Organische Umweltgeochemie MariNEO

Marine nitrogen cycle feedbacks to the Eocene-Oligocene climatic transition

Funded through the IODP priority program of the Deutsche Forschungsgemeinschaft (DFG)

2023-ongoing

Project Description

The marine nitrogen cycle regulates oceanic primary productivity and the emission of nitrous oxide (N2O), a potent greenhouse gas. The microbial redox processes constituting the marine nitrogen cycle are sensitive to environmental change, such as temperature, pH, and oxygenation. While marine nitrogen cycle responses to past warming events are increasingly studied, its behavior during significant cooling transitions remains poorly understood. This project investigates feedbacks between the nitrogen cycle and climate during the Eocene-Oligocene Transition (EOT; ~33.9-33.4 Ma), an interval of the Cenozoic when Earth’s climate shifted from a greenhouse to an icehouse state. The EOT was marked by declining pCO2, global cooling, reorganization of ocean circulation, biotic changes, and a rise in pH. We hypothesize that these environmental changes fundamentally reorganized the nitrogen cycle, which acted as a feedback on cooling via changes in N2O production and marine biota via changes in nitrogen availability. To address these hypotheses, the project uses a multi-proxy approach across 13 globally distributed sites using lipid biomarkers and bulk sediment nitrogen isotopes. Proxy records will be integrated with the Earth system modeling to provide quantitative estimates of changes in individual nitrogen cycle processes and their consequent feedbacks on climate and ecosystems. The outcomes of this project will provide a global reconstruction of the nitrogen cycle during a major cooling event. Contrasting the EOT with prior research on warming events will reveal the thresholds and directionality of nitrogen-climate feedbacks, enhancing our understanding of the interconnections between biogeochemical and climate change.