N2O dynamics in the western Arctic Ocean during the summer of 2017

Jang-Mu Heo,Ju-Hyoung Kim,Seong-Su Kim,Alison M Macdonald,Hyo-Ryeon Kim,Sung-Ho Kang,Il-Nam Kim,Jinyoung Jung,Kyoung-Ho Cho,Jae-Hyun Lim,Ki-Tae Park,Joo-Eun Yoon,Sang-Min Eom,Eun Jin Yang

doi:10.1038/s41598-021-92009-1

Abstract

The western Arctic Ocean (WAO) has experienced increased heat transport into the region, sea-ice reduction, and changes to the WAO nitrous oxide (N2O) cycles from greenhouse gases. We investigated WAO N2O dynamics through an intensive and precise N2O survey during the open-water season of summer 2017. The effects of physical processes (i.e., solubility and advection) were dominant in both the surface (0–50 m) and deep layers (200–2200 m) of the northern Chukchi Sea with an under-saturation of N2O. By contrast, both the surface layer (0–50 m) of the southern Chukchi Sea and the intermediate (50–200 m) layer of the northern Chukchi Sea were significantly influenced by biogeochemically derived N2O production (i.e., through nitrification), with N2O over-saturation. During summer 2017, the southern region acted as a source of atmospheric N2O (mean: + 2.3 ± 2.7 μmol N2O m−2 day−1), whereas the northern region acted as a sink (mean − 1.3 ± 1.5 μmol N2O m−2 day−1). If Arctic environmental changes continue to accelerate and consequently drive the productivity of the Arctic Ocean, the WAO may become a N2O “hot spot”, and therefore, a key region requiring continued observations to both understand N2O dynamics and possibly predict their future changes.

Highlights

To investigate the hydrographic conditions during the summer of 2017 in the western Arctic Ocean (WAO), we analyzed the vertical distributions of θ, S, dissolved oxygen (DO), and dissolved inorganic nitrogen (DIN) along a latitudinal transect from the Bering Strait to the Chukchi Borderland (Fig. 1a–c,e,f) and used a θ–S diagram to examine the composition of water masses (Fig. 1d)
We investigated the distributions of the N 2O concentration and flux, their controlling factors, and the role of the WAO as a source or sink for atmospheric N 2O during the summer of 2017
The mean N 2O saturation was higher in the southern Chukchi (SC) (113% ± 10%, over-saturation) than in the northern Chukchi (NC) (95% ± 5%, under-saturation)

Summary

Introduction

Prior to the study presented here, no intensive investigation synthesizing information on the dynamics of WAO N2O (i.e., distributions of the concentration and flux and their controlling environmental factors) in the water column (from the surface to the bottom) had been conducted. Based on an intensive and precise N 2O survey of the WAO water column during the open-water season of summer 2017, we (1) present spatial distributions of N2O concentrations and fluxes, (2) identify physical and/ or biogeochemical factors controlling the distributions, (3) determine whether the WAO is a source or sink for atmospheric N2O, and (4) speculate regarding future changes in the WAO N 2O flux in response to rapid Arctic climate changes.

Results

Conclusion