Ocean convection linked to the recent ice edge retreat along east Greenland

Abstract

Warm subtropical-origin Atlantic water flows northward across the Greenland-Scotland Ridge into the Nordic Seas, where it relinquishes heat to the atmosphere and gradually transforms into dense Atlantic-origin water. Returning southward along east Greenland, this water mass is situated beneath a layer of cold, fresh surface water and sea ice. Here we show, using measurements from autonomous ocean gliders, that the Atlantic-origin water was re-ventilated while transiting the western Iceland Sea during winter. This re-ventilation is a recent phenomenon made possible by the retreat of the ice edge toward Greenland. The fresh surface layer that characterises this region in summer is diverted onto the Greenland shelf by enhanced onshore Ekman transport induced by stronger northerly winds in fall and winter. Severe heat loss from the ocean offshore of the ice edge subsequently triggers convection, which further transforms the Atlantic-origin water. This re-ventilation is a counterintuitive occurrence in a warming climate, and highlights the difficulties inherent in predicting the behaviour of the complex coupled climate system.

Wind‐Driven Coastal Upwelling and Downwelling in the Shelfbreak East Greenland Current

“…From summertime observations we know that a low‐salinity surface layer is present in the Iceland Sea also offshore of the east Greenland shelf (Jónsson, ; Latarius & Quadfasel, ; Swift et al, ; Våge et al, ). Våge et al () showed that in fall and winter the strong downwelling‐favorable northeasterly wind and the corresponding Ekman transport are able to shift the freshwater toward the coast. Similarly, the offshore Ekman transport associated with the upwelling may be a mechanism by which freshwater is transported from the shelf into the interior basin.…”

“…During downwelling events anomalously light water was forced off the shelf at depth and embedded within the core of the shelfbreak current. These events may be a source of low‐salinity water to the upper layer of the Denmark Strait overflow plume (Rudels et al, ), facilitate shelf‐fjord exchange (Fraser & Inall, ; Jackson et al, ), and precondition the region offshore of the ice edge for wintertime convection (Våge et al, ). Such redistribution of freshwater along the east coast of Greenland may have large‐scale impacts.…”

A revised ocean glider concept to realize Stommel's vision and supplement Argo floats

“…6.3) contains detailed considerations for an aluminium hull. However, it is likely that alternative composite materials must be considered for the hull (Osse and Eriksen, 2007;Webb, 2006).…”

“…The newly produced or transformed dense waters return southward between Iceland and Greenland through Denmark Strait and east of Iceland across the Greenland-Scotland Ridge, contributing to the lower limb of the AMOC. Transects worked by a slow glider will provide crucial observations in the Norwegian Atlantic Current at Svinøy (Høydalsvik et al, 2013), in the deep convection regions in the Greenland and Iceland seas Våge et al, 2018), and in the Lofoten Basin, which is a hotspot for Atlantic water transformation (Bosse et al, 2018). The transect in Fram Strait will capture the properties and variability in the return Atlantic water along the Polar Front in the northern Nordic Seas (de Steur et al, 2014).…”

“…The transect in Fram Strait will capture the properties and variability in the return Atlantic water along the Polar Front in the northern Nordic Seas (de Steur et al, 2014). Particularly the interior Greenland and Iceland seas and the east Greenland shelf are under-sampled, and the observations will be useful in understanding the role of wintertime open-ocean convection in the western basins of the Nordic Seas and the effect of an ice edge in retreat toward Greenland (Moore et al, 2015;Våge et al, 2018).…”