Abstract
The Southern Ocean is an important region for global nitrous oxide (N2O) cycling. The contribution of different source and sink mechanisms is, however, not very well constrained due to a scarcity of seawater data from the area. Here we present high-resolution surface N2O measurements from the Atlantic sector of the Southern Ocean, taking advantage of a relatively new underway setup allowing for collection of data during transit across mesoscale features such as frontal systems and eddies. Covering a range of different environments and biogeochemical settings, N2O saturations and sea-to-air fluxes were highly variable: Saturations ranged from 96.5% at the sea ice edge in the Weddell Sea to 126.1% across the Polar Frontal Zone during transit to South Georgia. Negative sea-to-air fluxes (N2O uptake) of up to −1.3 µmol m−2 d−1 were observed in the Subantarctic Zone and highest positive fluxes (N2O emission) of 14.5 µmol m−2 d−1 in Stromness Bay, coastal South Georgia. Although N2O saturations were high in areas of high productivity, no correlation between saturations and chlorophyll a (as a proxy for productivity) was observed. Nevertheless, there is a clear effect of islands and shallow bathymetry on N2O production as inferred from supersaturations.
Highlights
Nitrous oxide (N2O) is a strong greenhouse gas and currently the third largest contributor to radiative forcing after carbon dioxide (CO2) and methane (CH4) (Hartmann et al, 2013)
High-resolution (1 min averages of measurements at 1 Hz) N2O data were collected from the surface waters of the Atlantic sector of the Southern Ocean during transit and station work, covering highly varied areas across the Antarctic Circumpolar Current (ACC) and the Antarctic Zone (AAZ)
These data from the austral summer 2011/2012 add substantially to the limited observations of N2O emissions from the Southern Ocean, increasing observations from the Scotia Sea by 20,674 values (188 data points from 1989 previously published by Weiss et al (1992)) and by 9730 from the Weddell Sea (250 data points from 1984 previously published by Weiss et al (1992)), and show unprecedented fine-scale variability compared to the existing data
Summary
Nitrous oxide (N2O) is a strong greenhouse gas and currently the third largest contributor to radiative forcing after carbon dioxide (CO2) and methane (CH4) (Hartmann et al, 2013). The oceans, including coastal zones, estuaries and rivers, are estimated to contribute approximately 25% to global N2O emissions (Ciais et al, 2013). The Southern Ocean alone is estimated to account for 5% of global emissions (0.9 Tg a−1 N (nitrogen equivalents), (Nevison et al, 2005)). Measurements of oceanic N2O concentrations in this region are scarce and these emission estimates are based on atmospheric measurements at Cape Grim and a few seawater measurements in the Southern Ocean from 1977–1993 (Nevison, Weiss & Erickson, 1995; Nevison et al, 2005 and references therein). How to cite this article Grefe et al (2018), Nitrous oxide variability at sub-kilometre resolution in the Atlantic sector of the Southern Ocean.
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