PROPERTY FIELDS IN AN EFFLUENT PLUME OF THE MISSISSIPPI RIVER

Surface property distributions were mapped in the Mississippi River pl ume during May and August, 1993 while following surface drifters. Prev ailing winds were the primary factor controlling the orientation of th e plume. In May, under typical southeasterly winds, the plume turned a nticyclonically towards the coast, while in August, under anomalous we sterly winds, the plume turned east. Remote imagery of sea surface tem perature and suspended sediments confirmed the direction of the plume. Optimally interpolated maps of surface salinity, temperature, chlorop hyll a fluorescence, and transmissivity from underway sampling, and pe riodic nutrient samples, reveal the plume structure. In May concentrat ions of nitrate, silicate, and phosphate decreased linearly with incre asing salinity. Chlorophyll a increased to peak concentrations of 10 m u g l(-1) in the plume, although higher pigment biomass was observed n ear the coast. In August nitrate and silicate concentrations decreased conservatively near the mouth of SW Pass, except where pigment biomas s was enhanced in a convergent surface front. Surface nutrient concent rations in the plume also decreased with increasing salinity. The obse rvations provide the first Lagrangian view of surface property distrib utions in the Mississippi River plume, and indicate that significant t emporal variability exists in physical and biological properties withi n a day after waters are discharged from the river delta. (C) 1997 Els evier Science B.V.