozoic cooling trend, and is characterized by a sudden growth of the Antarctic ice sheets. The role of changes in oceanic basin configuration and the evolution of key oceanic gateways in triggering these climatic variations remains disputed. Here we implement a new state-of-the-art paleogeography model in the Norwegian Earth System Model (NorESM-F) to investigate the effect of oceanic gateway changes on the Eocene – Oligocene climate. We run different cases using realistic max/min depth configurations of the Atlantic – Arctic oceanic gateways, the Tethys Seaway, and the Southern Ocean gateways, and investigate the ocean and climate sensitivity to these changes. In addition, we run separate simulations investigating the impact on the carbon cycle. The models show that changes in the Atlantic – Arctic gateways (i.e. Greenland – Scotland Ridge and the Fram Strait) cause the most significant changes in ocean circulation and climate compared to the Southern Ocean gateways or the Tehthys Seaway. The Iceland mantle plume caused depth variations on the Greenland – Scotland Ridge at this time, and our model result indicate that variations in dynamic support from the Iceland plume could have played a key role in the Eocene – Oligocene climate transition. Essentially, reduced dynamic support from the plume deepen the Greenland – Scotland Ridge and cause freshwater leakage from the Arctic Ocean which inhibits deep water formation in the North Atlantic, reducing the AMOC and ultimately cool the Northern Hemisphere.
How to cite: Straume, E., Nummelin, A., Gaina, C., and Nisancioglu, K.: Cooling of the Northern Hemisphere triggered by Northeast Atlantic opening at the Eocene – Oligocene Transition , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11913, https://doi.org/10.5194/egusphere-egu21-11913, 2021.
The early Eocene is a warm period with very high atmospheric CO2 levels, which receives many interests from climate modelling aspects. To simulate the early Eocene paleoclimate, a realistic reconstruction for land-sea distribution, paleotopography and paleobathymetry is the fundamental step. Here, we present global paleogeographic reconstructions for the early Eocene (~55 Ma), based on integrated paleogeographic data set, the Plate-tectonic reconstruction software (GPlates) and Geographic Information System software (ArcGIS). Comparing with previous paleogeographic reconstructions, we improve the reconstructions incorporated many latest geologic data and data set, including: (1) better representations of the Tethys Sea, some marginal or inland seas in the East and Southeast Asia, Atlantic and Arctic region, and the Drake Passage and Tasmanian Gateway; (2) integrated paleoelevation data of global high plateaus and mountains, especially the paleotopography of East Asia, and adopting the latest paleotopographic reconstruction data of the Antarctic; and (3) using the updated data set of oceanic crust paleo-age and oceanic sediment thickness to reconstruct the paleobathymetry.
How to cite: He, Z., Zhang, Z., and Guo, Z.: Reconstructing early Eocene (~55 Ma) paleogeographic boundary conditions for use in paleoclimate modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10665, https://doi.org/10.5194/egusphere-egu21-10665, 2021.
The early Eocene is a warm period with a very high atmosphere CO2 level in the Cenozoic. It provides a good reference for our future climate under the Representative Concentration Pathway 8.5 scenario. Therefore, the early Eocene climate has received many attentions in modeling studies, for example, the Deep-Time Model Intercomparison Project (DeepMIP). However, the early Eocene palaeogeographic conditions show remarkable contrasts to the present conditions. Meanwhile, there are a few different reconstructions for the early Eocene palaeogeography, which may cause further model spreads in simulating the early Eocene warm climate. Here, we present a series of experiments carried out with the NorESM1-F, under the framework of DeepMIP. In these experiments, we consider three different palaeogeographic reconstructions for the early Eocene. We also compare our simulations with climate proxy records, to validate which palaeogeographic reconstructions can reproduce simulations that agree better with the climate proxy records.
How to cite: Zhang, Z., Zhang, Z., and Guo, Z.: Early Eocene simulations with three different palaeogeographic conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14704, https://doi.org/10.5194/egusphere-egu21-14704, 2021.
Geological evidence shows that the Asian inland environment experienced enhanced aridity from the Early to the Late Eocene. The underlying mechanism for this enhanced Eocene aridity in the Asian inland is still not well illustrated and varies between global cooling and early Tibetan Plateau uplift. In this report, we evaluate the climate impact of three factors, global cooling, topographic uplift and land–sea reorganization, on the enhanced Eocene aridity in Asian inland, in the perspective view from paleoclimate modeling. Paleoclimate modeling supports the Eocene aridification in Asian inland explored by paleoclimate reconstruction. Both the early uplift of Tibetan Plateau and global cooling induced by atmospheric CO2 reduction contributed to the enhanced aridity in Asian inland in the late Eocene. The Eocene land sea redistribution caused the precipitation increase in Asian inland and hence didn’t contribute to the enhanced aridity there. The uplift of the central Tibetan Plateau during the early stage of the India–Asia collision is emphasized more to be responsible for the long-term Asian inland aridification during the Eocene, playing at least an equally important role as the global cooling induced by decrease in atmospheric CO2. The variation of atmospheric CO2 is likely more important in modulating the regional aridity, leading to the short-term fluctuations in this Eocene Asian inland aridification.
How to cite: Li, X., Zhang, Z., Zhang, R., and Yan, Q.: The roles of global cooling and early Tibetan Plateau uplift on the enhanced aridity in Eocene Asian inland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3578, https://doi.org/10.5194/egusphere-egu21-3578, 2021.
Global cooling, the early uplift of the Tibetan Plateau, and the retreat of the Paratethys are three main factors that regulate long-term climate change in the Asian interior during the Cenozoic. However, the debated elevation history of the Tibetan Plateau and the overlapping climate effects of the Tibetan Plateau uplift and Paratethys retreat makes it difficult to assess the driving mechanism on regional climate change in a particular period. Some recent progress suggests that precisely dated Paratethys transgression/regression cycles appear to have fluctuated over broad regions with low relief in the northern Tibetan Plateau in the middle Eocene–early Oligocene, when the global climate was characterized by generally continuous cooling followed by the rapid Eocene–Oligocene climate transition (EOT). Therefore, a middle Eocene–early Oligocene record from the Asian interior with unambiguous paleoclimatic implications offers an opportunity to distinguish between the climatic effects of the Paratethys retreat and those of global cooling.
Here, we present a complete paleolake salinity record from middle Eocene to early Miocene (~42-29 Ma) in the Qaidam Basin using detailed clay boron content and clay mineralogical investigations. Two independent paleosalimeters, equivalent boron and Couch’s salinity, collectively present a three-staged salinity evolution, from an oligohaline–mesohaline environment in the middle Eocene (42-~34 Ma) to a mesosaline environment in late Eocene-early Oligocene (~34-~29 Ma). This clay boron-derived salinity evolution is further supported by the published chloride-based and ostracod-based paleosalinity estimates in the Qaidam Basin. Our quantitative paleolake reconstruction between ~42 and 29 Ma in the Qaidam Basin resembles the hydroclimate change in the neighboring Xining Basin, of which both present good agreement with changes of marine benthic oxygen isotope compositions. We thus speculated that the secular trend of clay boron-derived paleolake salinity in ~42-29 Ma is primarily controlled by global cooling, which regulates regional climate change by influencing the evaporation capacity in the moisture source of Qaidam Basin. Superimposed on this trend, the Paratethys transgression/regression cycles served as an important factor regulating wet/dry fluctuations in the Asian interior between ~42 and ~34 Ma.
How to cite: Ye, C., Yang, Y., Fang, X., Zhang, W., Song, C., and Yang, R.: Paleolake salinity evolution in the Qaidam Basin (NE Tibetan Plateau) between ~42 and 29 Ma: Links to global cooling and Paratethys sea incursions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13526, https://doi.org/10.5194/egusphere-egu21-13526, 2021.
The Cenozoic Asian aridification has been related to the retreat of the Paratethys, the uplift of the Tibet, and/or global cooling. However, the details of the mechanisms responsible for this paleoclimate shift remain poorly constrained. Modern observations indicate that interactions between mid-latitude westerlies and the Pamir-Tian Shan Mountains significantly impact hydroclimate patterns in central Asia today, and may have played an important role in driving Asian aridification during the Cenozoic. However, the timing when this topographic-atmospheric framework was established remains poorly constrained.
Here, we present magnetostratigraphy, U-Pb geochronology, thermochronology, paleoclimatology, stable carbon and oxygen isotope geochemistry, and climate modelling techniques to the Cenozoic sedimentary sequences in the Tajik Basin. Our results show that: 1) the penultimate and ultimate retreat of the Paratethys from central Asia occurred at ~41 and ~37.4 Ma, respectively; 2) the Pamirs have experienced active deformation and accelerated exhumation during the late Oligocene to early Miocene; 3) the windward (western) side of the Pamir and Tian Shan has been characterized by a wetter climate changes, whereas, the leeward (eastern) side of the orogen has been characterized by more arid conditions since the Late Oligocene; 4) This distinct east-west hydroclimate differences, when integrated with climate modeling results, suggests that at least part of the Pamir-Tian Shan mountains had reached elevations ≥ 3 km and acted as a moisture barrier for the westerlies since ~25 Ma. We suggest that the interactions between the westerlies and the Pamir-Tian Shan orogen played an important role in driving Asian aridification since the Late Oligocene.
How to cite: Wang, X., Carrapa, B., Zhang, X., Oimuhammadzoda, I., and Chen, F.: Uplift of the Pamir and Tian Shan set hydroclimate patterns in central Asia since the late Oligocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7781, https://doi.org/10.5194/egusphere-egu21-7781, 2021.
Mid Miocene Climate Optimum (MMCO) is an interesting period. Indeed since Mid Eocene (40 Ma) the large trends of climate evolution are: a large decrease of pCO2 and a drastic cooling. The MMCO appears as a short period when these trends were reversed, during 2 Ma, followed by a new period of cooling. Using the IPSL CM5A2 coupled model, we simulated the MMCO using two different pCO2 values (2.5 PAL and 1.5 PAL) and for the Miocene Climate Transition MCT for which we used a pCO2 value of 1.5 PAL. Superimposed to these very long runs we further simulated sensitivity of these experiments to insolation at the top of the atmosphere for Antarctica ice-sheet. In our referent simulation, the astronomical parameters remained unchanged as present day, whereas we performed new simulations with maximum and minimum insolation at the top of the atmosphere for December, January, February (at 75°S). These series of experiments will be analyzed and compared with available data. Moreover, we will compare our results to other simulations using various OAGCMs. We will emphasize on the consistency between the climate simulated at high latitude and the prescribed ice-sheet reconstruction of Antarctica.
How to cite: Segalla, D., Ramstein, G., Sepulchre, P., Fluteau, F., and Colleoni, F.: Simulation of the transition between Mid Miocene Climate Optimum (17-15 Ma) and Miocene Climate Transition (14 Ma), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14742, https://doi.org/10.5194/egusphere-egu21-14742, 2021.
3.6 Ma represents a time period when Earth transitioned from single pole ice sheets to permanent ice sheets existing in both hemispheres. However, it remains unclear how this transition had its impact on East Asian summer monsoon system, which controls living of a large population. Here, we present a high-resolution (2~4 kyr) monsoon precipitation record from the Chaona section on the central Chinese Loess Plateau during the 3.95-2.95 Ma, using the magnetic parameter-based precipitation proxy (χfd/HIRM). The results reveal intensified precessional and semiprecessional fluctuations during high eccentricity, emphasizing direction role of low latitude insolation played in forcing Asian monsoon precipitation. The precipitation records also show that the 41-kyr cycles intensified after 3.3 Ma, in contrast with decreased obliquity variation amplitude of summer insolation. We interpret the enlarged 41-kyr precipitation cycles in our records as a result of high latitude ice sheet forcing. Together, our work provides an example demonstrating both high and low latitude forcing of Asian monsoon precipitation during the late Pliocene.
How to cite: Wang, H., Nie, J., and Luo, Z.: High and low- latitude forcing of East Asian monsoon precipitation change during the late Pliocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7074, https://doi.org/10.5194/egusphere-egu21-7074, 2021.
The mid-Piacenzian warm period (3.264 to 3.025 Ma) is the most recent geological period with present-like atmospheric pCO2. A specific interglacial (Marine Isotope Stage KM5c, MIS KM5c; 3.205 Ma) has been selected for the Pliocene Model Intercomparison Project phase 2 (PlioMIP 2). We carried out a series of experiments according to the design of PlioMIP2 with two versions of IPSL atmosphere–ocean coupled general circulation model (AOGCM): IPSL-CM5A and IPSL-CM5A2. Our results show that the simulated MIS KM5c climate presents enhanced warming at mid- to high latitudes when compared to the PlioMIP 1, resulting from the enhanced Atlantic Meridional Overturning Circulation caused by the high-latitude seaway changes. The sensitivity experiments, conducted with IPSL- CM5A2, show that, apart from the pCO2, both modified orography and reduced ice sheets contribute substantially to mid- to high latitude warming in MIS KM5c. When considering the pCO2 uncertainties (+/−50 ppmv) during the Pliocene, the response of the modeled mean annual surface air temperature to changes to pCO2 (+/−50 ppmv) is not symmetric, which is likely due to the nonlinear response of the cryosphere (snow cover and sea ice extent).
How to cite: Tan, N., Contoux, C., Ramstein, G., Sun, Y., Dumas, C., Sepulchre, P., and Guo, Z.: Modeling a modern-like pCO2 Warm period with two versions of IPSL AOGCM, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10560, https://doi.org/10.5194/egusphere-egu21-10560, 2021.
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