CL1.1.1

Earth has undergone dramatic temperature fluctuations and the tectonic process of continental breaking up and reassembling in the past 540 million years. How these caused changes in the global hydrological cycle is an interesting question. To study the evolution of the global hydrological cycle since the Cambrian, we carried out 55 equilibrium simulations to simulate climate evolution in the past 540 million years, using CESM1.2.2. It is found that the global mean precipitation is closely correlated with the global mean surface temperature (GMST), especially oceanic precipitation has high correlation with GMST, with a coefficient of 0.92. Land precipitation also has statistically significant correlation with GMST. However, the correlation coefficient is much lower. Further analysis shows that land precipitation is also determined by continental fragmentation, mean latitudes, and total area, and that the semi-arid area is most sensitive to GMST changes.

How to cite: Hu, Y., Li, X., and Li, Z.: The hydrological cycle in the past 540 million years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8237, https://doi.org/10.5194/egusphere-egu22-8237, 2022.

Coals and evaporates are the most commonly used paleoclimate indicators, regarded as representatives of humid and arid climate conditions in the geological record, respectively. However, the quantitative and systematic climate significance of coals and evaporates in the Earth history still unknown. Here, we perform a series of simulations to simulate global climate conditions of Phanerozoic, using an Earth system model CESM 1.2.2 and reconstructed paleotopographies (Scotese, 2018). Combining with a global-scale complication of coals and evaporate from the present back to Devonian (Boucot et al., 2013), climate variables of annual average surface temperature (AAST), annual average precipitation (AAP) and annual average net precipitation (AANP) of the area where coals and evaporates formed are extracted for analysing quantitative climate conditions of coals and evaporates. The preliminary results show that (1) AAST of evaporate areas vary with global mean temperature, while the variation of coals areas’ AAST reflect a stage change,which are consistent with the stage evolution of land plant and lignin-degrading fungi; (2) AAP and AANP of coals and evaporates areas are relatively stable through the Earth history. Coals areas have general more AAP and AANP than evaporates in 25%-75% quantiles but have similar range with evaporites areas in 5%-95% quantiles.

Key words: coals, evaporates, plant evolution, deep-time climate, numerical simulation

References

Scotese C R, 2018. PALEOMAP PaleoAtlas Rasters[J].

Boucot A J, Chen X, Scotese C R, 2013. Lithology Data Tables[J].

How to cite: Bao, X. and Hu, Y.: Climate conditions of coals and evaporates in the Earth history, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4335, https://doi.org/10.5194/egusphere-egu22-4335, 2022.

Snowball Earth is a hypothesized state in the deep past of Earth in which the ocean was completely or nearly completely covered by sea ice, resulting from a runaway ice-albedo feedback. Here, we address how the treatment of sea-ice thermodynamics affects the initiation of a Snowball Earth in the global climate model ICON-A run in an idealized slab-ocean aquaplanet setup. Specifically, we study the impact of vertical resolution and brine pockets of ice by comparing the 3-layer Winton and a 0-layer Semtner scheme, and we investigate the impact of limiting ice thickness to 5m.

The internal heat storage of ice is increased by higher vertical resolution and brine pockets, which weakens surface melting and increases global albedo by allowing snow and ice to persist longer into the summer season. The internal heat storage weakens the melt-ratchet effect, as is confirmed with offline simulations with the two ice schemes. The result is a substantially easier Snowball Earth initiation and an increase in the critical CO₂ for Snowball initiation by 50%. Limiting ice thickness impedes Snowball initiation as the removal of excess ice leads to an artificial heat source. Yet, the impact is minor and critical is decreased by 5% only.

The results show that while the sea-ice thickness limit plays only a minor role, the internal heat storage of ice represents an important factor for Snowball initiation and needs to be taken into account when modeling Snowball Earth initiation.

How to cite: Hörner, J., Voigt, A., and Braun, C.: Snowball Earth initiation and the thermodynamics of sea ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5167, https://doi.org/10.5194/egusphere-egu22-5167, 2022.

Dust, as one of the most common types of atmospheric aerosol, affects climate in many different ways. Atmospheric dust scatters and absorbs sunlight and reduces solar radiation received at the surface; it absorbs and emits longwave radiation, having a greenhouse effect; it has a complex indirect effect on climate by serving as cloud nuclei; when deposited on snow or ice, it reduces the surface albedo and warms the surface. Despite its importance in the climate system, how the dust emission and atmospheric dust loading varied during the Earth history is unclear. Here I will give a summary of the atmospheric dust loading as well as its climatic impact for a few typical periods of the Earth. All the results are from numerical simulations and are still premature due to uncertainties in vegetation cover and soil erodibility, and biases and inability of the climate model used.

In present day, the atmospheric dust loading is slightly more than 20 Tg, and has a small impact on the global climate. Such dust loading was diminished during the mid-Holocene (~6 thousand years ago; 6 ka) and the reduced dust induced a very slight global warming (~0.1 °C) but a cooling of the Northern Hemisphere by weakening the Atlantic meridional ocean circulation (AMOC). During the cold last glacial maximum (~21 ka), the atmospheric dust loading was ~2-3 times that of present day. Had not been this dust, the LGM climate would have been colder by ~2 °C and AMOC weaker by ~30%. Clearly, the snow-darkening effect of dust was dominative during this cold time period. For earlier periods with different continental configurations, the atmospheric dust loading also varied significantly. For 80 million years ago (Ma), the continents were dispersive and the total area of the continents was small, the atmospheric dust loading was only ~1.4 Tg. For 240 Ma, the continents clustered into a supercontinent and centered around the equator, the atmospheric dust loading ~21 Tg. For a continental configuration (130 Ma) that had an area in between 80 Ma and 240 Ma, the atmospheric dust loading was ~6.1 Tg. The dust had a cooling effect of <1 °C in all these three periods. For time periods earlier than 400 Ma when land vegetation had not evolved yet, the atmospheric dust loading could have been ~10 times of present day and cooled the climate by ~10 °C. However, such cooling effect disappeared and became a warming effect when the climate was entering a snowball Earth state, due to stronger and stronger snow-darkening effect.

Overall, there was more dust during a cold time period due to stronger winds, weaker hydrological cycle and more dust sources, and the dust had a warming effect to the climate. During the warm time periods, dust tended to have a cooling effect because there was too little snow and ice for the snow darkening by dust to be effective. There was also more dust during periods when the area of continents was larger and more clustered, due to drier land surface.

How to cite: Liu, Y., Lin, Q., Zhang, M., Liu, P., Zhang, J., and Liu, Z.: Evolution of Dust and Its Climatic Impact during Earth’s History, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4906, https://doi.org/10.5194/egusphere-egu22-4906, 2022.

Dust in the atmosphere affects climate by directly absorbing and scattering solar radiation. In present days, most of dust is emitted from dry regions over North Africa and Arabian Peninsula. It has been shown that it impact on global mean surface temperature, African monsoon, the number of tropical cyclones over the Atlantic Ocean, ENSO variability and the strength of Atlantic meridional ocean circulation (AMOC). The climate of late Paleozoic ice age bears some similarity to late Cenozoic climate. However, late Paleozoic ice age was a period of continental convergence and supercontinents formation. On different continental configurations, the area of dry regions may vary considerably, so that dust emissions and atmospheric dust loading changed accordingly. As  expected, the impact of dust on climate during this period was also very different from that of present days. In this work, we use the fully coupled global climate model CESM1.2.2 to examine the influence of dust on climate during late Palaeozoic ice age. Dust aerosols simulated by bulk aerosol model alter atmospheric radiation through scattering and absorbing both shortwave and longwave radiation. Results show that during late Palaeozoic ice age, sources of dust were mainly distributed on the western continent in the subtropics. The total amount of the atmospheric dust loading was less than that of present days due to the smaller subtropical continental area. Such dust induced a significant cooling of surface temperature at low latitudes by altering radiation. Dust falling on southern hemisphere continents covered by ice and snow caused a rising of surface temperature.

How to cite: Lin, Q. and Liu, Y.: Influence of Dust on Climate during the late Palaeozoic ice age, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6918, https://doi.org/10.5194/egusphere-egu22-6918, 2022.

The Late Permian climate is the background state for the climate perturbations which lead to the
Permian-Triassic Boundary (~252 Ma). The Permian-Triassic Boundary mass extinction is well established as
the largest of Earth’s mass extinctions with an estimated 90% loss of species. Climate perturbations linked to
carbon emissions from Siberian Trap volcanism are attributed as the drivers of the mass extinction through
extreme temperature increases and changes in ocean circulation and biogeochemistry. Fully-coupled Earth
System Models are required to investigate the sensitivities and feedbacks of the system to these widespread
climate perturbations. The Late Permian climate is simulated with a modified version of the Max Planck
Earth System Model v1.2 similar to that used in the 6^th -phase of the Coupled Model Intercomparison Project.
Geochemical and palaeobiological proxy data are used to constrain the boundary conditions of the modelled
climate state.
The simulated Late Permian climate state is characterised by a 100 year global mean 2 m surface air
temperature of 19.7°C, rising up to 37.7°C in the low-latitude continental interior. Prevailing 100 year global
mean total precipitation patterns indicate that the continental interior was largely arid from ~50°N to ~50°S and
a rainfall maximum of up to 6.5 mm day^-1 is present at the equatorial boundary of the Tethys and Panthalassic
Oceans. Dynamic terrestrial vegetation in the model is dominated by woody single-stemmed evergreens and
soft-stemmed plant functional groups. The 100 year global mean surface ocean of the Late Permian illustrates
a warm-pool across the equatorial boundary between the Tethys and Panthalassic Oceans with a maximum
temperature of 31.7°C decreasing to temperatures as low as -1.9°C near the poles. Surface salinities vary
broadly across the global oceans with 100 year global mean values ranging from 21.9, in well flushed regions
of strong freshwater flux, to 49.2, in low-latitude regions of restricted exchange. Large-scale seasonal mixing
below 60°S in the Panthalassic Ocean dominates the global meridional overturning circulation. These model
data fit within the bounds represented by the available proxy data for the Late Permian. Additionally, I will
present first results of the ocean biogeochemical state in the Hamburg Ocean Carbon Cycle model with an
extended Nitrogen-cycle. I will also illustrate the results of our investigation into the influence of the Late
Permian monsoon variability on the terrestrial vegetation and ocean carbon cycles.

How to cite: Burt, D., Ilyina, T., and Kleinen, T.: Dynamics and variability of the Late Permian climate-carbon state in an Earth System Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6804, https://doi.org/10.5194/egusphere-egu22-6804, 2022.

In this study, we investigate the meridional temperature gradients during the past 250 million years. We compare the differences between proxy data of oxygen isotopes and lithologic indicators and globally coupled atmosphere-ocean climate system model simulation results. Two climate models are employed, CESM1.2.2 and HadleyCM3. There are several significant differences between the model results and Scotese’s reconstruction and proxy data: 1) the tropical surface temperatures are usually higher in the model simulations than both Scotese’s reconstruction (Scotese 2016; Scotese et al. 2021) and proxy data (e.g., Huber and Caballero 2012, Song et al. 2019; Zhu et al. 2019), whereas the surface temperatures in high latitudes are usually lower; 2) the meridional temperature gradients in the model simulations are smaller in low latitudes but larger in the middle latitudes than Scotese’s reconstruction. These comparisons are helpful for paleoclimatology understanding and for future paleo-temperature reconstructions.

How to cite: Wei, M., Yang, J., Hu, Y., Liu, Y., Li, X., Bao, X., Guo, J., Lan, J., Li, Z., Lin, Q., Man, K., yin, Z., and Yuan, S.: Meridional temperature gradients during the past 250 million years: Proxies versus Models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7520, https://doi.org/10.5194/egusphere-egu22-7520, 2022.

Global climates have undergone tremendous fluctuations during the past 250 million years, primarily driven by variations in tectonic dynamics, atmospheric greenhouse gases, and solar irradiance. Paleoclimate modeling has offered a feasible approach to investigating secular climate change for such a long span of time deep in the past. Nevertheless, global mean surface temperatures (GMSTs) simulated by previous studies scarcely depict the trend of past climate change. In this study, using the Community Earth System Model version 1.2.2 (CESM1.2.2), we present an ensemble of snapshot simulations during the past 250 million years based on the reconstructed GMSTs. An energy balance analysis is carried out to explore and quantitatively describe the causes of temperature change for the past 250 million years. We find that different levels of global mean warming for the past 250 million years compared with the pre-industrial period predominantly results from relative increase in greenhouse gas emissivity (12.2 °C), with the changing paleogeography (5.6 °C) and solar constant (3.0 °C) playing secondary roles. It is highlighted that the individual effect of heat transport convergence varies inconspicuously in spite of considerable changes of paleogeography and mean climate states during this time. The simulations are potentially valuable resources for extensive studies including climate dynamics analysis in geological timescales and paleoclimate-proxy intercomparison.

How to cite: Li, X., Guo, J., Lan, J., Lin, Q., Yuan, S., Yang, J., Liu, Y., and Hu, Y.: Climate evolution during the past 250 million years simulated by the Community Earth System Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10701, https://doi.org/10.5194/egusphere-egu22-10701, 2022.

Over million-year timescale the carbon cycle evolution is driven by mantle CO₂ degassing (source) and by continental weathering that drawdowns atmospheric CO₂ through silicate weathering reactions (sink). Based on a novel geochemical proxy of chemical weathering intensity (i.e. using measurements of Hf and Nd isotope ratios in clay-size fractions of sediments) and clay mineralogy, we discuss the links between tectonic, continental weathering and climate evolution during the late Cretaceous. That period records the very first step of the last greenhouse to icehouse transition and is concomitant to major uplift phases affecting the African and South-American margins.

Two sites along the South American Atlantic margin (ODP 356 and 1259) were targeted based on their relatively complete record of upper Cretaceous sediments. At Site 356, our results indicate the occurrence of enhanced chemical weathering during the Campanian and Maastrichtian following the uplift of the Southeastern Brazilian margin that promoted the establishment of more hydrolysing conditions.

At Demerara Rise (Site 1259), our data suggest a coupling between physical erosion and chemical weathering, which may be explained in this area by the presence of persistent hydrolysing conditions typical of equatorial climate and reduced tectonic activity. From the Turonian to the early Campanian, i.e. a period of relative tectonic quiescence, our data suggest that climate was likely the main driver controlling the evolution of chemical weathering intensity. By contrast, from the middle Campanian to Maastrichtian, we propose that mountain uplift, although moderate, induced a marked increase in chemical weathering intensity.

Together, this new data acquired at two 2 sites that encountered different regional climatic, geologic and tectonic conditions suggest that chemical weathering markedly intensified during the late Cretaceous and likely acted as a major sink for atmospheric CO₂. While the onset of weathering increase at both sites appear to postdate the initiation of global temperature decrease, we suggest here that this process could have participated to accelerating or maintaining colder climate conditions at that time.

Key Words: late Cretaceous – paleoclimate – weathering – uplift - clay mineralogy – Hf-Nd isotope

How to cite: Corentin, P., Pucéat, E., Pellenard, P., Guiraud, M., Blondet, J., Freslon, N., Bayon, G., and Adatte, T.: Hafnium-neodymium isotope evidence for enhanced weathering and tectonic-climate interactions during the Late Cretaceous, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7744, https://doi.org/10.5194/egusphere-egu22-7744, 2022.

The physiological evolution of vegetation affects the interaction between vegetation and climate. Angiosperms have higher leaf vein density than all other plants throughout evolutionary history, contributing to higher transpiration capacities. However, the climatic response to changes in physiological functions of angiosperms has remained to be determined. Here, Community Earth System Model (CESM) version 1.2.2 and BIOME4 vegetation model are applied to simulate the world without angiosperms by reducing the maximum carboxylation rate (Vmax) to 1/4 (Boyce et al, 2009), in conditions of both fixed and non-fixed vegetation distribution. First, we maintain the pre-industrial vegetation distribution, the results illustrate that the world without angiosperms would have less productivity, higher global mean temperature, consisting with the results of Boyce and Lee (Boyce and Lee, 2010). In addition, the warmer southern hemisphere and colder northern hemisphere are identified, which are caused by the decrease of the strength of Atlantic Meridional Overturning Circulation (AMOC). Second, we consider changes of vegetation structure, the results show that temperature and precipitation would vary significantly locally, and the area of tropical forest would decline sharply in the world without angiosperms, which may affect biodiversity. The evolution of physiological functions of angiosperms influences climate and provides potential competitive advantages for angiosperms to dominate modern vegetation.

How to cite: Guo, J., Hu, Y., and Liu, Y.: The Impact of Angiosperms Physiological Evolution on Earth Systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6721, https://doi.org/10.5194/egusphere-egu22-6721, 2022.

Paleogeographic change is a major forcing of climate on long (multi-million years) time scales. In response to these changes, the vegetation cover can show drastic variations, due to topographic changes, or global climate modification for example. For the Cenozoic, however, the fossil record available to estimate the evolution of the vegetation cover is highly heterogenous and remains fragmentary in some regions. Moreover, although climate models are increasingly associated with elaborated land surface models, it remains difficult to estimate the accuracy of the results and compare the numerical results with data.

Here we take advantage of several available paleoclimate simulations obtained using the IPSL-CM5A2 land system model. They include the state of the art of current knowledge on the evolution of land-sea distribution and topography, and span the whole Cenozoic. Alternative paleogeographies are also tested, to clarify the impact of a particular region on climate, especially when no consensus exists on some regions. The impact of different scenarios for the incipient Tibetan Plateau in the Eocene, and for the orographic evolution of eastern Africa and Mongolia in the Miocene, are explored. We compare the response of the vegetation cover simulated with the ORCHIDEE land surface model with the biomes simulated using the BIOME4 model. The results obtained with these two models are evaluated by comparing them to data from regions diplaying the most complete fossil record. The concept of paleo-biome is discussed and suggestions for improvement are presented.

How to cite: Tardif, D., Sepulchre, P., Condamine, F., and Couvreur, T.: Evolution of vegetation during the Cenozoic simulated by different land surface models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1078, https://doi.org/10.5194/egusphere-egu22-1078, 2022.

Oceanic Anoxic Events (OAEs) were geologically short-lived events of widespread ocean deoxygenation and marine organic carbon burial and occurred mostly during the Cretaceous period. The development of OAEs is largely attributed to the impact of massive volcanism on climate and marine biogeochemistry; however, the lack of similar events during other carbon-cycle perturbations suggests additional mechanisms. We use the IPSL-CM5A2 Earth System Model to assess the role of changing paleogeography in priming the Cretaceous Ocean for large-scale decrease in intermediate and deep oxygen concentrations. We focus on three time-slices that present differences in potential gateway (e.g. the Central American Seaway) depth and basin configuration (e.g. the North Atlantic): the Aptian age (~120 Ma), the Cenomanian-Turonian boundary (~94 Ma) and the Maastrichtian age (~70 Ma). This set of simulations illustrates the impact of paleogeography on global circulation and its consequences for intermediate and deep water oxygenation. We also show results for two different atmospheric CO2 concentrations (2x and 4x pre-industrial) to study the additional influence of differing climatic states on oxygenation and primary productivity, and their importance relative to ocean dynamics.

How to cite: Donnadieu, Y., Papadomanolaki, N., Laugie, M., Sarr, A., and Ladant, J.-B.: Modeling the Impact of Paleogeography on Cretaceous Ocean Deoxygenation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11663, https://doi.org/10.5194/egusphere-egu22-11663, 2022.

The evolution of central Asian drylands during the Cenozoic is a hot topic in paleoclimate research, but the underlying mechanism remains unclear. Here, we investigate this topic with climate modeling based on six key geological periods. Our results indicate that central Asian drylands have existed since the early Eocene, after which they move northward and become narrower. Although changed land–sea distribution and decreased atmospheric CO2 concentration promote the aridification of drylands, they only slightly affect the latitudinal distribution of drylands. By comparison, the growth of Asian high-topography areas, especially the Tibetan Plateau (TP), makes central Asian drylands move northward, concentrate in narrow latitudinal bands, and increase in intensity. Good model-data qualitative agreement is obtained for stepwise aridification in midlatitude inland Asia north of ~40°N, and the uplifted main and northern TP by the early Miocene likely forced drylands to change in this region.

How to cite: Zhang, R., Zhang, Z., Jiang, D., Ramstein, G., Dupont-Nivet, G., and Li, X.: Modeling the evolution of central Asian drylands during the Cenozoic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3321, https://doi.org/10.5194/egusphere-egu22-3321, 2022.

Unmitigated scenarios of greenhouse gas emissions produce climates like those of the Early Eocene by 2150 CE, suggesting that we are effectively reversing a more than 50-million-year cooling trend in less than two centuries. Terrestrial records of rivers and floodplains from Paleogene sedimentary basins in the US Western interior and Europe indicate an increase in flash floods and droughts at paleo-mid latitudes, indicating increased precipitation intensity and intermittency. In the Uinta Basin, Utah magnetostratigraphic analyses, absolute age dates, and biostratigraphy allow the reconstruction of changes in hydroclimate from the Early Paleocene, to the Paleocene-Eocene Thermal Maximum (PETM), and through the Early Eocene Climatic Optimum (EECO). Here we observe that the largest shifts in hydroclimate are not linked to the PETM but rather occur during the warm Late Paleocene and then at the end of the EECO. This is indicated by the river sedimentary record that shows a shift from normal rivers, such as are characteristic at mid-latitudes today, to flood-prone rivers in late Paleocene. The rivers shifted back to normal at the end of the EECO. Coeval changes are observed in floodplain paleosols where the late Paleocene and early Eocene paleosols indicate sustained droughts and intermittent seasonal rains. At the PETM there is no change in the state of hydroclimate, but rather a further intensification of floods and droughts. Comparison to other terrestrial basins at mid-latitudes shows similar patterns. These results show that the most dramatic shifts in hydroclimate were not linked to the largest amplitude of atmospheric drivers at the PETM, but rather suggest a threshold-driven relationship between the atmospheric drivers and hydroclimate. This may suggest that significant changes in hydroclimate are to be expected already before 2150 CE. 

How to cite: Slawson, J. and Plink-Bjorklund, P.: Long-term increase in precipitation intermittency and intensity at Paleogene mid latitudes , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10287, https://doi.org/10.5194/egusphere-egu22-10287, 2022.

Predicted future climate scenarios share similar characteristics with the Eocene ‘greenhouse’ period. However, short-term Early Eocene terrestrial climate variability is still poorly constrained mainly due to the rarity of adequately resolved climate archives. This lack of information restricts not only the evaluation of past continental climate conditions but additionally limits regional climate modelling efforts but also the validation of model outputs. Here, we present highly-resolved biomarker-based (bacterial membrane lipid and leaf wax) paleoclimate data from the UNESCO World Heritage Site Messel Fossil Pit (Germany) that cover an interval of ca. 640 ka. The drilled Messel paleolake succession, characterized by finely laminated and frequently varved black pelites (referred to as ‘oil shale’) represent a regional climate and environmental archive from the latest Early to Middle Eocene (~48.0-47.4 Ma) of western Central Europe. Downcore mean annual air temperature (MAAT) reconstructions inferred from bacterial-derived branched glycerol dialkyl glycerol tetraethers (brGDGTs) show a long-term cooling trend and range from 14 to 22°C. High-resolution sampling within the basal and middle core interval reveal several short-term negative temperature excursions of 4-5°C, respectively. Moreover, we measured compound-specific δ²H and δ¹³C of excellently preserved odd carbon numbered mid- and long-chain leaf wax n-alkanes in order to estimate past regional hydroclimatic conditions. δ²H values of terrestrial long- and aquatic mid-chain n-alkanes show exceptional variations of up to 45‰ and 60‰, respectively. In contrast, δ¹³C values of long-chain n-alkanes are within 5‰ (-28‰ to -33‰) while mid-chain δ¹³C values vary by 11‰, ranging between -26‰ and -37‰. Our results indicate that the Early to Middle Eocene temperature history of central western Europe, particularly on short geological timescales was much more variable than previously assumed. We recognize two abrupt shifts in MAAT that coincide with lower δ²H values and therefore may point to either wetter climate conditions or changed atmospheric moisture trajectories. We emphasize that the long-term decline in estimated MAAT towards the top of the Messel section has to our best knowledge not been quantified from any time-equivalent terrestrial archive in Central Europe, but resembles Early Eocene cooling patterns well-documented from the global oceans.

How to cite: Schmitt, C., Vasiliev, I., Martínez-García, A., and Mulch, A.: Variable Early Eocene continental hydroclimate in Central Europe? , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1701, https://doi.org/10.5194/egusphere-egu22-1701, 2022.

Cenozoic evolution of South Asian Monsoon and mechanisms driving changes recorded in the geological record remain highly debated. An intensification of monsoonal rainfall recorded in sediment archives from the earliest Miocene (23-20 million years ago, Ma) is generally attributed to Himalayan uplift. However, Indian Ocean paleorecords place the onset of strong monsoons around 13 Ma, linked to strengthening of the Somali Jet that forces Arabian Sea upwelling.  In this contribution we reconcile these divergent records using Ocean-Atmosphere and ocean biogeochemistry models. Our results show that factors forcing monsoon circulation versus rainfall are decoupled and diachronous : Asian topography predominantly controlled early Miocene rainfall patterns, with limited impact on ocean-atmosphere circulation. Yet the uplift of East African and Middle Eastern topography played a pivotal role in the establishment of modern Somali Jet structure above the western Indian Ocean, while strong upwelling initiate in response to the emergence of the Arabian Peninsula. Our results emphasize a polygenetic history of the South Asian Monsoon with multiple paleogeographic controls: although elevated rainfall seasonality was likely a persistent feature since the India-Asia collision in the Paleogene, the modern-like monsoonal atmospheric circulation was only reached recently, in the late Neogene.

How to cite: Sarr, A.-C., Donnadieu, Y., Bolton, C., Ladant, J.-B., Licht, A., Fluteau, F., Laugié, M., Tardif, D., and Dupont-Nivet, G.: Reconciling South Asian Monsoon Rainfall and Wind Histories, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2399, https://doi.org/10.5194/egusphere-egu22-2399, 2022.

Reconstructing deep ocean temperature is important to infer deep water mass structure and hence ocean circulation patterns in the past. The late Paleocene-early Eocene experienced the warmest climates of the Cenozoic, with highly elevated CO₂ levels and no ice sheets on the continents [1,2]. Benthic foraminiferal δ¹⁸O records suggest relatively stable deep ocean conditions on long time scales (>100 kyr) in this hothouse [2–4]. However, interpretations from benthic δ¹⁸O records are complicated by influences of factors other than temperature, such as the isotope composition of the seawater (δ¹⁸O_sw), pH, and species-specific physiological effects [5,6]. Carbonate clumped isotope thermometry (Δ₄₇) has the major advantage that it is independent of the isotope composition of the fluid source, and is not measurably affected by other non-thermal influences [7–10]. Early Cenozoic clumped isotope reconstructions from the North Atlantic have revealed surprisingly large deep-sea temperature swings under hothouse conditions [11]. Extreme warming is recorded at the onset of the Early Eocene Climatic Optimum (EECO) [11]. To explore the spatial extent of these deep-sea temperature changes, we reconstructed early Eocene Δ₄₇-based deep-sea temperatures from the South Atlantic Ocean, a location that is considered to capture a global signal [2–4]. We find similar deep-sea temperatures as those from the North Atlantic. Cooler temperatures of ~12 °C stand out in the interval (54–52 Ma) before the peak warmth of the EECO (52–50 Ma) of ~20 °C. This result overthrows the classic view of a gradual early Eocene warming trend based on benthic δ¹⁸O records, at least for the deep Atlantic Ocean. Our findings raise new questions on the regions of deep water formation, changes in deep ocean circulation, and the driving mechanisms in the early Cenozoic hothouse.

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[10] Meinicke, N. et al. (2020). Geochimica et Cosmochimica Acta, 270, 160-183.
[11] Meckler, A. N. et al. (in revision).

How to cite: Agterhuis, T., Ziegler, M., Koene, B. L. P., de Vries, L., Roozendaal, A., and Lourens, L. J.: South Atlantic deep-sea temperatures across the onset of the Early Eocene Climatic Optimum based on clumped isotope thermometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10815, https://doi.org/10.5194/egusphere-egu22-10815, 2022.

The meridional heat transport is primarily governed by the geometry between the Earth and the Sun and it has been shown in previous studies that it is nearly invariant in different climates. Nevertheless, the processes, which contribute to the whole transport, do not stay invariable, but their changes compensate each other. Thus, the changes in the various transport processes give an insight into the climate system and its changes in different conditions, such as the high CO₂ concentrations of the Early Eocene Climatic Optimum (EECO).

In our work we investigate the meridional heat transport and its elements in climate model simulations from DeepMIP focusing on the EECO. The meridional heat transport is divided into atmospheric and ocean heat transport. The atmospheric heat transport is further divided into moist and dry energy transport and also into transport by the meridional overturning circulation, transient eddies and stationary eddies. Annual and seasonal changes are compared in the preindustrial control simulation, in the 1xCO₂ simulation and in simulations with high CO₂ concentration values (3xCO₂, 4xCO₂, 6xCO₂). We found that in a warmer climate, where the hydrological cycle is expected to be stronger, the transport of the meridional overturning circulation at the tropics, so the circulation of the Hadley cell, is more intense. Also, at the subtropics the energy transport of monsoon systems and at the mid-latitudes the energy transport of cyclones and anticyclones is different than in the control climate.

How to cite: Kelemen, F. D. and Ahrens, B.: Partitioning meridional heat transport in Early Eocene Climatic Optimum model simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10380, https://doi.org/10.5194/egusphere-egu22-10380, 2022.

The late Miocene and early Pliocene is marked by a major
oceanographic and geological event called the Late Miocene Biogenic
Bloom (LMBB). This event is characterized by high accumulation rates of
opals from diatoms and high calcite accumulation rates from calcareous
nannofossils and planktic foraminifera. The LMBB extends over several
million years and is present in the Pacific, Atlantic and Indian Oceans. Two
hypotheses have emerged from the literature to explain this event: a
global increase in the supply of nutrients to ocean basins through chemical
alteration of the continents and/or a major redistribution of nutrients in the
oceans. The objective of this study is to provide a more comprehensive
look at the temporal and geographical aspects of the LMBB. We have
compiled ocean drilling data (ODP-IODP) covering the late Miocene and
early Pliocene. This compilation contains sedimentation rates as well as
CaCO3, opal and terrigenous accumulation rates. After a careful screening
of the database, checking that all data are on the same time scale, we first
work on global trends of sedimentation and biogenic production before
going into more details. For instance, we show that the magnitude of the
Biogenic Bloom strongly varied between the three oceanic basins.
Normalization to a post-LMBB state allows comparison of rates of increase
in CaCO3 accumulation in different geographical areas (grouping several
sites). A very strong LMBB signature is present in oceanic area bordering
the western side of Australia. In the Atlantic Ocean, it is mainly present
near the equator and over South Africa. The LMBB signature is less
pronounced in the Indian Ocean but remains trackable near the northern
coasts of the basin. Moreover, it is also heterogeneous in terms of the
mineralogy produced and deposited in the deep ocean between regions.
For example, in the equatorial eastern Pacific, the LMBB signature is
present in the silica accumulation term but not in carbonates accumulation
one. Outputs from coupled ocean/atmosphere models (IPSL-CM5A2) using
late Miocene paleogeography and integrating a marine biogeochemistry
module (PISCES) have been gathered and will be discussed in regard to
our database.

How to cite: Pillot, Q., Suchéras-Marx, B., Sarr, A.-C., Bolton, C., Ladant, J.-B., and Donnadieu, Y.: Spatial heterogeneity of the Late Miocene Biogenic Bloom, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5621, https://doi.org/10.5194/egusphere-egu22-5621, 2022.

The intensification of the Northern Hemisphere glaciations at the end of the Pliocene epoch represents one of the most substantial climatic shifts during Cenozoic. Paradoxically, sea surface temperatures in the high latitude North Atlantic Ocean increased between 2.9–2.7 Ma, against a background of global cooling and declining atmospheric pCO₂. To investigate the origin of this high latitude warming, we obtained sedimentary geochemical proxy data from the Gulf of Cadiz to reconstruct the variability of Mediterranean Outflow Water, an important heat source to the North Atlantic. In fact, we find evidence for enhanced production of Mediterranean Outflow Water during the mid-Pliocene to late Pliocene. We argue that the injection of this warm water on intermediate levels drove a sub-surface heat channel into the high-latitude North Atlantic where it warmed the sea surface. We further used Earth System Models to numerically constrain the impact of enhanced Mediterranean Outflow Water production on the northward heat transport within the North Atlantic. In accord with the proxy evidence, the numerical model results show the formation of a sub-surface channel that funneled heat from the subtropics into the high latitude North Atlantic. We further suggest that warming of the North Atlantic realm by this mechanism might have substantially delayed ice sheet growth at the end of the Pliocene.

How to cite: Bahr, A., Kaboth-Bahr, S., Stepanek, C., Amorim Catunda, M. C., Karas, C., Ziegler, M., García-Gallardo, Á., and Grunert, P.: Mediterranean heat injection to the North Atlantic delayed the intensification of Northern Hemisphere glaciations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2042, https://doi.org/10.5194/egusphere-egu22-2042, 2022.

The Northern Annular Mode (NAM) is the leading mode of atmospheric climate variability in the middle and high Northern latitudes in the present-day climate. Its most prominent regional expression is the North Atlantic Oscillation (NAO), a mode of variability that is well-known and has a strong influence on North Atlantic weather patterns. According to the IPCC AR6 WGI report, the current generation of climate models are ‘skillful’ in simulating the spatial features and variance of the historical and present-day NAM/NAO. However, what kind of NAM or NAO patterns can we expect in a warm future climate?

To answer this question, we have performed equilibrium climate simulations of a warm ‘future’ as well as a warm past climate. Specifically, we have simulated the mid-Pliocene climate, a warm (~400 ppm CO₂) geological period approximately 3Ma ago, using a global coupled climate model (CESM1.0.5). Our simulations compare well to higher latitude sea-surface temperature reconstructions. We have performed sensitivity studies using a pre-industrial and a mid-Pliocene geography, as well as two levels of radiative forcing, as a part of intercomparison project PlioMIP2. But the question remains, to what extent can we treat the mid-Pliocene as an ‘analog’ for a future warm climate?

Looking at Northern hemisphere winter (DJF) sea-level pressure data, we find that the annular ‘belts of action’ move poleward partially due to increase in CO₂, but mainly due to the mid-Pliocene boundary conditions. Over the North Pacific Ocean, sea-level pressure variability slightly increases with CO₂, but greatly reduces due to the mid-Pliocene geography. The NAM seems to behave more ‘annular’ and less ‘sectoral’ or regional due to the mid-Pliocene climate boundary conditions. We will focus on the mechanisms that explain the differences between the past and future simulations.

How to cite: Oldeman, A., Baatsen, M., von der Heydt, A., van Delden, A., and Dijkstra, H.: Atmospheric variability in the Northern Hemisphere winter in a warm past and a future climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2957, https://doi.org/10.5194/egusphere-egu22-2957, 2022.

The North American Southwest (SW NA) has recently experienced periods of extreme drought, largely due to an increased intensity in evaporation. Yet, there remains large uncertainty in the predicted future changes of precipitation over this region. As a result, the future of SW NA hydroclimate remains uncertain.  The North American Monsoon (NAM) is an atmospheric circulation feature of SW NA hydroclimate that is generated by interactions between topography and moisture surge from the Gulf of California and the Gulf of Mexico.  Previous research has shown a weakened NAM in response to elevated levels of atmospheric CO₂.  However, when analyzing proxy paleoclimate reconstructions during the Pliocene, various records suggest wetter conditions during that time.  We use the mid-Pliocene (3.3 – 3.0 Millions of years ago) as an analog for ongoing climate change because this interval featured topography, geography, and biome assemblages similar to today, but a warmer global mean temperature by 2 - 4 °C compared to pre-industrial, and a sustained 400 ppm CO₂.  Here we are testing whether a high resolution simulation (25 km) can better capture the NAM and provide different sensitivity to boundary conditions compared to low resolution (100 km) simulations, using the same Community Earth System Model.  Increased resolution has been shown to improve the representation of features within the NAM for simulations of the present.   Our pre-industrial simulations display a more extensive monsoon region with high spatial resolution, which indicates a dependency of simulated NAM on resolving topographic features such as the Rockies, Basin and Range, and Gulf of California, all of which can only be captured at high spatial resolutions.  Simulations of the mid-Pliocene displayed weakened NAM precipitation along the west coast of the southwestern North America at a low resolution when compared to the pre-industrial run.  Yet, this weakening signal is limited to the Pacific side of the orographic slopes in the high resolution simulation, with the rest of the monsoon region featuring increased precipitation.  Ongoing work will explore the sources for this resolution dependency, and will quantify contributions of mesoscale systems, such as tropical and extratropical cyclones, to precipitation in the monsoon region.

How to cite: Albright, M. G., Feng, R., Zhu, J., Otto-Bliesner, B., Li, H., and Bhattacharya, T.: Mid-Pliocene North American Monsoon in Weather Resolving Coupled Simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5586, https://doi.org/10.5194/egusphere-egu22-5586, 2022.

The mid-Pliocene warm period (mPWP, ~3.3 – 3 Ma) is the most recent geological period with a CO₂ concentration similar to the present day (~400 ppm). The Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) focuses on the KM5c time slice (3.205 Ma), giving insight into the climate dynamics of this period. Sea surface temperature (SST) proxies indicate amplified warming over the North Atlantic in the mPWP with respect to the pre-industrial period, which may be linked to an intensified Atlantic Meridional Overturning Circulation (AMOC). Zhang et al. (2021) reported a stronger mPWP AMOC in all the PlioMIP2 simulations but found no consistent relation to either the Atlantic northward ocean heat transport (OHT) or average North Atlantic SSTs. We therefore look further into the drivers and consequences of a stronger AMOC in the mPWP compared to pre-industrial simulations.

Within the PlioMIP2 ensemble, we find that all model simulations with a closed Bering Strait and Canadian Archipelago show strongly reduced freshwater transport from the Arctic Ocean into the North Atlantic. The resulting increase in sea surface salinity in the subpolar North Atlantic and Labrador Sea stimulates deepwater formation in these areas. The stronger AMOC is therefore primarily a response to the closure of the Arctic gateways. We also look at the different components of the Atlantic OHT, associated with either the overturning circulation or the wind-driven gyre circulation. While the ensemble mean of the overturning component is increased significantly in magnitude in the mPWP, it is partly compensated by a reduced gyre component. Our results point towards a complex interplay between atmospheric and oceanic processes and indicate that considering these components separately allows for a better understanding of the climatic response to the AMOC strength.

How to cite: Weiffenbach, J., Baatsen, M., and von der Heydt, A.: Drivers and consequences of a stronger mid-Pliocene Atlantic Meridional Overturning Circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6006, https://doi.org/10.5194/egusphere-egu22-6006, 2022.

The reconstruction of deep-ocean temperatures is key in the study of the different climate states in the geological past. Reconstructions covering the Pliocene-Pleistocene transition shed light on the global climatic change that followed the mid-Pliocene warm period and culminated in full glaciation of the Northern Hemisphere.

Global δ18O records measured on seafloor dwelling foraminifera constitute the backbone of our understanding of the climatic trends and transitions of the last 65 million years [1,2]. These records suggest that the glacial intensification over the last 2.8 Ma experienced the onset of Quaternary-style ice age cycles and the progression towards a more deterministic climate system increasingly sensitive to orbital forcings. Deep-sea temperature variability across this time is thought to have stayed in a 4ºC range with near-freezing temperatures occurring at every glacial maximum, especially after the Mid-Pleistocene transition [2,3]. However, temperature signals based on carbonate δ18O data are built upon uncertain assumptions of non-thermal factors such as those regarding the isotopic composition of the ancient seawater.

Carbonate clumped thermometry (𝛥47) is based on thermodynamic principles that determine the ordering of isotopes within the carbonate crystal lattice [4]. It is independent of the fluid composition. 𝛥47 thermometry has recently been used to anchor Mg/Ca records of the Miocene while revealing a comparatively warm deep ocean [5].

Here we present 𝛥47-based deep-sea temperature constraints across the Pliocene-Pleistocene transition obtained from benthic foraminifera of ODP Site 1264 in the South Atlantic Ocean. In combination with benthic δ18O analyses, we furthermore interpret our measurements into global ice volume and ocean circulation changes in the Atlantic Basin across the major onset of the Northern Hemisphere Glaciation.

[1] Zachos, J., et al. (2001), Science 292, 686-693.

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

[3] Elderfield, H., et al. (2012) Science, 337(6095), 704-709.

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

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

How to cite: Domínguez Valdés, E., Kocken, I., Agterhuis, T., Müller, I., Bode, N., Kroon, D., Lourens, L., and Ziegler, M.: South Atlantic deep-sea temperature evolution across the Pliocene-Pleistocene transition from clumped isotope thermometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11222, https://doi.org/10.5194/egusphere-egu22-11222, 2022.