The Early-Middle Pleistocene Transition (EMPT), a global climate event that occurred between 700-1250 thousand years (kyr) ago, was characterized by a drastic change in the deep thermohaline circulation, resulting in more intense and longer-lasting interglacial periods. High-resolution records documenting environmental changes on the ocean seafloor associated with the EMPT in the North Atlantic are still limited. This knowledge is crucial for evaluating and modeling climate variability in the near future. The Gulf of Cadiz (Iberian Margin) is a key region as a gateway between the Mediterranean Sea and the North Atlantic Ocean, being affected at intermediate depths by the Mediterranean Outflow Water (MOW). The MOW plays an important role in modulating the North Atlantic salt budget. Therefore, past climate variability in the Mediterranean region may have affected the MOW intensity and global thermohaline circulation. Thus, the present study aims to understand the environmental parameters influencing the distribution of benthic foraminifera species and their significance in regional oceanographic dynamics. 

Benthic foraminifera inhabit diverse (sub)seafloor environments and respond to factors such as oxygen levels, as well as the quantity and quality of food. Although other factors might influence the assemblage, strong bottom current regimes favor abundances of a group known as the “elevated epifauna”. Previous studies in the Gulf of Cadiz have found that elevated epifauna abundance correlates with MOW intensity in the modern ocean, suggesting it as a potential indicator of MOW intensity in the past.

Here we present results from a high-resolution study of benthic foraminifera assemblage of the period from Marine Isotope Stages (MIS) 26 to 19 at IODP Site U1387 (559 m water depth), drilled into the Faro drift on the southern Portuguese margin. Our study identifies two distinct phases: the first phase (MISs 25 to 22, 959–866 kyr) experienced persistent and intensified MOW flow, as evidenced by an increase in the abundance of elevated epifauna. This phase also exhibits an increase in the abundance such as Globobulimina spp., species that live under oxygen and trophic conditions prevailing at the boundary between dysoxic and anoxic environments, suggesting stronger influence of relatively low oxygen Mediterranean waters. As soon as the MOW intensity declines in the second phase (MIS 21 to MIS 19, 866 – 761 kyr), there is a decrease in the Globobulimina spp. abundance, and an increase in oxygenated-preferred species abundance. We hypothesize that phase I is highly influenced by Mediterranean-sourced waters, whereas phase II improved oxygen conditions indicate potential dominance of Atlantic-sourced waters due to a lesser Mediterranean water contribution. To validate these results, Neodymium isotope analyses (εNd) are being conducted to help distinguishing between the prevailing water masses. Following our hypothesis, we are expecting more positive values during phase I, indicating stronger MOW influence, and more negative values for phase II, suggesting weaker MOW influence and dominantly Atlantic-sourced waters. These findings will further contribute to our understanding of the interplay between climate change and oceanographic dynamics in the Gulf of Cadiz during the EMPT.

How to cite: Molina, G., D. Pena, L., Garcia-Solsona, E., Paredes, E., Mega, A., and Voelker, A.: Hydrodynamic changes in the Gulf of Cadiz during the Early-Middle Pleistocene Transition revealed by benthic foraminifera and radiogenic isotope data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-624, https://doi.org/10.5194/egusphere-egu24-624, 2024.

The intricate interplay among atmospheric CO₂ concentrations, surface ocean pH dynamics, and their profound impact on marine ecosystems is of paramount importance in the context of contemporary climate change. Pre-industrial atmospheric CO₂ concentrations oscillated in phase with glacial-interglacial cycles, showcasing low levels during glacial periods and elevated concentrations during interglacial periods. Nevertheless, this natural variability has been significantly disrupted due to the surge in anthropogenic CO₂ emissions over recent decades. According to the Intergovernmental Panel on Climate Change, if global atmospheric CO₂ concentrations persist in rising at the current rate, it is anticipated that the average ocean pH will decrease by 0.3 pH units in surface waters by the conclusion of this century. This scenario could exacerbate the impacts already observed in marine calcifying organisms, including in marine calcifying organisms such as planktonic foraminifera, affecting their diversity, abundance, and calcification. The main objective of this study is to understand the surface ocean pH evolution in a seasonal upwelling region, during two distinct interglacial periods in Earth's history: the Marine Isotopic Stage 5e (MIS 5e), the last interglacial without anthropogenic influence; and the Holocene, the present interglacial but subjected to anthropogenic influence. In upwelling regions, the upwelling of aged and CO₂-rich subsurface waters together with high rates of primary production and respiration, is expected to regionally amplify ocean acidification. This study concentrates on the reconstruction of surface ocean pH using boron isotopes in a surface planktonic foraminifera species, Globogerinoides bulloides. This species is typically found in upwelling regions and was preserved in the marine sediment corer MD03-2699 (39°02.20′N, 10°39.63′W). Our preliminary findings indicate a pH difference between MIS 5e and the Holocene, with lower pH values during the Holocene.  It is argued that during the Holocene, a potential increase in wind intensity may have triggered a strong and persistent upwelling increasing productivity and respiration, consequently leading to lower pH. Additionally, the increase of atmospheric CO₂, reconstructed from Antarctic ice cores during this period could also contribute to the ocean pH reduction. These variations in upwelling and/or atmospheric CO₂ could be a pivotal factor influencing the observed pH differences, contributing to our comprehension of natural pH variations on the western Iberian margin through advanced pH reconstruction techniques and other multi-proxy environmental data integration for both periods in the region.

How to cite: Mega, A., Calvo, E., D. Pena, L., Salgueiro, E., Rebotim, A., Voelker, A., Cruz, J., and Abrantes, F.:  pH variations during the last and current interglacial stages at the western Iberian margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-722, https://doi.org/10.5194/egusphere-egu24-722, 2024.

Water vapor is the essential substance for precipitation and a crucial component of the global hydrological cycle. Quantifying the contributions of terrestrial and oceanic moisture sources is crucial for comprehending regional precipitation and hydroclimate changes. Previous studies have extensively investigated the East Asian summer monsoon and its precipitation changes using geological climate records, but it remains unclear how water vapor from different source regions affects the orbital-scale precipitation change in East Asia. In this study, a long-term transient simulation using a water vapor tracking climate model was conducted for the past 300 kyr to investigate the contributions of terrestrial and oceanic moisture sources to precipitation changes in the northern East Asian monsoon region (NEA, 35-45°N, 105-120°E). The results showed that for the climatologically annual NEA precipitation, the global land source was the primary moisture source, accounting for approximately 57.6% of the total precipitation, followed by Pacific Ocean source contributing 20.9%, while other sources had a minor contribution. The orbital-scale changes of annual NEA precipitation, dominated by the precipitation of the rainy season from May to September, were mainly characterized by a significant 23-kyr cycle and a weak 100-kyr cycle. Analyses of water vapor sources found that the significant 23-kyr cycle in NEA precipitation was caused by the superposition of the synchronous 23-kyr cycles of precipitations from the land and Pacific Ocean sources, while the nonsynchronous 100-kyr cyclic changes of precipitations from the land and Pacific Ocean sources led to the weak 100-kyr cycle of NEA total precipitation. The dominant 23-kyr cycle of NEA precipitation reflects the effect of precession forcing, while the weak 100-kyr cycle implies the impact of the high-latitude ice sheet forcing, which triggers the antiphase change in the moisture contribution rates of the land and Pacific sources in the glacial-interglacial cycle. This study highlights the importance of terrestrial and oceanic moisture sources associated with external forcings in understanding the orbital-scale East Asian monsoon precipitation changes. As a preliminary attempt to track the orbital-scale variations of the terrestrial and oceanic moisture sources of East Asian monsoon precipitation by conducting a water vapor tracking transient simulation, this study provides new insights into the temporal-frequency characteristics and physical mechanisms of orbital-scale East Asian monsoon precipitation variations from the perspective of water vapor sources.

How to cite: Xie, X. and Liu, X.: Deciphering orbital-scale precipitation changes in the northern East Asian monsoon region: insights into the roles of terrestrial and oceanic moisture sources, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2999, https://doi.org/10.5194/egusphere-egu24-2999, 2024.

Despite efforts to understand the response of marine ecosystems to the impact of climate variability in the Iberian Margin [1-6], the effects of warming on phytoplankton community composition and total primary production remain an open question. Here, we present a high-resolution record of sediment-preserved lipids from the Iberian Margin (IM) over the last millennium, with special attention to the modern rise in atmospheric CO₂. To address the temporal variation of marine primary production and terrestrial organic matter input, we studied GC-MS/FID-determined lipid compounds from cores PO287-06-2G (off the Douro River in the northern IM), PO287-26-3G (off the Tagus River in the central IM) and POPEI-VC2B (on the Algarve continental shelf in the southern IM). Lipids of typical marine origin (C₂₇, C₂₈, and C₃₀ sterols, phytol, and C₃₇ and C₃₈ alkenones) and of typical terrestrial origin (odd long-chain n-alkanes nC₂₁-nC₃₅ and even long-chain n-alcohols C_22OH-C_32OH) were evaluated. As proxies for specific phytoplankton groups, we used the signatures of 4α-23,24-trimethyl-5α-cholest-22(E)-en-3β-ol (30d²² sterol) for dinoflagellates, 24-methylcholesta-5,22-dien-3β-ol (28d^5,22 sterol) for diatoms and heptatriaconta-15E,22E-diene-2-one (C_37:2 alkenone) for coccolithophores. The results showed a significant difference between the northern, central, and southern sites of the Iberian Margin, caused by the different regional environmental factors in each area. Higher concentrations of lipids are observed off Douro River, there is a higher relative contribution of cholesterol off Tagus River, suggesting the importance of zooplanktonic production in the central area, and there is a higher contribution of coccolithophores lipid signatures in the Algarve continental shelf. In terms of temporal variability, there is an alternation between coccolithophores and dinoflagellates lipid signatures over the millennium, with significant diatom sterol signatures at specific ages of the Industrial Era (since 1850 CE) and in the early MCA (900-1100 CE) for all sites. The temporal variability is most likely driven by changes in local and hemispheric ocean circulation and coastal upwelling conditions in the Iberian Margin.

References: [1] Abrantes et al., 2017; [2] Abrantes et al., 2011; [3] Salgueiro et al, 2008; [4] Ribeiro and Amorim 2008; [5] Abrantes 2000; [6] Rodrigues et al., 2009

How to cite: Gebara M.S. Cordeiro, L., S. Carreira, R., Ferreira, F., A. Rodrigues, T., and F. Abrantes, F.: Using lipid biomarker signatures to reconstruct marine primary production in the Iberian Margin over the last millennium, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6745, https://doi.org/10.5194/egusphere-egu24-6745, 2024.

The time between 1,200 kyr BP and today includes the Mid-Pleistocene Transition, the Mid-Bruhnes Event, and the late Pleistocene. The Early-Mid Pleistocene Transition (~920 kyrs BP) is one of the most dramatic shifts in high-latitude climate and marked by the onset of the strong 100 kyr glacial-interglacial cycles. The Mid-Bruhnes Event marks a significant increase in the amplitude of the glacial-interglacial cycles. It has been identified mostly in marine sediments and Antarctic ice cores, but it is currently discussed whether it was a globally synchronous phenomenon, including the African continent. Marine records suggest a shift towards increased aridity in parts of Africa, and terrestrial records from eastern Africa indicate a generally wet climate, possibly with a transition from stable to unstable, as suggested by the Olorgesailie record. 
At this time, robust Australopithecines went extinct, and only the genus Homo survived as H. ergaster, which ultimately led to the emergence of our own species, H. sapiens. The time vector also includes the second major expansion wave of H. ergaster out of Africa (1.39–0.9 Ma, after the first wave at ~1.9–1.4 Ma), possibly through the Sinai land bridge, but expansions through the Gibraltar strait and via the Bab el- Mandeb strait and into the southern Arabian Peninsula are also subject to lively discussed.
Here, we present the first insights into a comprehensive linear and non-linear analysis of five prominent records, which are (1) the dust record from ODP site 659 from western Africa, (2) the dust record from the Arabian Sea from ODP site 721/722, (3) the river runoff record from MD96-2048, (4) the combined dust and river runoff wetness index from ODP site 967, and (5) the south-western European ICDP record from Lake Ohrid. We use correlation metrics, such as the windowed Spearman correlation coefficient, to test for spatiotemporal synchronicity, asynchronicity, and possible interferences with the hominin fossil record. Furthermore, we use non-linear analysis, such as recurrence plots and recurrence quantification analysis, to test whether prominent climate transitions or spatiotemporal shifts in the fossil record are in temporal alignment with recurrence-based insights.

How to cite: Fischer, M. L., Marwan, N., Foerster, V., Schaebitz, F., Scerri, E. M. L., Schwanghart, W., Kaboth-Bahr, S., and Trauth, M. H.: Linear and non-linear Time Series Analysis of pan-African Hydroclimate spanning the past 1,200 kyr, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12155, https://doi.org/10.5194/egusphere-egu24-12155, 2024.

The retrieval of sediment cores from Site U1385 during Expedition IODP 397 off the Iberian Margin has yielded a high-fidelity record extending back to the base of Pliocene. This record provides an unprecedented opportunity to investigate the onset of millennial climate variability associated with the intensification of Northern Hemisphere Glaciation (iNHG) during the late Pliocene. Elemental ratios, specifically Ca/Ti and Zr/Sr, measured by core scanning X-ray fluorescence (XRF) have uncovered four distinct millennial climate events in Marine Isotope Stages (MIS) G6, G4, G2 and 104. These single ‘precursor events’ precede the onset of pronounced millennial climate variability marked by multiple events beginning with MIS 100 (2.54 Ma).

The planktic δ¹⁸O record of Globigerina bulloides exhibits an increase associated with the peak in Zr/Sr and minimum in Ca/Ti, indicating colder temperatures during the stadial event in MIS G4 (2.69 Ma). A comparison with the δ¹⁸O record of mixed benthic foraminifera (Cibicidoides wuellerstorfi and Uvigerina peregrina) indicates that the identified cold stadial in MIS G4 coincided with the end of MIS G4 just before the deglaciation to MIS G3. We therefore suggest it represents a terminal stadial event, which is common during the latest part of glacial stages during the Quaternary. Moreover, the precursor stadial events of MIS G6, G4, G2 and 104 at Site U1385 can be correlated 1:1 to peaks in ice-rafted debris (IRD) in the high-latitude North Atlantic, indicating a connection to iceberg calving and freshwater forcing. Our results indicate that ice sheets had grown large enough during the glacial stages of the latest Pliocene to induce a significant response to freshwater forcing upon deglaciation.

How to cite: Du, M., Crowhurst, S., Mleneck-Vautravers, M., Hodell, D., Abrantes, F., Alvarez Zarikian, C., and 397 Scientific Party, E.: Late Pliocene onset of millennial climate variability during the intensification of Northern Hemisphere Glaciation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13153, https://doi.org/10.5194/egusphere-egu24-13153, 2024.

The Devonian is a warmer-than-present geological period spanning from 419 to 359 million years ago (Ma) characterized by 29 identified ocean anoxic/hypoxic events. Despite decades of extensive investigation, no consensus regarding the mechanisms responsible for ocean anoxia has been achieved. Our study contributes to this general research effort, focuses on the astronomical pacing of anoxia throughout the Devonian and is substantiated by growing geologic records suggesting a link between astronomical forcing and anoxic events during this period. To investigate the role of the astronomical forcing we used the Earth system Model of Intermediate Complexity (EMIC) cGENIE, which has proven to be a reliable choice to simulate ocean oxygen spatial patterns and values. In this project, we first tested the impact of continental configuration and ocean biogeochemistry (pCO$_2$, PO$_4$ and pO$_2$) on the equilibrium of the system and the related dissolved ocean oxygen concentration. Then, we produced an in-depth analysis of the astronomical forcing contribution to ocean anoxia for well-chosen continental reconstruction and biogeochemical quantities values. Our results indicate that variations in continental configuration, even small, can exert a strong impact on ocean anoxia, underscoring the influence of paleoreconstructions uncertainties on the biogeochemical tracers of cGENIE. The astronomical forcing reveals to be able to modify the nature of the equilibrium of the system, going from a single-state value solution to an oscillatory behaviour. Our findings also offer insights into potential ocean lockdown mechanisms, providing plausible explanations for the prolonged persistence of certain anoxic events over several hundred thousand years.

How to cite: Gérard, J., Huygh, J., Sablon, L., Crucifix, M., and Da Silva, A.-C.: On the impact of astronomical forcing on ocean anoxia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15130, https://doi.org/10.5194/egusphere-egu24-15130, 2024.

The lower Carboniferous is marked by the onset of the Late Paleozoic Ice Age (LPIA), one of the most severe and longest in Earth history, with a duration of nearly 100 million years [1]. The onset of the glaciation is associated with bursts of anoxia of different magnitudes through the Tournaisian and Visean stages (in the lower Carboniferous). These anoxic events are the Lower Alum Shale (LASE [2]) at the base of the middle Tournaisian, The Tournaisian Carbon Isotope Excursion (TICE, also called KOBE [3]) in the middle Tournaisian, and the Visean Carbon Isotope Excursion (VICE [4]). The particularity of these anoxic events is their development during a relatively cold period and their longer durations (5-10 Myr) compared to most other anoxic events. Clues have been accumulated pointing to the possibility that anoxia and glaciation may have been paced by changes in Earth’s orbit parameters ([5], [6], [7], [8]). These changes are the astronomical (Milankovitch) cycles (Eccentricity, Obliquity, and Precession) with specific durations. They impact the incoming solar radiation and seasonal contrasts, hence global climate. Cyclostratigraphy (The identification of astronomical cycles in the geological record) is the tool to establish a chronological framework (ATS) of the lower Carboniferous in order to reach precise estimates for the duration of these anoxic events. This precise timing is essential to get a better understanding of the climate response to astronomical forcing in the early Carboniferous. We also intend to delve into Milankovitch forcing related to ice age evolution and to understand the connection of anoxic events with climate dynamics and orbital forcing. In addition, precession and obliquity cycles are directly related to the Earth-Moon distance (and the length of the day). Through our study, we will provide a duration of precession and obliquity cycles which would allow to provide the Earth-Moon distance and length of the day for this period. Therefore, five geologic sections have been selected in the Namur-Dinant basin in Belgium and one section in Germany. Sections will undergo a high-resolution sampling then multiple analyses will be applied (major and trace elements, total organic carbon (TOC), and stable carbon isotopes(δ¹³C)). Different cyclostratigraphic techniques will be applied (e.g., MTM, ASM, TimeOpt, COCO, EHA) on specific paleoclimate proxies to build the chronostratigraphic framework. In fine, precession and obliquity cycles are directly related to the Earth-Moon distance (and the paleo-length of the day). Through our study we will provide a duration of precession and obliquity cycles which would allow us to provide the Earth-Moon distance and length of the day for this period, marked by a period of resonance of oceanic dissipation [9]. The study aims to deepen our understanding of the carboniferous ice age, its triggers, and Earth’s intricate climatic mechanisms.

[1]Crowley & Baum 1991. [2] Rakociński et al., 2021. [3] Yao et al., 2015. [4] Liu et al., 2019.  [5] Batenburg et al., 2019. [6] Batenburg et al., 2023. [7] Christine et al., 2020. [8] De Vleeschouwer et al., 2017. [9] Farhat et al., 2022.

How to cite: Boukhalfa, D. and Da Silva, A.-C.: Transition to glacial state through the lower Carboniferous and impact of orbital forcing on sedimentary records and anoxia expansion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16072, https://doi.org/10.5194/egusphere-egu24-16072, 2024.

New insights about the Marine Isotope Stage (MIS) 5 over the North Atlantic area are presented in this study. The MIS 5 interval covers a timeframe from  ̴130 ka to 70 ka and it has been the last major interglacial interval occurred on Earth. In particular, the MIS 5e sub-interval, is a key period to study the possible evolution for human induced climate changes. It also represents an opportunity to interpret the natural climate evolution beyond the anthropic impact being interested by global temperatures assumed to be warmer than the pre-anthropogenic ones (e.g. Kopp et al., 2009). Likewise, the North Atlantic region is interesting for climatic studies being involved in the modulation of the global climate and in particular the Iberian margin is a well-known source of rapidly accumulating sediment offering a high-fidelity record of millennial climate variability.

With this contribution we show preliminary results concerning changes in hydrography and coccolithophores productivity from two sites recovered on the Promontorio dos Principes de Avis, SW Iberian Margin: U1385 (37°34.285’N; 10°7.562’W – 2585 meters below sea level), drilled during the Integrated Ocean Drilling Program Expedition 339, and U1586 (37º37.283’N; 10º42.628’W - 4691 meters below sea level), drilled during the International Ocean Discovery Program Expedition 397.

The phytoplankton group of coccolithophores has proved to be a high-quality environmental proxy since their geographic distribution and abundance is strongly influenced by parameters such as sea-surface temperature, salinity, sunlight and nutrient availability. Accordingly, coccolithophores are here used to describe paleoproductivity fluctuations in surface waters and upwelling strength as well as paleoceanographic changes linked to global climate evolution.

References

Kopp, R.E., Simons, F.J., Mitrovica, J.X., Maloof, A.C. & Oppenheimer, M. (2009). Probabilistic assessment of sea level during the last interglacial stage. Nature, 462 (863-867)

How to cite: Argenio, C., Flores, J.-A., Balestra, B., Amore, F. O., Hodell, D., Abrantes, F., Alvarez Zarikian, C., and Scientific Party, E.: Paleoceanographic and paleoclimatic analyses throughout the MIS 5 interval: preliminary results from calcareous nannoplankton, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16409, https://doi.org/10.5194/egusphere-egu24-16409, 2024.

The past subsidence episodes of the northern Upper Rhine Graben allowed the accumulation of thick sedimentary sequences that can function as excellent data source for paleoclimate reconstructions. A 323 m long sediment core drilled in 2020-2021 near Riedstadt-Erfelden (~14 km WSW of Darmstadt) is therefore likely a high-resolution geoarchive documenting climate dynamics during the Plio-Pleistocene epochs. So far, the chronostratigraphic framework is based only on lithostratigraphic assignments. This study presents inclination values and magnetic susceptibility obtained from whole-core measurements and discusses initial stratigraphic ideas based on the resulting preliminary magnetic polarity stratigraphy and cyclostratigraphic assessments of the ‘Riedstadt-Erfelden’ core.

Here, we highlight on the quasi-cyclic components of the core, and provide an interpretation in the light of paleomagnetic dating.

How to cite: Zeeden, C., Paknia, M., Scheidt, S., Kaboth-Bahr, S., Vinnepand, M., and Hoselmann, C.: Exploring the Plio/Pleistocene stratigraphy of the Upper Rhine Graben from a core taken at a Riedstadt/Hesse, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18823, https://doi.org/10.5194/egusphere-egu24-18823, 2024.

The reservoir age of waters and carbon sequestration increased in the deep Atlantic Ocean during the last glacial period. The glacial northern deep water (GNADW) formation reached shallower depths than during the ensuing interglacial, and the underlying southern-sourced bottom water (GAABW) was filling the basin, generally poorly ventilated. The mechanisms within the deep ocean that facilitate the flip from glacial-to-interglacial modes are as yet to be understood.  

Here we present analysis performed on foraminifera (benthic δ13C, abundance of oxygen-tolerant benthic species and ¹⁴C age difference between benthic and planktonic species), together with the n-hexacosan-1-ol index (biomarker of the oxygenation of the deep-sea floor) in three deep cores at the Atlantic Iberian margin (ca. -5,000 m depth; 40°N). The locations selected follow the pathway of the Northeast Atlantic Deep Water (NEADW): MD03-2698 (Tagus Iberian margin), D219 (Rincão da Pomba) and MD13-3473 (Tore inner basin). Additionally, results of polar northern and southern sites (U1308 and TN057-21 respectively) are discussed as a reference for evaluating long-distance connections. 

The hypothesis to be tested is whether the deep waters off Iberia were northern- or southern-sourced during the deglaciation within the Tore seamount, a crater-shaped geological structure, 300 km off the Iberian continental shelf. It includes an inner basin down to -5,500 m, isolated from the oceanic basin by a summit rim at -2,200 m. The external connection with the Atlantic is by two narrow NW and NE gateways down to –4,300 m. This makes the area a singular spot to decipher the NEADW-end member of the Atlantic deep circulation. 

We find benthic (Cibicidoides wuellerstorfi) δ¹³C values around 0 ‰ in the interior of the Tore before 18 ky, slightly heavier than those known from shallower Iberian sites (ca. -3,500 m). This points to isolation of the Tore basin from the influence of GAABW. This contrasts with the other sites MD03-2698 and D219 which record δ¹³C around -0.6 ‰, similarly to TN057-21 values. Inside the Tore, benthic foraminifera species grouped according to their oxygen tolerance are oligotrophic during the glacial (oxygen-rich, more ventilated conditions) and mesotrophic over the Holocene (intermediate ventilation).

The carbon residence time measured in MD03-2698 and D219, as estimated from the ¹⁴C age difference between benthic and planktonic foraminifera, confirms previous reservoir ages in the deep Iberian margin (MD99-2334K; JC89-SHAK03-6K, JC89-SHAK05-3K). In the inner basin (MD13-3473), the estimation is not valid, probably due to increased bioturbation, lower sedimentation rates and mixing turbiditic flow. 

The hexacosanol index marks the lowest ventilation pattern culminating around 16 ky (MD03-2698, D219), an apparent inflection point from when the ventilation shifts from southern to northern sourced deep waters, the former not registered in the inner Tore (MD13-3473). This occurs in line with a large reduction in the Atlantic meridional overturning circulation (AMOC) and maximum extent of ice sheets. Taken together, interactions between atmospheric, marine, cryosphere and terrestrial climate elements, as recorded by different proxies during the stadial multi-step structure associated within Heinrich event 1 (H1.1) are giving clues to the processes bringing about deglaciation.

How to cite: Lebreiro, S. M., Antón, L., Nave, S., Waelbroeck, C., Bard, E., Skinner, L., Reguera, I., Michel, E., Bravo, N., Lopez, J. F., Martrat, B., Rodrigues, T., Bellido, E., and Sierro, F.: Testing the deep water source variations in the Atlantic Iberian margin over the last deglaciation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17892, https://doi.org/10.5194/egusphere-egu24-17892, 2024.

Organism body size is a critical aspect of marine ecosystems and is influenced by climate change on seasonal to geologic time scales. Recent integration of mechanistic models of metabolism, laboratory experiments, and fossil records has opened a new avenue for understanding the roles of thermal sensitivity and hypoxia tolerance in body-size evolution. Here we explore climatic factors driving intraspecific body size variability of benthic ostracods in the central and eastern North Atlantic Ocean. We analyzed over 300 adult shell sizes of multiple ostracod species in the genus Krithe at Sites Chain 84-24-4PC (42°N, 33°W, 3427 m water depth) for the past ~50,000 years and IODP U1588 (37°N, 9°W, 1139 m water depth) for the past ~700,000 years. Chain 84-24-4PC and U1588 are predominantly influenced by North Atlantic Deep Water (NADW) and Mediterranean Outflow Water (MOW) today, respectively. Results show that size reduction corresponded to up to 5 °C deglacial warming during the interval 22-14 ka (MIS 2-1) at the Chain 84-24-4PC core site. Even more striking, size varies 60-70% during major glacial-interglacial transitions (MIS6-5, MIS12-11, and MIS16-15) at Site U1588. The differences observed in the magnitude of size reduction between the two sites are likely influenced by the varying ranges of temperature and, potentially, oxygen variability at their respective water depths. We discuss the potential of using body size changes to reconstruct variability in temperature and oxygen across glacial-interglacial cycles.

How to cite: Huang, H.-H. M., Deutsch, C., Cronin, T., Alvarez Zarikian, C., Guedes Abrantes, F., and Hodell, D. and the Expedition 397 Scientists: Body size variability of North Atlantic benthic fauna driven by bottom-water temperature and oxygen during late Quaternary glacial-interglacial cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13997, https://doi.org/10.5194/egusphere-egu24-13997, 2024.

Although valuable information of North Atlantic circulation paleo-reconstructions by the measurement of oxygen isotopes of benthic and planktonic foraminifera exists, it is still not well-understood how deep-water currents changed over the last ~800,000 years. Moreover, recent studies have shown that some species of microfossils can adapt to low oxygen concentrations, which consequently can impact the reliability of the paleo-reconstructions that are based on these fossils. Marine sediments off the Portuguese Margin have been shown to play a pivotal role in paleoclimate research, and studies have suggested that climate shifts at Mediterranean latitudes are interconnected to changes in deep-water circulation patterns. Changes in bottom-water oxygenation (ventilation) can provide information about changes in deep-water circulation patterns, which can be measured by the enrichment versus depletion of redox-sensitive trace metals. Here we provide the results of a low-resolution geochemical analysis of redox-sensitive trace metals (for example, molybdenum (Mo), vanadium (V), and uranium (U)) to investigate deep-water ventilation changes in the North Atlantic over the last ~800,000 years at Hole U1586A drilled during IODP Expedition 397. Sediment samples underwent a multi-acid digestion technique and were analyzed via an Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for redox-sensitive trace metals. Additionally, sequential iron (Fe) extractions were carried out to differentiate between labile versus mineral Fe phases. Preliminary results suggest minor changes in deep-water ventilation that correspond to glacial-interglacial cycles since the mid-Pleistocene. Future work will involve high-resolution geochemical analyses to better understand the interconnection of deep-water circulation and climate change.

How to cite: Haygood, L., Riedinger, N., Hodell, D., Abrantes, F., and Alvarez Zarikian, C. and the Expedition 397 Scientific Party: Investigating North Atlantic Deep-Water Ventilation Changes: Preliminary Results from IODP Expedition 397 Hole U1586A, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6679, https://doi.org/10.5194/egusphere-egu24-6679, 2024.