Storing carbon in the deep ocean is a key-feedback mechanism that allows astronomical forcing to drive the late Pleistocene glacial/interglacial variations. As carbon storage is intrinsically linked to oxygenation, proxies for sediment oxygenation have been used to quantify changes in carbon storage during the late Pleistocene. However, evidence for astronomically-paced changes in carbon storage beyond the late Pleistocene is limited, hindering our understanding of the stability of this feedback mechanisms.

Here we used molecular fossils (biomarkers) in marine sediment cores that span the last ~3.5 million years to assess the long-term impact of astronomical forcing on deep ocean oxygenation, and hence carbon storage, and explore the stability of this deep ocean feedback mechanism. Using high-resolution records from three independent cores from the North Atlantic, we find that the concentration of biomarkers from anaerobic bacteria is eccentricity paced during the middle and late Pleistocene with high abundances during glacials and absence during interglacials. We interpret this data to reflect a decrease in oxygenation and hence increase in carbon storage during the most recent glacials. Across the MPT this pacing changes to obliquity forcing and we show that this forcing is persistent into the late Pliocene, highlighting the stability of this feedback mechanism. However, prior to 2.7 Myr we find no biomarkers of anaerobic bacteria across the North Atlantic, suggesting reduced carbon storage prior to the intensification of the glaciation of the Northern Hemisphere. Our findings indicate that the lowering of atmospheric CO₂ by the sequestration of carbon in the deep ocean in response to astronomical forcing persisted throughout the Quaternary and was essential for the development of Plio/Pleistocene ice ages, but this feedback mechanisms did not persist into the warm Pliocene.

How to cite: Naafs, D., Pancost, R., Blewett, J., Lauretano, V., Hefter, J., Pounton, S., Stein, R., and Haug, G.: The long-term stability of the deep ocean carbon storage feedback mechanisms across the Plio- and Pleistocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2331, https://doi.org/10.5194/egusphere-egu23-2331, 2023.

The dynamical evolution of the solar system is chaotic with a Lyapunov time of only ~5 Myr for the inner planets. Due to the chaos it is fundamentally impossible to accurately predict the solar system's orbital evolution beyond ~50 Myr based on present astronomical observations. We recently developed a method to overcome the problem by using the geologic record to constrain astronomical solutions in the past. Our resulting optimal astronomical solution (called ZB18a) shows exceptional agreement with geologic records to ~58 Ma (Myr ago) and a characteristic resonance transition around 50~Ma. Here we show that ZB18a and integration of Earth's and Mars' spin vector based on ZB18a yield reduced variations in Earth's and Mars' orbital inclination and Earth's obliquity (axial tilt) from ~58 to ~48 Ma. The changes in the obliquities have important implications for the climate histories of Earth and Mars. For instance, reduced variations in Earth's obliquity from ~58 to ~48 Ma would have affected Earth's climate across the late Paleocene - early Eocene (LPEE). Remarkably, a nearly ubiquitous phenomenon in long-term geologic records across the LPEE is a very weak or absent obliquity signal. We propose here that the reduced amplitude in Earth's obliquity, as predicted by our astronomical solution ZB18a, contributed to the weak/absent obliquity signal in geologic records from ~58 to ~48 Ma. Dynamical chaos in the solar system hence not only affects its orbital properties, but also the long-term evolution of planetary climate through eccentricity and the link between inclination and axial tilt.

How to cite: Zeebe, R.: Missing Obliquity Signal in Late Paleocene and Early Eocene Climate Records due to Solar System Chaos, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3965, https://doi.org/10.5194/egusphere-egu23-3965, 2023.

It is commonly accepted that the Milankovitch cycles have modulated the glacial-interglacial cycles during the Quaternary Period. However, how the climate during the Neoproterozoic snowball Earth events, the most extreme glaciations that have occurred on Earth, was affected by the orbital forcings remains largely unclear. Especially, whether the snowball Earth deglaciation might occur more easily at some orbital configurations than others is an important question. Here a coupled atmosphere-land model (CAM3 and CLM3) is used to investigate the response of temperature and hydrological cycle during a snowball Earth to this forcing at an atmospheric CO₂ level of ~0.1 bar. To simplify the analysis, we have chosen to remove the continents. The results show that the climate is very different under different orbital configurations. The globally averaged annual surface temperature can differ by 2.4 °C while the difference in the monthly mean can reach 3.7 °C in the subtropical region. Surprisingly, we find that the Milankovitch theory does not only work in the extratropical region but also in the tropics; the snow thickness in the tropical region is inversely proportional to the summer insolation received in this region. After adding an explicit meltpond module, we find that the threshold CO₂ that is needed to trigger the deglaciation may be reduced from 0.12 bar (low eccentricity) to 0.07 bar (high eccentricity). Moreover, the summer insolation in the tropics is more important than that in the subtropical region for the formation of a perennial meltwater belt. Hence, we conclude that the orbital forcing is important to the snowball Earth climate at its late stage and would assist Earth to get out of this state when the eccentricity was high.

How to cite: Wu, J. and Liu, Y.: Response of the Snowball Earth Climate to Orbital Forcing at High CO2 Level, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4198, https://doi.org/10.5194/egusphere-egu23-4198, 2023.

The Sahara region has experienced periodic wet periods over the Quaternary and beyond. These North African Humid Periods (NAHPs) are astronomically paced by precession which controls the position of the African monsoon system. However, most IPCC-class climate models cannot generate enough precipitation to reconcile the magnitude of these events and so the driving mechanisms remain poorly constrained. Here, we present an 800kyr climate dataset produced using a recently developed version of the HadCM3B coupled climate model that simulates 20 NAHPs over the past 800kyr which have good agreement with the timing and amplitude of NAHPs identified in proxy data. Our results confirm that precession determines their pacing, but we identify that their amplitude is strongly linked to eccentricity via its control over ice sheet extent. During glacials, cooling due to enhanced ice-sheet albedo suppresses the amplitude of the NAHPs during periods of precession minima. Our results highlight the importance of both precession and eccentricity, and the role of high latitude processes in determining the timing and amplitude of the NAHPs. This may have implications for the out of Africa dispersal of plants and animals throughout the Quaternary.

How to cite: Armstrong, E., Tallavaara, M., Hopcroft, P., and Valdes, P.: North African Humid Periods over the past 800000 years – Timing, Amplitude and Forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5479, https://doi.org/10.5194/egusphere-egu23-5479, 2023.

The last 30 million years (Myr) of Cenozoic climate change broadly charted the transformation from a world with solitary Antarctic ice sheets through to a bipolar glaciated Earth. Highly resolved records of carbonate content (%CaCO₃) provide insight into regional impacts of ever shifting climate, cryosphere and carbon cycle interactions. Here, we use X-ray fluorescence (XRF) ln(Ca/Fe) data collected at Ocean Drilling Program Site 1264 (Angola Basin side of Walvis Ridge, SE Atlantic Ocean) to generate the first SE Atlantic %CaCO₃ record spanning 30-0 Myr ago (Ma). Minimal changes in terrigenous-derived XRF data supports that the %CaCO₃ reflects the balance between productivity and dissolution in this region. This XRF data also helped to formulate a comprehensive and continuous depth and age model for the entirety of Site 1264 (~316 m; 30-0 Ma). These verified depth and age models constitute a key framework for future palaeoceanographic studies at this location.

We identify three phases with distinctly different orbital imprints of CaCO₃ deposition in the SE Atlantic. The shifts between these phases broadly occur across major developments in climate, the cryosphere and/or the carbon cycle: 1) strong ~110 kyr eccentricity pacing prevails during Oligo-Miocene global warmth (~30-13 Ma); 2) eccentricity-modulated precession imprints more strongly after the mid Miocene Climate Transition (mMCT) (~14-8 Ma); 3) strong obliquity pacing prevails in the late Miocene (~7.7-3.3 Ma) following widespread cooling and the increasing influence of high-latitude processes.

The lowest %CaCO₃ (92-94%) occur between 18.5-14.5 Ma, potentially reflecting increased dissolution or decreased productivity driven by widespread early Miocene warmth. Deposition recovered after the mMCT (~14 Ma), likely associated with changes in regional surface and/or deep-water circulation following Antarctic reglaciation. The highest Site 1264 %CaCO₃ and MARs indicate the late Miocene Biogenic Bloom (LMBB) occurs between ~7.8-3.3 Ma. The LMBB’s onset (~7.8 Ma) and peak productivity (~7 Ma) at 1264 are contemporaneous with the LMBB in the equatorial Pacific Ocean; however the termination is ~1 Myr later in the Atlantic compared to the Pacific. Globally synchronous patterns in the LMBB, including the onset and peak, may be driven by an increased nutrient input into the global ocean, for instance from enhanced aeolian dust and/or weathering fluxes. Regional diachrony and variability in the LMBB’s expression may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation during the latest Miocene.

How to cite: Drury, A. J., Liebrand, D., Westerhold, T., Beddow, H. M., De Vleeschouwer, D., Hodell, D. A., Rohlfs, N., Wilkens, R. H., Lyle, M., Bell, D. B., Kroon, D., Pälike, H., and Lourens, L. J.: Orbital pacing of Southeast Atlantic carbonate deposition since the Oligocene (30-0 Ma): tracing entwined climate and carbon cycle interactions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9202, https://doi.org/10.5194/egusphere-egu23-9202, 2023.

The Saharo-Arabian desert is part of the largest near-continuous chain of drylands stretching from north-western Africa to the northern China. This harsh and often hyper-arid belt acts as a transition zone separating major biogeographic realms, including the Palearctic, Afrotropics and Indomalayan. This aridity is thought responsible for the creation of unique geographic endemism between Africa and Eurasia. However, there are no direct hydroclimate records from the Arabian hyper-arid interior before the mid-Pleistocene, leaving the terrestrial hydroclimate and the role of Arabia as a biogeographic crossroads or barrier largely unknown.

We use desert speleothems preserved from the northern Arabian interior to identify past humid phases over the last 8 million years. These are particularly useful terrestrial climate archives as they act as underground rain gauges, requiring a minimum of ~300 mm a^-1 precipitation, pedogenesis and vegetation cover to form. Moreover, they can be accurately and precisely dated and are subsequently a valuable tool in identifying past large-scale hydrological and vegetation changes in ancient drylands. Our data reveal evidence of multiple ‘windows of opportunity’ of climate amelioration, allowing biogeographic exchange and dispersals to occur across the Arabian hyper-arid zone. Further, the novel analyses of the isotopic composition (d¹⁸O and d²H) of speleothem fluid inclusion waters, representing ‘fossil rainwater’, reveal the diminishing influence of tropical rain-belt precipitation in Arabia across Earth’s transition from a largely ‘ice-free’ northern hemisphere to an ‘ice-age’ world. The extent of Arabian aridity may thus be important in controlling biogeographic dispersals through the Arabian corridor, becoming increasingly less favourable through time. This is supported by fossil evidence which suggest that exchange between biogeographic regions across the Old World Savannah Biome were favoured in the Late Miocene, but became increasingly latitudinally fragmented from the Pliocene onwards. These results have significant implications for understanding the drivers of dryland aridity in non-polar deserts globally. 

How to cite: Markowska, M., Vonhof, H. B., Groucutt, H. S., Petraglia, M. D., Scholz, D., Weber, M., Gerdes, A., Martinez-Garcia, A., Stewart, M., Martin, A. N., Drake, N., Breeze, P. S., Nicholson, S. L., Fleitmann, D., and Haug, G.: Recurrent humid phases interrupt an overall aridity trend in Arabia over the past 8 million years creating windows of opportunity for biogeographic dispersals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9980, https://doi.org/10.5194/egusphere-egu23-9980, 2023.

The fluctuating climatic conditions of the Saharo-Arabian desert belt are increasingly important for both palaeoclimatic and palaeoanthropological debates. Currently, Saharo-Arabia acts as a vast biogeographic barrier between the Afrotropical and Palaearctic realms. On orbital timescales, northward incursions of the African (ASM) and Indian (ISM) Summer Monsoons activated fluvio-lacustrine systems and led to the formation of grassland habitats. The formation of these habitats has been considered a crucial factor in Homo sapiens dispersals into the Saharo-Arabian deserts and beyond. The so-called “northern route” favours a terrestrial dispersal through green palaeohydrological corridors. However, a maritime “southern route” during the sea-level low-stand of Glacial Termination-II (T-II) has also been proposed. The precise phasing between the onset of wetter conditions and rising sea-levels may thus be a crucial factor for testing these alternative hypotheses. Here, we present a precisely dated high-resolution (<100 yrs) stalagmite record from Mukalla Cave, Yemen, at a key location on the “southern route”. Wetter conditions in Southern Arabia prevailed from ~127.7 to ~121.1 ka BP and occurred when sea-levels were already higher than at present, revealing a phase-lag of several thousand-years between sea-level rise and the onset of pluvial conditions. This lag is likely related to the colder conditions of Heinrich Stadial-11, which supressed the interhemispheric pressure gradient and the ASM and ISM throughout T-II despite rising insolation. δ¹⁸O_ca values indicate rainfall intensity during the ~127.7 to ~121.1 ka BP interval 1) followed low-latitude insolation, and 2) was the greatest in the last 130,000 years.  Additionally, a mixed C3/C4 grassland environment, as revealed by stalagmite δ¹³C_ca values, was present in the now desert interior of Yemen. Combined with archaeological evidence, we discuss the potential implications our results have for H. sapiens biogeographical shifts and dispersal processes across Saharo-Arabia during early MIS 5.

How to cite: Nicholson, S., Jacobson, M., Groucutt, H., Markowska, M., Vonhof, H., Hosfield, R., Pike, A., Burns, S., Matter, A., and Fleitmann, D.: Last Interglacial Saharo-Arabian palaeoclimate variability and Homo sapiens dispersal: insights from the speleothem record of Southern Arabia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10195, https://doi.org/10.5194/egusphere-egu23-10195, 2023.

During the Mid Pleistocene Transition (MPT; 1.2-0.7 Ma) the periodicity of glacial cycles changed from 40 ka to ~100 ka, without a coinciding change in orbital forcing. The MPT therefore results from feedback and changes in the climate system and ice dynamics triggered by the changes in radiative forcing. However, it remains unclear which physical processes are critical for the transition.

Here we explore the role of basal sliding and glacial isostatic adjustment (GIA) in the MPT. Basal sliding is thought to have changed across the MPT due to the erosive action of the ice sheets gradually removing the regolith cover and exposing the underlying bedrock, therefore increasing the friction at the base. GIA modulates this effect by enabling the formation of large proglacial lakes, changing the ice margin from a land-based to a marine environment. We simulate the evolution of the Northern Hemisphere ice sheets during the past 1.5 million years, using an ice-sheet model forced by a climate matrix method.

We show that changing the basal friction has an effect on glacial terminations and consequentially glacial cycle periodicity. Larger friction leads to thicker ice sheets that are more likely to survive a climatic optimum. However, we show that using an unchanging friction coefficient through the Pleistocene, our model still produces change from 40 ka to 100 ka periodicities signifying the MPT. This suggest that the regolith hypothesis is not necessary to explain the MPT.

In addition, we show that the formation of proglacial lakes is required for achieving a full deglaciation of the large Late Pleistocene ice sheets. Ice that floats on water experiences no friction at the base, resulting in high ice velocities. This results in more ice in lower regions and enhances the melt of ice. Here, we find a strong modulating role of GIA. When neglecting bedrock adjustment, thus preventing the formation of large proglacial lakes, we fail to simulate a full deglaciation.

How to cite: Scherrenberg, M. D. W., van de Wal, R. S. W., and Berends, C. J.: A song of ice and friction: the impact of basal friction and proglacial lakes on Pleistocene glacial cycles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12664, https://doi.org/10.5194/egusphere-egu23-12664, 2023.

Cyclostratigraphy and astrochronology are leading methods for determining geologic time. While this technique is dependent on the accuracy of astronomical calculations, the chaos of the solar system limits the confidence of these calculations when applied to ancient periods. High-resolution paleoclimate records, such as those found in Middle Eocene drift sediments from the Newfoundland Ridge (Integrated Ocean Drilling Program Sites (IODP) Expedition 342), offer a unique opportunity to reverse this approach. These sediments, with their high sedimentation rates and distinct lithological cycles, provide an ideal setting for this type of study. However, the stratigraphies of IODP Sites U1408-U1410 are complex and contain several hiatuses. We have overcome this challenge by creating a composite of the two sites and constructing a conservative age-depth model. This has allowed us to create a reliable chronology for this high-resolution sedimentary archive. We have used two different techniques to extract astronomical components (g-terms and precession constant) from proxy time-series, which have produced consistent results. Our study has found that astronomical frequencies are up to 4% lower than those reported in astronomical solution La04. These results provide new constraints on the variability of g-term on million-year timescales, as well as evidence that the g4-g3 "grand eccentricity cycle" may have had a 1.2-Myr period around 41 Ma, instead of its current 2.4-Myr periodicity. Our estimates of the precession constant also confirms previous indications of a relatively low rate of tidal dissipation in the Paleogene. The Newfoundland Ridge drift sediments thus offer a reliable means of reconstructing astronomical components, providing a new target for future astronomical calculations.

How to cite: De Vleeschouwer, D., Penman, D., D'haenens, S., Wu, F., Westerhold, T., Vahlenkamp, M., Cappelli, C., Agnini, C., Kordesch, W., King, D., van der Ploeg, R., Pälike, H., Kirtland-Turner, S., Wilson, P., Norris, R. D., Zachos, J. C., Bohaty, S., and Hull, P.: North Atlantic Drift Sediments Constrain Eocene Tidal Dissipation and the Evolution of the Earth-Moon System., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12739, https://doi.org/10.5194/egusphere-egu23-12739, 2023.

The Sahel is highly sensitive to both floods and droughts, risking food and other resources on which nearly 100 million people depend. Understanding how natural variations of precipitation and vegetation fluctuate in response to orbital forcing across major shifts in boundary conditions, like temperature, ice volume, and land surface, can help constrain the regional sensitivity to a wide range of external forcings. However, these interactions between climate and ecosystem changes remain uncertain for sub-Saharan Africa due to the lack of long, highly resolved, quantitative, terrestrial records that span major global and regional shifts in deep time. Here we present leaf wax precipitation and vegetation records from targeted study windows throughout the last 25 million years, derived from long-chain n-alkane hydrogen (δD_wax) and carbon (δ¹³C_wax) isotopes, respectively, in a sediment core from ODP Site 959 in the Gulf of Guinea, where westerly winds and major river systems transport Western Sahel-sourced leaf waxes. Analyses of trend, amplitude of variability, and periodicity document a range of rainfall and vegetation responses to orbital forcings, depending on the specific boundary conditions of the study window. We find that the Western Sahel got wetter, yet more C₄-rich, over the Neogene. Orbital-scale precipitation was highly variable throughout the study periods, but particularly strong during the warm Miocene. While unlike many East African leaf wax isotope records that are precessionally driven, obliquity appears to play a role in the late Pleistocene, suggesting that climate-driving orbital parameters may vary regionally. Further, because of the high resolution and temporal coverage of these new biomarker isotope records, we can examine nonlinear relationships between precipitation and vegetation fluctuations, including prior to C₄-expansion when we find strong correlation despite minimal variation in δ¹³C_wax, advancing our understanding of climate and ecosystem feedbacks millions of years ago.

How to cite: Lupien, R., Uno, K., Kuzina, M., and de Menocal, P.: Terrestrial West African climate and environmental responses to orbital forcing across Neogene boundary condition changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12750, https://doi.org/10.5194/egusphere-egu23-12750, 2023.

Astronomical insolation forcing is an important driver of past and future climate and environmental change and acts on time scales from seasonality to millions of years. The amount of insolation the Earth’s surface receives affects, e.g., surface temperature, polar- and mountainous ice dynamics and oceanic circulation, which all shape Earth’s surface and climate variability on different time scales. Astrchronology is the field that uses geologic records of climate rhythms to quantify, with unprecedented accuracy, the transit of time through deep Earth history acting as powerful geo-chronometers for major geologic events.

Rhythmic sedimentary successions are very frequent in the geological records of North Africa, namely in Tunisia, which can often be attributed to cyclicities of orbital parameters driving Earth’s climate variability. Unlike Europe, China and USA, where cyclostratigraphic studies have extensively been carried out, examples of significant studies in North Africa are scares (e.g., Ben Ameur et al., 2022; Omar et al., 2021; Omar & Yaich, 2022; Thibault et al., 2016). Other studies were carried out but have almost exclusively been done using very classic and weakly significant paleoclimate proxies. Southern, central and northern Tunisia, where strongly cyclic sedimentary series were developed from the Ordovician to the Holocene, provides a powerful candidate for cyclostratigraphy with many Formations that were deposited during these times, and are amenable for integrated stratigraphy.

In this study, we investigate the feasibility of cyclostartigraphy on Phanerozoic cyclic strata in North Africa from outcropping series and well-logging data, covering a wide variety of paleoenvironments from continental deposits to deep basin sequences through hemi-pelagic sediments. The targeted geologic intervals are thoroughly chosen from Paleozoic, Mesozoic, Cenozoic and Quaternary. The main objectives are to (1) develop floating orbital scales for several Phanerozoic sedimentary rocks constituting potential source rocks feeding most of Tunisian petroleum reservoirs, (2) highlight currently under-investigated geologic intervals for cyclostratigraphy in Tunisia and (3) testify the most advanced techniques for astrochronology to decode the orbital periodicities potentially recorded within the studied sections.

Ben Ameur, Mariem et al. 2022. “Middle to Late Holocene Sedimentary Filling History of the Sebkha El Melah in South-Eastern Tunisia.” Sedimentology 69(5): 2348–66.

Messaoud, Jihede Haj, Nicolas Thibault, Chokri Yaich, and Johannes Monkenbusch. 2020. “The Eocene ‐ Oligocene Transition in the South ‐ Western Neo ‐ Tethys ( Tunisia ): Astronomical Calibration and Paleoenvironmental Changes Paleoceanography and Paleoclimatology.” : 1–25. https://doi.org/10.1029/2020PA003887.

Omar, Hamdi, Anne Christine Da Silva, and Chokri Yaich. 2021. “Linking the Variation of Sediment Accumulation Rate to Short Term Sea-Level Change Using Cyclostratigraphy: Case Study of the Lower Berriasian Hemipelagic Sediments in Central Tunisia (Southern Tethys).” Frontiers in Earth Science 9(March): 1–20.

Omar, Hamdi, and Chokri Yaich. 2022. Advances in Science, Technology and Innovation Orbital Tuning of the Berriasella Jacobi Ammonite Zone in Central Tunisia (Southern Paleotethys). Springer International Publishing. http://dx.doi.org/10.1007/978-3-030-72547-1_42.

Thibault, Nicolas et al. 2016. “The End-Cretaceous in the Southwestern Tethys (Elles, Tunisia): Orbital Calibration of Paleoenvironmental Events before the Mass Extinction.” International Journal of Earth Sciences 105(3): 771–95.

How to cite: Omar, H., Yaich, C., Fakhfakh, H., Boukhalfa, D., Ben Ameur, M., Lahmer, B., Akermi, W., Gharsalli, N., and Arfaoui, I.: Phanerozoic Cyclostratigraphy in North Africa: Case studies from Tunisia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13463, https://doi.org/10.5194/egusphere-egu23-13463, 2023.

The Late Devonian oceans were susceptible to the development of anoxic conditions, as evidenced by repeated widespread organic-rich shale deposition. Understanding how these anoxic facies were deposited will provide insight into Devonian climatic modes. To this end, we constructed a high-resolution cyclostratigraphic model based on portable XRF-generated elemental ratio records from a Frasnian-Famennian (~372 Ma) black shale section. These black shales are associated with the Kellwasser Crisis, one of the largest mass extinctions of the Phanerozoic, which is not fully understood to this day. The studied section at Winsenberg is located in the Rhenish Massif in Germany and represents a basinal setting at southern low paleolatitudes. Spectral analysis was carried out on the Si/Ca ratios generated by XRF, which is interpreted as the detrital (distal) vs carbonaceous (local) input. The resulting astrochronology suggests a duration of ca. 1 Myr from the base of the Lower Kellwasser to the F-F boundary at the top of the Upper Kellwasser level. This corresponds to an average sedimentation rate of 0.9 cm/kyr. Both the Lower and Upper Kellwasser shales occur at the onset of a 405 kyr eccentricity cycle. We further interpret the Ti/Al record as a riverine runoff signal, as Ti is associated with the coarse-grained fraction, and K/Al as a chemical weathering signal, as K is leached easier than Al. Both tuned records exhibit eccentricity-modulated precession cycles. On precession and short eccentricity timescales, Ti/Al and K/Al are positively correlated, suggesting an orbitally forced wet/dry monsoonal climate in the region where the section was deposited. On longer timescales, the weathering signal becomes decoupled from the riverine runoff signal, highlighting that K/Al (chemical weathering) decreased even during wetter periods. This decoupling is linked to soil maturation in the hinterland, as potassium leaching from mature soils became increasingly limited. Soil build-up and maturation forms a potential mechanism for nutrient storage and subsequent release into the ocean, potentially triggering eutrophication and anoxia.

How to cite: Wichern, N., Bialik, O., Percival, L., Kaskes, P., Nohl, T., Becker, T., and De Vleeschouwer, D.: Deciphering the role of terrestrial/atmospheric interactions in Late Devonian Kellwasser black shale deposition: A High-Resolution Cyclostratigraphic study of the Winsenberg section (Rhenish Massif, Germany), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13598, https://doi.org/10.5194/egusphere-egu23-13598, 2023.

In recent years, several groups have analyzed or re-analyzed stratigraphic data in order to derive astronomical information on the past evolution of the Earth-Moon system. Depending on the approach and on the type of sediment that is analyzed, the retrieved data are of different nature. For tidal deposits, one may attempt to obtain the number of lunar days in a lunar month, or the number of lunar months per year (e.g. Williams, 2000), or even retrieve the nodal period of the Moon (Walker & Zahnle, 1986). In contrast, for cyclostratigraphic analyses, the derived quantity is the precession frequency of the Earth (e.g. Meyers and Malinverno, 2018). The problem for the geologist is then to derive all the other parameters of the Earth-Moon system from this single initial observation. 
The AstroGeo tools (www.astrogeo.eu) are designed to help the geologists in this task by providing conversions from one geological proxy  to all the remaining parameters of the Earth-Moon system  that can be derived from this single observation.  These tools developed in the AstroGeo project rely on the physical model recently developed in Farhat et al. (2022). The AstroGeo lunar tool is the first of a series that will be available for the geologists and astronomers community. It allows to input any of the possible observables of the Earth-Moon system (age, semi-major axis, length of the day, precession frequency and angle of obliquity), with some uncertainty, and to derive all the other parameters by interpolating the results of Farhat et al. (2022). At the same time, new data can be plotted versus the nominal solution, together with the already known data that will be kept in an evolving data base. These tools will be available on the AstroGeo website (www.astrogeo.eu). I will present these new tools along with the recent progress of the AstroGeo project.

Ref : Farhat, M., Auclair-Desrotour, P., Boué, G., Laskar, J., 2022, The resonant tidal evolution of the Earth-Moon distance
 Astronomy & Astrophysics, 665, L1
https://www.aanda.org/articles/aa/pdf/2022/09/aa43445-22.pdf

How to cite: Laskar, J., Farhat, M., Boué, G., Auclair-Desrotour, P., Sinnesael, M., Gastineau, M., and Bendjeddou, S.: Past Evolution of the Earth-Moon System. The AstroGeo tools for geological proxies., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14200, https://doi.org/10.5194/egusphere-egu23-14200, 2023.

The mechanisms that amplify orbitally-driven changes in insolation and drive the glacial cycles of the past 2.6 million years, the Pleistocene, are poorly understood. Previous studies indicate that cloud-phase feedbacks oppose ice sheet initiation when orbital configuration supports ice sheet growth. Cloud phase was observationally constrained in a recent study and provides evidence for a weaker negative cloud feedback in response to carbon dioxide doubling. We observationally constrain cloud phase in the Community Earth System Model and explore how changes in orbital configuration impact the climate response. Constraining cloud phase weakens the negative high latitude cloud phase feedback and unmasks positive water vapor and cloud feedbacks (amount and optical depth) that extend cooling to lower latitudes. Snowfall accumulation and ablation metrics also support ice sheet expansion as seen in proxy records. This indicates that well-known cloud and water vapor feedbacks are the mechanisms amplifying orbital climate forcing.

How to cite: Hahn, L., Sagoo, N., Storelvmo, T., Tan, I., Danco, J., Raney, B., and Broccoli, A.: Observationally Constrained Cloud Phase Unmasks Orbitally Driven Climate Feedbacks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16726, https://doi.org/10.5194/egusphere-egu23-16726, 2023.

The mechanism of short-term and high-magnitude sea-level oscillation has long been debated between glacio- and aquifer-eustasy (Miller et al., 2005; Haq, 2014), largely due to the sparse robust evidence for the aquifer-eustasy, and the little knowledge about hydrological dynamics behind it. Non-marine/ continental greenhouse archives (e.g. lake level) and their temporal correlation to marine successions (e.g. sea level) could give clue to aquifer-eustasy (Wagreich et al., 2014). The Songliao Basin (SLB), in Northeast China, is one of the largest Mesozoic terrestrial inland basins and has deposited the near whole Cretaceous successions (Wang et al., 2013). The greenhouse Late Santonian-Early Campanian Lower Nenjiang Formation (K₂n¹⁺²), recovered from three boreholes in SLB provides a unique opportunity for validating and decoding the aquifer-eustasy. Initially the cyclostratigraphy of logging gamma ray (GR) and Thorium (Th) series from three boreholes was implemented, which in junction with the radioactive ages renewed the chronology framework of SLB. Using the astronomically tuned GR and Th series, the lake level of SLB, which is recovered from sedimentary noise modeling (Li et al., 2019) and presents the water table of groundwater reservoir, shows a clear out-of-phase relationship with the coeval sea level, validating the aquifer-eustasy hypothesis. The lake level shows prominent ~1.2Myr cycles and a well-coupled relationship with sea level and obliquity modulation, indicating that the orbital obliquity drove the lake level and modulated the water exchange between ocean and continent during the Cretaceous greenhouse period. The strong precipitation indicated by the negative excursion of Ostracods δ¹⁸O (Chamberlain et al., 2013) well correlates to the high lake level, high obliquity, and low sea level, suggesting that during obliquity modulation maxima, more moisture was precipitated into the high-latitude continents, consequently recharging the aquifer and raising the lake level while drawing down the sea level and vice versa. The close correspondence between reported marine incursion layers (Hu et al., 2015) and lowstand of sea level casts a doubt on marine incursion hypothesis in the SLB, more work is needed to reconcile this paradox. Overall, this study gives robust geological evidence for aquifer-eustasy and firstly decodes its role on Cretaceous short-term eustasy.

How to cite: Zhang, Z., Huang, Y., and Wang, C.: Obliquity-forced aquifer-eustasy during the late-Cretaceous greenhouse world, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17045, https://doi.org/10.5194/egusphere-egu23-17045, 2023.

The Miocene Climatic Optimum (MCO) is an intriguing period of global climate history. Spanning from approximately 17 to 14 Ma, the MCO saw increased concentrations of greenhouse gasses and a rise in global temperature of 6 to 7 degrees Celsius. The MCO disrupted the long-term cooling trend of the Cenozoic and is often invoked as a potential analogue for understanding contemporary global climate change. It is not well understood, however, if and how the dynamics that drove the MCO (e.g., orbital pacing) may have conditioned regional-scale climate phenomena, particularly those associated with the interior of continents. Here we establish detailed, orbital-scale, terrestrial environmental responses to the MCO using magneto-cyclostratigraphic chronology. We identify six drought events in the Asian interior that are associated with prominent δ¹³C positive excursions, δ¹⁸O cooling Mi-events, global SST and sea-level fluctuations, as well as with the 405-kyr eccentricity band. We also document antiphase variability of precipitation across the monsoon-westerly influenced boundary. We contend that a predominant long eccentricity signal was of overriding significance as an orbital factor in regulating the rhythm of climatic change during the MCO.

How to cite: cao, Y.: Predominant orbital forcing on Asian hydroclimate linked with deep-sea records during the Miocene Climate Optimum, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-194, https://doi.org/10.5194/egusphere-egu23-194, 2023.

We address the evolution of the shelf architecture of the Northeast Brazilian Equatorial Margin during the Plio-Pleistocene, using a coupled approach of sequence stratigraphy based on 3D seismic data, and cyclostratigraphy based on well-log data. The main purpose of this study is to highlight the major forcing processes that control evolution and architecture of the shelf during the Plio-Pleistocene.

Our results reveal nine pronounced seismic sequences within the Plio-Pleistocene series, which are correlated to the long 405-kyr eccentricity cycles. Inside the two youngest 405-kyr cycles, we observe nine Falling Stage System Tracts (FSST) matching the short (97-128 kyr) eccentricity cycles. Finally, we identify three major depositional episodes (mega-sequences) in the Plio-Pleistocene: (i) the first episode (from ~4 to ~2.4 Ma) is characterized by small amplitudes of sea-level variations with low to none erosive structures and the absence of clear transgressive series, (ii) the second phase (from ~2.4 to ~0.9 Ma) records a drastic increase of erosional features as well as the apparition of thicker transgressive series and slope failures, and (iii) the third phase (from ~0.9 to present-day) is characterized by a dramatic change in the shelf geometry, most of the sediments are deposited on the slope during FSST while the outer shelf is greatly exposed and eroded during low sea levels. Our results suggest that long-term increase in amplitude of sea level variation is the main driver of the geometrical changes of the Brazilian shelf.  

Boundaries of mega-sequences at 0.9 and 2.4 Ma likely reflect major climatic phases at respectively the Intensification of Northern Hemisphere Glaciation and the Mid-Pleistocene Transition. A significant change in the shelf architecture at around 0.4 Ma, acting as a prominent shift in the depositional system from one prograding to another aggrading, is likely related to the substantial sea-level rise together with the long-lasting Marine Isotopic Stage 11. We conclude that changes in the Brazilian shelf geometry during the Plio-Pleistocene was likely paced by orbitally forced sea-level cycles superimposed on long-term trends and phases in the climate and sea level.

How to cite: Tortarolo, L., Rabineau, M., Gorini, C., Boulila, S., Do Couto, D., Dos Reis, T., and Guizan Silva, C.: Orbital control of relative sea level changes in the Plio-Pleistocene of the Northeast Brazilian Equatorial Margin., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-227, https://doi.org/10.5194/egusphere-egu23-227, 2023.

Records from a wide range of geological archives covering the last few glacial-interglacial cycles show large inconsistencies in the East Asian summer monsoon variability, which severely hampers our understanding of the evolution and potential mechanisms of the regional East Asian climate on orbital timescales. Here, we examine the simulated temperature and precipitation in East Asia based on a series of equilibrium simulations conducted for the past 425 ka, and we investigate the sensitivity of temperature and precipitation to potential forcings. Our simulations show that, in East Asia, the seasonal mean temperature is dominated by a ∼20-kyr cycle, and the annual mean temperature (AMT) is dominated by a ∼100-kyr cycle, which is consistent with previous modeling efforts and geological reconstructions. Additional sensitivity experiments indicate that the greenhouse gas concentration, in combination with the ice volume, is the dominant force for the variations of AMT in East Asia on orbital timescales. For the precipitation in East Asia, our equilibrium simulations and additional sensitivity experiments, together with comprehensive model-data intercomparison analysis, suggest that the cycles of simulated annual mean precipitation over East Asia are highly model-dependent, although the dominant ∼20-kyr cycle in summer precipitation appears to be a robust feature. Overall, the results highlight the large model uncertainty with regard to the relative roles of forcings in hydroclimate variations in East Asia on orbital time scales. There is, therefore, an urgent need to implement more realistic precipitation schemes in models in order to decrease the model spread in simulated precipitation.

How to cite: Dai, G. and Zhang, Z.: Simulated cycles of East Asian temperature and precipitation over the past 425 ka, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4300, https://doi.org/10.5194/egusphere-egu23-4300, 2023.

The geometry of the Earth's orbit, and the movements around its axis, result in periodic changes in the solar radiation received by the Earth's surface. These cyclic variations throughout geologic time cause climatic changes that manifest in the hydrologic cycle and atmospheric and oceanic circulation. In turn, these processes result in sedimentary cycles that, although masked by diagenetic processes, record the Earth's orbital rhythm.

In the Middle Magdalena Valley Basin (VMM), the Cenomanian-Turonian interval is represented by the rocks of the La Luna Formation, which has a cyclic lithological character, since it consists of intercalation of limestones and shales rich in organic matter. 

This work seeks to understand the mechanisms that control cyclic sedimentation and organic matter accumulation in the Middle Magdalena Valley basin, as well as to calculate the temporal duration of stratigraphic cycles and determine whether these are related to eccentricity, obliquity, or precession. Also, We will compare with intervals in the tropical belt where previous studies have been carried out to determine whether the observed pattern is local (controlled by basin geometry) or regional (changes in the hydrological cycle caused by orbital parameters).

We present lithologic information from the Cenomanian-Turonian interval at Pozo la Luna-1, which has a thickness of 573 ft and consists of a succession of limestones with wackestone texture, locally with foraminiferal packstones, interbedded with thin to medium layers of marls and bentonites (<1cm).

Results from the δ13Corg content suggest that OAE2 is recorded in this section and is 69.18 ft thick with δ13C values between -27.18 and -23.94. Four phases of the OAE2 are interpreted: 1) build-up 2) Trough 3) Plateau and 4) Recovery. The time series analyses are developed in the "Astrochron" package (22). They are run on 1146 data of K/Th and Th/K ratios, distributed every 0.5ft. The methods "multi-taper method spectrogram of evolutive harmonic analysis", and "Evolutive average spectral misfit (eASM)" will be applied to detect the presence of cycles along the stratigraphic profile and to estimate their statistical significance compared to a noise level at different confidence intervals.

How to cite: Valencia Arias, C.: Orbital variations in the Cenomanian-Turonian, paleoclimatic implications and their relationship with the accumulation of organic-rich intervals in the Middle Magdalena Valley basin, Colombia., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10761, https://doi.org/10.5194/egusphere-egu23-10761, 2023.