25.01.2016: FB1-Seminar

11:00 h, Hörsaal, Düsternbrooker Weg 20

Abstract:

The Deep Western Boundary Current (DWBC) is the primary branch of the Atlantic Meridional Overturning Circulation's (AMOC) cold limb, bringing North Atlantic Deep Water equatorward along the continental slope. Recent work has highlighted stirring between the DWBC and off- slope water, calling into question the degree of connectivity of the current (i.e. Bower et al. 2011).

We show that changes in convection in the Labrador Sea, one of the sources of deep water, are reflected in measurements of the DWBC at Line W, on the continental slope southeast of New England. There is a strong decadal cycle of convection in the Labrador Sea, where there was intense convection in the 1990s but much weaker convection in the 2000s (Kieke et al. 2014, Fischer et al. 2010). This cycle is reflected in observations at the Line W moored array, which measured DWBC properties and velocity from 2004 to 2014, and in the accompanying shipboard measurements, which began in 1995. This decadal cycle is not apparent in measurements in the interior, at Hydrostation S near Bermuda, and we use these data as an interior end-member to quantify the travel time and stirring between the Labrador Sea and Line W.

We also study the dynamics of a possible mechanism for this stirring: the interaction between the northern recirculation gyre of the Gulf Stream and the DWBC. Using a Quasi-Geostrophic process model, we show that the meridional extent of the recirculation gyre is restricted by the slope that the DWBC is on. The recirculation gyre advects eddies to the base of the slope, and these eddies advect tracer and potential vorticity meridionally into the interior. This flux between the DWBC and the interior is dependent on the degree of instability of the Gulf Stream and the distance between the Gulf Stream and the DWBC.

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