The impact of mid-depth recirculations on the distribution of tracers in the North Atlantic
An interesting feature of the waters carried equatorward by the Deep Western Boundary Current in the North Atlantic is their sharp vertical differentiation in tracer concentration and, accordingly, tracer age. In this work I demonstrate that the structure and lateral extent of the recirculations in the intermediate and deep North Atlantic have substantive differences with depth that can help explain the observed pattern of transient tracers such as tritium, 3He and CFCs. While recirculations are present at all depths spanned by the boundary current, the distinct tracer minimum occurs at the depth where the recirculation extent is maximized. Overall, the effect of the large-scale recirculation at intermediate depths is to lengthen mixing pathways and to provide an alternate route for North Atlantic deep waters to enter the subtropical basin.
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