Climate and biogeochemical evolution of the Mediterranean Sea over the Plio-Pleistocene

• Applicant: Dr. Tanja Wald
• Subject Area: Palaeontology ; Oceanography
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 579295408

The Mediterranean region is recognized as one of the major climate change hotspots, being increasingly exposed to long-lasting heatwaves and droughts. This affects both the human health, and environmental resilience, on land and in the ocean. The marine biogeochemical cycles, and thus ocean ecosystems, can be heavily altered in response to climatic changes. Information about the response of the Mediterranean’s biogeochemistry to past climate changes can provide insights on the sensitivity of its ecosystems to global warming. Biomarkers and nitrogen isotopes are a powerful analytical combination to study past changes of climatic responses on land and in the ocean. However, the available reconstructions from the Mediterranean region are scarce. So far, Mediterranean reconstructions of past changes in marine nutrient cycling were performed on bulk sediments and chlorins. These analyses focused mainly on temporal anomalies in the nitrogen cycle during the deposition of sapropels in the eastern Mediterranean. Importantly, they do not cover the natural variability over glacial-interglacial periods. Sapropels are quasi-periodically occurring dark sediment layers with high organic carbon contents and have been linked to Green Sahara Periods, periods with savannah-like vegetation in the Sahara. Sapropels reveal drastic negative δ15N changes compared to marl layers, and were likely caused by increased N2 fixation rates during sapropel deposition due to a northward migration of the African monsoon rain belt. However, previous analyses have been limited by a low temporal resolution and/or the susceptibility to diagenesis, hindering the identification of pristine signals of the nitrogen cycle in the Mediterranean Sea. In addition, reconstructions of past changes in terrestrial climate are mainly based on dust deposition records, limiting a more quantitative evaluation of past changes in the hydrological cycle. The objective of this project is to reconstruct Plio-Pleistocene hydroclimate and related marine biogeochemical responses in the western and eastern Mediterranean Sea. The project covers both glacial-interglacial time scales and multiple sapropel layers and will be based on ODP sediment cores enabling both leaf wax biomarker isotopes (δD and δ13C) and foraminifera-bound δ15N analyses. The latter represents a novel method that focuses on the analysis of the organic material protected from diagenesis by the biomineral matrix of the foraminiferal shells. Together, the methods will enable a detailed investigation of the longer-term and orbital-scale variability of the climate and nitrogen cycle in glacial-interglacial time scales, as well as the climatic induced changes during sapropel formation.

• DFG Programme: Research Grants