West Florida Shelf Circulation on Synoptic, Seasonal, and Interannual Time Scales

Abstract

The continental shelf ocean circulation is driven by a combination of local and deep ocean forcing, where the local forcing is by surface momentum and buoyancy (heat and fresh water) fluxes and by land-derived fresh water fluxes, and the deep ocean forcing is by momentum and buoyancy fluxes transmitted across the shelf break. While all continental shelves share the same response physics, their geometries, river distributions, and boundary currents make their individual behaviors unique. Here we consider the responses of the West Florida Continental Shelf (WFS) to external forcing on time scales ranging from the passage of synoptic scale weather systems to interannual anomalies. Our approach is to combine measurements made over several years with applied numerical model experiments, and we describe several features of the time and space varying circulation that may have relevance to the ecological workings of the WFS. These include the role of the bottom Ekman layer in transporting cold, nutrient-rich waters of deep-ocean origin to the nearshore; seasonal reversals of the inner shelf currents; seasonal reversals of the outer-shelf currents that can occur independent of the Gulf of Mexico Loop Current to provide a WFS pathway for Mississippi River water in spring and summer; the formation of a spring cold tongue and the associated Green River phenomenon; and ventilations by deep-ocean water that may occur interannually.