An abrupt shift in the Labrador Current System in relation to winter NAO events

The behavior of the Labrador Current during the period from 1990 to 2007 is investigated with an eddy-resolving circulation model for the North Atlantic Ocean. An EOF analysis of the model output suggests that the variability in the Labrador Current can be partitioned into a western Labrador Current (WLC; from the 300-2500 m isobaths), and an eastern Labrador Current (ELC; from the 2500 to 3300 m isobaths). The model results demonstrate that the WLC transport experienced an abrupt increase during 2000-2002, consistent with data. This differed significantly from the ELC transport which was strong during the high winter NAO (North Atlantic Oscillation) years (1990-1995) and then steadily declined. This ELC trend is consistent with changes in the modeled Atlantic Meridional Overturning Circulation and convection depth. Our study proposes that the change in the WLC is due to a southwestward shift of the atmospheric circulation pattern starting in 2001, coincident with a change in the 2001 NAO index, and also in a westward shift of the action centers of the winter NAO events.