Persistent freshening of the Arctic Ocean and changes in the North Atlantic salinity caused by Arctic sea ice decline

Hui Li,Alexey V Fedorov

doi:10.1007/s00382-021-05850-5

Abstract

Arctic sea ice has been declining over past several decades with the largest ice loss occurring in summer. This implies a strengthening of the sea ice seasonal cycle. Here, we examine global ocean salinity response to such changes of Arctic sea ice using simulations wherein we impose a radiative heat imbalance at the sea ice surface, inducing a sea ice decline comparable to the observed. The imposed perturbation leads to enhanced seasonal melting and a rapid retreat of Arctic sea ice within the first 5–10 years. We then observe a gradual freshening of the upper Arctic ocean that continues for about a century. The freshening is most pronounced within the central Arctic, including the Beaufort gyre, and is attributed to excess surface freshwater associated with the stronger seasonal sea ice melting, as well as a greater upper-ocean freshwater storage due to changes in ocean circulation. The freshening of the Nordic Seas can also occur via a distillation-like process in which denser saline waters with increased salinity are exported to the subtropical/tropical North Atlantic by meridional overturning circulation. Thus, enhanced seasonal sea ice melting in a warmer climate can lead to a persistent Arctic freshening with large impacts on the global salinity distribution.

Highlights

A critical component of the Earth’s climate, the Arctic ocean responds quickly to global warming
The freshening is most pronounced within the central Arctic, including the Beaufort gyre, and is attributed to excess surface freshwater associated with the stronger seasonal sea ice melting, as well as a greater upper-ocean freshwater storage due to changes in ocean circulation
The amount of total sea ice volume loss is generally consistent with the strength of the imposed radiative perturbation, SW undergoes a greater sea ice volume loss than LW, despite similar changes in Arctic sea ice area (Fig. 1d), which suggests a slightly higher radiative imbalance in the SW experiment than in the LW

Summary

Introduction

A critical component of the Earth’s climate, the Arctic ocean responds quickly to global warming. Several studies estimate that the accumulation of liquid freshwater in the Arctic during the 2000s may have resulted from unbalanced freshwater fluxes, changes of the Arctic Oscillation (Johnson et al 2018; Cornish et al 2020) and increased sea ice loss, though some uncertainties remain (Serreze et al 2006; Bamber et al 2012; Woodgate et al 2012; Haine et al 2015; Wang et al 2018b). As sea ice plays a central role in regulating surface freshwater input and more generally the hydrological cycle of polar regions (Aagaard and Carmack 1989), the question of Arctic freshening and its relationship to sea ice decline becomes critical for ocean global circulation. The goal of this study is to investigate Arctic sea ice decline as a mechanism for the current and future Arctic freshening

Objectives

Results

Conclusion