An episodic chlorophyll plume on the West Florida Shelf

The episodic formation of an extensive pigment plume on the West Florida Shelf was detected using historical Coastal Zone Color Scanner (CZCS) data collected between 1979 and 1986. The phenomenon is confirmed by in situ observations made in March 1992. The plume occurs mainly during spring, when high pigment concentrations persist 1–6 weeks in a pattern which extends >250 km southward along the shelf. In general, the shelf and continental slope had low pigment concentrations during summer and high pigment concentrations during spring. The information currently available is insufficient to determine the cause of the plume with certainty. Plume formation may be associated with one or a combination of the following processes: (1) discharge from small, local rivers along the NW Florida coast; (2) seasonal changes in steric height differences between the shelf and deep Gulf of Mexico waters; (3) circulation of water associated with the Loop Current and upwelling in the DeSoto Canyon; and (4) discharge from the Mississippi and Mobile Rivers.