Circulation and Transport in the Hudson Shelf Valley

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

It has long been known that submarine valleys over continental shelves and submarine canyons over continental slopes provide important pathways for transporting material such as sediment, nutrients and biological organisms across continental shelves and slopes. Previous studies have focused almost exclusively on deeper continental slope canyons. In contrast to slope canyons, shallower shelf valleys are strongly influenced by surface and bottom forcing, such as winds and waves, and often subject to large seasonal variations in stratification. Also in contrast to slope canyons, shelf valleys extend into shallow water, where sediment transport and biological processes are particularly active, and can therefore potentially facilitate cross-shelf transport of sediment and upwelling of nutrients to the near-surface euphotic zone. Shelf valleys provide a direct connection between the shelf region that is most strongly impacted by human activity and deep waters of the continental slope and open ocean. The research objectives are guided by previous studies of slope canyons and preliminary analysis of observations in Hudson Shelf Valley, a narrow and long valley that cuts across the continental shelf of the Middle Atlantic Bight. Along-valley (cross-shelf) flows in Hudson Shelf Valley are primarily wind-driven and often reach 50 cm/s, an order of magnitude larger than cross-shelf flows on the adjacent continental shelf, making it an important conduit for cross-shelf exchange. The goal is a quantitative understanding of the response of flows in shelf valleys, particularly the along-valley transport, to wind forcing that will be broadly relevant to a wide range of shelf valleys. The approach is a sequence of idealized numerical modeling runs aimed at understanding the dynamics and quantifying the transport and vertical structure of the flow in shelf valleys in terms of relevant non-dimensional parameters, and complemented by analysis of existing observations from Hudson Shelf Valley and more realistic simulations of Hudson Shelf Valley to evaluate the relevance of the idealized model results to a realistic shelf valley. Analysis of historical observations and numerical simulations will be used to address fundamental scientific questions concerning the circulation and transport in shelf valleys and the contribution of valley flows to heat, salt and nutrient balances on the shelf. Broader impacts: Better understanding of the circulation and transport in shelf valleys, and specifically Hudson Shelf Valley, will provide the physical background for studies of biological productivity and contaminant/larval dispersal on the shelf. It will also help quantify tracer and momentum exchanges between the continental shelf and the slope sea. The project will have educational impacts through the involvement of a full-time graduate student and participation by undergraduate students.