Quantifying Shelf-Basin Exchange at Submarine Canyons in the southern Middle Atlantic Bight using data from Underwater Glider Surveys and Numerical Modeling Experiments

Haixing Wang1, Donglai Gong1, HaoCheng Yu1, Yinglong J Zhang1, Dr. Courtney Kay Harris, Ph.D.2, Marjorie A. M. Friedrichs3, Travis N Miles4 and Jeanna Hudson1, (1)Virginia Institute of Marine Science, Gloucester Point, VA, United States, (2)Virginia Institute of Marine Science, William & Mary, Gloucester Point, VA, United States, (3)Virginia Institute of Marine Science, William & Mary, Gloucester Point, United States, (4)Rutgers University, Marine and Coastal Sciences, New Brunswick, United States
Abstract:
Submarine canyons are known hotspots of enhanced water mass exchange between the continental shelf and the deep ocean. Physical oceanographers have investigated processes such as upwelling and downwelling, and internal tides and waves in submarine canyons, as well their role in enhancing shelf-slope exchange. Off the Mid-Atlantic coast of the U.S., there are multiple shelfbreak submarine canyons. These canyons host abundant biological assemblages and are popular recreational and commercial fishing grounds. Compared with non-canyon area on the U.S. eastern seaboard, and with some of the larger submarine canyons further north (i.e. Hudson Canyon), the canyons in the southern Mid-Atlantic region (i.e. Washington, Wilmington, and Norfolk) are under-sampled. Our work investigates the impact of these canyons on the regional shelf-slope exchange of water and tracers. We completed four glider surveys in the Norfolk, Washington, and Wilmington canyons during 2013-2018. We compared our survey data with other glider survey data in non-canyon areas in the same region. We also conducted numerical experiments based on realistic bathymetry and forcing using an unstructured-grid ocean model (SCHISM). The glider observations show that, (1) under similar wind conditions, hydrographical responses of upwelling and downwelling are stronger in submarine canyons compared to non-canyon shelfbreak region; (2) the upwelling and downwelling hydrographical responses in canyons are commonly transient in response to changing wind, sea surface height distribution, and tides. The numerical experiments show that internal tides are prevalent in canyons, and the tidal oscillation of water layers add on to the wind-driven canyon processes, and they work together to enhance the shelf-deep ocean exchange.