A complex effect of Iminger Rings on deep convection and mixed layer recovery in the Labrador Sea

Abstract

Deep convection in the Labrador Sea has a significant role in the formation of the lower branch of the AMOC. It is known that the eddy mesoscale activity in the Labrador Sea, represented by the Irminger rings (IR), has an impact on the convection process. Irminger rings are mesoscale anticyclonic eddies detached from the deep western boundary current (DWBC). Their property affecting the convection process is strong stable stratification that blocks ventilation from the surface, but there is still no numerical analysis of this effect. This work is focused on the study of Irminger Rings formation mechanisms and their impact on the depth and intensity of convection. The research is based on data from the regional model of the Subpolar North Atlantic NNATL12 (NEMO 4.0.6). The calculation of the terms of the vorticity equation is used to assess the influence of barotropic and baroclinic mechanisms in the generation of Irminger Rings. An automatic identification method of IR centers in numerical simulation data is suggested. A stable correlation was found between the number of observed IRs and the heat transport of the DWBC (R2 = 0.71). It was established that the heat transport of the DWBC to the central part of the Labrador Sea is mainly produced by eddies, and the vertical thermohaline structure of IRs is similar to the structure of the DWBC. The IRs are clearly traced in the mixed layer depth domain during the winter - in the eddy area, the convection depth is much smaller (~1600 meters) than in the area where eddies are not observed. It is found that in the absence of IR in the central Labrador Sea, the convection depth is 3.5% higher, even though the area covered by IRs is about 82 times smaller than the central basin of the Labrador Sea. The influence of IR on the process of deepening and recovering of the mixed layer depth is also described.