A permanent N2O sink in the Nordic Seas and its strength and possible variability over the past four decades

Abstract

AbstractNordic Seas have been assumed to be a net sink of the ozone‐depleting greenhouse gas N2O. However, few studies have been conducted in this region. N2O profile data obtained during the 5th Chinese National Arctic Research Expedition demonstrate that the N2O distribution pattern in the Nordic Seas differs from that of most other oceans. N2O sink characteristics of this region are confirmed by the undersaturation of N2O in the water column. Distributions of N2O in three subbasins of the Nordic Seas vary in the upper 1000 m but are homogenous below 1000 m due to a shared origin in the Greenland Basin (GB). Air‐sea exchange and vertical convection are thought to be dominant factors in N2O distribution in the GB, resulting in a distribution pattern that correlates significantly with the atmospheric mixing ratio variation over the past 40 years. Although recent studies have shown that weakened convection and/or enhanced Arctic outflow below the mid‐depth have occurred, our results show that these variations have yet to significantly affect the above relationship. The distribution could be considered a “historical record” that can be used to evaluate the air‐to‐sea flux over the past 40 years in the GB. The annual amount of N2O absorbed by the GB is ∼0.016–0.029 Tg N, which is equal to 0.4–0.8% of the world ocean emissions. This amount should not be simply neglected because it is absorbed by a region that accounts for only 0.03% of the world ocean area.