Astronomical insolation forcing is well established as the underlying metronome of Quaternary ice ages and Cenozoic climate changes. Yet its effects on earlier eras (Mesozoic, Palaeozoic and pre-Cambrian) are less understood. In this Review, we explore how cyclostratigraphy can help to distinguish climate modes over the pre-Cenozoic era and aid our understanding of climate responses to astronomical forcing over geological time. The growing uncertainties with geologic age mean that pre-Cenozoic astronomical solutions cannot be used as tuning targets. However, they can be used as metronomes to identify the pacing of distinct climate states. Throughout the pre-Cenozoic, global average temperature differences between climate states were even more extreme (5–32 °C) than in the Cenozoic (14–27 °C), and these, combined with an evolving biosphere and changing plate tectonics, led to distinct Earth-system responses to astronomical forcing. The late Palaeozoic icehouse, for example, is characterized by a pronounced response to eccentricity, caused by nonlinear cryosphere and carbon-cycle behaviour. By contrast, the Devonian warmhouse and the Late Cretaceous hothouse featured recurrent episodes of marine anoxia that may have been paced by astronomical forcing. Formally defining 405,000-year eccentricity cycles as chronostratigraphic units (astrochronozones) throughout the Phanerozoic eon will enable a more comprehensive understanding of how astronomical forcing has shaped Earth’s climate over geologic time.

How to cite: De Vleeschouwer, D., Percival, L. M. E., Wichern, N. M. A., and Batenburg, S. J.: Pre-Cenozoic cyclostratigraphy and paleoclimate responses to astronomical forcing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17195, https://doi.org/10.5194/egusphere-egu24-17195, 2024.

The preservation of orbital signals in sedimentary records, a crucial aspect for the reliability of astronomical time scales, has been insufficiently explored, presenting challenges in interpretation. In this study, we focus on the effect of inconsistent sedimentation rates on the preservation of these orbital signals from a modeling perspective. We delve into how inconsistent sedimentation rates influence the retention of these orbital signals. Employing stochastic statistical models, our research simulates diverse sedimentary environments, we show that 405-kyr eccentricity tuning is the most reliable approach for constructing ATS among different tuning strategies, particularly in environments characterized by high energy conditions and unsteady sedimentation such as fluvial or deltaic settings. This discovery holds substantial importance in refining geological time scales. We introduce an innovative approach to evaluate sedimentation rates within these records. Our study demonstrates the robustness of the cyclostratigraphic method and deepens our understanding of the preservation of sedimentary records, thereby enriching our grasp of Earth's intricate geological past.

How to cite: Wang, M., Li, M., Hajek, E. A., Kemp, D. B., Wu, Y., Zhu, H., and Jin, Z.: Detection of orbital signals in the sedimentary record through stochastic statistical modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3705, https://doi.org/10.5194/egusphere-egu24-3705, 2024.

The climate variations in the past are strongly connected with the cycles of orbital forcing. The orbital forcing redistributes incoming solar energy on the Earth surface, especially over different latitudes. These cycles affect significantly seasons on millennial time scales. The most important influence on climate is provided by the variations of orbit eccentricity, obliquity and precession of Earth axis of rotation. The so-called Milankovitch cycles of eccentricity and obliquity are connected with the processes of glaciations during the last 3 Ma. Actually, all orbital cycles affect paleoclimate, where the effects of eccentricity dominate. The influence of orbital forcing on paleoclimate variations is investigated by two long time series of eccentricity from Laskar’s solution and sea level variations, reconstructed for the last 65 Ma. Common cycles of eccentricity and sea level in 18 different frequency bands are extracted by the Method of Partial Fourier Approximation. The short-periodical cycles, whose periods are below 400 kyr, have relatively good agreement for the last 3 to 7 Ma. The long-term oscillations of sea level and orbit eccentricity with periodicities between 0.8 Myr and 10.8 Myr have excellent agreement in 4 frequency bands, whose duration is 65 Myr. In other 5 frequency bands a good correlation exists for the last 35 – 40 Ma. The estimated amplitudes of sea level cycles are between 2 and 5 m with accuracy of about 0.4 m. The jumps inside of sea level time series are determined by a high-sensitive Method of Jump Detection, based on numerical integration of the time series. The detected jumps determine various data segments, whose duration is below 2.8 Myr and the rate of their linear trends is between 0.3 cm/kyr and 3 cm/kyr. The remarkable result is that all detected jumps occur during the extrema of eccentricity, while the jumps of sea level during glacial cycles in the last 3 Ma occur only in eccentricity minima. These results can help better understanding of climate response to orbital forcing. 

How to cite: Chapanov, Y.: Climate Variations Connected with Earth Orbit Eccentricity , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12267, https://doi.org/10.5194/egusphere-egu24-12267, 2024.

The Silurian Ireviken Event is a biogeochemical event characterised by extinctions among several marine groups and a major perturbation to the global carbon cycle. In the Altajme core from Gotland, Sweden, the associated Ireviken Carbon Isotope Excursion (ICIE) reaches peak values of ~6‰. Within the ICIE, the main peak of -6‰ (δ¹³C_carb) is superimposed by multiple short-term and small amplitude positive peaks (+1.00 ‰ δ¹³C_carb), while the tail of the main peak is superimposed by multiple small amplitude negative peaks (-1.55 ‰ δ¹³C_carb). To understand the processes behind these recurrent small amplitude peaks, the high-resolution XRF scanning data of the Altajme core were used to identify astronomical cycles to put astrochronological constraints on the δ¹³C_carb curve. Based on the XRF data and its resulting astrochronology, the small amplitude positive and negative δ¹³C_carb peaks occur during insolation minima in intervals enriched in carbonate relative to the surrounding lithology. The XRF proxy data indicates that during times when elevated carbonate content coincides with elevated δ¹³C_carb values, insolation minima induced an arid environmental state in the basin. This led to decreasing runoff and a strong anti-estuarine circulation, which in turn lowered pelagic productivity and increased photozoan carbonate production, resulting in the deposition of carbonates with elevated δ¹³C_carb values. This contrasts to the concomitant insolation maximum, which induced a semi-arid state in the basin, resulting in some runoff, a (sluggish) anti-estuarine circulation in the basin, some pelagic productivity and carbonates being primarily produced by heterozoans, resulting in the deposition of marly carbonates with low δ¹³C_carb values. The XRF proxy data indicates that during times when carbonate-rich intervals coincide with more negative δ¹³C_carb values, insolation minima induce a semi-arid state in the basin, resulting in some runoff, a (sluggish) estuarine circulation in the basin, some pelagic productivity and carbonates being primarily produced by heterozoans resulting in the deposition of marly carbonates with low δ¹³C_carb values. This contrasts with the concomitant insolation maximum which induced humid conditions in the basin, resulting in increased runoff, a (strong) estuarine circulation and high primary productivity, leading to the deposition of marly shales with higher δ¹³C_carb values. The shifting baseline climatic conditions during the Ireviken Event are inferred to have changed the response of the depositional environments to astronomical forcing, in changing (carbonate) productivity and circulation, which in terms modulated the carbon cycle, resulting in an imprint of astronomical cycles in the ICIE.

How to cite: Arts, M., Cramer, B., Calner, M., Rasmussen, C. M. Ø., and Da silva, A.-C.: Changes in the response of the carbon cycle to astronomical forcing during the Silurian Ireviken biogeochemical event, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18468, https://doi.org/10.5194/egusphere-egu24-18468, 2024.

The investigation into water circulation mechanisms within greenhouse environments, particularly their link to orbital forcing and consequent impacts on organism-environment coevolution, is garnering increased attention. A key uncertainty is the nature of variations in continental and oceanic water reservoirs on an ice-free Earth and the primary factors driving sea level changes. Traditional approaches like sequence stratigraphy and sedimentology have provided rough and limited insights, hindering a detailed and comprehensive understanding of water circulation in deep time. Therefore, high-resolution inversion of sea and lake level changes is vital for studying global hydrological cycle. Employing advanced sedimentary noise models (DYNOT and ρ₁), based on astrochronology and time-series analysis, this research reconstructs detailed water-level variations in key regions: the continental Songliao Basin of Northeast China, the marine Basque-Cantabric Basin in Spain, and the marine Espírito Santo Basin in the western South Atlantic, covering the entire Maastrichtian Stage to the Cretaceous-Paleogene (K-Pg) boundary. These reconstructions, corroborated by sedimentary facies analysis and paleosol studies, reveal 1.2 Myr and 2.4 Myr periodic variations in sea and lake levels, exhibiting a 'seesaw' pattern of opposite trends. This indicates that sea level fluctuations might be influenced by changes in continental water reservoir content, providing new insights into the complex interplay between terrestrial and marine hydrological systems.

How to cite: Ji, K., Li, M., Gong, F., Zhang, H., Yuan, S., and Zhang, D.: High-Resolution Sea and Lake Level Reconstructions of the Late Cretaceous: Evidence for a 'Seesaw' Ocean-Land Water Circulation Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9579, https://doi.org/10.5194/egusphere-egu24-9579, 2024.

The Qiangtang Basin, situated on the Tibetan Plateau, is a basin that contains hydrocarbons and has significant potential for hydrocarbon exploration. However, reconstructing sea-level changes and understanding the sedimentary evolution of the Qiangtang Basin has been hindered by the lack of robust high-resolution geochronology. Meanwhile, the Late Triassic stratigraphy of the Qiangtang Basin has also reported the Carnian pluvial episode, the driving mechanism of which is controversial. In this study, the cyclostratigraphy of the Late Triassic Boli La and Bagong Formations in the Qiangtang Basin was analyzed using high-resolution gamma-ray data. Time series analysis shows that there are 405 kyr eccentricity cycles in the gamma-ray data series. The gamma-ray series was tuned to 405 kyr. Then, we establish a floating astronomical timescale with a length of 17.04 Myr. This astronomical time scale establishes an anchored astronomical time scale using the age of the volcanic rocks found in the top of the Bagong Formation in the drill core as an anchor point. Using the anchored astronomical chronology, we reconstructed the Late Triassic sea level change in the Qiangtang Basin using a recently developed sediment noise model. The reconstructed sea level change is generally consistent with the global sea level curve. The antiphase relationship between the filtered long-term obliquity cycles and the sea-level curves reconstructed from the sedimentary noise model suggests that the long-term obliquity cycles may have been the main driver of the Late Triassic greenhouse sea-level change. Meanwhile, the modulation maxima of the long-term obliquity-modulated cycles correlate well with high sea level, episodic negative carbon isotope excursions, global warming, and marine biotic crises, suggesting that obliquity forcing may have played a prominent role during the Carnian Pluvial Episode. Our results suggest that orbital forcing enhanced the hydrological cycle during the Carnian Pluvial Episode. Our study provides a precise, high-resolution time scale for studying the sedimentary evolution of the Qiangtang Basin, as well as a broader perspective on the relationship between the Carnian Pluvial Episode and astronomical forcing.

How to cite: Zhang, Q., Fu, X., and Wang, J.: The cyclostratigraphy of the Late Triassic Qiangtang Basin in Tibet and the orbital forcing for the Carnian Pluvial Episode, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4352, https://doi.org/10.5194/egusphere-egu24-4352, 2024.

The Iberian Margin provides a remarkably accurate record of millennial-scale climate variability, making it an invaluable site for deciphering historical changes in climate and oceanography. This region’s exceptional sensitivity to high latitude processes, such as meltwater discharges into the Northeast Atlantic, significantly influence ocean dynamics, nutrient supply, and climate change impacts. These processes play a pivotal role in understanding the complex interplay between the ocean, ice, and climate systems. IODP 339 Site U1385, also known as the “Shackleton site”, drilled at a water depth of 2582 mbsl, reaching a total depth of 155.9 m below the seafloor. The oxygen isotope and carbon isotope records confirm that Site U1385 contains a continuous hemipelagic sedimentation from the Holocene to 1.45 million years (MIS 47), providing a reference record of millennial-scale climate variability. Here, we present a high-resolution Sea Surface Temperature (SST) record that unveils the climate variability over the last 1.45 million years.  This record provides a comprehensive interpretation of the millennial climate variability of major climatic disruptions, namely the Mid Brunhes Event and Mid Pleistocene Transition (MPT). SST data reveals a clear change on the orbital-driven forcing on the MPT time interval 1200 to 800 ka, thereby contributing to our understanding the underlying mechanisms on glacial/interglacial and centennial to millennial scales. Furthermore the SST record shows extreme cold events occurred not only after the MPT but also during and after this enigmatic period. The highest temperatures were recorded during Interglacial periods, overall the record and coincident with maximum insolation (precession minimum), suggesting an orbital dependence of the Sea Surface Temperature (SST) over the past 1.45 million years. This SST record significantly contribute to documenting the major climate shifts and their relation to global climate change. This becomes particularly crucial as the IODP Expedition 397 enables the extension of this exceptional sediment record into the Pliocene.

How to cite: Rodrigues, T., O. Grimalt, J., Casado, M., Gonzalez, Y., J. Crowhurst, S., Abrantes, F., and Hodell, D.: Decoding major Climate Mysteries over the last 1.5 million years: Sea Surface Temperature Reconstruction at IODP Site U1385, Iberian Margin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13215, https://doi.org/10.5194/egusphere-egu24-13215, 2024.

Marine Isotope 31 Stage (MIS-31) records one of the highest high-latitude precession-paced insolation values of the last 5 million years (Laskar et al., 2004). According to this configuration, some studies (e.g. Raymo et al., 2006) predicts a +20 m eustatic sea-level rise for this time interval, reflecting significant retreat of some combination of the West Antarctic Ice Sheet, marginal East Antarctic ice, and the Greenland Ice Sheet, and consequently significant variations in the ocean and climate dynamics at global scale.

In this study we show data of variability in the coccolithophore assemblage from IODP Site 1385 (Shackleton Site, IODP 339 and IODP 397) in the interval ca. 1 Ma (close to the Jaramillo event). These sediments are sensitive recorders of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) oscillations, which makes this site a significant location to test the interhemispheric connection hypotheses.

Peaks in abundance of Gephyrocapsa (<3mm), as well as in other Noelarhaddaceae such as Reticulofenestra asanoi and other morphotypes (equivalent with minimum differences at total coccoliths recorded), were interpreted as a signal of paleoproductivity, revealing strong changes during MIS 31. Alternatively, cold water indicators (Coccolithus pelagicus ) or the census of Helicosphaera carteri l(inked to stratification processes) are considered, showing an alternative pattern along the studied interval. After the refinement of the age-model, these data should be compared with other records in close or remote areas (e.g. Flores and Sierro, 2007, Maiorano et al., 2009), to understand the relevance of this interval, particularly sensible in the Antarctic environment, where a potential relevant melting peak was suggested (Scherer et al., 2009).

Preliminary results (Jiménez Espejo et al., 2013) reveal a distinct turnover during MIS 31 and different evolution of surface and bottom-waters that could be linked with enhanced circulation of NADW during warm periods. This scenario is consistent with stratification pulses interpreted at the top of MIS 32, where cold and stratified water pulses are influenced by and increase in reworked material coming from proximal regions as a result of eustatic sea-level drops.

Laskar, J., Robutel, P., Joutel, F., Gastineau, M., Correia, A.C.M., & Levrard, B. Astrophys. 428, 261-285 (2004).

Raymo, M., Lisiecki, L., Nisancioglu, K. Science. 313, 492-495 (2006).

Maiorano, P., Marino, M., Flores, J.A. Mar. Micropaleontol. 71, 166–175 (2009).

Flores, J.A., Sierro, F.J. Deep-Sea Res. II 54 (21–22), 2432–2442. (2007)

Scherer, R. P., Bohaty, S., Dunbar, R., Esper, O., Flores, J., Gersonde, R., Harwood, D., Roberts, A., and Taviani, M. Geophysical Research Letters. 35, (2009)

Jiménez Espejo et al., 11th INTERNATIONAL CONFERENCE ON PALEOCEANOGRAPHY

1-6 September, 2013. Sitges - Barcelona (2013)

How to cite: Flores, J.-A., Balestra, B., Clark, W., Jiménez-Espejo, F. J., Kuroda, J., Salgueiro, E., Grimalt, J., Herbert, T., Bárcena, M. A., Abrantes, F., Hodell, D., Alvarez Zarikian, C., and 397 Scientific Party, E.: Paleoproductivity and surface water dynamics evolution during the MIS 31 in the Shackleton Site as revealed Coccolithophores, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15648, https://doi.org/10.5194/egusphere-egu24-15648, 2024.

Speleothem oxygen isotope records from China have provided the most detailed insights into the past Asian summer monsoon variability of any paleoclimate archive (“proxy”) to date in the past 640 ka, showing the dominance of the orbital precession rhythm. However, fundamental disagreement exists on what the oxygen isotope records represent in terms of the hydroclimate changes, in particular on the orbital scale. Based on the oxygen isotope records and other hydroclimate proxies from 15 speleothems at Haozhu Cave in central-eastern China, as well as the model simulations for the periods of Marine Isotope Stages 6 and 11, we show the orbital-scale ‘dipole’ hydroclimate in monsoonal eastern China, with wetter (drier) conditions in the central but drier (wet) conditions in the north when summer insolation was low (high) and East Asian summer monsoon was weak (strong). Of significance is the finding that the hydroclimate contrast in East China was greatly enhanced during glacial-interglacial transitions, with the wettest hydroclimate in the north but widespread drought in the central, when the heat content of both the global ocean and the Indo-Pacific Warm Pool upper ocean reached the maximum. We propose that the orbital-scale westerly jet transition affects the East Asian summer rainband position and thus the orbital hydroclimate pattern in eastern China, and the low latitude tropical Indo-Pacific ocean moisture transport amplifies the hydroclimate contrast during glacial-interglacial transitions

How to cite: Zhang, H., Griffiths, M. L., Cheng, H., Dai, G., Ruan, J., Sun, Y., Lu, L., Guo, W., Huang, J., and Xie, S.: Combined high-and low-latitude forcing of orbital East Asian hydroclimate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21881, https://doi.org/10.5194/egusphere-egu24-21881, 2024.

The U-Pb geochronology of carbonates holds significant application value and potential in the field of geoscience. The Isotope Laboratory at Xi'an Jiaotong University has pioneered the development of Carbonate Laser Ablation and Dilution (LA&ID-MC-ICPMS) U-Pb dating techniques, based on research into Quaternary cave secondary carbonate geochronology. By combining the high spatial resolution and rapid analysis speed of the laser method with the controllable sample volume and high testing accuracy of the dilution method, a comprehensive system for Carbonate U-Pb geochronology testing has been established.

Moreover, with advancements in in-situ laser and isotopic dilution techniques for Carbonate U-Pb dating, we conducted tests using the laser method on various carbonate standards, both domestic and international, achieving U-Pb age results consistent with standard values within the error range. This laboratory also reported, for the first time in China, high-precision laser U-Pb dating results for Quaternary cave secondary carbonates, in alignment with ages obtained via dilution methods in foreign laboratories. Furthermore, our laboratory's entire Pb background is currently at a world-class level (~10 pg), and the testing results for cave secondary carbonates are consistent within the error range with dilution methods abroad and the laser method in our laboratory, validating its accuracy.

The laboratory has developed robust, high-precision laser and isotopic dilution techniques for Carbonate U-Pb dating, surpassing the limitations of U-Th dating. Through U-Pb dating and oxygen isotope analysis of stalagmite SB20 obtained from Sanbao Cave in Shennongjia, Hubei, our investigation reveals that SB20's growth period spans from 1.25 to 1.50 million years ago, depicting roughly 10 orbital cycles in δ¹⁸O. Consequently, we have established East Asia's inaugural δ¹⁸O record within the monsoon region, preceding the Mid-Pleistocene Transition (MPT). This novel stalagmite record affirms the predominant influence of low-latitude monsoons, driven by solar radiation forcing, on the East Asian region, showcasing discernible precession cycles. The current emphasis on global climate change research is substantial. By amalgamating prior scientific accomplishments, the interplay between the thermodynamic circulation system governed by ice volume in higher latitudes and the dynamic circulation system regulated by low-latitude monsoons shapes a multifaceted Earth scientific framework. This study furnishes pivotal evidence for the comprehensive exploration of a "high-low latitude" climate circulation theory in the context of climate orbital dynamics.

Keywords: Carbonate U-Pb geochronology; MPT; Stalagmite records; precession cycles

How to cite: Kang, L., Hai, C., Wang, J., Niu, X., Zhang, H., Ruan, J., Ning, Y., Zhao, J., and Li, Y.: The Precession Cycles in East Asian Stalagmite Records Before the MPT Constrained by Carbonate U-Pb Dating , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5931, https://doi.org/10.5194/egusphere-egu24-5931, 2024.

       The Indonesian Throughflow (ITF) plays a pivotal role in large-scale ocean-atmosphere interactions in the tropics, regulating the heat and freshwater budget between the Pacific and Indian Oceans. In the context of global warming in the 21^st century, The Indonesian Throughflow are projected to be weaken (medium confidence) by CMIP6 simulations. As an analog of possible future warming, the Last Interglacial (LIG, Marine Isotope Stage 5e or Eemian), with global surface temperature reached about 2 °C above present, serves as an outstanding period to explore the climate response to the external forcing and the mechanisms behind it.

       We use the model outputs from a set of Last Interglacial snapshot simulations carried out by CAS-FGOALS (the Chinese Academy of Sciences Flexible Global Ocean–Atmosphere–Land System model) under the protocol of PMIP for four time periods at 130, 128, 125, and 115 ka. Compared to the piControl simulations (the annual mean ITF flux is 18.46Sv), an annual mean ITF flux increase of about 30.6% - 35.9% was found in the LIG snapshot simulations (24.11 - 25.08Sv). During the LIG, the tropical western Pacific Ocean thermocline was deepened while the tropical eastern Indian Ocean thermocline was relatively shallowed, which was closely tied to the strengthening of the surface easterlies above the tropical western Pacific. Correspondingly, the gradient of the sea surface height between the tropical western Pacific and the tropical eastern Indian Ocean increased, causing pressure contrast between the two basins and probably contribute to the ITF strengthening. We also find that the thermocline gradient between the tropical western Pacific and tropical eastern Pacific was increased, suggesting a La Niña-like state during the LIG. Comparisons of models and proxies further support our conclusions. An examination of the changes in the thermocline water temperature (TWT) record from the eastern Indian Ocean found an enhancement of ITF during MIS 5. Besides, the Maritime Continent was supposed to be more humid by pollen records from west Java and sediment composition from Halmahera Sea.

       Further analysis suggested that the strengthened ITF during the LIG is inconsistent with the weakened one in the 21^st century. While the future global warming is primarily driven by increased CO₂ levels, the climate changes during the LIG were principally caused by changes in orbital parameters.

How to cite: Wei, S., Zheng, W., Du, J., Yu, Y., and Tian, J.: Intensification of the Indonesian Throughflow in a Coupled GCM During the Last Interglacial, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16683, https://doi.org/10.5194/egusphere-egu24-16683, 2024.

The Mediterranean Sea is thought to play a role in changing past ocean circulation and North Atlantic climate, through the outflow of warm, saline intermediate waters (Mediterranean Outflow Water; MOW) into the North Atlantic. Previous studies mostly focused on the Gulf of Cádiz, immediately after the MOW existing the Mediterranean, but how the MOW varied along the northward transport is still unclear. Fine grain-size parameters have been widely employed to infer paleo-flow speeds of near-bottom currents in the deep sea, in particular the terrigenous non-cohesive “sortable silt” (denoted as SS) controlled by selective deposition. Here we present terrigenous sediment grain size results on IODP Site U1588 (37°57.61′N, 9°30.99′W, 1339 m water depth), which was retrieved from the Iberian Margin during the IODP Expedition 397. Our aim is to reconstruct strength variations in the lower branch of the MOW over the past ~250,000 years. After removing organic matter (leached with 10% H₂O₂ at 85 ℃) and marine carbonates (leached with 0.5 M HCl), the terrigenous detrital component of about 100 samples were measured on a Malvern Mastersizer 3000 instrument. Our grain-size results show a bimodal distribution, with a small peak near 1 μm and the main mode between 5–8 μm. The correlation between the percentage and mean of the sortable silt fraction (10–63 μm) is significant (R²=0.43, P<0.01), permitting the use of SS-mean as a reliable indicator of the deep-sea current strength. The calculated SS-mean is from ~14.2 to 18.2 μm, corresponding to the flow speed of ~3.3 to 10.2 cm/s. Based on the shipboard age model, our results show a persistent low-latitude forcing of MOW flow speed over the past 250,000 years, with strong precessional and glacial cycles.

How to cite: Wu, J., Chen, X., He, Z., Deng, Q., Zhong, L., Pang, X., Hodell, D., Abrantes, F., and Zarikian, C. A. and the Expedition 397 Scientific Party: Strength variability of the Mediterranean Outflow Water during late Quaternary: Preliminary results from IODP Site U1588, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19442, https://doi.org/10.5194/egusphere-egu24-19442, 2024.

IODP Expedition 397 recovered a continuous record of precessionally-paced lithological cycles to the base of the recovered section (~9.55 Ma) at Site U1587.  On board ship, three intervals were selected for multi-disciplinary dissection of the cycles in time windows comprising three precessional cycles each ((early Pleistocene 2.284-2.345 Ma, late Pliocene 3.427-3.496 Ma, and late Miocene 5.638-5.5707 Ma).  These three intervals are grounded in continuous XRF scanning that allows for a reliable astrochronology based largely on precessional variability. Carbonate cyclicity follows northern hemisphere precession throughout high carbonate content associated with high northern hemisphere summer insolation.  The cycles cannot be explained solely by changes in carbonate production or preservation, as the clay-rich phases of the cycles are often expanded relative to the carbonate-rich phases.  Sea surface temperature (SST) recorded by alkenone biomarkers shows fluctuations in tandem with the carbonate cycles.  For the Pliocene and Pleistocene, higher carbonate correlates to warmer SST and interglacial conditions as inferred from stable isotope measurements.  The pattern flips in the Messinian test interval, with high carbonate associated with colder and more glacial climate.  Clay mineralogy shows cyclic fluctuations associated with changes in riverine and eolian inputs.  High illite (high dust?) corresponds to high carbonate content in the Miocene and Pleistocene test intervals, while the opposite is observed for the Pliocene.   An abrupt change in cycle spacing near the terminal Messinian likely records a tectonic event that perhaps influenced transport and deposition of the detrital components.

How to cite: Herbert, T., Abrantes, F., Brooks, H., Flores, J.-A., Hodell, D., McManus, J., Mitsunaga, B., Palone, C., Pang, X., Wu, J., Yu, J., and Zarikian, C. and the Expeditiion 397 Scientific Party: Precessional Climate Cyclicity on the Iberian margin: Miocene-recent, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19840, https://doi.org/10.5194/egusphere-egu24-19840, 2024.

The latest Miocene and Early Pliocene (7-3.6 Ma) include key paleoclimatic and paleoceanographic events such as the Messinian Salinity Crisis (MSC), the late Miocene to Pliocene biogenic bloom (hereafter referred as “biogenic bloom”) and its potential termination, as well as the warm early Pliocene, a commonly used analogue for future global warming. Limited information exists regarding how these events impacted North Atlantic ocean circulation and carbonate sedimentation, mainly due to the lack of continuous, high-resolution records in high latitudes. During the summers of 2021 and 2023, the International Ocean Discovery Program (IODP) Expeditions 395C and 395 drilled a transect of five sites in the North Atlantic (at ~60°N). Preliminary results indicate that IODP Site U1562 has continuous sediment recovery, significant variations in carbonate content, as well as good preservation of calcareous fossils across the latest Miocene to Pliocene, making it a suitable candidate for high-resolution paleoclimatic reconstructions. Here, we estimate carbonate sedimentation and paleoproductivity for this site using high-resolution X-Ray fluorescence (XRF) records, derived from elemental intensities measured in core half-sections. Ratios between biogenically derived and detrital elements reveal the orbitally controlled pacing of carbonate production/deposition, as well as a stepwise, sustained decrease in biogenic sedimentation that occurred during the early Pliocene. The latter shift could have been linked to ocean current reorganizations related to the termination of the MSC or the “biogenic bloom”. Finally, we use a cyclostratigraphic approach to explore the possibility of building an astronomically tuned age model for this site using the XRF records.

How to cite: Karatsolis, B. T., Sinnesael, M., and 395/395C scientists, E.: Astronomical pacing and abrupt changes in North Atlantic biogenic sedimentation during the latest Miocene and Early Pliocene: the IODP Site U1562 case study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8238, https://doi.org/10.5194/egusphere-egu24-8238, 2024.