Mesoscale response of diatom populations to a wind event in the plume of the Hudson River

Abstract

Effects of a southwest wind event on distributions of dissolved inorganic nitrogen and diatom biomass are described and evaluated in terms of interactions between circulation, static stability of the water column, and the suspension and growth of diatom populations. A diatom bloom, dominated by Skeletonema costatum, developed in response to upwelling as a consequence of the vertical transport of biomass from the aphotic zone (deduced from distributions and rate measurements), a decrease in sinking rate from 1.0 to 0.3 m d −1 (from sediment trap collections), and lower dilution rates (from hydrography). Carbon-specific growth rate of diatoms showed little variability based on measurements made before and during the bloom, i.e., variations in diatom production were primarily due to variable loss rates rather than to growth. The influence of diatom production associated with the coastal plume of the Hudson River (areas 1000 km 2) was observed to extend ca. 100 km seaward of the zone of most active production. Episodes of cross-shelf transport and onshore accumulation of phytoplankton biomass appear to alternate with periods of high surface production in the plume.