Decadal Variability of the Convective Intensity in the Labrador Sea: Contribution of the Preconditioning

The decadal variability of the convective intensity in the Labrador Sea is investigated using forty-three years of model output from a prognostic coupled ice-ocean model that simulates both the Arctic and Atlantic Ocean. The subdomain of interest extends from 60°W to 40°W and 45°N to 65°N. The surface density field and the mixed-layer depth indicate that a quasi-decadal oscillation exists in the convective site that is located along the continental slope, off the eastern Labrador coast. The selection of the convective site and its intensity in March are associated with the oceanic state at the preconditioning stage in the previous November. The doming of the isopycnals near the surface determines the depth of vertical mixing during the violent mixing phase of the convective process. A simple analytical one-dimensional model reproduces most of the variability in the convective intensity in the region of deep-water formation. The analytical model computed with variability only in the ocean suggests the convections at the decadal timescales are subject to changes in the upper ocean stratification. In addition, the oceanic density structure is dominantly controlled by the temperature variations. Basin-wide decadal oscillations in the North Atlantic seem to influence the variability in the Labrador Sea via heat transport from the subtropics. The entire cycle involves decadal Rossby adjustment, advection of heat and the thermohaline circulation through the convective process. The basin-scale density varability also seems to be governed by the temperature changes in the upper ocean.