Eclectic Modelling of the North Atlantic. II. Transient Tracers and the Ventilation of the Eastern Basin Thermocline

摘要

Renewal rates of the waters of the thermocline in the eastern North Atlantic are estimated by combining linear quasi-geostrophic dynamics with steady and transient tracers into a unified eclectic, reservoir model. The two-dimensional model first employed is rejected when it is found that it generates oxygen-utilization rates (OUR) that are too high. The three-dimensional model that replaces it shows that the OUR is indeterminate, with possible ranges from the north and east. The problem of using transient traces is mathematically equivalent to that of distributed-system boundary-control theory, the open-ocean boundary conditions playing the role of the unknown control variables. The missing time histories of this new set of unknowns means that tritium and helium-3 distributions are only comparatively weak constraints on the flow field, but do set upper bounds on the vertical exchange with surface waters. Surface Ekman pumping is adequate to explain the interior distributions without additional buoyancy ventilation, although this latter process is possible. Keywords: Ocean models; Mathematical models. Reprints. (EDC)