Recent increases in Arctic freshwater flux affects Labrador Sea convection and Atlantic overturning circulation

Qian Yang,M R Van Den Broeke,Mads H Ribergaard,Don Chambers,John Mortensen,Paul G Myers,Jennifer Bonin,Timothy H Dixon

doi:10.1038/ncomms10525

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is an important component of ocean thermohaline circulation. Melting of Greenland's ice sheet is freshening the North Atlantic; however, whether the augmented freshwater flux is disrupting the AMOC is unclear. Dense Labrador Sea Water (LSW), formed by winter cooling of saline North Atlantic water and subsequent convection, is a key component of the deep southward return flow of the AMOC. Although LSW formation recently decreased, it also reached historically high values in the mid-1990s, making the connection to the freshwater flux unclear. Here we derive a new estimate of the recent freshwater flux from Greenland using updated GRACE satellite data, present new flux estimates for heat and salt from the North Atlantic into the Labrador Sea and explain recent variations in LSW formation. We suggest that changes in LSW can be directly linked to recent freshening, and suggest a possible link to AMOC weakening.

Highlights

The Atlantic Meridional Overturning Circulation (AMOC) is an important component of ocean thermohaline circulation
Several lines of evidence suggest that the ice sheet was relatively stable from 1980 to the early 1990s, and we use that assumption in our modelling of GRACE data and freshwater flux calculations
Longer time series will be required to confirm this link, but our preliminary results suggest that detailed studies of Labrador Sea hydrography and proximal sources of freshwater, including Greenland, have the potential to improve our understanding of AMOC variability and sensitivity to anthropogenic warming

Summary

Introduction

The Atlantic Meridional Overturning Circulation (AMOC) is an important component of ocean thermohaline circulation. -called ‘hosing experiments’, where freshwater may be distributed over broad or narrow regions of the North Atlantic in numerical models, have been used to study the sensitivity of the AMOC to freshwater flux[11,12,13,14,15,16,17] Some of these studies suggest that AMOC strength is sensitive to Greenland melting[11,17], while others do not[12,14,16]. We derive a new estimate for recent increased freshwater flux into the sub-polar North Atlantic, and suggest that because of the clockwise nature of ocean circulation around Greenland[23], most of this increase is being focused towards the Labrador Sea (Fig. 1), magnifying its impact and increasing the likelihood of significant effects on the AMOC

Methods

Results

Conclusion