Reconstructing past changes in oxygen content can be challenging due to some limitations of the proxies used, which are often not continuously represented in the sedimentary record. Here, we present a series of past oxygen reconstructions in the Mediterranean Sea based on the measurement of U/Mn ratios over foraminifera diagenetic coatings. We first test the feasibility of the proxy through different oxygen content locations and explore the fixation of the geochemical signal over different foraminiferal carriers and through the redox zone. The feasibility of the proxy is further tested by direct comparison with oxygen reconstructions based on benthic foraminiferal assemblages, supporting the robustness of our oxygen content proxy. This proxy has been applied over the last deglaciation and the Holocene in a collection of cores covering a wide range of depths in the western Mediterranean, as well as key sites in the eastern Mediterranean. This exercise provides a new insight into the evolution of the Mediterranean thermohaline circulation during the last deglaciation. Our reconstructions confirm the development of the already described deglacial organic-rich layer in the western Mediterranean, but prove that this stagnation process started in relation to the Heinrich 1 ice melting. Surprisingly, they also provide evidence for the development of a strong oxygen minimum zone in intermediate layers of the western Mediterranean, suggesting that the deep water oxygen depletion was much weaker. This finding confirms that the previously described weakening of the western Mediterranean deep water convection associated with this event was closely linked to a smoother circulation of the Levantine Intermediate Waters (LIW). Our reconstructions also support a general reorganization of the Mediterranean circulation during the Younger Dryas, which, according to Nd isotope data (Trias-Navarro et al., 2023), it was associated with a general intensification of the LIW outflow into the western Mediterranean. This western basin began to re-ventilate at this time, leading to a progressively thinner oxygen minimum zone at intermediate depths, while the re-intensification of deep convection occurred later, after 9 kyr. This change coincides with the onset the deep anoxic conditions development that led to the formation of the last sapropel in the eastern Mediterranean. Curiously, at this time in the western Mediterranean, maximum oxygenation occurred at the depth of the present LIW, suggesting the appearance of a different source of well ventilated water mass (Selvaggi et al., in review). Overall, these results indicate a tight but complex connection between the convection cells of the eastern and western Mediterranean, but also reflect the high sensitivity of this circulation system to past climate changes and their control in the development of intense deoxygenation events.
Trias-Navarro, S., et al. (2023). Eastern Mediterranean water outflow during the Younger Dryas was twice that of the present day. Communications Earth & Environment, 4(1), 147. https://doi.org/10.1038/s43247-023-00812-7
Selvaggi, M. et al. (in revision). Environmental Conditions Controlling Cold-Water Coral Growth in the Southern Alboran Sea Since the Last Deglaciation. Global and Planetary Change. Available at SSRN: https://ssrn.com/abstract=4991071 or http://dx.doi.org/10.2139/ssrn.4991071
How to cite: Cacho, I., Pena, L., Frigola, J., Català, A., de la Fuente, M., Trias-Navarro, S., Campderrós, S., Selvaggi, M., Torner, J., Margaritelli, G., Pérez-Asensio, J. N., Corbera, G., Evangelinos, D., and Lirer, F.: Deglacial deoxygenation event in Mediterranean intermediate waters, a prelude to the last sapropel formation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16103, https://doi.org/10.5194/egusphere-egu25-16103, 2025.
The Paleocene-Eocene Thermal Maximum (PETM) ~56 million years ago, provides one of the best geological analogues for investigating how marine oxygen levels respond to rapid global warming and massive perturbations to the global carbon cycle. Various studies on PETM shelf sections have documented the deposition of an extensive organic-rich sapropel horizon, which provides a unique geological archive into better understanding the crucial drivers and interactions responsible for PETM deoxygenation within shallow shelf settings. Changes in relative sea level and/or the hydrological cycle during the PETM have both been invoked as potential drivers behind this marine deoxygenation. However, there is currently a lack of high resolution dated PETM records which integrate and resolve the temporal relationship between these mechanisms and the onset of shelf deoxygenation. Therefore, we have investigated Kheu River; a key PETM section in the northern Caucasus which has previously produced several geochemical records indicating the prevalence of intermittent shallow marine anoxia and euxinia within the sapropel horizon. Our new datasets, together with published palaeoceanographic and palaeoclimatic proxy-based reconstructions from Kheu River, have been evaluated using a sequence stratigraphic framework and calibrated to an orbitally-tuned age model. Similar shallowing and deepening trends inferred from co-variations in geochemical, micropalaeontological, and sedimentological datasets suggest bottom water redox conditions at Kheu River were influenced by changes in relative sea level over ~105-year timescales. Despite this however, we show the deposition of the sapropel horizon occurred more rapidly during the first ~26 kyr of the PETM carbon isotope excursion (CIE), consistent with an intensified hydrological cycle driver. This transient hydrological driven deoxygenation event is also coeval with an interval of maximum continental weathering, nutrient, and sediment influx at Kheu River, suggesting shallow shelf environments were sites of diverse and dynamic biogeochemical process interactions during the onset of the PETM CIE. These results underscore the complexity of shallow marine ecosystem responses to climate forcing. They also provide valuable insights into the drivers of marine deoxygenation in a rapidly warming world, which can help us better predict future deoxygenation patterns.
How to cite: Staitis, M., Chapman, M., Pedentchouk, N., Marca, A., Dennis, P., and Dickson, A.: Intensified hydrological cycle, not sea level rise, caused PETM shelf deoxygenation , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-726, https://doi.org/10.5194/egusphere-egu25-726, 2025.
The oxygen concentration of oceanic deep waters in the Pacific and atmospheric carbon dioxide (pCO2) have been found to be intrinsically linked during glacial-interglacial cycles through processes such as organic carbon remineralization and the storage of dissolved inorganic carbon in the deep ocean. However, the persistence of this link over the Neogene is unclear. Here, we present a reconstruction of oxygenation history over the past 24 million years at IODP Site U1438B (4700.5 m water depth) in the Philippian Sea, where the bottom waters are mainly originated from the Lower Circumpolar Deep Water (LCDW). The employed proxies for oxygenation are the Alcohol Preservation Index (API) and U/Ba ratio. Our results reveal an overall trend of decreased bottom water oxygenation since the early Miocene, which aligns with the long-term decline in atmospheric pCO2. Notably, we identify a period of significant decrease of oxygenation from 16–12 million years ago (Ma), concurrent with the most significant CO2 decline in the Neogene centered at the East Antarctic ice sheet (EAIS) expansion. We propose that this significant decreases of oxygenation, indicative of increase in deep-ocean respired carbon pool, was caused by weakened LCDW ventilation due to the EAIS expansion. Interestingly, during the Arctic polar ice sheet expansion at the Pliocene-Pleistocene transition at around 3-2 Ma, LCDW oxygenation also weakened significantly, although the LCDW was unlikely affected by the hypothesized sub-Arctic deep water. Nevertheless, our results support an intrinsic connection between the deep Pacific respired carbon pool and atmospheric CO2 that has existed since the early Miocene.
How to cite: Dong, K. and Jia, G.: Changes in Deep Water Oxygenation in the Philipean Sea Over the Past 24 Million Years: Insights from IODP Site U1438B, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3423, https://doi.org/10.5194/egusphere-egu25-3423, 2025.
Quantitative records of bottom water oxygen (BWO) are critical for understanding deep ocean change through time. Because of the stoichiometric relationship between oxygen and carbon, BWO records provide insight into the physical and biogeochemical processes that control the air-sea partitioning of both gases over Quaternary glacial-interglacial cycles with important implications for climate and benthic habitats. Here, we present new geochemical datasets from Ocean Discovery Program (ODP) Site 1240 in the eastern equatorial Pacific to constrain BWO using a multiproxy approach (aU, Mn/Al, Δδ13C, and U/Ba). This combination of approaches, and a co-registered proxy record of the rain rate of organic carbon to the site (Baxs flux), allows us to quantitatively identify changes in BWO and to parse local and basin-wide contributions to the signal.
Our results provide direct evidence for the role of orbital precession and obliquity in driving deep sea respired carbon and oxygen concentrations, not just during deglaciations, but during both glacial and interglacial periods. We find variations in BWO on the order of ~50 μmol/kg that occur with ~23 kyr peridiocity during the substages of Marine Isotope Stage 5, and variations of ~100 μmol/kg on glacial-interglacial timescales. These findings have important implications for the role of insolation in driving deep ocean respired oxygen and carbon concentrations and point to physical and biogeochemical changes in the Southern Ocean as key drivers of planetary-scale carbon change.
How to cite: Jacobel, A., Pallone, C., Costa, K., Anderson, R., and McManus, J.: Orbital Influences on Deep Ocean Oxygen Concentrations and Respired Carbon Storage, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1807, https://doi.org/10.5194/egusphere-egu25-1807, 2025.
In fjords, oxygenation depends on exchange or no exchange of deep fjord basin water. In sill fjords, water mass exchange is directly linked to the density of the water mass found around sill depth. Along the coast of Norway, warming water entails reduced density and less frequent renewal events. To evaluate to what degree such observed changes are within the range of natural variability, we need to expand our knowledge base beyond observations. Here, we present reconstructions of fjord oxygenation and associated water mass density in and outside of western Norwegian sill fjords. Sediment records covering the last few centuries will be presented, covering the transition from the Little Ice Age towards the recent warming, hence documenting responses taking place while transferring from a somewhat colder to warmer than preindustrial climate. The fjord basins were characterized by a transition from less well oxygenated to better oxygenated fjord bottom water. Drivers of change in fjord oxygenation and how the fjord basin changes are impacted by oceanographic changes taking place in the more open coastal oceans will be discussed.
How to cite: Risebrobakken, B., Ferraro, M., Polovodova Asteman, I., Tisserand, A., Moros, M., Blindheim, D. I., Haflidason, H., Darelius, E., and Weiner, A.: Oxygenation of western Norwegian fjords, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9257, https://doi.org/10.5194/egusphere-egu25-9257, 2025.
The glacial cycles of the late Pleistocene directly influenced the oxygenation pattern of the global ocean, due to physical and biological changes responding to orbital and climatic change. These changes in past oxygenation had profound implications for carbon storage in seawater and marine sediments. Here we show how different Earth system processes affect benthic oxygen concentrations over repeated glacial cycles in the fully coupled Earth system model Bern3D. We further investigate how these oxygen changes relate to changes in marine carbon storage. Pioneering work on glacial-interglacial marine carbon cycle changes predicted linear relationships between Apparent Oxygen Utilization (AOU) and regenerated Dissolved Organic Carbon (DIC) changes, which are commonly used to estimate marine, and in some cases even atmospheric, carbon reservoir changes from reconstructions of these quantities. The new simulations show that the often-postulated linear correlations break in simulations of climatic change, often even in a closed atmosphere-ocean system that does not take into account weathering-burial imbalances. The underlying conceptual and box models do not capture essential dynamics of the real world systems, most importantly saturation disequilibria in the surface ocean. Hence, the linear relationships between these variables break in 3-d dynamic circulation models. AOU is therefore not a reliable measure for regenerated carbon in the ocean interior1,2 over glacial cycles and thus not a direct tracer of remineralisation. However, the perturbations of the oxygen cycle are, albeit in an intricate manner, related to those of the carbon cycle, and thus oxygen proxy reconstructions provide a constraint on carbon flux changes. For example, spatial and temporal patterns of oxygen concentration changes provide strong constraints for temporal changes of several Earth system processes (e.g. sea ice expansion, circulation and remineralisation) and oxygen proxy records are thus indispensable to test alternative scenarios of past ocean carbon cycle and atmospheric CO2 in Earth system models.
References
1 Cliff, E., Khatiwala, S. and Schmittner, A., 2021. Glacial deep ocean deoxygenation driven by biologically mediated air–sea disequilibrium. Nature Geoscience, 14(1), pp.43-50.
2 Schmittner, A. and Fillman, N.J., 2024. Carbon and carbon-13 in the preindustrial and glacial ocean. PLOS Climate, 3(7), p.e0000434.
How to cite: Adloff, M., Pöppelmeier, F., Stocker, T. F., and Joos, F.: The relationship of transient oxygen and carbon cycle changes in simulations of repeated glacial cycles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16248, https://doi.org/10.5194/egusphere-egu25-16248, 2025.
The Benguela Upwelling System (BUS) is one of the world’s most productive marine ecosystems, driven by wind-induced upwelling that delivers nutrient-rich deep waters to the surface, fueling high primary productivity. Dissolved oxygen (DO) in the BUS exhibits a pronounced latitudinal gradient, with the northern BUS (NBUS, 15°S–23°S) persistently hypoxic (<60 mmol O₂/m³), in stark contrast to the well-oxygenated southern BUS. Climate warming intensifies these challenges, as rising ocean temperatures, stronger upwelling, and increased oxygen consumption drive reductions in DO levels, threatening fisheries, benthic biodiversity, and ecosystem services.
This study addresses key questions on the long-term changes in DO dynamics in the NBUS: (1) What is the long-term variability in the total DO inventory over the past four decades (1980–2020)? (2) What are the primary drivers of oxygenation and deoxygenation trends? (3) What role does SACW play in regulating oxygen levels? (4) How does the OMZ vary in spatial extent, volume, and boundary depth over time? (5) What are the relative contributions of physical and biogeochemical processes to DO variability?
To investigate these questions, we employ a coupled physical-biogeochemical modeling system based on the Nucleus for European Modeling of the Ocean (NEMO v4.2.2) coupled with the Biogeochemical Flux Model (BFM v5.3). The model, with a horizontal resolution of 1/16° (~7 km), simulates pelagic-benthic interactions, lower trophic-level dynamics, and sediment remineralization, as driven by ERA5 atmospheric reanalysis and GLOFASv2.1 river discharge data.
Our results reveal a vertical dipole in oxygen trends. Positive trends dominate the upper 200 meters, linked to a declining SACW fraction (0–400 meters), while negative trends at 400–950 meters are primarily driven by ocean warming. OMZs show contrasting patterns, with the threshold OMZ (<120 mmol O₂/m³) expanding and the core OMZ (<20 mmol O₂/m³) contracting. This study highlights the complex interplay between warming, upwelling intensification, and ocean circulation in shaping oxygen dynamics in this highly productive marine system.
How to cite: Lovato, T., Talaat Salama, A., Lovecchio, E., Butenschön, M., Zavatarelli, M., and Henson, S.: Long-Term Changes in Oxygen Dynamics in the Northern Benguela Upwelling System, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11797, https://doi.org/10.5194/egusphere-egu25-11797, 2025.
The decline of ocean oxygen concentrations is an environmental issue of increasing concern. Detrimental changes have been observed in the last century, most prevalently in coastal marine environments. Drivers include warming, increased water stratification, higher biological oxygen demands, and other anthropogenic influences such as eutrophication. Current trends are predicted to continue in coming decades to centuries, but model uncertainties in future outcomes and severity persist. Long-term records of marine oxygen dynamics are crucial for improving climate models, contextualizing modern deoxygenation trends and understanding underlying mechanisms. Efforts to expand the toolbox of proxies capable of resolving low-oxygen states in the geological past are ongoing. Redox sensitive trace elements (e.g., manganese, iodine or uranium) in biogenic calcium-carbonates are among the emerging proxies. I will explore aspects of coastal oxygen dynamics and elemental cycling relevant for the calibration of trace element proxies on the example of manganese-to-calcium ratios (Mn/Ca) in benthic foraminifera. I showcase studies demonstrating (1) the potential of foraminiferal Mn/Ca as high-resolution archives of oxygen changes, and its current limitations, (2) the use of micro-analytical techniques such as laser-ablation ICP MS analyses and µXRF imaging in calibration approaches, and (3) the influence of biological factors on oxygen-proxy relationships. In conclusion, understanding the complexity of geochemical cycling in the light of oxygen thresholds, environmental settings and biological controls is critical for developing robust trace element proxies. Continued efforts of refining the manganese and other trace element proxies offer promising avenues towards quantitative reconstructions of bottom-water oxygen concentrations in the low oxygen-range, and a better understanding of past and present states of the marine environment.
How to cite: Brinkmann, I.: Coastal oxygen changes and element cycling: foraminifera as benthic monitors, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12568, https://doi.org/10.5194/egusphere-egu25-12568, 2025.
Calcareous benthic foraminifera can develop pores in their shells for gas exchange with seawater. Pore patterns, like porosity, pore density, and pore size, are influenced by environmental factors like bottom water dissolved oxygen concentration (BWDO). Some benthic foraminiferal species increase their test porosity under low BWDO, making them a useful proxy for reconstructing past oxygenation. The pore patterns proxy for BWDO is validated in the Southeast Pacific (SEP) by examining six benthic foraminifera species compared to estimate BWDO on the sediment sites. Specimens were collected from surface sediments at 24–3,252 m water depths across the SEP (12°–44°S) and selected based on their Rose Bengal staining, oxygen isotopes, and calibrated sediment radiocarbon age to reflect modern conditions. The benthic foraminiferal species measured in this study typically have a planispiral shell with pores on two sides: pores on the umbilical side, which faces the water column, and the spiral side, commonly used for attachment. Both sides are measured to test their role in oxygen uptake. Porosity, pore density, and size were measured on all visible chambers and, specifically, on the penultimate and antepenultimate chambers. In the SEP, the main response to BWDO changes occurs on the umbilical side of the benthic foraminifera, while some oxygen uptake might also happen on the spiral side. Combined benthic foraminifera species, and solely C. wuellerstorfi, increase umbilical porosity under lower BWDO. These findings align with global calibrations, supporting the quantitative use of the benthic foraminifera pore patterns proxy to reconstruct past BWDO in other oceans, with an error range of around ±60 µmol kg-1 for BWDO above 100 µmol kg-1 and around ±20 µmol kg-1 for BWDO lower than 100 µmol kg-1.
How to cite: Garrido, S., Hoogakker, B. A. A., Richirt, J., Reyes-Macaya, D., Hernández-Almeida, I., Cardich, J., Castillo Bruna, A., Fouet, M. P. A., Gayo, E. M., Hebbeln, D., Farías, L., and Jorissen, F.: Temporal, morphological, and taxonomic frameworks for calibrating benthic foraminifera pores patterns as a proxy for paleoxygenation in the Southeast Pacific, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9638, https://doi.org/10.5194/egusphere-egu25-9638, 2025.
Global ocean oxygen depletion is a growing concern, with direct observations showing widespread decline that is not fully captured by existing models. The dynamics of oxygenation are critical to marine ecosystem health and are influenced by physical and biogeochemical factors. To reconstruct past variation of dissolved oxygen content, foraminiferal iodine to calcium (I/Ca) ratio has been developed. This proxy is based on the fact that iodine speciation is dependent on oxygen content and that only iodate ions (IO3-) can be incorporated into the calcite lattice by substitution for carbonate ions. However, our knowledge of foraminiferal I/Ca behavior needs improvement because the relationship between planktonic foraminiferal I/Ca and oxygen content in the upper 500m water column appears to be empirical and the influence of physical and biogeochemical parameters has not been fully addressed yet, and thus prohibits the development of a fully quantitative proxy.
In this study, we present the first planktic foraminiferal I/Ca data from core-top material (late Holocene) in the Mediterranean Sea and a compilation of previously published core-top and plankton tow I/Ca data from the global ocean. We use this database to examine the influence of the maximum and minimum oxygen concentration, temperature, salinity, nutrients, pH, alkalinity, chlorophyll, water velocities and mixed layer depth on the I/Ca proxy. Additionally, we assess the effects of water depth and sample age to monitor possible iodine accumulation during the foraminiferal test settling and early diagenetic effects. We also investigate the potential for differential behaviour between foraminiferal species by categorising by the presence/absence of symbionts.
We find unexpectedly low I/Ca as low as 1 µmol/mol in samples from the western basin of the Mediterranean Sea, providing the first low I/Ca from fossil foraminiferal which lived in waters thought to be highly oxygenated. Principal Component Analysis (PCA) confirms the dominance of oxygen content on foraminiferal I/Ca, however, analysis of the foraminiferal I/Ca residuals after subtraction of oxygen dependence suggest a potential role of temperature. No clear trend is not observed between the residuals and sample age, suggesting a negligible influence of burial diagenesis. Iodine accumulation during the settling of foraminiferal tests has been proposed to explain the high I/Ca of fossil samples when compared to plankton tows, but no trends are visible between our residuals and water depth, implying that there is no systematic effect from post-mortem settling. The cause of low foraminiferal I/Ca in oxygenated waters remains unclear and may involve poorly constrained local oxygen variability, the chemical dynamics of iodine, iodine incorporation mechanisms, or other unknown parameters.
How to cite: Guarinos, V., Tachikawa, K., Chalk, T., Garcia, M., Siani, G., Revel, M., Schulz, H., and Sierro, F.: Investigating I/Ca ratio in planktic foraminifera: an integrated approach in the Mediterranean Sea and beyond, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8311, https://doi.org/10.5194/egusphere-egu25-8311, 2025.
Posters on site: Thu, 1 May, 16:15–18:00 | Hall X5
The early Toarcian Oceanic Anoxic Event (T-OAE, ∼183 Ma) provides an analog to the consequences of extreme climate change and major perturbation of the global carbon cycle. This disruption of the Earth’s system in the Early Jurassic caused the extension of anoxic and euxinic waters, notably in the Alpine-Mediterranean Tethys and across the northern European epicontinental shelf and north African margin, as indicated in the geological record by the widespread occurrence of organic-rich black shales. This event has been extensively studied in marine and continental records. However, the environmental dynamics during the recovery phase of the T-OAE are still poorly understood.
The Southern Alps of northern Italy are a critical region for reconstructing the evolution and dynamics of the T-OAE. The best outcrops of the associated black shales are found in the Belluno Basin, a narrow pelagic trough that formed between two carbonate platforms in the earliest Jurassic. Here, they are found in successions featuring large-scale rhythmic alternations between limestone and marlstone, which are interpreted as having a mostly primary origin.
In this study, we integrate petrographic, geochemical, and mineralogical data from the Vajont Gorge section near Longarone to investigate short-term signals (on a couplet scale) and long-term paleoenvironmental trends (on an outcrop scale) after the peak of the T-OAE.
Our results reveal that the recovery phase from the negative carbon-isotope excursion of the T-OAE is accompanied by a gradual increase in carbonate deposition or preservation. We argue that a significant portion of this mud-grade carbonate originated from calcareous nannoplankton and aragonitic muds shed off platforms. However, the short-term signal of the initial variations in the aragonite input into the deeper basin was lost due to early diagenetic carbonate redistribution processes.
Furthermore, our findings suggest that the lithological rhythms are linked to cyclic variations in the strength of bottom-water currents. We hypothesize that these variations in bottom current activity were caused by episodic reactivation of the thermohaline circulation in the Belluno Basin, which could have facilitated the amelioration of bottom-water oxygen conditions after prolonged phases of water mass stagnation during the peak of the T-OAE.
How to cite: Meissner, J., Cobianchi, M., Munnecke, A., and Picotti, V.: Shift in Sedimentary Dynamics in the Belluno Basin (Southern Alps, Italy) after the Peak of the Early Toarcian Oceanic Anoxic Event, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17939, https://doi.org/10.5194/egusphere-egu25-17939, 2025.
Marine phosphatization events cause episodic carbonate fluorapatite (CFA) precipitation on seamounts, and are commonly linked to growth hiatuses in ferromanganese (Fe-Mn) crusts, provide critical archives for reconstructing past ocean oxygen dynamics and phosphorus cycling due to the tight relationship with oceanic oxygen minimum zones(OMZs). However, the complete record of these events and their paleoenvironmental significance remains poorly understood, in large part due to poor age constraints. Here, we apply U-Pb dating to CFA in Fe-Mn crusts from Western Pacific seamounts. These data exhibit good alignment with Sr isotope ages, revealing six potential phosphatization events. This established CFA chronology tightens the timespan of phosphatization events and refines the age framework of Fe-Mn crusts. We subsequently utilize a multiproxy approach to demonstrate that the phosphatization events occurred coeval with the expansion of oceanic OMZs. The Western Pacific Fe-Mn crusts thus document major perturbations in global oceanic phosphorus cycling, which appear to have been driven by climate-induced increases in primary productivity linked to changes in global ocean circulation. These findings offer insights into potential implications for nutrient cycling, marine ecosystems, and the evolution of OMZs.
How to cite: Peng, J., Li, D., Poulton, S., O’Sullivan, G., Chew, D., Fu, Y., and Sun, X.: Episodic intensification of marine phosphorus burial and oceanic oxygen minimum zone expansion over the last 80 million years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2369, https://doi.org/10.5194/egusphere-egu25-2369, 2025.
The tectonic change in geometry of two tropical seaways, the Central American Seaway (CAS) and Indonesian seaway, during the mid-Miocene to mid-Pliocene (~16-3 Ma BP) is thought as a key factor for the development of the present-day tropical Pacific oxygen minimum zone.
The aim of this study is to investigate the dual impact of sill depth changes in the Central American and the Indonesian seaways on the ocean circulation and oxygen minimum zone in the tropical Pacific. To this end, we performed a series of sensitivity experiments with the global climate model KCM where sill depths of both tropical seaways were set at different depths, ranging from shallow to deep levels.
Our results based on a separate effect of CAS changes support previous modelling studies showing that CAS closure have led to an intensification of the Atlantic Meridional Overturning Circulation due to a termination of fresh-water supply from the tropical Pacific to the North Atlantic. The open CAS increases meridional sea surface height gradient in the tropical Pacific which drives eastward subsurface flow in the region. This, in turn, facilitates stronger west-to-east oxygen supply and subsequent overall oxygen enrichment in the subsurface Pacific waters with strongest anomalies observed in the eastern tropical Pacific.
Another important task of this study is to investigate how various sill depths of the Indonesian seaway can additionally adjust an individual effect of open CAS-induced changes for ocean currents in the Pacific and the tropical Pacific oxygen minimum zone.
How to cite: Khon, V., Hoogakker, B., Schneider, B., Segschneider, J., and Park, W.: Impact of the Central American and the Indonesian seaways on the ocean circulation and oxygen minimum zone in the tropical Pacific, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18887, https://doi.org/10.5194/egusphere-egu25-18887, 2025.
Ocean oxygen concentration has been reported to decline over the past few decades due to the ongoing climate crisis. The development of the Oxygen Minimum Zone (OMZ) during the Pliocene (5.3–2.6 Ma) offers a valuable analog for understanding ocean oxygenation under modern climate change, as the Pliocene shares similar climatic conditions with those in the present. However, the mechanisms controlling OMZ development during this period are not fully understood, highlighting the need for suitable proxies to provide further insights. Recent studies have proposed the planktic foraminifer Globorotaloides hexagonus as a potential direct indicator of OMZ variability, assisting investigations into oxygen-depleted environments. While previous research suggests that modern G. hexagonus responds to change in water oxygen concentration through variations in shell porosity, its application in paleo-reconstructions remains unexplored. Thus, the biogeochemical relationship between G. hexagonus and OMZs requires additional investigation. In this study, we quantified the abundance of G. hexagonus at Ocean Drilling Program (ODP) Site 1241 in the East Equatorial Pacific to investigate its relationship with oxygen concentrations during glacial-interglacial cycles in the Pliocene. Our results indicate significant variability in G. hexagonus abundance, suggesting changes in OMZ. The results initially focus on Marine Isotope Stages (MIS) 96-100 (~2.55–2.4 Ma), where a correlation appears between the trend in G. hexagonus abundance and precession variability cycles (insolation). In contrast, no significant variability patterns are observed around MIS M2 (~3.3 Ma). We then selected four samples characterized by high and low G. hexagonus abundance and captured their images using scanning electron microscopy (SEM). A deep learning algorithm, initially trained for pore morphometry in benthic foraminifera, was retrained specifically to analyze G. hexagonus SEM images, enabling efficient obtaining of pore parameters (porosity, pore size, and pore density). Significant differences in porosity between high- and low-abundance groups suggest that increased porosity is associated with stronger OMZ, consistent with the abundance counts. Statistical analysis indicates that porosity variations are primarily driven by changes in pore size rather than pore density. Although the current findings cover only the ~2.55–2.4 Ma interval, they provide robust evidence for oxygenation-related adaptations in G. hexagonus abundance and pore morphology. Furthermore, extending the G. hexagonus abundance study from 3.3-2.4 Ma and including Mn/Ca analyses on the tests of G. hexagonus will provide more robust evidence on the controlling forces behind the variability in OMZ intensity during the Pliocene.
How to cite: Huang, Y.-H., Glock, N., and Groeneveld, J.: Reconstructing the OMZ in the east Pacific during the Pliocene using G. hexagonus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2419, https://doi.org/10.5194/egusphere-egu25-2419, 2025.
The sedimentary sequence of the eastern Mediterranean is often marked by organic-rich layers called sapropels. Sapropel formation was mainly caused by excess freshwater input and the subsequent reduction of ventilation due to an enhanced African monsoon combined with deglacial water input. However, the paleoriver discharge from the North Africa under interglacial and glacial boundary conditions and its impact on the sapropel formation has not been fully clarified yet. We obtained an Nd isotopic composition (εNd) record of the detrital fraction as well as a grain size indicator of a marine sediment core from the eastern side of the Gulf of Sirte to reconstruct the reactivation of Libyan fluvial fossil systems for the past 240,000 years. The εNd record showed a systematic increase from a baseline of -12 to -9 to -8 for sapropels S1 to S9, including the glacial sapropel S6. This εNd shift was synchronous with barium enrichment and depleted planktonic foraminiferal oxygen and carbon isotopic compositions that marked the sapropels. Based on a new εNd map of source regions in North Africa, the higher εNd values can be explained by preferential weathering of volcanic fields and soils and increased river discharge under both interglacial and glacial conditions. The grain size indicator showed an increase in fine river particles relative to coarse atmospheric dust when detrital εNd was higher, supporting this interpretation. These observations are consistent with the available detrital εNd records, suggesting that the higher isotopic signals during sapropel formation are a basin-wide feature in the Gulf of Sirte. The hydrological cycle in the study area was estimated to be more sensitive to precessional forcing than to high-latitude climate conditions, being consistent with previous modelling studies.
How to cite: Tachikawa, K., Beny, F., Vidal, L., Guihou, A., Sonzogni, C., conrod, S., Pratiwi, A., Deschamps, P., and Schultz, H.: Paleoriver discharge controlled by precession cycle in the North Africa over the past 240,000 years: relationship to sapropel formation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7994, https://doi.org/10.5194/egusphere-egu25-7994, 2025.
Ice core records show a sigificant decline in atmospheric oxygen concentrations during the last 800ka (Stolper et al., 2016). Recent data from blue ice seem to show similar oxygen concentrations from around 800 ka to 1500 ka (Yan et al 2021) and this change has been suggested as one possible driver of the Mid Pleistocene Transition (MPT) from 40ka (one obliquity cycle) to 80 or 120 ka glacial cycles (two or three obliquity cycles). We have shown that not only shallow but also deep terrestrial pyrite oxidation and potentially oxidation of organic substance on shelves exposed during sea-level lowstands in glacials is a significant source of both CO2 and a significant sink for O2 (Kölling et al 2019). Since these reduced phases are only recharged in the upper meters of the inundated shelf sediments during interglacials, the reservoir of the CO2 producing and oxygen consuming material is gradually declining over the Pleistocene. In our model, the MPT is the time, when the sea-level decline during one 40ka obliquity cycle is not enough to expose significant amounts of reduced shelf sediments anymore. We suggest that the CO2 release through subareal oxidation of pyrite and organic substance on exposed shelves might be a substantial ingredient adding to the obliquity driven increase in high latitude insolation to terminate a glacial phase. The lack of this additional CO2 contribution might thus be a cause of glacial cycles failing to terminate whithout any significant change in orbital conditions. In our model, the oxygen demand by pyrite oxidation causes a step decline to 21.16 vol% in the beginning of the Pleistocene at 2.6 Ma, a gradual decline to 21.11 Vol% at 1.2 Ma (MIS 36) and a steeper decline after the MPT. The major step declines in oxygen concentrations driven by pyrite oxidation are modelled in MIS 20 (-0.02 vol%), MIS16 (-0.04 Vol%) and MIS 12 (-0.03 Vol%). In our model, the Pleistocene decline in atmospheric oxygen is a side effect of the terrestrial oxidation of pyrite and organic substance in glacially exposed shelf sediments. We think, there is no "100 ka" driver for longer glacial cycles, but the magnitude and timing of this CO2 producing and O2 consuming process might be crucial to terminate glacials and might thus be responsible for failed terminations /missing interglacials specifically after the MPT.
How to cite: Koelling, M.: Sea-level driven Pleistocene decline in atmospheric oxygen concentrations after the MPT, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17995, https://doi.org/10.5194/egusphere-egu25-17995, 2025.
The Ionian Sea is a deep-marine basin in the central Mediterranean Sea affected by great earthquakes and tsunamis linked to the tectonic activity of the Calabrian and Hellenic subduction zones. The sedimentary record presents gravity-driven deposits in the basin (turbidites, debrites, megabeds) and includes a particular unit formed during oxygen depletion (10–6.3 kyr), corresponding to the sapropel S1 layer. The S1 record in the Ionian Sea was typically described as a carbon-enriched layer with a thickness of a few centimeters. New data collected during the FOCUS-X2 campaign (2022), off Etna, reveal an exceptional 15 m thickness at 2050 m of water depth for the interval of 10-6.3 kyr.
Sediment core FX2-CS14 is located in a fault graben, which acts as a sediment trap. It offers an unprecedented opportunity to study the sedimentary records variations along the last 22 kyrs and to analyse in detail the S1-equivalent sapropel unit. Core FX2-CS14 dataset is comprised of: major element composition, physical properties, X-ray imagery (XCT), grain size measuremets, and radiocarbon dates. Organic geochemical analyses included measurements of organic carbon, nitrogen, δ13C isotopic composition, and biomarkers (lignin and cutin).
The sedimentary facies before and after the S1-equivalent layer include: 1) Debrites, 2) Turbidites, 3) Fine brown deposits, 4) Light brown hemipelagites with foraminifera and bioturbation, and 5) Tephra. The S1-equivalent unit displays numerous millimeter-scale laminated facies, including up to 3-5 unique sub-facies and micro-turbidites (which are rare or not visible outside of this period), likely due to better preservation. Bioturbation and benthic foraminifera are absent in the S1-equivalent unit, except during its interruption (S1i), indicating seafloor anoxia. This anoxia enables high-resolution studies of climatic and oceanographic variations during the sapropel S1 equivalent period.
The geochemical analyses show that the sapropel S1-equivalent deposits have low organic carbon (0–1%) due to sapropel dilution by large volume of detrital sediment (690 gravity-flow event beds). Organic geochemistry reveals depleted δ¹³C, indicating terrestrial input, and mixed sedimentary origins of the organic matter. The sedimentary record of this coring site shows marine and continental signals, with evidence of older components, likely influenced by floods and river discharge. The extended unit highlights intense land-ocean exchanges and strong connectivity.
The frequency of gravity deposits (turbidites) increases significantly from ~5 events/1000 years in the recent period to ~60 events/1000 years during the S1-equivalent unit. In recent period, the gravity-driven deposits frequency seems consistent with the occurrence of strong earthquake (M ≥6). However, during the S1-equivalent period, turbidites are probably related to other triggering mechanism. Micro-turbidite (≤2 mm) could result from decadal-scale, climate-driven torrential floods triggering turbidity currents (or hyperpycnal flows).
How to cite: Belliard, H., Babonneau, N., Cattaneo, A., Tesi, T., Nogarotto, A., Coussin, V., and Gutscher, M.-A.: When seafloor anoxia sharpens paleoenvironmental reconstructions: signature of sapropel S1 and exceptional preservation of fine laminations to decipher climatic and oceanographic variations in the Ionian Sea., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10221, https://doi.org/10.5194/egusphere-egu25-10221, 2025.
Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW) form the two main intermediate depth water masses from the Southeast Pacific Ocean. They sequester and store copious quantities of atmospheric gases, such as CO2 and O2, and are the most important global oxygen source to the thermocline and equatorial region. These intermediate ocean water masses thus regulate and modulate the benthic ecosystem and nutrient cycling. They are also sensitive recorders of changes in ocean circulation and play a critical role in contributing or triggering interhemispheric overturning changes by changing its depth, distribution, and properties. It is therefore important to understand the environmental feedback to the variations in intermediate ocean to define the tipping points in the ocean-climate system.
The variability of the AAIW specifically during abrupt climatic transitions such as the Antarctic Isotope Maxima event (AIM 8) is not yet constrained due to scarcity of well-dated high-resolution records. Antarctic Isotope Maxima (AIM) events are millennial-scale abrupt warming events during Marine Isotope Stage 3 (MIS-3; 57-29 kya) identified in the Antarctic ice core records. They are characterized by 1 to 3°C warming and cooling phase and are potentially triggered by AMOC instability due to freshwater discharge, internal sea-ice-ocean-atmospheric variability and Southern Ocean dynamics. Here, we use a high-resolution sediment core, Ocean Drilling Program (ODP) Site 1233 (41º00′S; 74º27′W at 838m water depth), recovered from intermediate water depths in the SE Pacific to study the physical and biogeochemical characteristics of the AAIW during AIM 8 using stable isotope measurements from epifaunal and infaunal benthic foraminifera.
The reconstructed [O2] shows a rapid rise in values to about 350 μmol/kg during the abrupt AIM 8 event, providing key insights on ocean ventilation and water mass structure. A stark contrast in the rate of change in [O2] signal in comparison to the rate of change in δ¹³C and δ¹⁸O signals in the interval 37–39.4 ka explains sensitivity of interior ocean ventilation as response to changing water mass structure or rates of warming. Our high-resolution study thus resolves the rates of changes in the water masses influencing oxygenation of the interior ocean at its source location in the SE Pacific. Our results highlight the drivers of oxygenation changes such as changes in ventilation, thermocline dynamics, and ocean circulation operating independently or in combination during the abrupt AIM 8 event. The magnitude and rate of ocean ventilation changes can potentially be used as an analogue for Last Glacial Maximum to define a tipping point within the ocean-climate system.
How to cite: Nadar, P. M. J., Kleiven, K., Ninnemann, U., and Irvali, N.: Oxygenation and Ventilation in the Intermediate Southeast Pacific Ocean during abrupt Antarctic warming event AIM8 , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17056, https://doi.org/10.5194/egusphere-egu25-17056, 2025.
The Humboldt eastern boundary upwelling system, due to its proximity to the equator is highly sensitive to equatorial Pacific disturbances, particularly those associated with the El Niño Southern Oscillation (ENSO). This has consequences for the so-called oxygen minimum zone, an extensive area of low oxygen waters at intermediate depths that impacts marine biota. During warm El Nino events, the OMZ tends to shrink in its upper margin along both Peru and central Chile but the magnitude of the change is sensitive to the characteristics of El Niño events. Here, we focus on the subtropical OMZ off Chile (18°-38°S) and document OMZ volume and pattern changes during extreme El Niño events (1982/83 and 1997/1998) based on a regional coupled model simulation. This is contrasted to changes that occurred in 1972/73 that correspond to the occurrence of a moderate El Niño event in the tropical Pacific. The results indicated that the volume of the subtropical OMZ off Chile decreased on average by 27-48% during these El Niño events, which was associated with a coastal oxycline deepening that peaked during the development phase of the events. However, we find that the magnitude of the change varies a lot between events with in particular the 1972/73 El Niño exhibiting the largest changes in volume. The model analyses reveal that the OMZ volume reduction resulted from a combined effect of changes in the poleward transport oxygen-poor waters by the Peru-Chile undercurrent and the contribution of Ekman pumping (negative wind stress curl) and mesoscale eddy fluxes.
How to cite: Pizarro-Koch, M., Dewitte, B., and Aguirre, C.: Response of the subtropical oxygen minimum zone off Chile to El Niño events in a regional biogeochemical model: remote vs local forcings, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20639, https://doi.org/10.5194/egusphere-egu25-20639, 2025.
Posters virtual: Fri, 2 May, 14:00–15:45 | vPoster spot 5
EGU25-3477 | ECS | Posters virtual | VPS7
Unusual mass-occurrence of small, uncoiled ammonites in a black shale of the Maiolica Formation in the Umbria-Marche Basin (Central Italy)Fri, 02 May, 14:00–15:45 (CEST) | vP5.8
The unique mass-occurrence of tiny heteromorph ammonites found in a single layer in the Mt. Cipollara locality of Cerreto d'Esi (Maiolica Formation, Umbro-Marchean Basin, Italy) provides critical insights into the depositional environments of the Cretaceous upper Maiolica Formation. The mechanisms behind the formation and preservation of these ammonite assemblages within black shales remain poorly understood. To solve this knowledge gap, we constrained by means of biostratigraphy and stable Carbon isotopes the whole sections hosting the ammonites-rich layer. The latter was then subjected a high-resolution paleoecological analyses. Samples were collected systematically across multiple stratigraphic levels to ensure comprehensive coverage. The ammonite assemblages were documented, focusing on their morphology, abundance, and associated sedimentary structures. Additionally, sedimentological petrographic examinations were conducted to elucidate depositional processes. Our results reveal a rich assemblage dominated by the family Leptoceratoididae, exhibiting relatively good preservation within a predominantly dysoxic low-energy environment at the bottom. Calcareous nannofossils data suggest the presence of a well-stratified water column, with a low salinity water cap. The multidisciplinary analyses indicates that these black shales served not only as a repository for ammonite remains but also reflected localized paleoecological conditions characterized by reduced turbulence and increased organic deposition. This unique sedimentary context suggests that the deposition of these assemblages could have been influenced by both regional sea-level fluctuations and local hydrographic conditions. In conclusion, the study of the Mt. Cipollara heteromorph ammonites underscores the complexity of Cretaceous paleoenvironments and provides an enhanced understanding of the occurrence of black shales within the Maiolica Formation.
How to cite: Conti, C., Faraoni, P., Mancini, A. M., Luca, M., and Negri, A.: Unusual mass-occurrence of small, uncoiled ammonites in a black shale of the Maiolica Formation in the Umbria-Marche Basin (Central Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3477, https://doi.org/10.5194/egusphere-egu25-3477, 2025.
EGU25-16338 | Posters virtual | VPS7
Carbon cycle perturbations during the Pliensbachian-Toarcian transition in the Monte Serrone section (Northern Apennines, Italy)Fri, 02 May, 14:00–15:45 (CEST) | vP5.9
The Pliensbachian/Toarcian event (P/T-E) and the Toarcian Oceanic Anoxic Event (T-OAE) are two intervals of carbon cycle perturbations linked to massive 12C-enriched carbon emissions, causing severe biotic and environmental changes. Here organic carbon isotope, mineralogical composition and sedimentology have been analyzed across the Pliensbachian-Toarcian transition from the Monte Serrone section (Umbria-Marche Basin), which was deposited in a pelagic setting in the western Tethys. A marked negative carbon-isotope excursion occurred across the Pliensbachian-Toarcian boundary and lower Toarcian, respectively, which can be used to identify PTE and T-OAE in the study area. The P/T-E and T-OAE intervals witnessed carbonate production crisis revealed by reduced carbonate contents. We hold that the 0.5 m-thick laminated black shales indicated that the T-OAE was a highly condensed succession because it included the full duration of the T-OAE. Therefore, the T-OAE interval at Monte Serrone coincided not only with diminished carbonate production but also with reduced siliciclastic input, forming quite thin black shale deposition. Abundant marine organisms were present preceding the T-OAE. Nevertheless, none of them survived during the most negative carbon-isotope excursion of the T-OAE, revealing a biotic crisis at this time. Elevated seawater temperature could induce this crisis in the study area. The recovery of benthic foraminifera was delayed at Monte Serrone.
How to cite: Nie, Y., Fu, X., and Rigo, M.: Carbon cycle perturbations during the Pliensbachian-Toarcian transition in the Monte Serrone section (Northern Apennines, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16338, https://doi.org/10.5194/egusphere-egu25-16338, 2025.
EGU25-11624 | Posters virtual | VPS7
Early Cretaceous Oceanic Anoxic Events (OAEs) in Peri-Tethyan shallow-water carbonate systems: Evidence from the Latium-Abruzzi Carbonate Platform (Ernici Mts, Central Italy)Fri, 02 May, 14:00–15:45 (CEST) | vP5.10
While the effects of OAEs are well known for the pelagic successions of the Tethys Ocean, little is known about their impact on the Peri-Tethyan shallow water carbonate systems. Here we present the preliminary results of a study related to the geological mapping of the sheet 390 – Frosinone of the Geological Map of Italy (CARG Project), focussed on the identification and description of the perturbation induced in the Lower Cretaceous shallow water carbonate succession of the Latium-Abruzzi Carbonate Platform by the well-known Early Cretaceous Oceanic Anoxic Events (OAEs).
In the Ernici Mts. (central Apennines, Italy), an Upper Triassic to Upper Cretaceous shallow-water carbonate succession is exposed (Cosentino et al., 2010; Fabbi et al., 2023). This study specifically examines the Lower Cretaceous "calcari ciclotemici a gasteropodi" fm. (CCG - Berriasian p.p. - lower Aptian p.p.), which mainly consists of whitish limestones with intercalations of light grey dolostones. Within this succession, a layer of black dolostone, about ten centimetres thick, has been observed in several outcrops of the dolomitic lithofacies (CCGa) of CCG, at the same stratigraphic position.
Two stratigraphic sections were measured to characterise the microfacies and compositional variations observed between the light-coloured (whitish to light grey) and black layers. SEM images, along with Energy-Dispersive X-ray Spectroscopy (EDS) and Wavelength-Dispersive X-ray Spectroscopy (WDS) analysis indicated the presence of siderite and pyrite aggregates (Meng et al. 2024). These aggregates appear in high concentration starting from the basal part of the blackish dolostone layer and gently decrease towards the upper part of the study interval. TOC and sulphates show similar trends.
Changes in chemical composition between the whitish and blackish dolostones (CCGa) were investigated in situ using the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) facility at Roma Tre University. The results show a significant increase in elemental concentration of P, Fe, Zn, As, Ba, Pb, and U, as well as in the Fe/Al ratio in the blackish dolostones. These elements are generally considered as redox-sensitive proxies associated with anoxic paleoenvironments (Bodin et al., 2007; Craigie, 2018).
Biostratigraphic calibration performed on the collected samples has established a Hauterivian p.p. age for the investigated CCGa levels. A preliminary attempt for U-Pb dating of the CCGa black dolostone was carried out through LA-ICP-MS investigations at Roma Tre and ETH facilities. In the Tera-Wasserburg diagram, the U-Pb measurements on CCGa black dolostone yielded a lower intercept age of 125.7± 1.8 Ma (MSWD=1.6; N=19). These promising results suggest that the changes in the elemental concentration of the redox-sensitive proxies observed in the CCGa black dolostone were induced by the late Hauterivian Faraoni Oceanic Anoxic Event.
How to cite: Artegiani, F., Cipollari, P., Cosentino, D., Rabiee, A., Guillong, M., Rossetti, F., Cipriani, A., and Fabbi, S.: Early Cretaceous Oceanic Anoxic Events (OAEs) in Peri-Tethyan shallow-water carbonate systems: Evidence from the Latium-Abruzzi Carbonate Platform (Ernici Mts, Central Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11624, https://doi.org/10.5194/egusphere-egu25-11624, 2025.
EGU25-15403 | Posters virtual | VPS7
Past analogues of deoxygenation events in the Mediterranean Sea: Comparison between shallow and deep settingsFri, 02 May, 14:00–15:45 (CEST) | vP5.11
Human-induced carbon emissions are altering the modern climate, with severe repercussions on ecosystems. Among others, anthropogenic pressure is causing deoxygenation of the bottom water, with the widespread establishment of hypoxic zones in several Mediterranean areas. The geological archives allow the investigation of past deoxygenation dynamics (sapropel events) and their impact on marine ecosystems. Here, we compare the causes and the evolution of deoxygenation dynamics that occurred during two different time periods (Messinian and Holocene) in different paleoceanographic settings based on their micropaleontological content. The Messinian sapropel events are the result of increased export productivity during a relatively cold and arid context, triggering bottom anoxic conditions. The Holocene sapropel formed in response to weakening/stopping of the thermohaline circulation due to increasing temperature and freshwater input. Our results suggest that the deoxygenation dynamics in the Mediterranean in the near future will not follow the trend characteristic of the Holocene deep-sea sapropel because of the predicted drying trend. Differently, the paleoceanographic setting triggering the Messinian shallow-sea sapropels is comparable with the modern situation in different Mediterranean areas, where human-induced eutrophication is promoting deoxygenation. Based on these results, we suggest that the patchy deoxygenation trend in the Mediterranean Sea caused by climate warming may lead to a drastic change in the ecosystem services which would likely impact human activities.
How to cite: Lozar, F., Mancini, A. M., Morigi, C., Gennari, R., and Negri, A.: Past analogues of deoxygenation events in the Mediterranean Sea: Comparison between shallow and deep settings , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15403, https://doi.org/10.5194/egusphere-egu25-15403, 2025.
