Redrawing the Iceland\u2212Scotland Overflow Water pathways in the North Atlantic

Sijia Zou,M Susan Lozier,Xiaobiao Xu,Amy Bower,Heather Furey

doi:10.1038/s41467-020-15513-4

Abstract

Iceland-Scotland Overflow Water (ISOW) is a primary deep water mass exported from the Norwegian Sea into the North Atlantic as part of the global Meridional Overturning Circulation. ISOW has historically been depicted as flowing counter-clockwise in a deep boundary current around the subpolar North Atlantic, but this single-boundary-following pathway is being challenged by new Lagrangian observations and model simulations. We show here that ISOW leaves the boundary and spreads into the interior towards the central Labrador and Irminger basins after flowing through the Charlie-Gibbs Fracture Zone. We also describe a newly observed southward pathway of ISOW along the western flank of the Mid-Atlantic Ridge. The partitioning of these pathways is shown to be influenced by deep-reaching eddies and meanders of the North Atlantic Current. Our results, in tandem with previous studies, call for a revision in the historical depiction of ISOW pathways throughout the North Atlantic.

Highlights

Iceland-Scotland Overflow Water (ISOW) is a primary deep water mass exported from the Norwegian Sea into the North Atlantic as part of the global Meridional Overturning Circulation
This path begins with a southwestward leg along the eastern flank of the Reykjanes Ridge as far south as the Charlie−Gibbs Fracture Zone (CGFZ), which is the major gateway for ISOW to flow from the eastern to western North Atlantic[4,5] (Fig. 1)
With results from observed and simulated floats, we re-draw the major pathways of ISOW coming through the CGFZ: instead of turning northward along the western flank of the Reykjanes Ridge, most of the ISOW either follows a west-northwestward path or travels along a newly identified southward path along the western flank of the Mid-Atlantic Ridge (MAR)

Summary

Introduction

Iceland-Scotland Overflow Water (ISOW) is a primary deep water mass exported from the Norwegian Sea into the North Atlantic as part of the global Meridional Overturning Circulation. This path begins with a southwestward leg along the eastern flank of the Reykjanes Ridge as far south as the Charlie−Gibbs Fracture Zone (CGFZ), which is the major gateway for ISOW to flow from the eastern to western North Atlantic[4,5] (Fig. 1). West of the CGFZ, a number of studies have suggested that not all ISOW turns northward along the western flank of the Reykjanes Ridge to flow counter-clockwise around the rim of the Irminger Sea. Hydrographic sections in the western subpolar North Atlantic have revealed a tongue of higher-salinity water extending west-northwestward from the CGFZ at the ISOW level, suggesting an alternative westward spreading of ISOW15–18. Racapé et al.[19] reported that one of the five Deep-Argo floats initialized in the CGFZ followed a direct westward route from the CGFZ to the Flemish Cap, where it was able to join the Deep Western Boundary Current

Methods

Results

Conclusion