Dynamics and optics of the Hudson River outflow plume

In July and August 2000 a field experiment was conducted along the New Jersey coast to explore the linkage between dynamics of the outflowing Hudson River plume and the optical character of the inshore environment. A plume of low-salinity water periodically flows along the coast, trapped in an inshore zone of 5-15 km width and extending to over 100 km alongshore from its source. The plume is clearly distinguished in color satellite images because of its high content of particulates and colored dissolved organic matter (CDOM), which dominate the inherent optical properties (IOPs) of the inshore region. This plume water is dispersed into the interior of the shelf when winds turn to upwelling favorable. Using an array of five acoustic Doppler current profilers, we found a well-defined first mode empirical orthogonal function that showed strong southward flow and downwelling circulation during the plume state and weak northward flow with upwelling circulation during the upwelling state. Using filtered and nonfiltered measurements, the optical absorption IOP was separated into contributions from CDOM and particulates. The contributions from particulates were further separated into phytoplankton and detritus contributions using least squares fit with model spectra. It was found that the plume could be distinguished from upwelling by larger contributions to absorption from detritus and smaller contributions from CDOM.