Upwelling source depth in the presence of nearshore wind stress curl

Abstract

The influence of nearshore wind stress curl on the relative partitioning of bottom boundary layer (BBL) and interior transport within an idealized, two-dimensional coastal upwelling system is studied theoretically and using a numerical model. A nearshore reduction in upwelling favorable wind stress amplitude (1) reduces the width of the inner shelf, (2) reduces the local wind-driven Ekman transport, and (3) increases the cross-shelf momentum flux divergence. Relative BBL transport, defined as the transport entering the surface mixed layer (SML) from the BBL divided by offshore transport in the SML, decreases under reduced nearshore wind stress. This effect is dominated by the reduced local SML Ekman transport and to a lesser degree by local curl of surface and bottom stresses. We consider the quantitative impact for a range of shelf slopes, stratifications, and wind stress curl scales. The relative contribution of bottom boundary layer transport co-varies with upwelling source depth and is therefore expected to alter nutrient fluxes into the euphotic zone as well as the resultant biological response. Copyright 2012 by the American Geophysical Union.