Long-term mean and event-related pigment distributions during the unstratified period in South Atlantic Bight outer margin and middle shelf waters

Abstract

Phytoplankton pigment distributions in the South Atlantic Bight (SAB) during the unstratified period (November through April) and dynamics influencing these distributions are examined using multi-year Coastal Zone Color Scanner (CZCS) and Advanced Very High Resolution Radiometer (AVHRR) coverage, oceanographic and meteorological data from buoys and coastal stations, and Fleet Numerical Meteorology and Oceanography Center (FNMOC) wind fields. We examine: (1) long-term mean and event-related pigment distributions along the outer margin in relation to Gulf Stream and meteorological forcing, and (2) spatial coherence in pigment field temporal variation along the outer margin itself and between the outer margin and adjacent regimes. The highest mean unstratified period CZCS-derived chlorophyll (CZCS-Chl) is in the central SAB, immediately inshore of the region of the Gulf Stream offshore mode/Charleston Gyre. The highest event-related pigment concentrations are associated with the development of large-scale pigment field features, exhibiting along-shore orientation and association with development of temperature (SST) fronts. The role of wind and Gulf Stream forcing is supported in event studies of these features. Coherent temporal variation in CZCS-Chl is evident at along-shelf scales greater than that typical of Gulf Stream frontal eddies, particularly in the central SAB, where the coherence scale exceeds 600 km. Distinct pigment field coherence between the central SAB outer margin (ca. 400 km along-shore) and the Charleston Gyre/Gulf Stream offshore mode region is evident. The pigment field of middle shelf waters also exhibits significant coherence with that of the outer margin. The results show that non frontal eddy processes are important in determining the mean and event-related pigment distributions, as well as the spatial scale of coherent pigment field variation during the unstratified period.