Modeling the Pathways and Mean Dynamics of River Plume Dispersal in the New York Bight

Abstract

This study investigates the dispersal of the Hudson River outflow across the New York Bight and the adjacent inner- through midshelf region. Regional Ocean Modeling System (ROMS) simulations were used to examine the mean momentum dynamics; the freshwater dispersal pathways relevant to local biogeochemical processes; and the contribution from wind, remotely forced along-shelf current, tides, and the topographic control of the Hudson River shelf valley. The modeled surface currents showed many similarities to the surface currents measured by high-frequency radar [the Coastal Ocean Dynamics Applications Radar (CODAR)]. Analysis shows that geostrophic balance and Ekman transport dominate the mean surface momentum balance, with most of the geostrophic flow resulting from the large-scale shelf circulation and the rest being locally generated. Subsurface circulation is driven principally by the remotely forced along-shelf current, with the exception of a riverward water intrusion in the Hudson River shelf valley. The following three pathways by which freshwater is dispersed across the shelf were identified: (i) along the New Jersey coast, (ii) along the Long Island coast, and (iii) by a midshelf offshore pathway. Time series of the depth-integrated freshwater transport show strong seasonality in dispersal patterns: the New Jersey pathway dominates the winter?spring seasons when winds are downwelling favorable, while the midshelf pathway dominates summer months when winds are upwelling favorable. A series of reduced physics simulations identifies that wind is the major force for the spreading of freshwater to the mid- and outer shelf, that remotely forced along-shelf currents significantly influence the ultimate fate of the freshwater, and that the Hudson River shelf valley has a modest dynamic effect on the freshwater spreading.