AN EPISODIC CHLOROPHYLL PLUME ON THE WEST FLORIDA SHELF

The episodic formation of an extensive pigment plume on the West Flori da Shelf was detected using historical Coastal Zone Color Scanner (CZC S) data collected between 1979 and 1986. The phenomenon is confirmed b y in situ observations made in March 1992. The plume occurs mainly dur ing spring, when high pigment concentrations persist 1-6 weeks in a pa ttern which extends >250 km southward along the shelf. In general, the shelf and continental slope had low pigment concentrations during sum mer and high pigment Concentrations during spring. The information cur rently available is insufficient to determine the cause of the plume w ith certainty. Plume formation may be associated with one or a combina tion of the following processes: (1) discharge from small, local river s along the NW Florida coast; (2) seasonal changes in steric height di fferences between the shelf and deep Gulf of Mexico waters; (3) circul ation of water associated with the Loop Current and upwelling in the D eSoto Canyon; and (4) discharge from the Mississippi and Mobile Rivers . (C) 1996 Elsevier Science Ltd.