Oxygen isotope compositions (δ18O) have been widely used to reconstruct deep-time climate dynamics, which have been shown to vary through time and space. Reconstruction of the spatial pattern of these records relies on robust estimates of palaeolocations derived from Global Plate Models (GPMs). However, several different GPMs exist which vary in their palaeogeographic reconstruction, potentially impacting estimates of deep-time latitudinal temperature gradients and latitudinal-band temperatures. Since global mean temperatures are calculated as the sum of area-weighted latitudinal-band temperatures, variations in GPMs may also influence global mean temperature estimates. Here, we tested whether GPM choice impacts reconstructions of Early Palaeozoic climate by analysing an extensive Ordovician δ18O dataset compiled from bulk rocks, brachiopods, and conodonts. Using four open-access GPMs to reconstruct the paleogeographic distribution of sampled localities from our Ordovician δ18O dataset, we quantified discrepancies in palaeolatitudinal-band temperatures and global mean temperatures. Our results indicate that variations in GPM palaeogeographic reconstructions alone can lead to large differences (3–3.5°C) in palaeolatitudinal-band temperature and global-mean temperature estimates. Our findings suggest that GPM choice can substantially impact reconstructions of deep-time climate dynamics and careful consideration of the differences in palaeogeographic reconstructions between GPMs is required.
How to cite: Ma, X., Jones, L. A., Eichenseer, K., and Fan, J.: Palaeogeographic reconstructions shape understanding of deep-time climate change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21799, https://doi.org/10.5194/egusphere-egu25-21799, 2025.
The South China Craton experienced large changes in climate, eustasy and environmental conditions during the Late Ordovician Hirnantian Ice Age, but their impact on the watermass architecture of the Yangtze Sea has not yet been thoroughly evaluated. Here, we reconstruct the salinity-redox structure of the Yangtze Sea based on five Upper Ordovician-Lower Silurian shale successions representing a lateral transect from a deep-water area of the Inner Yangtze Sea (IYS; Shuanghe section) across the shallow Hunan-Hubei Arch (Pengye, Jiaoye and Qiliao sections) to the relatively deep-water Outer Yangtze Sea (OYS; Wangjiawan Section). Carbon isotope (13Corg) profiles show that the Guanyinqiao Bed (recording the peak Hirnantian glaciation) thins and is less completely preserved at sites on the flanks of the Hunan-Hubei Arch than in deeper water areas to the SW and NE, reflecting bathymetric influences. Watermass salinities were mainly marine at Shuanghe and brackish at the other four study sites, with little variation among Interval I (pre-glaciation), Interval II (Hirnantian glaciation) and Interval III (post-glaciation). Redox proxies document mainly euxinia at Shuanghe and Wangjiawan and suboxia at the other sites during Interval I, with shifts towards more reducing (mostly euxinic) conditions at most sites during Intervals II and III, which shows that all the study sections were deep enough to remain below the redoxcline during the glacio-eustatic lowstand. Two features of the Shuanghe section mark it as being unusual: it alone exhibits fully marine salinities implying greater proximity to the open ocean than the other four sites, and it exhibits an especially large shift towards more reducing conditions during Interval III (i.e. the post-Hirnantian transgression), implying greater water depths. These features are difficult to reconcile with the standard palaeogeographical model for the Ordovician-Silurian South China Craton, which is characterized by a geographically enclosed and restricted IYS and a more open OYS, arguing instead for the SW end of the IYS to have been connected to the global ocean and the OYS to have been a restricted oceanic cul-de-sac. A review of sedimentological and facies data for the IYS region suggests that our re-interpretation of the Ordovician-Silurian palaeogeography of the South China Craton is viable, although further vetting of this hypothesis is needed.
How to cite: Wang, X., Liu, Z., and Shen, J.: Watermass architecture of the Ordovician-Silurian Yangtze Sea (South China) and its palaeogeographical implications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7655, https://doi.org/10.5194/egusphere-egu25-7655, 2025.
The Ordovician–Silurian transition (O-S) was a period of dramatic climatic, environmental, and biological changes marked by severe mass extinction, glaciation, intense volcanism, marine anoxia, and widespread deposition of organic-rich shale. Silicate weathering has been proposed as a potential driver for the extreme climate change and invoked as a driver for marine anoxia during this time. However, the changes in chemical weathering across O-S transition are poorly constrained. Here, we present high-resolution Li isotope (δ7Li) records of marine shales from South China, spanning the Upper Ordovician to Lower Silurian to track changes in continental weathering across the O-S transition. We find significant positive δ7Li excursions in the Late Ordovician (Katian stage) and early Silurian (Rhuddanian stage), reflecting a shift to incongruent weathering, associated with secondary clay formation. Clay formation can retain cations on the continents, resulting in inefficient atmospheric CO2 consumption through silicate weathering. We therefore propose that enhanced clay formation may have sustained the long-term greenhouse conditions during Early Silurian, although volcanic degassing may have acted as a trigger. The greenhouse conditions would have reduced the thermohaline circulation and oxygen solubility, facilitating the development of prolonged anoxia throughout the Early Silurian and delayed the biotic recovery of marine ecosystems during this period. Marina anoxia could enhance the burial of huge amounts of organic matter in the sedimentary record as globally distributed organic-rich black shales, which ultimately caused the drawdown of atmospheric CO2 and allowed the climate recovery.
How to cite: Li, Y., Tian, H., Sun, H., Cheng, P., Li, T., and Gao, H.: Late Ordovician and early Silurian warming sustained by enhanced clay formation , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15107, https://doi.org/10.5194/egusphere-egu25-15107, 2025.
The Late Ordovician Mass Extinction (LOME) event is one of the most well-known climatic and environmental transition events in the Phanerozoic Eon. The Hirnantian glaciation and associated cooling during the latest Ordovician is widely considered to be the key driver for the major mass extinction event as well as changes in the climate and oceanographic systems1. Evidence from sedimentological, faunal, and geochemical data from around the globe has demonstrated that the transition from pre-glacial, to glacial, and post-glacial times was associated changes in carbon cycling, a large drop in eustatic sea level, and a series of extinction pulses2. The extinction patterns of marine fauna and perturbations to the carbon cycle have been well documented. However, the effects on the microbial communities that underpin marine food webs and mediate essential biogeochemical cycles are poorly constrained. New pristine outcrop samples have provided an opportunity for a detailed microbial lipid biomarker and stable isotope investigation on a succession that spans the Late Ordovician (Katian Stage) to Early Silurian (Rhudanian stage) time interval3. Here, we investigate how the significant environmental changes associated with the LOME and HICE affected the microbial communities.
Lipid biomarker and stable isotope (δ13Corganic, δ13Ccarbonate, δ15Ntotal) stratigraphic records were acquired from a 10-m interval of outcrop section from Cornwallis Island, Nunavut, Canada. Rock extracts were analyzed for a suite of branched and polycyclic hydrocarbon biomarkers utilizing the sensitivity and selectivity of Metastable Reaction Monitoring-Gas Chromatography-Mass Spectrometry (MRM-GC-MS). Baseline conditions, prior to the HICE, exhibit typical Ordovician marine biomarker characteristics which have been observed from various lithologies and different Ordovician marine depositional settings. These characteristics include low hopane/sterane (H/St) ratios, high relative abundance of C29 steranes from green algae, and high abundances of 3-methylhopanes (many times the Phanerozoic average), likely sourced from methanotrophic bacteria4. The rising and falling limbs of the HICE locally at our site are associated with a significant increase in total organic carbon (TOC) content (<9.5 wt.%) and are concomitant with an increase in the absolute abundances of regular steranes from marine algae. The observed jump in algal productivity and increased TOC content coincides with facies and biofacies indicators of a brief rise and then fall of global sea level documented in number of other sections, globally. By contrast, the biomarkers in the peak interval of the HICE locally, is associated with bacterial dominated productivity in an oligotrophic marine setting as indicated by high H/St ratios and low TOC content (≥0.3 wt.%). Low TOC content is a hallmark of the sea level low stand interval in many other sections, globally. These findings support and advance findings from earlier studies that Hirnantian climate and oceanographic changes caused major structural changes to marine food webs, particularly in low latitude regions where most of the graptolite extinctions have been documented.
1Finnegan, S. et al. Science (2011)
2Finnegan, S. et al. PNAS (2012)
3Melchin, M. J. & Holmden, C. Palaeogeography, Palaeoclimatology, Palaeoecology (2006)
4Rohrssen, M. et al. Geology (2013)
How to cite: Marshall, N., Holmden, C., Melchin, M., and Love, G.: Lipid biomarker chemostratigraphy in Arctic Canada: Evaluating microbiology ecology and carbon cycling during Hirnantian cooling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13232, https://doi.org/10.5194/egusphere-egu25-13232, 2025.
During the Ordovician-Silurian boundary interval, the Hirnantian Glaciation and the first major biodiversity crisis of the Phanerozoic, the Late Ordovician Mass Extinction (LOME), occurred. As one of the Phanerozoic “Big Five” extinction events, LOME is widely regarded as being closely linked to environmental changes such as anoxia induced by the Hirnantian Glaciation. However, due to the lack of high temporal resolution data in most previous studies, evolutionary patterns of different clades remain unclear. Trilobites, one of the most diverse clades during the Paleozoic, suffered catastrophic losses during this event, never recovering to the same level of dominance in the marine ecosystem and ultimately disappearing during the end-Permian Mass Extinction. Although previous studies (stage- or biozone-level, generally ~1-3 Myr) based on individual or limited number of stratigraphic sections suggested marine anoxia as the driver of benthic extinctions or the main cause of biodiversity decline, the vast morphological and occurrence data of trilobites have not been fully utilized to depict the morphological evolution of marine life due to technical constraints, hindering our understanding of the evolutionary history of life during this critical interval.
Here we compiled global trilobite fossil records and morphological descriptions spanning LOME from literature. Using the newly developed quantitative stratigraphic method, HORSE, we analyzed tens of thousands of fossil records to generate a global high-resolution trilobite diversity curve (~25 kyr as imputed temporal resolution) which has never been achieved before. The manual, labor-intensive annotation hindered the development of image-based large-scale annotated fossil datasets, thereby limiting large-scale morphological data analysis. However, high-dimensional embeddings extracted from morphological descriptions with large language models (LLMs) quantified global trilobite morphological similarities and allowed the generation of a high-resolution morphological disparity curve. Comparison between these two curves revealed that, while severe biodiversity losses are a defining feature of mass extinction events, its impacts on morphological disparity are more complicated. Although greater morphological disparity typically indicates higher ecological or functional diversity, the coupled diversity and disparity dynamics during the glaciation could be explained by either the intensity of extinctions or strong internal constraints. This study aims to reveal in significant detail the connections between marine biodiversity changes and morphological evolution during the Hirnantian Glaciation and LOME, as well as the relationships between these biotic changes and abiotic factors, thereby enhancing our understanding of the patterns and underlying mechanisms of the Late Ordovician Mass Extinction.
How to cite: Shen, H., Chu, T., and Fan, J.: AI-Powered Analysis of Global Trilobite Diversity and Morphology During the Late Ordovician Mass Extinction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15140, https://doi.org/10.5194/egusphere-egu25-15140, 2025.
The Late Paleozoic Ice Age (LPIA) represents Earth's longest icehouse period in the Phanerozoic and the only recorded greenhouse–icehouse–greenhouse cycle on a vegetated Earth. Sedimentary archives provide evidence of glaciation events, but the mechanisms driving the LPIA's onset (~330 Ma) and end (~260 Ma) remain debated. Here we investigate the climatic transitions associated with the LPIA using both non-dimensional (COPSE) and spatially resolved climate models, emphasizing the interplay between paleogeography, silicate weathering, and solid Earth degassing. By integrating new paleogeographic reconstructions constrained by fossil and lithological climatic paleo-indicators, we identify high-weatherability zones and assess their evolving influence on carbon fluxes. Additionally, the Variscan orogeny's role is examined to evaluate how physical erosion enhances chemical weathering and CO₂ drawdown.
Simulations highlight that maintaining icehouse conditions required not only a decrease in solid Earth degassing but also an enhancement in silicate weathering driven by the combined effects of increased topography and runoff. These processes amplified the consumption of CO2, supporting the initiation of a widespread glaciation. In contrast, the transition back to greenhouse conditions appears driven by a progressive decrease in exposed land for high intensity weathering. Climate sensitivity played a significant role in modulating these transitions, and model adjustments to this parameter improved alignment with CO₂ proxy data.
Our findings provide new insights into the interactions between tectonics, paleogeography, and biogeochemical processes in shaping Earth's climatic history. By leveraging geological evidence to refine long-term carbon cycle models, this work underscores the critical importance of accurately representing the paleogeography to understand ancient climate transitions and inform projections of future climate change.
How to cite: Marcilly, C., Torsvik, T. H., and Jones, M. T.: Late Paleozoic climate transition from a long-term climate modelling perspective , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5818, https://doi.org/10.5194/egusphere-egu25-5818, 2025.
The Late Paleozoic Ice Age (LPIA) was the latest phase of widespread glaciation on Earth before the current Late Cenozoic Ice Age. At its peak around 300 million years ago, ice sheets in southern Pangea reached their maximal extents. This knowledge comes from a plethora of geological evidence but has so far not been explored by fully three-dimensional coupled models of land ice and climate. Here we present results from the first peak-LPIA simulations with interactive ice sheets using CLIMBER-X, a fast coupled Earth-system model featuring a statistical–dynamical atmosphere and a frictional–geostrophic ocean. For a range of likely greenhouse-gas concentrations, we investigate how orbital geometry, topography, and the initialization of ice sheets affect the growth and distribution of land ice during the late Carboniferous. We find an especially distinct dependency on orbital geometry, with ice covering almost whole Gondwana in one case and being limited to the South American part in another, while keeping the greenhouse gases constant. We then plan to use the precipitation and ice-sheet cover output from the climate model to calibrate landscape evolution modeling with Fastscape and thereby obtain estimates of the global sediment flux during the LPIA.
How to cite: Eberhard, J., Feulner, G., Willeit, M., Davies, H. S., Bovy, B., Braun, J., and Petri, S.: Late Carboniferous ice sheets in a coupled Earth-system model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20768, https://doi.org/10.5194/egusphere-egu25-20768, 2025.
The late Paleozoic ice age (LPIA) was the longest-lived glaciation of the Phanerozoic, and the demise of LPIA is the Earth’s only recorded transition from an icehouse to a greenhouse state. The P1 glaciation (Asselian-Sakmarian) was the most extensive phase of the LPIA, characterized by rapid climate change and several significant events, including widespread aridification in the low latitudes of Pangaea, episodic glacial expansion in Gondwana, and considerable fluctuations in CO2 concentrations. This study investigates the early Asselian warming event and its connection to volcanic activity during the Early Permian, using data from two stratigraphic sections in the North China Craton (NCC). We analyzed organic carbon isotopes (δ13Corg), total organic carbon (TOC), total sulfur (TS), aluminum, mercury content, and chemical weathering indices to track climate and carbon isotope changes during P1 Glaciation of the LPIA. Our results suggest that the early Asselian climate warming may have been driven by volcanic activity through the release of greenhouse gases. This study also contributes to understanding the correlation between volcanism and carbon perturbations during the LPIA.
How to cite: Wang, L., Lv, D., Li, J., Zhang, Z., Isbell, J., Raji, M., Du, W., Li, Z., and Jiang, D.: Enhanced continental weathering and carbon-cycle perturbations linked to volcanism during the P1 Glaciation of the Late Paleozoic Ice Age, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20307, https://doi.org/10.5194/egusphere-egu25-20307, 2025.
The continental distribution and surface conditions of a planet strongly impact its climate. Continents on Earth are believed to have emerged above sea level in the Archean Eon, although the exact timing and emerged surface area are widely debated. We use the Isca climate model, a framework for the modelling of idealised planetary atmospheres, to explore the climatic impact of various land-ocean configurations on a 2.7 Ga Archean Earth. We find that the addition of land consistently produces a global cooling and introduces hemispheric asymmetry to the large-scale atmospheric circulation and equator-to-pole temperature gradient. The magnitude of the climate response increases with overall land fraction, while the degree of hemispheric asymmetry is more sensitive to the difference in land fraction between hemispheres. These effects are driven by changes in the surface energy balance, which are caused by the distribution of land and associated changes in albedo and the availability of water for evaporation. These results are comparable to similar work on tidally-locked exoplanets, and further highlight the importance of including land in climate simulations for Archean Earth and Earth-like exoplanets, particularly if the goal is an assessment of a planet’s habitability.
How to cite: Taylor, A., Thomson, S., Wilmes, S.-B., Mayne, N., and Green, M.: The effect of land distribution on Neo-Archean atmospheric circulation and surface climate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11732, https://doi.org/10.5194/egusphere-egu25-11732, 2025.
Greenhouse gases trap heat in the Earth’s atmosphere and warm our planet and on geological time-scales CO2 is the most influential greenhouse gas in modulating atmospheric temperature. During most of the Phanerozoic (past 540 million years), our planet was warmer than today, and a greenhouse-dominated climate (80%) was only interrupted by three periods of cold glacial conditions during the end-Ordovician (Hirnantian) glaciation, the Permo-Carboniferous (~330-260 Ma) and the second half of the Cenozoic (34-0 Ma). Icehouses are characterized by lower CO2 concentrations and temperatures, and a modern CO2 threshold for continental-scale glacial inception is estimated to 500 ppm. But with a fainter sun, the glacial inception threshold during the Hirnantian (445 Ma) glaciation was probably closer to 1000 ppm.
CO2 concentrations cannot be measured in deep time, and we therefore must rely on proxies, or models. For the past 450 million years, CO2 proxies during greenhouse climates average ~1100 ppm whilst the Phanerozoic icehouse intervals average ~480 ppm. But a proxy-based picture of CO2 concentrations before 450 Ma is lacking and thus CO2 levels for most of Earth’s history must be estimated from carbon-cycle models. Models are also important for capturing the processes (sources and sinks) that can explain shifting greenhouse and icehouse climates and can loosely be classified as inverse or forward models, pending on whether isotopic proxy data are parametrized or predicted from the model, respectively. Both model types, however, incorporate several biological and geological/tectonic forcing parameters that should be similar in all models.
Carbon-cycle models predict very different atmospheric CO2 levels for large of the Phanerozoic, differing by more than 4000 ppm and model-proxy differences can exceed 5000 ppm. Many of the relatively large, modelled differences in atmospheric CO2 are arguable caused by differences in time-dependent parametrization of plate tectonic degassing and silicate weathering, and benchmarking of carbon-cycle models are urgently required. In this contribution we focus on carbon-cycle modelling with GEOCARB_NET — a user-friendly version of the GEOCARB model. In GEOCARB_NET input parameters can easily be changed, tested, and compared with other models (e.g., COPSE, SCION and GEOCLIM). The system also contains databases for CO2 proxies and temperatures that be visualized together with CO2 predictions. We highlight how key input parameters can seriously affect reconstructed CO2 levels but also how models and proxies can better be reconciled.
How to cite: Torsvik, T., Royer, D., Marcilly, C., and Werner, S.: Carbon-cycle modelling and Phanerozoic climate change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5831, https://doi.org/10.5194/egusphere-egu25-5831, 2025.
Climate-model simulations are important tools for testing hypotheses about the drivers of shifts in climate and ecosystem distributions throughout the Phanerozoic. Initial simulations of Phanerozoic climates have been carried out using the HadCM3L climate model, with 109 time slices across the 540 million years. Each time slice represents a distinct stage, with CO2 concentrations prescribed to align the modeled global mean surface temperatures (GMST) with estimates of past GMST.
However, these simulations utilized modern plant functional types (PFT) and globally homogeneous surface properties across all Phanerozoic timescales. In reality, vegetation has evolved through time. So, use of modern PFT may introduce significant errors in climatically relevant variables (e.g., albedo). Consequently, the estimated values of modeled temperatures through time may be inaccurate.
The aim of this project is to implement more realistic representations of vegetation in the simulations, by utilizing PFTs that are appropriate for each time slice. For example, the early Ordovician would be characterized by low-lying, sparse vegetation dominated by bryophyte-like plants, which likely exhibited simple anatomy and physiology, were restricted to moist lowland habitats, and lacked deep anchoring structures.
As a first step towards this aim, we have set up a series of simulations that are simple continuations of the existing simulations, run for 110 years, but including more vegetation-specific outputs. Our analysis included visualizations of the Phanerozoic vegetation fraction, which pointed out clear inaccuracies, such as the unrealistic representation of vegetation during the early Phanerozoic. These findings emphasize the limitations of the original model’s assumptions about vegetation. Furthermore, we demonstrated that vegetation significantly influences surface temperature and found strong relationships between climate variables (such as precipitation and surface air temperature) and vegetation distribution. Our results underscore the need to make realistic adjustments to vegetation parameters in HadCM3L simulations.
How to cite: Chu, T., Lunt, D. J., and Fan, J.: Assessing the Impact of Vegetation Data on HadCM3L Phanerozoic Climate Simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21897, https://doi.org/10.5194/egusphere-egu25-21897, 2025.
Global pCO₂ levels have fluctuated significantly throughout the Phanerozoic, closely aligning with Earth’s warm, ice-free periods and cold, glacial climates. However, the extent to which these variations in pCO₂ are linked to weathering processes remains a topic of active debate. In this study, we quantify the effective elastic thickness of all major modern terrains and reconstruct their paleogeographic positions over the past 250 million years. We then estimate the weighted average continental effective elastic thickness within the tropics (e.g., within 10°, 15°, and 20° of the equator) and compare these values to global pCO₂ levels over time. Our analysis reveals a strong positive correlation between global pCO₂ levels and the weighted average continental effective elastic thickness in the tropics. We propose that variations in the mechanical strength of continents at low latitudes are linked to transitions between cold and warm climatic states. Specifically, when non-rigid continents drift into tropical regions, weakened and deformed rocks become more susceptible to exhumation and erosion in the warm, wet tropics, thereby enhancing Earth’s capacity for carbon sequestration through chemical weathering. Conversely, when rigid continents dominate the tropics, exhumation and erosion are inhibited, leading to relatively high atmospheric pCO₂ levels. If validated, we apply this correlation between continental rigidity and global pCO₂ to project future pCO₂ levels based on the assembly of the next supercontinent. Our findings suggest that, excluding human influence, global pCO₂ levels could increase fivefold over the next 250 million years. This underscores the critical role of continental strength, beyond just lithology or rock composition, in the tropics in driving physical and chemical weathering processes that shape Earth's climate state.
How to cite: Cheng, F., Zuza, A., Li, Z., Liu, Y., Jolivet, M., Guo, Z., and Xiao, W.: Continental Rigidity in the Tropics Shapes Earth’s Climate state, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14653, https://doi.org/10.5194/egusphere-egu25-14653, 2025.
The El Niño–Southern Oscillation (ENSO), originating in the central and eastern equatorial Pacific, is a defining mode of interannual climate variability with profound impact on global climate and ecosystems. However, an understanding of how the ENSO might have evolved over geological timescales is still lacking, despite a well-accepted recognition that such an understanding has direct implications for constraining human-induced future ENSO changes. Here, using climate simulations, we show that ENSO has been a leading mode of tropical sea surface temperature (SST) variability in the past 250 My but with substantial variations in amplitude across geological periods. We show this result by performing and analyzing a series of coupled time-slice climate simulations forced by paleogeography, atmospheric CO2 concentrations, and solar radiation for the past 250 My, in 10-My intervals. The variations in ENSO amplitude across geological periods are little related to mean equatorial zonal SST gradient or global mean surface temperature of the respective periods but are primarily determined by interperiod difference in the background thermocline depth, according to a linear stability analysis. In addition, variations in atmospheric noise serve as an independent contributing factor to ENSO variations across intergeological periods. The two factors together explain about 76% of the interperiod variations in ENSO amplitude over the past 250 My. Our findings support the importance of changing ocean vertical thermal structure and atmospheric noise in influencing projected future ENSO change and its uncertainty.
How to cite: Hu, Y., Li, X., Hu, S., and Cai, W.: Persistently active El Niño–Southern Oscillation since the Mesozoic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4792, https://doi.org/10.5194/egusphere-egu25-4792, 2025.
The Carnian Pluvial Episode was marked by episodic climate perturbations and multiple negative carbon isotope excursions (NCIEs) in (in)organic carbon. Its onset (NCIE-1) corresponds to an extended period of climate disruption, including global warming and an intensified hydrological cycle, as evidenced by increased siliciclastic inputs into marine basins and hygrophytic palynological assemblages. To investigate climatic/biotic changes of NCIE-1, we analyzed plant, algal, and bacterial lipid biomarkers and δ2H of leaf-wax n-alkanes from the Dolomites (Italy) in northwestern Tethys. Coeval δ2H reductions in n-alkanes by up to ca. 40‰ align with NCIE-1, indicating increased rainfall and altered hydroclimate in this initial carbon cycle perturbation. Concurrently, elevated biomarker concentrations reveal enhanced terrestrial inputs and marine primary production, with shifts in land plant communities via n-alkane distributions and alterations in marine algal communities by sterane assemblages. The biomarker dataset emphasizes the immediate impact of the NCIE-1 on both the terrestrial and marine ecosystems. Such a hydroclimate-biotic change in Dolomites suggests a complicated interaction amongst carbon and hydrological cycle via atmospheric-ocean dynamics during Carnian urgent to be investigated.
How to cite: Huang, Y., Dal Corso, J., Gianolla, P., Lunt, D., Farnsworth, A., Roghi, G., Wang, Y., Naafs, D., Dang, X., Benton, M., and Pancost, R.: Hydroclimatic change at the immediate start of the Carnian Pluvial Episode (Late Triassic), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4630, https://doi.org/10.5194/egusphere-egu25-4630, 2025.
The Late Paleocene – Early Eocene period is characterised by several short-term warming episodes superimposed on already high temperatures and CO2 levels. These hyperthermal events are associated with negative carbon isotope excursions, which are thought to represent significant changes in the carbon cycle through input of isotopically light carbon into the exogenic carbon pool. Next to carbon release from melting permafrost, one large-scale carbon reservoir that might have been the source of this disturbance is marine methane hydrates. To study the potential role of this carbon reservoir in more detail, we expand the carbon cycle box model LOSCAR to include a methane hydrate reservoir. By adapting the carbon cycling parameterisations in the original LOSCAR ocean boxes to allow for organic carbon burial, and by determining a temperature-dependent gas hydrate stability zone in the sediment, we model the time-varying volume of marine methane gas hydrates. In order to investigate the dynamic response between methane hydrates and temperature fluctuations in the Eocene, we run simulations using the Early Eocene as a background state and orbital solutions plus noise as forcing, shedding new light on the role of methane hydrates in late Paleocene – early Eocene climate fluctuations.
How to cite: Elbertsen, M. and Cramwinckel, M.: Assessing the role of methane hydrates in the Late Paleocene – Early Eocene hyperthermals using a carbon cycle box model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17767, https://doi.org/10.5194/egusphere-egu25-17767, 2025.
Studying warm climates of the geological past is essential to improving our understanding of the Earth’s climate and carbon cycle under elevated atmospheric CO2 levels. A major challenge in simulating past climates lies in the accurate reconstruction of the paleogeography – the spatial distribution of land, mountains, oceans, and their bathymetry. However, the impact of paleogeography and its uncertainty on modelled paleoclimates and model-data misfits is poorly quantified. Here, we quantify the impact of paleogeographic boundary conditions on the simulation of early Cenozoic climates (66 to 34 million years ago) using the IPSL-CM5A2 Earth System Model. We performed a series of paleoclimate simulations for key time slices, such as the early and middle Eocene climatic optima (EECO and MECO), using the most recent paleogeographic reconstructions and with varying atmospheric CO2 concentrations. We tested alternative paleogeographic scenarios, with particular focus on the different reconstructions of the Neo-Tethyan region and the India-Asia collision. In addition, we evaluate the impact of using different global reference frames, including the latest paleomagnetic reference frame of Vaes et al. (2023, Earth-Science Reviews). We show that the choice of reference frame and paleogeographic reconstruction can significantly impact global ocean circulation as well as regional temperature and precipitation patterns. To assess how paleogeography affects model-data comparisons, we compared model predictions against available paleoclimate proxy records. We find that changes in paleogeographic boundary conditions lead to notable differences in the reconstructed position of proxy sites. This may affect interpretations of past climates based on proxy records, such as reconstructions of latitudinal temperature gradients or climate sensitivity calculations. Our findings highlight the importance of paleogeography for paleoclimate modelling, and we discuss how future improvement of paleogeographic reconstructions may contribute to advancing our understanding of past climates and the carbon cycle.
How to cite: Vaes, B., Sternai, P., Licht, A., Maffre, P., Chalk, T., Pineau, E., and Donnadieu, Y.: The impact of paleogeographic boundary conditions on early Cenozoic climate simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16077, https://doi.org/10.5194/egusphere-egu25-16077, 2025.
The Late Eocene is a period of global cooling and high-latitude tectonic changes culminating in the Eocene Oligocene Transition (34 Ma ago), one of the major climatic shifts of the Cenozoic. Across the Late Eocene, the Earth went from a largely ice-free greenhouse during the early Eocene climatic optimum to an icehouse with the ice sheet inception over Antarctica. This long-term cooling happened simultaneously with a decrease in the atmospheric content in carbon dioxide whose causes are still unclear. During the same period, marine gateways surrounding Antarctica (Drake Passage and Tasman Gateway) opened and deepened and Atlantic-Artic gateways changed configurations, thereby allowing the onset of oceanic currents such as the circumpolar current isolating Antarctica.
Here, we investigate how coupled changes in the configuration of these gateways impact the oceanic circulation and carbon cycle, in particular the distribution of δ13C. Applying for the first time the carbon isotopes-enabled version of PISCES (Buchanan et al. 2021) to the Late Eocene, we present and analyze a set of experiments with different gateways configurations with a specific focus on the reorganization of ocean circulation and its consequence on carbon isotopes distribution and gradients. We then compare our model results to available proxy data and discuss hypotheses regarding Late Eocene δ13C changes.
How to cite: Fabre, E., Ladant, J.-B., Sepulchre, P., and Donnadieu, Y.: Impact of marine gateways on oceanic circulation and carbon cycle in the Late Eocene, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16029, https://doi.org/10.5194/egusphere-egu25-16029, 2025.
The Early Eocene, with CO2 levels exceeding 800 ppm, is a well-suited period for studying the effects of elevated atmospheric CO2 concentrations on climate, vegetation and their interplay. Here, we present insights from a model – data comparison using simulations with a dynamic global vegetation model (LPJ-GUESS) and a comprehensive global paleobotanical data set. The vegetation model is driven by climate input from four climate models of the Deep-Time Model Intercomparison Project Phase 1 (DeepMIP 1) under varying CO2 concentrations. Using climate input from two models with CO2 concentrations between three to six times pre-industrial CO2, we successfully replicate the extension of tropical, sub-tropical and temperate forests into higher latitudes, consistent with the paleobotanical record. Notably, tropical forest extent as suggested by paleobotanical data is also captured at CO2 concentrations exceeding four times pre-industrial CO2, contrasting with previous modeling results. However, input from the other two climate models produce excessively dry conditions in subtropical regions, misaligning with the paleobotanical evidence. Our vegetation distribution results will inform the next phase of the DeepMIP (DeepMIP 2). In addition, our comparison provides insights into the performance of climate and vegetation models under high CO2 concentrations, with implications for simulating future climate change and its impacts.
How to cite: Brugger, J., Thompson, N., Salzmann, U., Utescher, T., Forrest, M., Lunt, D. J., Rehfeld, K., and Hickler, T.: Global vegetation of the warm Early Eocene: insights from a model - data comparison, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16228, https://doi.org/10.5194/egusphere-egu25-16228, 2025.
The Paleocene-Eocene Thermal Maximum (PETM) around 56 million years ago was a 5-6°C global warming event, representing one of the most important geologic analogues to present-day climate change. Considering that the carbon release rate that triggered the PETM was likely around a magnitude lower than current anthropogenic carbon emissions, it is of major importance to identify the climatic, geologic and biological factors that drove the severity and 200 kyr long duration of the PETM hyperthermal. Based on carbon isotope records of the period, it was suggested that a loss and a 70-100 kyr lagged regrowth of biospheric organic carbon stocks may have contributed to the long duration of the carbon cycle perturbation. In this work, we aim to identify the biological mechanisms that could explain such a sustained loss of vegetation-mediated carbon sequestration on land, and whether these dynamics can be expected under current anthropogenic carbon release. We developed a new, eco-evolutionary vegetation model, grounded in principles of eco-evolutionary optimality, to simulate changes in vegetation structures and traits, organic carbon sequestration and vegetation-mediated silicate weathering enhancement throughout the PETM climatic excursion. By comparing modelled vegetation dynamics with vegetation reconstructions derived from palynofloral records, we show that the PETM warming may have exceeded the capacity of vegetation systems to respond to the environmental changes through evolutionary adaptation of functional traits and climatic tolerances, resulting in reduced fitness and functioning. The magnitude of the warming and the creation of previously non-existent climatic environments during the period further resulted in a limited capacity of plants to avoid the warming-induced stress through dispersal and migration. Our results show that a global warming of similar magnitude as during the PETM could result in a long-lasting loss of vegetation-mediated carbon sequestration and a reduction in the efficiency of the Earth system to regulate perturbations.
How to cite: Rogger, J., Korasidis, V., Bowen, G., Shields, C., Gerya, T., and Pellissier, L.: Loss of vegetation-mediated carbon sequestration during the Paleocene-Eocene Thermal Maximum, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15065, https://doi.org/10.5194/egusphere-egu25-15065, 2025.
The Mid-Pliocene Warm Period (mPWP) provides a valuable analog for near-future climate warming with an estimated global mean temperature 2.5–4°C higher than today and atmospheric CO₂ concentrations ranging from 360 to 420 ppm. Vegetation changes during the mPWP were significant, playing a crucial role in the climate through feedback mechanisms. Studying the climate-vegetation interactions provides insights into their strength, temporal dynamics, and their role in extreme events. We plan to investigate these interactions by examining vegetation changes under various climate scenarios, including distinct vegetation configurations. As a first step in this research, we will develop a set of vegetation scenarios from exploratory model runs which will then be used as boundary conditions in future runs—in combination with other varying conditions such as varying GHG levels, paleogeography, orbital configurations, and aerosol emissions— to incorporate vegetation dynamics in the mPWP experiments.
Here, we present preliminary results regarding the changes in spatial coverage of different vegetation during mPWP scenario runs and our proposed vegetation scenarios. The vegetation scenarios are developed from mPWP simulations with varying atmospheric CO₂ concentrations of 350 ppm, 400 ppm, and 490 ppm. These simulations were performed with the Community Earth System Model version 1.2, a fully coupled climate model, and Biome4, an offline equilibrium vegetation model. We will show the responses of paleo vegetation to climates under different CO₂ levels and quantify the stability of vegetation around the globe within the different scenarios. Based on these results, we will propose a set of vegetation scenarios for use in future studies.
How to cite: Zeller, E., Macarewich, S., Kaplan, J. O., Sarr, A.-C., Zhu, F., Zhu, J., Otto-Bliesner, B., Tessler, M. E., Amrhein, D., Baldwin, J. W., Meegan-Kumar, D., Poulsen, C. J., and Tierney, J. E.: Vegetation response to varying CO2 conditions during the Mid-Pliocene Warm Period., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13510, https://doi.org/10.5194/egusphere-egu25-13510, 2025.
Two prominent forcing factors occurring during the Cenozoic are the Indian Asian collision and the atmospheric drawdown of carbon dioxide concentration from 4 to 1 PAL. Both of them have been intensively studied, but only a few studies were devoted to disantengling them and to explore their impact on the meridional ocean circulation. Indeed, there are some interactions between these two factors and other important features occurred during this period, especially concerning the geometry of straits (Tan et al., GRL 2022). In this study, we simulate, with a coupled GCM model (CESM version 1.0.5), the response to both of these factors with idealized boundary conditions. Using four long-lasting simulations with two different values of pCO2 (4 and 1 PAL) mixed with the presence or absence of TP, we demonstrate that the ocean heat transport in North Pacific and Atlantic ocean is differently impacted by the uplift of the TP. Such a response has been pointed out by Su et al., Climate of the Past 2018 and depicts a large increase of AMOC and decrease of PMOC from Eocene to present-day, but in this study, they only used a pCO2 of 1 PAL.
This last feature was a severe limitation to compare these simulations to data. Moreover, the sea-ice response played an important role, which would be undoubtedly reduced at a CO2 concentration of 4 PAL. In this new study, we disentangle the effect of the pCO2 decrease from 4 to 1 PAL and the uplift of the Tibetan Plateau. We pin-point the important result that, even with 4 PAL CO2, the Tibetan Plateau uplift led to major changes of the meridional ocean circulation, including pronounced differences in North Pacific and North Atlantic.
Moreover, our simulation with present-day TP and 1 PAL corresponding to the pre-industrial and the other extreme simulation, no TP and 4 PAL corresponding to the early Eocene, can be, therefore, compared to data, especially over the northern hemisphere, for which the Pacific and Atlantic ocean model response is largely different. Thanks to the availability of data over North Atlantic, it is possible to show that the simulated cooling is in agreement with these reconstructions using different marine proxies. In contrast, over North Pacific, not enough sea surface temperature reconstructions (SST) are yet available over 30°N to assess the SST cooling inferred by the simulation. (Hollis, GMD 2019 ; Lunt et al., Climate of the Past 2021).
In summary, this study claims for more data in North Pacific during the early Eocene. More importantly, it pin-points the important role of the Tibetan Plateau uplift on building a modern circulation in North Atlantic.
How to cite: Ramstein, G., Su, B., Phan, C., and Tremblin, M.: Disentangling the role of two prominent climate forcing factors in the large decrease of temperatures since the Eocene : a pCO2 drawdown and the Tibetan Plateau uplift, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8270, https://doi.org/10.5194/egusphere-egu25-8270, 2025.
The rise of the Tibet Plateau played a significant role in Asian climate evolution, especially the eastern Tibet which forms the transitional area where the South Asian Monsoon and East Asian Monsoon systems interact, and the formation of modern high-relief topography of eastern Tibet potentially makes its the cradle of Hengduan Mountain biodiversity hotspot.
We reconstruct the uplifting history of the eastern Tibet in three Cenozoic basins, including Gonjo, Relu and Markam basins based on multiple proxies. These basins are NW-SE directed basins with an elevation of ~4000 m at present. Today, the climate in these basins is semi-humid monsoonal with a mean annual air temperature of 0-5 ℃ and annual precipitation of 400-600 mm/yr. Aeolian deposits are pervasively developed at the bottom of the eastern Tibet Cenozoic basins before early Eocene (>50 Ma), especially in the Gonjo and Relu basins. Fluvial and lacustrine strata were deposited in the middle part of Gonjo Basin and the lower part of Relu Basin (50-45 Ma). Large number of lacustrine sediments (45-34 Ma) exists in the middle of the Relu Basin and the top of the Markam Basin. Oxygen and clumped isotopes from the Gonjo Basin suggested an earlier uplift from 0.7 km to 3.8 km during the middle Eocene (50-40 Ma; Xiong et al., 2020). The CLAMP and clumped isotope results for the Relu Basin indicated a rise in elevation from 0.6 km to 3.7 km between 45 to 34 Ma (He et al., 2022). The Markam Basin remained at a moderate elevation of 2.6 km between 42 to 39 Ma, then rose rapidly to 3.8 km by 36 Ma as indicated by CLAMP and oxygen isotope paleoaltimetry (Zhao et al., 2023). Combined with published paleoelevation results, the elevational history of eastern Tibet revealed as: During the early Eocene, it remained as lowland, and then underwent moderate to quick rise in the middle Eocene, approached to near present elevations by the latest Eocene of ~35 Ma.
The rise of the eastern Tibet during warm-house period significantly changed the climate as well as the biodiversity within and around Tibet. Before the rise of eastern Tibet, the climate was dry with typical intermountain desert system. Accompany with the rise of eastern Tibet, a Mediterranean climate developed in eastern Tibet characterized by bi-modal precipitation with two peaks during the spring (MAM) and autumn (SON) seasons, and a lower precipitation in the summer (JJA) seasons (He et al., 2022; Chen et al., 2023). Another line of evidence that supports the Mediterranean-like climate comes from the plant fossils. A typical semi-arid or arid flora that includes Palm, Eucalyptus, Palibinia and Quercus shows some similarity to Mediterranean vegetation. This flora co-evolved with the rise of eastern Tibet in the Relu and Markam basins, and even dispersed to the southeastern China. The high-relief topography, coupled with this distinctive Mediterranean climate system, significantly contributes to the development of the highly diversified species.
How to cite: Xiong, Z., Ding, L., Farnsworth, A., Zhao, C., and Tian, X.: The late Eocene rise of eastern Tibet and its impact on climate and biodiversity , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1269, https://doi.org/10.5194/egusphere-egu25-1269, 2025.
It is debated as to whether the modern-like East Asian monsoon formed during the late Oligocene–early Miocene or the Eocene. To resolve this dispute requires a comprehensive and updated synthesis of the available geological records and a reliable modelling study. Here, we investigate Cenozoic climate patterns over East Asia by compiling geological records and conducting climate modelling for key geological periods based on our improved paleogeographies. Geological records suggest that a zonal (semi-)arid climate pattern was dominant over tectonic timescales during most of the Paleogene in large areas of East Asia, with marked fluctuations between dry and wet conditions over orbital timescales, and a modern-like monsoon-dominated climate pattern has formed since the late Oligocene–early Miocene (ca. 28–22 Ma). Our simulations show that a zonal dry belt extended across East Asia during the late Eocene, and a monsoon-dominated pattern had already formed over East Asia by the early Miocene. In addition, our simulations further indicate a strong sensitivity of East Asian rainfall to orbital forcing, which can explain the seemingly unstable character (i.e., wet–dry fluctuations) of the dry belt across East Asia during the Eocene. Furthermore, our results suggest that paleogeographic changes, particularly uplift of the Tibetan Plateau to moderate–high elevations and its paleolatitude approaching present-day location during the late Oligocene–early Miocene, rather than atmospheric CO2 levels, played a crucial role in the establishment of the modern-like East Asian monsoon.
How to cite: He, Z., Zhang, Z., Guo, Z., Tan, N., Zhang, Z., Zhang, C., Wu, H., and Deng, C.: The origin of the modern-like East Asian Monsoon: insights from new data synthesis and climate modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14249, https://doi.org/10.5194/egusphere-egu25-14249, 2025.
Contemporary global warming is known to lag behind the rapid increase in atmospheric CO2 levels. This delay, largely due to heat uptake and storage in the vast ocean interior, remains one of the key uncertainties in projecting climate change in future decades. Here, we present decadal-resolution paleoclimate reconstructions of atmospheric CO2 and temperature to evaluate the carbon-climate coupling dynamics over an approximately 700-year time window of the middle Miocene, 16 million years ago. The middle Miocene is characterized by perturbations in the global carbon cycle caused by volcanic degassing, and global warming of about 6ºC relative to today. By analyzing fossil leaves and lipid biomarkers from the annually-varved Clarkia Lake deposit in Idaho, USA, we establish concurrent and continuous CO2 and temperature records that capture short-term fluctuations superimposed on long-term warming and CO2 increasing trends. Statistical analysis shows that CO2 consistently lead temperature variation on a multi-decadal scale. Climate model emulators further confirm the role of ocean heat storage in shaping this delayed transient response. High temporal resolution reconstructions can provide constraints on Earth’s climate changes from a distant greenhouse world yet on societally relevant time scales, offering critical insights to improve our understanding of carbon-climate coupling dynamics. Such paleoclimate constraints are crucial for reducing uncertainties in projecting the near-term climate change under increasing CO2 levels.
How to cite: Zhang, Y., Starr, D., Leng, Q., Chan, D., Sachnik, J., Liang, J., Yang, H., Xu, Y., Kim, B., Shen, R., Feng, R., and Pearson, A.: Carbon-Climate Coupling Dynamics Revealed by Decadal-Resolution Middle Miocene Records, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7762, https://doi.org/10.5194/egusphere-egu25-7762, 2025.
The mid-Piacenzian (3.264–3.025 Ma) is regarded as being the most recent warm period with atmospheric CO2 levels comparable to those of the present-day, thus reconstruction of corresponding climate change provides a good reference for our understanding the current and future global warming. In this study, we undertook climate reconstructions for East Asia using the modern analogue technique, based on fossil pollen records. The results show significant spatial variations in paleoclimate, with a warmer zone in the northwest and a colder zone in the eastern monsoonal regional. To better understand the data–model discrepancies, particularly with respect to the overall warming trend indicated by the simulations, we decomposed the physical processes in the simulation based on the surface energy budget equation. Our findings suggest that the cooling effects of cloud radiative forcing, non-surface albedo feedbacks induced by clear-sky shortwave radiation, and latent heat flux contributed to the cooling trend in the eastern zone. In contrast, the warming observed in the northwestern zone was driven primarily by increased clear-sky downward longwave radiation. These results highlight the complex responses of different regions to climatic change and the key role of cloud and radiation processes in controlling regional climate.
How to cite: Wu, H., Chen, L., Sun, Y., Zhang, W., Yu, Y., and Zhang, C.: Spatial patterns and mechanisms of the temperature response in East Asia to mid-Piacenzian warming, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10515, https://doi.org/10.5194/egusphere-egu25-10515, 2025.
The Mid-Pleistocene Transition (MPT), which occurred approximately 1.25 to 0.85 million years ago, marks a critical geological period characterized by a shift in Earth's glacial cycles from a roughly 41 kyr periodicity to a 100 kyr periodicity. However, the stratigraphic framework is constrained by low sedimentation rates, the absence of high-resolution isotope stratigraphy, and low-resolution or absent biostratigraphic control. In this study, we examined four piston cores collected from the western-central Pacific to more accurately determine the geochronology of the surficial sediments in the deep sea. Through integrated magnetostratigraphy, a proposed chronology since the Pliocene was established, and astronomical tuning was also conducted in one of the four cores. In conjunction with XRF scanning, the geochemical properties were studied to reveal regional changes since the MPT. Our findings indicate the following paleoceanographic evolution: concurrent with global cooling and aridification in Asia, there has been an increase in wind and dust flux in the western Pacific, an enhancement in biological productivity, and a reduction in the degree of seabed redox post the MPT. Additionally, we also found that throughout the MPT (approximately 1.2 to 0.7 Ma), the deep-sea paleoceanographic environment of the Western Pacific has maintained relative stability.
How to cite: Wang, H., Yi, L., Yang, Y., and He, G.: High-resolution records of the mid-Pleistocene Transition in pelagic sediments of the western Pacific, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5667, https://doi.org/10.5194/egusphere-egu25-5667, 2025.
As the terminal zone for marine sulfate reduction, the sulfate-methane transition zone (SMTZ) facilitates anaerobic oxidation of methane coupled with sulfate reduction (AOM-SR), integrating the biogeochemical cycles of carbon and sulfur. This process indirectly influences the redox balance of surface geological environments. To investigate the biogeochemical characteristics within paleo-SMTZs, we examined two representative nodules from the Early Silurian, South China. The diagenetic barite and 34S-enriched euhedral pyrite within these nodules indicate a close association with SMTZ. The sedimentary microtextural evidence of the authigenic growth sequence of framboidal pyrite and pronounced heterogeneity δ34Spyr suggests a multi-stage genesis of nodules. In Type-1 nodules, δ34Spyr at the edges are as low as 8.6‰. significantly less than the 18.8‰ observed at the centers. At the grain scale, the δ34S within individual pyrite grain ranges from -1.9‰ to 29.1‰. We propose that the formation of Type-1 nodules occurred in three stages: (1) nodule embryos with 34S-depleted pyrite edges formed in the sulfate reduction zone based on a diffusion-precipitation model; (2) within the SMTZ, barite dissolution and reprecipitation promote nodule growth, forming 34S-enriched euhedral pyrite and causing strong heterogeneity in the sulfur isotope distribution within some pyrite grains.; and (3) below the SMTZ, sulfate depletion leads to extensive replacement of barite by other minerals. The pronounced concentric structure in Type-2 nodules indicates multiple formation episodes; the initial stage aligns with that of Type-1 nodules, while needle-shaped minerals at the edges formed in response to vertical spatial shifts within SMTZ. Additionally, calcite, typically associated with SMTZs, is notably rare within these nodules. Instead, quartz replaces calcite as the nodule matrix and commonly undergoes pseudomorphic replacement of barite. We suggest that the substantial enrichment of quartz over calcite within nodules results from microbial activity altering pore water pH and alkalinity, serving as a petrographic fingerprint of organoclastic sulfate reduction within paleo-SMTZs.
How to cite: Tang, Q., Liang, C., Ji, S., Cao, Y., and Liu, K.: Lithofacies and in-situ sulfur isotope characteristics of nodules across the Ordovician-Silurian boundary marine shale in South China: Indicative significance for sedimentary environment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-107, https://doi.org/10.5194/egusphere-egu25-107, 2025.
Climate change and organic carbon burial events in the Late Ordovician-Early Silurian are well-documented, yet the mechanisms driving these events remain debated. Through high-resolution gamma-ray logging (GR) and trace element records, we establish a 12.6 Myr astronomical timescale for the Late Ordovician-Early Silurian Wufeng-Longmaxi Formation in the Sichuan Basin. Million-year-scale sea level fluctuations are reconstructed by modeling sedimentary noise in the 405 kyr-tuned GR series. Energy decomposition analysis of astronomical orbital parameters suggests that changes in land-sea water exchange, driven by enhanced tropical water vapor and heat within a ~2.1 Myr eccentricity-modulated gyre, likely served as the primary driver of seawater deposition. Maxima in total organic carbon coincides with peaks in the long-term 1.1 Myr obliquity modulation cycle, with the long-term 2.1 Myr eccentricity cycle occurring at a maximum or minimum. This long-term trajectory may have driven carbon cycle perturbations and differential organic matter enrichment by influencing various climate-related factors. During the Late Ordovician-Early Silurian, a new resonance state emerged, characterized by ~2.1 Myr eccentricity and ~1.1–1.0 Myr inclination, likely associated with long-term Earth-Mars resonance and potentially constraining the chaotic evolution of the solar system over geological timescales.
How to cite: Wang, J., Yuan, G., Hu, Z., Hu, J., and Cai, Q.: Orbitally-paced climate change and organic carbon burial during the late Ordovician-early Silurian, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1205, https://doi.org/10.5194/egusphere-egu25-1205, 2025.
The surface productivity variations are still unclear through the Ordovician-Silurian crisis, which is belong to one of the “Big Five” extinction. Here, we present barium (Ba) concentration and isotope data from organic matter-enriched anoxic siliceous sediments of various facies (X sites from proximal to distal regions) during the OST from South China. Our data show that both raw Ba and ratios of Ba to aluminum (Ba/Al) are higher than that in numerous ancient black shales and modern high productivity area, document elevated Ba accumulations during this interval. Besides, a larger gradient (~ 1 ‰) of Ba isotope (138Ba) gradient between the shallow-water to deep-water sites, additional support higher marine productivity was the reason of the higher Ba burial in these sediments. These data provide evidence that elevated organic carbon fluxes from the surface ocean (other than redox conditions) was likely the main control on accumulation of these organic matter-enriched sediments, and thus provide the sources of “shale gas” during this interval.
How to cite: Shen, J.: The oceanic primary productivity variations during the Ordovician and Silurian transtion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7465, https://doi.org/10.5194/egusphere-egu25-7465, 2025.
Atmospheric CO2 is thought to play a fundamental role in Earth’s climate regulation. Yet, for much of Earth’s deep geological past, atmospheric CO2 has been poorly constrained, hindering our understanding of transitions between cool and warm climates. Beginning ~370 million years ago in the Late Devonian and ending ~260 million years ago in the Permian, the Late Palaeozoic Ice Age was the last major glaciation preceding the current Late Cenozoic Ice Age and possibly the most intense glaciation witnessed by complex lifeforms. From the onset of the main phase of the Late Palaeozoic Ice Age in the mid-Mississippian ~330 million years ago, the Earth is thought to have sustained glacial conditions, with continental ice accumulating in high to mid-latitudes. However, open questions remain about the role of CO2 and nature of Earth’s climate during the onset and demise of glacial conditions.
This presentation will showcase an 80-million-year-long boron isotope record within a proxy framework for robust quantification of CO2, paired with new strontium, carbon and oxygen isotope records. Our records reveal that the main phase of the Late Palaeozoic Ice Age glaciation was maintained by prolonged low CO2, unprecedented in Earth’s history. About 294 million years ago, atmospheric CO2 rose abruptly (4-fold), releasing the Earth from its penultimate ice age and transforming the Early Permian into a warmer world. Our findings demonstrate the central role of CO2 in driving Earth’ geological climatic and environmental transitions [1].
[1] Jurikova H., Garbelli C., Whiteford R., Reeves T., Laker G.M., Liebetrau V., Gutjahr M., Eisenhauer A., Savickaite K., Leng M.J., Iurino D.A., Viaretti M., Tomašových A., Zhang Y., Wang W., Shi G.R., Shen S., Rae J.W.B., Angiolini L. (2025) Rapid rise in atmospheric CO2 marked the end of the Late Palaeozoic Ice Age. Nature Geosci., https://doi.org/10.1038/s41561-024-01610-2.
How to cite: Jurikova, H., Garbelli, C., Whiteford, R., Reeves, T., Laker, G., Liebetrau, V., Gutjahr, M., Eisenhauer, A., Savickaite, K., Leng, M., Iurino, D. A., Viaretti, M., Tomašových, A., Zhang, Y., Wang, W., Shi, G. R., Shen, S., Rae, J., and Angiolini, L.: 80-Million-Year Atmospheric CO2 Record from the Late Palaeozoic Ice Age, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16102, https://doi.org/10.5194/egusphere-egu25-16102, 2025.
The bauxite is a critical paleoclimatic proxy, and it is also the main material for refining aluminum. Therefore, it is of great scientific, economic and strategic significance to study the mineralization of bauxites. The formation of bauxites is largely affected by intense chemical weathering, closely related to temperature, precipitation and vegetation cover. In paleoclimatic studies, bauxites are used to qualitatively indicate warm, humid and vegetated environmental conditions, but how bauxites in the deep time were quantitatively related to temperature and precipitation has not been established, which limits the paleoenvironmental indication of bauxites and the metallogenic prediction. Here, we combine geological records with climate simulations to establish the quantitative relationships of bauxites with temperature and precipitation since the Mesozoic era. The Earth system model CESM1.2.2 and the vegetation model BIOME4 were combined to simulate the climate and vegetation distribution. Then the environmental information of the paleo-locations of bauxites is extracted, and the quantitative relationships between bauxites, and temperature, precipitation and vegetation are established. We show that bauxites formed with an annual mean temperature of 24.8 °C and precipitation of 1097 mm y-1 after 250 Ma. The climatic variations of bauxites are due to land distribution, climate states, and vegetation coverage. Our research results provide a new understanding of the mineralization of bauxites, and also offer a reference for the exploration of bauxites.
How to cite: Bao, X.: Quantitative constraints on the environmental conditions of bauxite formation since Mesozoic , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20484, https://doi.org/10.5194/egusphere-egu25-20484, 2025.
Cretaceous Oceanic Red Beds (CORBs) represent important archives of paleoceanographic and paleoclimatic conditions during Earth’s greenhouse intervals. In this study, we focus on Upper Aptian and Upper Albian CORBs from the Trento Plateau (Southern Alps, NE Italy), integrating geochemical (ICP-OES, ICP-MS), rare earth element (REE), and thermomagnetic analyses to elucidate local and global factors controlling their deposition. Aptian CORBs exhibit higher and more variable oxygenation, favoring hematite formation and enrichment in light rare earth elements (LREEs), whereas Albian CORBs reflect slightly lower O2 levels and greater climatic stability. The absence of redox-sensitive elements such as Mo and Cr confirms that anoxia was not a limiting factor in either interval. Thermomagnetic data reveal incomplete magnetite oxidation in both Aptian and Albian samples, indicative of reduced oxygen availability during deposition. These depositional differences are linked to local tectonic subsidence of the Trento Plateau, which influenced sedimentation rates, as well as global climatic shifts following major Oceanic Anoxic Events (OAEs). Our multi-proxy approach highlights that, despite contrasting oxygenation histories, both intervals maintained sufficiently oxic bottom waters—whether through higher dissolved O2 or lower sedimentation rates—to enable the formation of CORBs. Our findings advance the understanding of mid-Cretaceous paleoceanography, demonstrating that CORBs can form under varying yet consistently oxic conditions, shaped by the interplay of tectonics, sediment supply, and climate feedbacks.
How to cite: Leone, S., Damaceno, M., Giorgioni, M., and Jovane, L.: CRETACEOUS OCEAN RED BEDS (CORBe) AND OXYGENATION: UNVEILING THE UPPER APTIAN AND UPPER ALBIAN PALEOCLIMATE AND PALEOCEANOGRAPHY, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1919, https://doi.org/10.5194/egusphere-egu25-1919, 2025.
The Indian Ocean, a crucial component of the global thermohaline circulation with a carbonate saturation state intermediate between the Atlantic and Pacific oceans, plays a vital role in climate variability. It serves as a major sink for atmospheric carbon dioxide (CO₂), sequestering approximately 20% of the world's anthropogenic carbon. However, a major gap exists in understanding the deep carbon cycle of the Indian Ocean because the evolution of deep-sea carbonate carbon reservoirs, as a key contributor to the long-term global carbon cycle, remains unknown across this ocean over the Cenozoic. Here, we present new regional carbonate compensation depth (CCD) reconstructions incorporating dynamic topography and eustasy impacts to quantify the storage and fluxes of carbonate carbon to the Indian seafloor since the early Cenozoic. The CCD is defined as the water depth at which carbonate supply from the surface is balanced with its dissolution, leading to the absence of carbonate components below the CCD. Due to the complexity of carbonate distribution across the Indian Ocean, we model the Cenozoic CCD across six regions: western North Indian, western and eastern equatorial Indian, western and eastern South Indian, and the Indian sector of the Southern Ocean. Utilizing updated age models and backtracking with lithology-specific decompaction from 118 deep-sea drill sites (DSDP, ODP, and IODP expeditions), we compute the CCD through a linear reduced major-axis regression of the carbonate accumulation rate (CAR) versus paleo-water depth. The regression analysis is carried out in 0.5 My time intervals. Our results illustrate distinct CCD patterns across the Indian Ocean, fluctuating regionally by ~1.5–2.5 km over the Cenozoic. The western equatorial Indian shows a long-term deepening trend from ~2.7 km at 44 Ma to ~4.9 at present, while the eastern equatorial maintains a deep CCD fluctuating between ~4.2 km and ~4.8 km since 19 Ma. The relatively shallow CCD of the Indian sector of the Southern Ocean, between ~2–4 km since 43 Ma, experiences pronounced variability across the Indian Ocean, indicating significant oceanographic changes and the complexity of diverse factors influencing the carbonate system in this high-latitude region. The highly variable CCDs across the Indian Ocean result in substantial regional heterogeneity in carbonate carbon flux corresponding to distinct oceanography characteristics such as deep-water carbonate chemistry and gradients of carbonate rain rate. The regional CCD models for the Indian Ocean are utilized to estimate the evolution of deep-sea carbonate carbon reservoir across the entire Indian during the Cenozoic in the context of the long-term global carbon cycle.
How to cite: Dalvand, F., Dutkiewicz, A., Wright, N. M., and Müller, R. D.: Carbonate Compensation Depth and Carbonate Carbon Flux in the Indian Ocean over the Cenozoic , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7951, https://doi.org/10.5194/egusphere-egu25-7951, 2025.
The Paleocene-Eocene Thermal Maximum (PETM, 56 Ma) is perhaps the most extensively studied paleoclimate event of massive carbon release because the intense global warming and widespread ocean acidification bear resemblance to the predicted worst-case near-future Earth conditions. While emission rate and carbon source were different from today’s perturbation, valuable lessons can be learned from studying the PETM. For instance, whether climate or carbon cycle feedbacks amplify or mitigate the environmental disruption, and what feedback processes contributed to the global climate response. In this study, we quantify the magnitude and sign of ‘net’ carbon cycle feedbacks by integrating: (1) estimates of volcanic carbon emissions from the North Atlantic Igneous Province (active ~56 Ma and considered a major source of carbon release), and (2) the net global environmental response recorded in paleoclimate records such as δ18O (temperature), δ11B (ocean pH), and δ13C (carbon cycle). The difference between the environmental response to volcanic emissions alone and the recorded global response is attributed to feedback processes. Our Earth system model results suggest that carbon release from positive carbon cycle feedbacks (e.g. non-volcanic) likely approached or exceeded volcanic emission rates at the onset of the PETM, raising pCO2 by 1330 ppm and the global temperature by 4.4°C. The ‘net’ feedback emissions are negative during the PETM recovery. Carbon isotopes indicate that a sustained low emission flux of isotopically light carbon is required to slow down the δ13C recovery driven by organic carbon burial, potentially pointing to additional thermogenic or biogenic methane release during the recovery phase.
How to cite: Vervoort, P., Doherty, D., Greene, S. E., Jones, S. M., Dunkley Jones, T., Gaskell, D., and Ridgwell, A.: Quantifying net carbon cycle feedbacks across the Paleocene-Eocene Thermal Maximum, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16652, https://doi.org/10.5194/egusphere-egu25-16652, 2025.
Long-term Cenozoic climate trends result from changes in the geological carbon cycle and associated surface input and output CO2 fluxes largely due to magmatic emissions and weathering of silicate minerals (Berner & Lasaga, 1989). Proxy records allow to detect absolute values of CO2 in different reservoirs to define major Cenozoic climatic events (e.g., PETM, EECO or MECO). However, interpreting the proxy-based time history of surface CO2 budget in terms of input and output CO2 fluxes is critical to assess the responsible processes behind the surface-deep carbon exchange and associated long term climate trends. Here, we use a newly developed technique (Castrogiovanni et al., 2024) based on a reversible-jump Markov chain Monte Carlo algorithm (rj-McMC) to invert the CO2 time series from the Proxy Integration Project (CENCO2PIP) (Hönisch et al., 2023) and obtain estimates of the surface input and output CO2 fluxes throughout the lower Cenozoic. We base the inversion on a general formulation of the geological carbon cycle and use the temperature time history from Hansen et al., 2023 as a further constraint to the inversion scheme. Results indicate a marked peak in the emission rate of CO2 at ˜56 Ma (PETM), enhanced CO2 emissions between 54-50 Ma (EECO) and at ˜40 Ma (MECO), whereas the output CO2 term associated to weathering responds to such variations of the input CO2 term. We conclude that magmatic CO2 emissions related to the closure of the Neo-Tethyan ocean and opening of the Nort-East Atlantic Ocean played a key role in driving lower Cenozoic climate trends.
References
Berner, R. A., & Lasaga, A. C. (1989). Modeling the Geochemical Carbon Cycle. 260(3), 74–81. https://doi.org/10.2307/24987179
Castrogiovanni, L., Sternai, P., Piana Agostinetti, N., & Pasquero, C. (2024). A reversible-jump Markov chain Monte Carlo algorithm to estimate paleo surface CO2 fluxes linking temperature to atmospheric CO2 concentration time series. Computers & Geosciences, 105838. https://doi.org/10.1016/J.CAGEO.2024.105838
Hansen, J. E., Sato, M., Simons, L., Nazarenko, L. S., Sangha, I., Kharecha, P., Zachos, J. C., von Schuckmann, K., Loeb, N. G., Osman, M. B., Jin, Q., Tselioudis, G., Jeong, E., Lacis, A., Ruedy, R., Russell, G., Cao, J., & Li, J. (2023). Global warming in the pipeline. Oxford Open Climate Change, 3 (1). https://doi.org/10.1093/OXFCLM/KGAD008
Hönisch, B., Royer, D. L., Breecker, D. O., Polissar, P. J., Bowen, G. J., Henehan, M. J., Cui, Y., Steinthorsdottir, M., McElwain, J. C., Kohn, M. J., Pearson, A., Phelps, S. R., Uno, K. T., Ridgwell, A., Anagnostou, E., Austermann, J., Badger, M. P. S., Barclay, R. S., Bijl, P. K., … Zhang, L. (2023). Toward a Cenozoic history of atmospheric CO2. Science, 382 (6675). https://doi.org/10.1126/SCIENCE.ADI5177/SUPPL_FILE/SCIENCE.ADI5177_SM.PDF
How to cite: Castrogiovanni, L., Sternai, P., Pasquero, C., Piana Agostinetti, N., Vaes, B., and Longman, J.: Input and output fluxes of surface CO2 throughout the lower Cenozoic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8497, https://doi.org/10.5194/egusphere-egu25-8497, 2025.
The Approximate Partial Radiative Perturbation (APRP) method is a powerful tool for investigating the effects of changes in cloud characteristics, driven by increased CO2 levels, on planetary albedo. The northern polar region is particularly sensitive to climate change. However, the summer temperature rise over the Arctic Ocean is relatively mild, and the mechanisms that suppress temperature increases are not fully understood.
We apply the APRP method to an ensemble of models participating in the Eocene Deep-Time Model Intercomparison Project (DeepMIP) and compare the effects of summer cloud feedback changes in the polar region to CO2 level increases from 1× pre-industrial (PI) level to 3/4× PI for both Eocene and modern conditions across the ensemble.
Our results reveal a wide range of results, both in magnitude and in sign (warming/cooling) of radiative changes, between models and even within the same models across different timeslices. Changes in cloud scattering are the primary contributors to the inter-model spread of cumulative APRP cloud effects. This spread is further amplified by differences in the sign of APRP cloud absorption effects.
In contrast, the models provide relatively consistent results for APRP cloud fraction effects, with most simulating modest positive feedback from cloud fraction changes due to CO2 increases. Nevertheless, the cumulative APRP cloud effects are minor compared to the net ocean-atmosphere energy flux changes over an ice-free Arctic Ocean. These fluxes might play a dominant role in inhibiting summer temperature increases in the polar region under elevated CO2 levels.
How to cite: Niezgodzki, I., Knorr, G., Lunt, D., and Lohmann, G.: Comparison of APRP cloud feedbacks to CO2 level rise on the summer Arctic climate across the Eocene Deep-Time Model Intercomparison Project ensemble, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6251, https://doi.org/10.5194/egusphere-egu25-6251, 2025.
The Eocene-Oligocene Transition (EOT; ~34 Ma) is one of the most significant climate shifts of the Cenozoic era, representing the transition from the last warmhouse state to a coolhouse state. The EOT had a significant impact on terrestrial ecosystems and was synchronous with the "Grande Coupure", a major episode of faunal turnover in western Europe associated with the influx of multiple clades of Asian tetrapods. The impact of the EOT displays considerable regional variability in sedimentary records, and its role in the opening of dispersal corridors for the Grande Coupure remains unclear.
In this study, we use sedimentology, magnetostratigraphy, biostratigraphy, and U-Pb geochronology to date a section comprising the EOT in the Çiçekdağı Basin, in central Anatolia, a region that sits on Balkanatolia, a biogeographic province proposed as a secondary dispersal pathway for the Grande Coupure that remains largely understudied. We then analyze stable and clumped isotopes from pedogenic carbonates to investigate the local paleoenvironmental evolution through the EOT.
Our record captures a fluvio-lacustrine system spanning the Priabonian and the lower Rupelian, including the Oi-1 glaciation (~33.65Ma). Our sedimentological analyses reveal significant paleoenvironmental changes, including a major sedimentary unconformity in the latest Priabonian interpreted as a lake retreat related to a regional increase in aridity. This event also marks the onset of a long-term aridity trend in our stable isotope data. Furthermore, the stable and clumped isotopes analysis provide preliminary surface temperature estimates (Δ₄₇)discuss the implications of these paleoclimatic findings for understanding the environmental drivers behind faunal dispersals of the Grande Coupure.
Keywords: Paleogene, EOT, Pedogenic carbonates, Anatolia, Clumped isotopes, Stable isotopes, Dispersals.
How to cite: Botté, P., Licht, A., Montheil, L., Jourdan, A.-L., Demory, F., Kaya, M., Ocakoğlu, F., Akkiraz, M. S., İbilioğlu, D., Coster, P., Métais, G., Raynaud, B., and Beard, K. C.: The Eocene-Oligocene Transition in Central Anatolia: lake retreats and increased aridity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6438, https://doi.org/10.5194/egusphere-egu25-6438, 2025.
The Langhian (15.98–13.82 Ma) was a stage of the mid-Miocene characterized by atmospheric CO2 levels higher than those of the present day and significantly warmer surface temperatures. Growing interest in the mid-Miocene arises from its potential as an analog for future climate scenarios. In this study, we conducted Langhian simulations using the climate model CESM1.2 and a new and unpublished geography, comparing them to simulations submitted for the Miocene Modeling Intercomparison Project Phase 1 (MioMIP), which utilizes the geography of Burls et al. (2021). The global mean surface temperature anomaly is similar for both geographies, averaging +5.5°C relative to pre-industrial levels, but exhibits strong local differences due to variations in ice sheets, topography, and bathymetry. A notable feature of our simulations is significant cooling in the northern Atlantic Ocean, driven by a collapse of the Atlantic meridional overturning circulation. Conversely, a strong Pacific meridional overturning circulation emerges, a phenomenon less commonly observed in other Miocene simulations. We further explore the sensitivity of the Langhian climate by varying CO2 concentrations, removing the Antarctic ice sheet, adjusting cloud parametrization, and incorporating dynamic vegetation. This study reveals a wide range of climate responses, emphasizing the critical influence of geography and other uncertain boundary conditions in achieving realistic Miocene climate simulations and improving data-model comparisons.
How to cite: Renoult, M. and de Boer, A.: Paleogeography and boundary condition sensitivities in mid-Miocene climate simulations with CESM1.2, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2832, https://doi.org/10.5194/egusphere-egu25-2832, 2025.
The late Miocene was an important stage for the formation of modern-like ecological and environmental patterns. Proxy data from the middle to late Miocene reveal that large-scale cooling and drying occurred, however, the reasons for this climate transition remain unclear. Through a compilation of proxy data and climate simulations, our results indicate that atmospheric CO2 decline markedly decreased the temperature and reduced the precipitation in most of the land area, while the paleogeographic changes enhanced cooling at northern high latitudes and increased precipitation in East Asia, East Africa and South America. In comparison, vegetation changes accelerated cooling at northern high latitudes and modulated precipitation at low- and mid-latitude continents. This deepens the understanding of the mechanism of the late Miocene climate transition.
How to cite: Zhang, R.: The role of vegetation feedback during the late Miocene climate transition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8336, https://doi.org/10.5194/egusphere-egu25-8336, 2025.
The control of the eccentricity on annual mean insolation is minimal. Yet, substantial variability in eccentricity timescales, especially the 400-kyr cycle, has been observed in tropical hydroclimate records. As suggested, this variability may have been significantly driven by long-term carbon cycle changes during the Plio-Pleistocene.
We present results from well-dated high-resolution paleoclimate proxies during the Plio-Pleistocene and an unprecedented transient climate simulation conducted with NCAR’s realistic Community Earth System Model version 1.2; the latter covers the climate history of the past 3Myr. The analyses of existing carbon isotope records (i.e., planktic and benthic δ13C) from deep marine sediment cores and other paleoclimatic (terrigenous dust flux) archives from the tropical ocean during the Pliocene and early Pleistocene (>1.5 Myr) reveal clear 400-kyr climate signals, suggesting eccentricity-paced changes in the long-term carbon cycle. Our model simulates 400-kyr variability in tropical hydroclimate. However, the climatic control on the robust feature of the carbon cycle (i.e., the 400-kyr oscillation) and its role and dynamics during the Plio-Pleistocene needs to be better understood. Our study investigates the interaction processes between various paleoenvironmental records and further focuses on different hypotheses following the antiphase relation of marine δ13C with the eccentricity cycle. First, we provide a combined perspective on the role of atmospheric circulation and, thus, dust in the dynamic of the carbon cycle and productivity. Also, come up with causes and links with the pacing of the carbon cycle and the ocean’s role. Second, assess the ecosystem response (vegetation) to changes in precipitation in connection with changes in atmospheric CO2.
How to cite: Jadhav, J., Timmermann, A., Sinha, N., and Yun, K.-S.: Elucidating the mechanisms of 400-kyr tropical hydroclimate variability during the Plio-Pleistocene, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3420, https://doi.org/10.5194/egusphere-egu25-3420, 2025.
Ocean interior acidification is predicted to exacerbate in the future due to persistent emissions of anthropogenic carbon dioxide (CO₂), which may excert disastrous impact on marine ecosystems. However, whether this trend is ubiquitous in the global oceans is not well understood. In this study, we reconstruct the pH changes of intermediate water in the northern South China Sea (SCS) since the Pliocene using bacterial branched glycerol dialkyl glycerol tetraethers. The results indicate a significant decline in pH during the Pliocene-Pleistocene transition, when atmospheric CO₂ was decreasing and thus not conductive to pH drop. We examined the controlling factors and found that weakened vertical mixing between intermediate and deep waters during this period played a crucial role in the decrease of intermediate water pH, rather than the influence by changes in atmospheric CO₂. Our findings highlight the effect of stratification of the ocean interior on the balance of the carbonate system in the SCS, which has been overlooked in modern observations and projections.
How to cite: Zhao, M., Cao, J., and Jia, G.: Enhanced acidification of intermediate water in the South China Sea during the Pliocene-Pleistocene transition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14215, https://doi.org/10.5194/egusphere-egu25-14215, 2025.
New Guinea represents an important potential influence over the consumption of atmospheric CO2 and global climate because of its large size, rapid erosion and strongly mafic composition. A new sediment record documenting erosion in northern New Guinea since 350 ka shows that stronger rain during interglacial times erodes more accreted continental crust than mafic arc crust. Although sediment is altered more during interglacials, this change in provenance results in a greater impact on the amount of CO2 consumed per unit weight. Thus silicate weathering is less efficient at removing CO2 when global climate is warmer, leaving more greenhouse gas in the atmosphere. New Guinea’s climatically modulated erosion thus acts as an amplifier of global climate variations on orbital timescales.
How to cite: Du, Y. and Clift, P. D.: Lower CO2 consumption from chemical weathering during warmer climates in North New Guinea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-116, https://doi.org/10.5194/egusphere-egu25-116, 2025.
The response of vegetation to past global warming, as revealed by geological records, can provide insights into future changes. We used pollen records to reconstruct spatial changes in the boundary between steppe and forest/forest-steppe for the Last Glacial Maximum (LGM), mid-Holocene, Last Interglacial (LIG), and mid-Pliocene, representing major changes in global temperature. The results showed that in the region east of 110° E, the trend of the boundary between steppe and forest/forest-steppe rotated anticlockwise by around 30°, 5° and 10°, during the warm periods of the mid-Holocene, LIG, and mid-Pliocene, relative to the LGM, mid-Holocene, and LIG, respectively. However, in the region west of 110° E, the boundary remained stationary during the mid-Holocene compared with the LGM, while it shifted northward during the LIG relative to the mid-Holocene, and it shifted southward during the mid-Pliocene relative to the LIG. Overall, our results indicate an enhanced east-west climatic contrast in northern China under past global warming. Climate simulation results showed that the warming-induced northward shift and westward extension of the western Pacific subtropical high promoted the northwestward displacement of the East-Asian monsoon rainfall belt. This suggests that in the future, under a warmer climate, the eastern region of northern China will become wetter, and that the extent of sandy desert will decrease.
How to cite: Huang, X., Yang, S., Jiang, W., Ding, M., Wang, Y., Sun, M., and Zhang, S.: Evidence for the enhancement of east–west climatic contrast in northern China under past global warming: paleovegetation records and numerical simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1207, https://doi.org/10.5194/egusphere-egu25-1207, 2025.
