The Vertical Structure of Eddy Freshwater Transport Inferred from Satellite Observations and Argo Profile Data
[25-May-2017] Melnichenko, O., Amores, A., Hacker, P., Maximenko, N., and Potemra, J.
Presented at the Global Ocean Salinity and the Water Cycle Workshop
Satellite observations and Argo profile data are used to investigate the vertical structure of meridional eddy freshwater transport in the interiors of the subtropical gyres. To overcome limitations arising from the relative sparseness of in-situ profile data, an eddy composite analysis is utilized; namely, the mean vertical structure of mesoscale eddies and their transport properties are evaluated by synthesizing all available data in the framework of the eddy tracking technique. In each of the five subtropical gyres, the role of mesoscale eddies is to pump freshwater into the gyre: the transport is poleward on the equatorward side of the gyre and equatorward on the poleward side. There are marked differences between the oceans, however. For example, in the North Pacific, North Atlantic, and the South Indian Ocean, the eddy freshwater transport is equally important on both sides of the gyre, while in the South Pacific and the South Atlantic the poleward side dominates. There, the role of eddies is not only to pump freshwater into the gyre but also to push the gyre center (determined as the SSS-maximum) equatorward. In the vertical, the eddy freshwater transport is largely confined to the upper 200 m of the water column. Exceptions are in the South Indian Ocean, where the eddy flux penetrates as deep as 400 m depth, closely following the subsurface "river of salt", and along the major oceanic fronts such as the Azores Current in the Atlantic and the Kuroshio extension in the Pacific. Relatively strong fluxes at depth are also observed in the subtropical North Atlantic at the level of the Mediterranean Water (MW) at around 1000 m depth, exemplifying the role of eddies in MW spreading. In the surface mixed layer, a good correspondence is found between the transport estimates made from the Argo profile data and from completely independent satellite SSS data, adding confidence to our results.