Pathways of cross-frontal exchange in the North Atlantic Current

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The North Atlantic Current (NAC) forms part of the boundary between the subtropical and subpolar gyres in the North Atlantic Ocean. The current has topographically controlled stationary meanders that appear to grow and decay. A region east of the current in the Newfoundland Basin contains water of mixed subpolar/subtropical properties, suggesting that there is exchange across the NAC. This study considers data from isopycnal RAFOS floats launched in the NAC region from 1993 to 1995. We use the RAFOS data to define the "frontal zone" as a pressure range where the jet is most likely to be found. This definition requires a latitudinal dependence as the NAC shoals to the north. Floats shallower and deeper than this range are defined to be on the subpolar and subtropical side, respectively. These definitions are used to estimate mixing that occurs between the current and its surroundings and to estimate the relative quantity of exchange of water parcels between the two gyres. Only small quantities of mass exchange from one gyre to the other are found, but there is a distinct asymmetry leading to a mean flux from the subpolar to subtropical sides. We also find that floats spend significant time in the frontal region and are frequently exchanged between fast and slow moving waters, particularly at the meander extrema. Diffusion, while in the jet, leads to eddy cross-frontal exchange which is important for the exchange of properties across the NAC. Copyright 2001 by the American Geophysical Union.

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Journal of Geophysical Research: Oceans