Nitrous oxide dynamics on the Siberian Arctic Ocean shelves

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.