Published in

Wiley, Journal of Geophysical Research. Oceans, 7(119), p. 4124-4140

DOI: 10.1002/2013jc009715

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Subtropical surface layer salinity budget and the role of mesoscale turbulence

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Data provided by SHERPA/RoMEO

Abstract

The subtropical North Atlantic exhibits the saltiest surface waters of the open ocean. Eventually that water is isolated from the surface and exported towards the Equator, as a subsurface salinity maximum (S-max) forming the lower limb of the subtropical cell. Climatologically the winter subtropical surface water, coinciding with the deepest mixed layer of ˜ 100m, is saltier and colder than the S-max. Towed CTD measurements in March/April 2013 (a component of the field program SPURS) within the North Atlantic subtropical surface salinity maximum reveal several relatively fresh, warm anomalies, which deviate strongly from climatological conditions. These features introduce a large amount of freshwater into the subtropical region, exceeding the amount introduced by local rain events. Observed scales and evolution of the features strongly suggest a connection to mesoscale dynamics. This is supported by high-resolution regional model output, which produces an abundance of features that are similar in scale and structure to those observed. It is hypothesized that turbulent transport in the surface ocean is a crucial process for setting mixed layer characteristics, which spread into S-max stratum. High variability in the EKE implies a high potential for interannual variability in the resulting S-max water properties by ocean dynamics in addition to the variability caused by air sea fluxes. This has likely consequences to the meridional transport of heat and freshwater of the subtropical cell in the North Atlantic and to the larger scale ocean and climate system.