Andreas Oschlies (GEOMAR Helmholtz Centre for Ocean Research).

Oceanic anoxic events have been associated with warm climates in Earth history, and there are concerns that current ocean deoxygenation may eventually lead to anoxia. On the contrary, results of a multi-millennial global-warming simulation reveal, after a transitory deoxygenation, a marine oxygen inventory 6% higher than preindustrial despite an average 3°C ocean warming. The initial, centennial-scale ~20% decline of oxygen is consistent with earlier studies and reflects changes in solubility and ocean overturning circulation as the ocean warms from the top. An interior-ocean oxygen source unaccounted for in previous studies explains two thirds of the oxygen excess reached after a few thousand years. It results from denitrification replacing part of today’s ocean’s aerobic respiration in expanding oxygen-deficient regions: The resulting loss of fixed nitrogen is equivalent to an oceanic oxygen gain and depends on an incomplete compensation of denitrification by nitrogen fixation. Elevated total oxygen in a warmer ocean with larger oxygen-deficient regions poses a new challenge for explaining global oceanic anoxic events and calls for an improved understanding of environmental controls on nitrogen fixation.

Brief Biography: Andreas got his PhD from the Christian-Albrechts-University of Kiel in 1994 with his work on the assimilation of satellite altimeter data into an eddy-resolving model of the North Atlantic Ocean. Currently, Andreas is a Professor and head of the Biogeochemical Modelling Research Unit at GEOMAR Helmholtz Centre for Ocean Research. His research focuses on physical, biogeochemical, and ecological constraints on the oceanic carbon uptake and its climate sensitivity, the development of mechanistic ecological and biogeochemical models and mixing processes and their representation in numerical models. He leads the Collaborative Research Centre “Climate-Biogeochemistry Interactions in the Tropical Ocean” (SFB754) and the German Priority Program “Climate Engineering: Risks, Challenges, Opportunities?” (SPP1689).