VARIABILITY OF PARTICULATE MATTER AND ABUNDANT ZOOPLANKTON OFF THE SOUTHEASTERN UNITED-STATES DURING SPRING OF 1984 AND 1985

The variability of particulate matter, chlorophyll a and zooplankton o ften depend strongly on physical processes. In this paper we compare d istributions observed on the southeastern shelf of the United States d uring April 1984 and 1985. April 1984 was characterized by high freshw ater runoff, vertical stratification and strong wind stress. In April 1985 all three variables were much lower. While alongshore flow was si milar in both years, cross-shelf flow was more pronounced in 1984. The most noticeable effect on zooplankton was their expatriation towards offshore. The near surface, offshore and deeper Ekman flows from north eastward wind events, in conjunction with intermittent sinking, tend t o trap most particulate matter that was produced nearshore in the near shore or middle shelf region. Offshore removal was transient following upwelling wind events during stratification conditions. Zooplankton a bundance on the inner and middle shelf was not only a function of near - and offshore production but also of cross-shelf and alongshore displ acement. Whereas the circumglobal copepod genus Paracalanus occurs abu ndantly in summer, spring and autumn on the inner and middle shelf, th e cosmopolitan genus Oithona which is abundant during summer is scarce during spring and appears to be affected by temperature and water col umn stability. The variability of particulate matter and zooplankton d uring early spring seems to be at least partly determined by atmospher e forcing and the amount of freshwater runoff.