Arctic freshwater impact on the Atlantic Meridional Overturning Circulation: status and prospects

Abstract

Arguably, the most conspicuous evidence for anthropogenic climate change lies in the Arctic Ocean. For example, the summer-time Arctic sea ice extent has declined over the last 40 years and the Arctic Ocean freshwater storage has increased over the last 30 years. Coupled climate models project that this extra freshwater will pass Greenland to enter the sub-polar North Atlantic Ocean (SPNA) in the coming decades. Coupled climate models also project that the Atlantic Meridional Overturning Circulation (AMOC) will weaken in the twenty-first century, associated with SPNA buoyancy increases. Yet, it remains unclear when the Arctic anthropogenic freshening signal will be detected in the SPNA, or what form the signal will take. Therefore, this article reviews and synthesizes the state of knowledge on Arctic Ocean and SPNA salinity variations and their causes. This article focuses on the export processes in data-constrained ocean circulation model hindcasts. One challenge is to quantify and understand the relative importance of different competing processes. This article also discusses the prospects to detect the emergence of Arctic anthropogenic freshening and the likely impacts on the AMOC. For this issue, the challenge is to distinguish anthropogenic signals from natural variability. This article is part of a discussion meeting issue ‘Atlantic overturning: new observations and challenges’.

Atlantic overturning: new observations and challenges

“…It is known that changes to freshwater in the subpolar North Atlantic are happening [ 52 , 53 ] and model experiments have shown that increased freshwater input could disrupt the AMOC [ 55 ]. Therefore, an unknown aspect of the Atlantic overturning is how glacial melt from Greenland [ 47 ] and/or freshwater export from the Artic [ 56 ] might impact the AMOC and on what time scale. Furthermore, it is unknown on what time scales, and by which processes, changes in deep water formation at high latitudes might propagate south.…”