- 1GR Marine Geosciences, Facultat de Ciències de la Terra, Universitat de Barcelona, Barcelona, Spain (icacho@ub.edu)
- 2Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas, Barcelona, Spain
- 3Dipartimento di Scienze della Terra, Sapienza Università di Roma, Roma, Italy
- 4Dipartamento di Fisica e Geologia, Universita di Perugia, Via Alessandro Pascoli, Perugia, Italy
- 5Departamento de Estratigrafía y Paleontología, Universidad de Granada, Granada, Spain
- 6MARUM Center for Marine Environmental Sciences, Bremen, Germany
- 7Department of Earth Science and Engineering, Imperial College London, London, United Kingdom
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.