Spatial variability in SeaWiFS imagery of the South Atlantic bight as evidenced by gradients (fronts) in chlorophyll a and water-leaving radiance

Ocean margin waters contain a host of dissolved and particulate materials of terrestrial and marine origin. The presence of these materials can confound the chlorophyll a (chl a) estimates retrieved by ocean-color satellites’ empirical algorithms. We apply edge detection software to chlorophyll a and water-leaving radiance (Lwn) data from 1998 sea-viewing wide field-of-view sensor (SeaWiFS) imagery to examine this problem within ocean margin waters off the southeastern continental United States (SEC) and South Atlantic bight (SAB). We identify the location of boundaries differentiating waters containing different backscattering components. Identifying those areas where apparent chl a gradients may be caused by differential backscattering helps to determine the location of those gradients caused by real changes in chl a concentrations. An onshore/offshore phytoplankton gradient and seasonal signal not previously detected in SEC waters was revealed from examination of cross-shelf transect data for the months of the study. Phytoplankton concentrations and associated gradients or fronts were connected with the inner, middle or outer shelf based on the biological response to local physical and atmospheric forcings. River flow and wind stress affect inner shelf chl a distributions, while offshore chl a distributions are controlled by Gulf Stream meanders. Carolina Capes’ oceanography influenced chl a frontal variability in that local region. We also explore the possibility of utilizing the edge detection algorithm to delineate boundaries between waters dominated by different algal classes.