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Annual and Eddy Subduction in the Salinity Processes in the Upper Ocean Regional Study (SPURS-1) Area
[12-Feb-2018] Anderson, J.E. and Riser, S.
Presented at the 2018 Ocean Sciences Meeting
During the first Salinity Processes in the Upper Ocean Regional Study (SPURS-1) a unique fleet of instrumentation was deployed in the approximate center of the evaporation dominated North Atlantic salinity maximum (~ 25°N, 38°W) to investigate the physical mechanisms controlling upper ocean salinity on a variety of space and time scales. Previous studies have shown that subsurface processes are as important as surface fluxes in maintaining the salinity maximum. In the present study, we examine the variability of mixed layer properties and subduction of high salinity water in the region during the one-year deployment period (October 2012-October 2013). Mixed layer properties in the sea surface salinity maximum region are warmer and saltier than ranges associated with subtropical underwater (STUW), indicating a source for STUW north of the region, significant mixing during/after subduction, or a broadening of properties associated with STUW. High spatial resolution objective maps of temperature, salinity, and mixed layer depth (MLD) (created from Argo, Seaglider, and mooring data) show small spatial variability during the late spring and summer months. As the mixed layer shoals in spring, temporal variability was high and spatial variability was at a maximum. Mixed layer variability is larger during the one-year study period than inferred from climatology. Estimation of annual mean and eddy varying subduction rates, from higher resolution, mesoscale resolving, mixed layer objective maps and satellite geostrophic velocities and wind stress fields, show this mixed layer variability has large impacts on subduction rates. Results show enhanced lateral induction contributions to annual subduction rates and the importance of using a time varying MLD for estimation of eddy contributions. While net eddy subduction rates in the region are small, eddies set up large temperature and salinity gradients on which other mechanisms may act. SPURS-1 results are also put into context with updated, Argo-era climatological values for the North Atlantic.

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