Spatial and temporal variability in flow at the mouth of Narragansett Bay

Abstract

Results are presented from field measurements of the spatial and temporal variability of circulation and exchange between Narragansett Bay and Rhode Island Sound (RIS) at both tidal and seasonal timescales. Data were collected during 13 acoustic Doppler current profiler (ADCP) surveys between April 1998 and July 1999. Significant horizontal and vertical structure was observed in the instantaneous, tidally driven flow and the residual, nontidal flow. This was especially evident through the deeper East Passage (EP), where persistent inflow was observed along the eastern side, and outflow along the western side of the channel. The residual volume transport of water to RIS is greater through the EP than through the West Passage entrance to the Bay, particularly in summer. Data from the offshore, or coastline‐normal survey lines reveal a strong seasonal variability in RIS circulation. A residual (5–15 cm s−1) cyclonic coastal current is recorded within RIS during summer, stratified conditions. This residual current, which was not present during the winter surveys, enhances Narragansett Bay‐RIS exchange by efficiently advecting the bay outflow to the southwest, away from the entrance. Results also indicate the resupply pathways for deep water to the entrance region vary in summer versus winter. Observed differences in RIS circulation, and related estuary‐shelf exchange, have significant implications for physical, chemical, and biological models of Narragansett Bay.