Ocean Deoxygenation Conference | Kiel 2018

Anthropogenic warming is expected to drive oxygen (O$_2$) out of the ocean causing a massive perturbation of the nitrogen (N) cycle leading to increasing N removal and oceanic N$_2$O production via denitrification, which would trigger enhanced N$_2$ fixation. Our intermediate complexity Earth system model simulations reveal that N$_2$ fixation does not compensate the enhanced N loss due increased phosphorus (P) limitation. However, emerging feedbacks between the carbon (C) and N cycle can stabilize the N-inventory and N$_2$O emissions under global warming. The expansion of water column denitrification under ocean deoxygenation is offset by decreasing benthic denitrification brought about by a reduction in export production. This latter is related to ocean warming and yields a decline in oceanic N$_2$O production, which contributes to the reduction in oceanic N$_2$O emissions by 2100. Our model simulations support the existence of strong regulatory feedbacks among the O$_2$-C-N and P-cycles that maintain N inventory homeostasis and contribute to stabilize climate against anthropogenic changes.