Across-Shelf Transport on a Continental Shelf: Do Across-Shelf Winds Matter?

Abstract

Wind-forced across-shelf flow on a continental shelf is often described as a two-dimensional balance between flow within a surface boundary layer generated by alongshelf winds and a compensating subsurface flow. Typically, the effects of across-shelf winds are ignored because transport in the surface Ekman layer parallel to winds is assumed zero. Recent studies, however, have shown that the traditional view of across-shelf transport breaks down in shallow waters where friction is important. In this study, a series of two-dimensional simulations is used to show that across-shelf winds can result in across-shelf velocities in the upper few meters of the water column that are similar in magnitude to those generated by alongshelf winds. This circulation has important consequences for the transport of surface-dwelling material, such as blue crab larvae off of Delaware and Chesapeake Bays. The effects of both alongshelf and across-shelf winds on simulated surface dwelling tracer patches are examined. These studies show that across-shelf winds can account for a large amount of surface on- and offshore transport within the stratified outer shelf and, in fact, can be the primary mechanism for across-shelf transport within the friction-dominated inner shelf. Simple estimates of the parameters that describe this transport agree very well with output from the simulations.