An upwelling case study on Florida's west coast

Using a combination of satellite sea surface temperature imagery; in situ currents, temperature, and sea level data; and a numerical circulation model, we describe an upwelling event observed along Florida's west coast. Although ubiquitous features of continental shelves, descriptions of coastal upwellings (or downwellings) are generally complicated by the continuum of processes in which they occur. For the case study presented the winds were light, and the baroclinic background currents were steady for several days prior to the event. These conditions allow the evolution of a specific wind-driven upwelling event to be viewed as an initial value problem. The data and the numerical model analysis show that the route of adjustment by the sea level and currents is a classical Ekman-geostrophic one. Sea level drops due to an offshore Ekman transport, causing a geostrophic alongshore jet, and the associated onshore flow within the bottom Ekman layer accounts for the appearance of cold water at the surface. This surface manifestation occurs as an elongated feature, centered about the 25 m isobath, that spans roughly half of the Florida peninsula from just north of Tampa Bay to Key West. The coldest water is observed offshore from Tampa Bay, and we explain this region of locally maximum upwelling on the basis of the coastline and isobath geometries.