Abstract
Changes in the Atlantic Meridional Overturning Circulation, which have the potential to drive societally-important climate impacts, have traditionally been linked to the strength of deep water formation in the subpolar North Atlantic. Yet there is neither clear observational evidence nor agreement among models about how changes in deep water formation influence overturning. Here, we use data from a trans-basin mooring array (OSNAP—Overturning in the Subpolar North Atlantic Program) to show that winter convection during 2014–2018 in the interior basin had minimal impact on density changes in the deep western boundary currents in the subpolar basins. Contrary to previous modeling studies, we find no discernable relationship between western boundary changes and subpolar overturning variability over the observational time scales. Our results require a reconsideration of the notion of deep western boundary changes representing overturning characteristics, with implications for constraining the source of overturning variability within and downstream of the subpolar region.
Highlights
Changes in the Atlantic Meridional Overturning Circulation, which have the potential to drive societally-important climate impacts, have traditionally been linked to the strength of deep water formation in the subpolar North Atlantic
North Atlantic Deep Water (NADW) that subsequently spreads to other ocean basins via the Deep Western Boundary Current (DWBC)[1,2] and interior pathways[3]
Because there is the possibility of a delayed impact of strong convection on the overturning due to a residence time of ~2–3 years for newly-formed upper NADW (UNADW) in the Labrador Sea interior[21,22], there is a valid argument that the initial OSNAP record, 21 months in duration, was insufficient to capture this impact
Summary
Changes in the Atlantic Meridional Overturning Circulation, which have the potential to drive societally-important climate impacts, have traditionally been linked to the strength of deep water formation in the subpolar North Atlantic. Winter convection in the Labrador Sea contributed minimally to the mean and variability of the subpolar MOC, even though unusually strong convection occurred in that basin during winter 2014/201511,12 These results contradict the view of convection in the Labrador Sea as the major contributor to MOC variability throughout the North Atlantic[13,14] via the propagation of density anomalies created by the varying strength of deep convection in this basin[15,16,17,18,19]. Though models disagree as to the strength of the linkage between Labrador Sea convection and the MOC, this linkage is a consistent model feature[20] These new observations raise the question about the source of Labrador Sea density anomalies and their impact on MOC variability in the subpolar basin. In this study we use the extended OSNAP data between August 2014 and May 2018 (46 months) a WGC Labrador Basin
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