Circulation and Exchange Across the Inner Shelf - The Importance of Surface Gravity Waves and Cross-shelf Wind Stress

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

One of the most important problems in coastal oceanography is determining the mechanisms and pathways of cross-shelf exchange (e.g. Ocean Sciences 2001). Cross-shelf and vertical exchange over the inner shelf has a major impact on a wide range of interdisciplinary processes, including the supply of nutrients to the euphotic zone during coastal upwelling, the movement of organisms between estuarine or inter-tidal waters and the mid shelf during different stages of their life cycles, the on-offshore movement of sediment, the offshore dispersal of pollutants, and the deposition of contaminants such as oil spills onto beaches. Despite the importance of the inner shelf, the dominant mechanisms responsible for exchange across the inner shelf and the associated dynamics remain uncertain. There have been few attempts to bridge the gap between nearshore surfzone studies focusing on wave-driven processes and shelf studies focusing on wind-driven processes (see Lentz et al 2001 for an exception). Consequently, nearshore models generally focus on the surfzone and typically do not consider wind forcing or stratification, while shelf models generally do not include wave forcing (e.g. Austin and Lentz 2002). In this study, researchers at the Woods Hole Oceanographic Institution will examine whether or not the cross-shelf circulation and exchange over a substantial portion of the inner shelf is forced by surface gravity waves and cross-shelf wind stresses. To do so, the scientist will analyze existing observations from coastal observatories and previous inner-shelf studies. A three element cross-innershelf array at the Martha's Vineyard Coastal Observatory (MVCO) will be deployed to obtain density and current profiles to determine the impact of stratification on the cross-shelf circulation. Direct covariance estimates of stress profiles will be made using an existing four-year time series of 2-Hz ADCP data from the MVCO, and a simple analytic model of the wave-driven cross-shelf circulation will be developed. Finally, a two-dimensional primitive-equation numerical model with a turbulence closure scheme will be used to investigate the influence of stratification and surface heat flux on the wind- and wave-driven circulation. The goal of this work is to reach a dynamical understanding of the wind-and wave-driven circulation over the inner shelf. In addition, the research will enhance the three-dimensional numerical modeling capability available to the coastal oceanographic community by providing observationally tested parameterizations of surface-gravity-wave forcing in a primitive-equation numerical model and stress observations for evaluating and refining existing turbulence closure schemes.