Wind-forced dynamics at the estuary-shelf interface of a large coastal plain estuary

Abstract

Wind-current relationships at the mouth of a large coastal plain estuary are examined using seasonal current, wind, and sea level records. Observations indicate a small portion of subtidal current is forced by along-shelf (AL) wind-induced coastal sea level fluctuations (remote forcing). However, subtidal fluctuations on the order of 10 cm/s appear to be largely forced by along-estuary wind stress (local forcing). Local forcing dominates the wind-driven subtidal current during principal AL and along-estuary wind conditions, but along-estuary wind stress accentuates the local effect while diminishing the remote effect. A simple two-dimensional analytical model helps clarify the competition between remote and local wind forcing of current near the estuary mouth, supporting the existence of a strong bi-directional current that is locally wind-driven, regardless of principal wind forcing. Both observed and model results indicate that the relative orientation of the wind stress with respect to the estuary and the adjacent shelf are important in determining the roles of remote and local forcing. Findings from this study challenge the application of traditional coastal pumping models for estuary-shelf exchange and have implications for larval recruitment and exchange of material between estuaries and inner shelves.