"The response of the marine nitrogen cycle to past ocean anoxia"

Speaker: Felix Elling

The marine nitrogen cycle has undergone large perturbations throughout Earth history, such as during Mesozoic Oceanic Anoxic Events (OAEs). Reconstructing past environmental changes during these events remains challenging due to the multitude of nitrogen transformation pathways. To better understand the nitrogen cycle during anoxic conditions, we studied Pliocene-Pleistocene sapropels in the Mediterranean Sea, which are organic-rich sediments deposited during multi-millennial anoxic events. By analyzing bulk sedimentary ¹⁵N isotopes and the excellently preserved organic biomarkers in these sediments, we were able to reconstruct the occurrence and environmental impact of multiple groups of nitrogen-transforming microorganisms. Our results indicate that the nitrogen cycle during sapropel deposition was drastically different from that of modern oligotrophic conditions in the Mediterranean. The systematic changes in abundances of specific nitrogen-transforming microorganisms over a sapropel cycle suggest the existence of a positive feedback loop controlling both, nitrogen cycling and primary productivity during sapropel events. This feedback loop was likely also present during Mesozoic OAEs and may explain the deposition of enormous amounts of organic matter as black shales (ultimately leading to petroleum source rocks).

Lunch will be provided. As always, please plan to bring reusable plates and cutlery to reduce waste.