A shift in the ocean circulation has warmed the subpolar North Atlantic Ocean since 2016

Damien Desbruyères,Léon Chafik,Guillaume Maze

doi:10.1038/s43247-021-00120-y

Abstract

The Subpolar North Atlantic is known for rapid reversals of decadal temperature trends, with ramifications encompassing the large-scale meridional overturning and gyre circulations, Arctic heat and mass balances, or extreme continental weather. Here, we combine datasets derived from sustained ocean observing systems (satellite and in situ), idealized observation-based modelling (advection-diffusion of a passive tracer), and a machine learning technique (ocean profile clustering) to document and explain the most-recent and ongoing cooling-to-warming transition of the Subpolar North Atlantic. Following a gradual cooling of the region that was persisting since 2006, a surface-intensified and large-scale warming sharply emerged in 2016 following an ocean circulation shift that enhanced the northeastward penetration of warm and saline waters from the western subtropics. The long ocean memory of the Subpolar North Atlantic implies that this advection-driven warming is likely to persist in the near-future with possible implications for the Atlantic multidecadal variability and its global impacts.

Highlights

The Subpolar North Atlantic is known for rapid reversals of decadal temperature trends, with ramifications encompassing the large-scale meridional overturning and gyre circulations, Arctic heat and mass balances, or extreme continental weather
The following 10 years were marked by a gradual cooling and punctuated by a sharp drop in 2014–2015—the well-documented Subpolar North Atlantic (SPNA) cold anomaly partly driven by anomalously strong ocean heat loss to the atmosphere[10]
An identical model setup is used to infer the mean and anomalous concentration of CSTG and CSPG from the surface to about 700 m depth

Summary

Introduction

The Subpolar North Atlantic is known for rapid reversals of decadal temperature trends, with ramifications encompassing the large-scale meridional overturning and gyre circulations, Arctic heat and mass balances, or extreme continental weather. It provides a favorable environment for surface waters to mix and sink towards the seafloor before spreading south as part of the Meridional Overturning Circulation (MOC), which transports climate-relevant properties globally (e.g., heat, carbon)[1,2] It is the primary gateway for warm and salty Atlantic waters to reach the Nordic Seas and Arctic Ocean[3], and exerts a key control on the mass and heat budgets of those rapidly-changing and most-vulnerable areas[4,5,6]. The thin dashed line shows anomalies in altimetry-derived sea surface height (global-mean removed) in the eastern SPNA

Methods

Results

Conclusion