Nitrous Oxide Dynamics in the Siberian Arctic Ocean and Vulnerability to Climate Change

Nitrous oxide (N2O) is a strong greenhouse gas and a major ozone depleting agent. Almost a quarter of global N2O emissions stems from the ocean, but projections of future releases are uncertain due to scarce observations over large areas and limited understanding of the drivers behind. Here, we focus on the vast continental shelf seas north of Siberia, a hotspot area of global change that experiences rapid warming and high nitrogen input via rivers and coastal erosion; yet N2O measurements from this region are extremely scarce. We combine water column N2O measurements generated during two expeditions with on-board incubation of intact sediment cores to fill this observational gap, constrain N2O sources and assess the impact of land-derived nitrogen that is expected to increase with permafrost thaw. Our data show elevated nitrogen concentrations in the water column and sediments near the mouths of large rivers, suggesting that land-derived nitrogen might promote primary production, but also nitrification and denitrification in the region. However, N2O concentrations were only weakly influenced by elevated nitrogen availability near river mouths. Comparison with a range of environmental parameters suggests that N2O concentrations might be controlled by interactions of nitrogen availability with turbidity and possibly temperature. Surface water N2O concentrations were on average in equilibrium with the atmosphere, but high spatial variability indicates strong local N2O sources and sinks. Water column profiles of N2O concentrations and low sediment-water N2O fluxes do not support a dominant sedimentary source or sink, but point at production and consumption processes in the water column as main drivers of N2O dynamics in the Siberian shelf seas. The projected increases in water temperature and input of freshwater, nitrogen and suspended material from rivers and coastal erosion with land permafrost thaw have the potential to affect not only net N2O production rates, but also N2O solubility in the water, and increase N2O emissions from the Arctic Ocean.