Rapid Export of Waters Formed by Convection Near the Irminger Sea's Western Boundary

I A.‐A Le Bras,F Straneo,N P Holliday,M F De Jong,J Holte

doi:10.1029/2019gl085989

Abstract

AbstractThe standard view of the overturning circulation emphasizes the role of convection, yet for waters to contribute to overturning, they must not only be transformed to higher densities but also exported equatorward. From novel mooring observations in the Irminger Sea (2014–2016), we describe two water masses that are formed by convection and show that they have different rates of export in the western boundary current. Upper Irminger Sea Intermediate Water appears to form near the boundary current and is exported rapidly within 3 months of its formation. Deep Irminger Sea Intermediate Water forms in the basin interior and is exported on longer time scales. The subduction of these waters into the boundary current is consistent with an eddy transport mechanism. Our results suggest that light intermediate waters can contribute to overturning as much as waters formed by deeper convection and that the export time scales of both project onto overturning variability.

Highlights

The deep limb of the Atlantic's overturning circulation is a critical component of the climate system
North Atlantic Deep Waters are formed in high-latitude marginal seas; the densest waters are formed in the Nordic Seas, and waters formed in the Labrador and Irminger Seas occupy intermediate depths
We investigated the interaction of convection and boundary currents using novel OSNAP and OOI mooring observations in the western Irminger Sea from 2014 to 2016

Summary

Introduction

The deep limb of the Atlantic's overturning circulation is a critical component of the climate system. In the high-latitude North Atlantic, subtropical waters are transformed into the cold, fresh, carbon- and oxygen-rich waters that fill the deep ocean, where they are isolated from the atmosphere for hundreds to thousands of years (Gebbie & Huybers, 2011). Understanding the processes which govern this subduction of waters into the deep ocean is key to quantifying the ocean's uptake of heat and carbon, and, understanding climate stability and variability on long time scales (Khatiwala et al, 2012). Waters formed by this open ocean convection dominate the variability in the overturning circulation's deep limb (Danabasoglu et al, 2016; Rahmstorf et al, 2015). In order for waters to enter the deep ocean they must be transformed to higher densities and exported equatorward (Spall & Pickart, 2001)

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