Physical and biological responses to the passage of a winter storm in the coastal and inner shelf waters of the northern Gulf of Mexico

Abstract

Hydrographic and biological properties in coastal and inner shelf waters of the northern Gulf of Mexico were monitored daily over 3 days in February 1984, immediately after the passage of a meteorological front. Strong northerly and westerly components of the wind resulted in upwelling of high salinity inner shelf water containing low nitrate and chlorophyll concentrations. Low salinity coastal water, with associated high concentrations of chlorophyll and nitrate, was transported offshore at the surface. Isopleths sloping from the surface to the bottom over a distance of approximately 10 km characterized an oceanographic front that separated the two water types of day 1. The frontal boundary became more compact and decreased in slope on day 2, and isopleths were essentially horizontal by day 3, with the coastal water overlying the inner shelf water. The passage of such winter storms at 3–8 day intervals could result in a periodic offshore transport of nutrient- and phytoplankton-rich water from the coastal boundary layer to the inner shelf regions. Laboratory experiments with the neritic copepods, Acartia tonsa and Centropages furcatus, showed that egg production increases dramatically within a few hours after an increase in food availability such as might occur in inner shelf waters during upwelling events. It is possible that winter storms and the associated redistribution of nutrients and phytoplankton have significant direct biological consequences in the inner shelf waters of the northern Gulf of Mexico.