Distribution and Driving Mechanism of N2O in Sea Ice and Its Underlying Seawater during Arctic Melt Season

Jian Liu,Jiexia Zhang,Man Wu,Yuhong Li,Liyang Zhan,Liqi Chen,Wangwang Ye,Jianwen Wen,Qingkai Wang

doi:10.3390/w14020145

Abstract

Nitrous oxide (N2O) is the third most important greenhouse gas in the atmosphere, and the ocean is an important source of N2O. As the Arctic Ocean is strongly affected by global warming, rapid ice melting can have a significant impact on the N2O pattern in the Arctic environment. To better understand this impact, N2O concentration in ice core and underlying seawater (USW) was measured during the seventh Chinese National Arctic Research Expedition (CHINARE2016). The results showed that the average N2O concentration in first-year ice (FYI) was 4.5 ± 1.0 nmol kg−1, and that in multi-year ice (MYI) was 4.8 ± 1.9 nmol kg−1. Under the influence of exchange among atmosphere-sea ice-seawater systems, brine dynamics and possible N2O generation processes at the bottom of sea ice, the FYI showed higher N2O concentrations at the bottom and surface, while lower N2O concentrations were seen inside sea ice. Due to the melting of sea ice and biogeochemical processes, USW presented as the sink of N2O, and the saturation varied from 47.2% to 102.2%. However, the observed N2O concentrations in USW were higher than that of T-N2OUSW due to the sea–air exchange, diffusion process, possible N2O generation mechanism, and the influence of precipitation, and a more detailed mechanism is needed to understand this process in the Arctic Ocean.

Highlights

N2 O is the third most important greenhouse gas in the atmosphere and the fastest growing ozone-destroying gas in terms of emissions, and its global warming potential (GWP) is 310 times that of equal-molecular CO2
For better comparison of the sea ice structure and N2 O distribution in different ice cores, we normalized the length of the two cores [25]
Our results demonstrated that: (1) There is a significant difference in the N2 O concentration between first-year ice (FYI) and multi-year ice (MYI); the average N2 O concentration of FYI is 4.5 ± 1.0 nmol kg−1, ranging from 3.7 to 6.3 nmol kg−1, while MYI is 4.8 ± 1.9 nmol kg−1, ranging from 2.1 to 7.7 nmol kg−1

Summary

Introduction

N2 O is the third most important greenhouse gas in the atmosphere and the fastest growing ozone-destroying gas in terms of emissions, and its global warming potential (GWP) is 310 times that of equal-molecular CO2. The N2 O mixing ratio in the atmosphere has reached 332 nL L−1 [1]. Oceans are an important natural source of N2 O, accounting for about 20% of the global N2 O sources [2]. Under the influence of atmospheric circulation, Arctic Oscillation and inputs of warm waters from the Pacific Ocean, the Arctic sea ice has a rapidly modifying structure, thickness, coverage, and chemical composition [3], with possible feedback effects on Arctic ecosystems [4,5]

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Conclusion