Energetics of the Internal Tide on Northern Georges Bank

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  • 1 Department of Fisheries and Oceans, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada
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Abstract

This paper discusses the energetics of the internal waves generated by the tide on the northern edge of Georges Bank in the outer Gulf of Maine–-a region of strong tidal flow, a density/temperature front, and abrupt topography. A series of bank-edge cross sections in early July 1988, using the towed vertically profiling Batfish, shows that during off-bank flow a large internal hydraulic jump develops over the bank slope. This disturbance propagates on bank during the reverse phase of the tide, evolving into two internal solitonlike features that impinge upon the frontal zone separating stratified bank-edge water from the homogeneous water on bank. Thermistor chain data from the bank edge show that two internal wave packets per tidal cycle are characteristic of the region during this time of year. The available potential energy plus kinetic energy of the internal disturbances, estimated using the Batfish and thermistor chain data, is found to be 35 J m−3 in a plug of fluid 60 m deep and 4 km long (cross bank). A simple model of bank-edge energetics indicates that the wave packets are potentially significant in frontal evolution and in the supply of inorganic nutrients to primary production in the frontal zone.

Abstract

This paper discusses the energetics of the internal waves generated by the tide on the northern edge of Georges Bank in the outer Gulf of Maine–-a region of strong tidal flow, a density/temperature front, and abrupt topography. A series of bank-edge cross sections in early July 1988, using the towed vertically profiling Batfish, shows that during off-bank flow a large internal hydraulic jump develops over the bank slope. This disturbance propagates on bank during the reverse phase of the tide, evolving into two internal solitonlike features that impinge upon the frontal zone separating stratified bank-edge water from the homogeneous water on bank. Thermistor chain data from the bank edge show that two internal wave packets per tidal cycle are characteristic of the region during this time of year. The available potential energy plus kinetic energy of the internal disturbances, estimated using the Batfish and thermistor chain data, is found to be 35 J m−3 in a plug of fluid 60 m deep and 4 km long (cross bank). A simple model of bank-edge energetics indicates that the wave packets are potentially significant in frontal evolution and in the supply of inorganic nutrients to primary production in the frontal zone.

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