Influence of the Advection of Labrador Sea Water on the Decadal Variability of the Eastern Subpolar North Atlantic

Abstract

The upper ocean heat content of the eastern subpolar North Atlantic (ESPNA) displays large decadal variations, in particular, a warming starting in the mid-1990s followed by a cooling trend from the mid-2000s to the mid-2010s. Using an eddy permitting ice-ocean model, we find a relationship between the eastward propagation of dense water formed in the Labrador and Irminger Seas, the barotropic horizontal circulation and the advective heat convergence in the ESPNA. The time evolution of the 3-year average anomalies of the barotropic streamfunction (BSF) shows a strong resemblance to that of the depth of the deep isopycnals. In particular, the propagation of dense water drives a response of the BSF in the intergyre gyre region. During the warming period, the advection of dense water is associated with a southeastward expansion of the subpolar gyre and a reduction of the supply of cold water from the western subpolar North Atlantic to the upper layers of the ESPNA. Sensitivity experiments suggest that atmospheric forcing can also enhance the trends in the heat content, but the latter cannot be related to trends of the local wind curl. However, circulation changes induced by the wind curl on some specific years can amplify the heat content changes.