Dynamics of Shelfbreak Processes and Shelf/Slope Exchange South of New England

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

Recent studies have identified a significant warming trend in the shelf waters of the northwest Atlantic Ocean as well as extreme warming events such as during the first half of 2012. These have had major impacts on both the continental shelf ecosystem and commercial fisheries. It is unclear at this time how changing continental shelf water mass properties and circulation affect shelfbreak processes and shelf/slope exchange and how the exchange processes in turn modify shelf water masses. This project is the initial phase of a larger research plan originally devised to explore multiple exchange mechanisms involving the meandering of fronts, impingement of warm core rings and wind forcing. To address these issues of shelf/slope exchange, observations from the recently commissioned Ocean Observatories Initiative's Pioneer Array, other historical and recent hydrographic measurements, and remote sensing products will be analyzed. The investigators will also conduct process-oriented numerical modeling to investigate the dynamical mechanisms of dominant exchange processes and to quantify their relative contribution. The ultimate goal of the larger effort is to obtain sufficient understanding of shelf/slope exchange processes and their dependence on key frontal and forcing parameters. This one-year project will focus on assessing the quality and quantity of Pioneer Array data and demonstrating its scientific utility to resolve the exchange processes. The results from this study will be communicated to members of the commercial fishing industry through joint meetings with the Commercial Fisheries Research Foundation of Rhode Island. Results on the dynamics, frequency, and inter-annual variability of exchange processes will be shared with fisheries scientists of the National Marine Fisheries Service to gain insight into how shelf/slope exchange processes may be affecting living marine resources on seasonal and inter-annual time scales. Presentations will be made at various public venues to talk about the scientific results and their societal implications. It is hypothesized that i) shelfbreak frontal meanders, impingement of Gulf Stream warm-core rings, and wind forcing all induce significant cross-shelf exchange, and ii) these exchange processes are subject to the influences by the changing upstream, offshore, and atmospheric conditions over a broad range of time scales. . A recently developed theory for the most unstable wavelength and growth rate of finite amplitude meanders of a shelfbreak front will be validated against observations. Transports for streamers of shelf water that move offshore in the periphery of warm core rings will be quantified and compared to a recent scaling developed from laboratory experiments and limited observations. The Pioneer Array data along with other hydrographic data over the continental shelf, including data collected by commercial fishermen, will be used to investigate the frequency and cross-shelf penetration of subsurface intrusions of slope water or warm core ring water. A process-oriented regional model will be used for the dynamical analysis as well as data interpretation.