Chlorophyll enhancement and mixing associated with meanders of the shelf break front in the Mid-Atlantic Bight

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Meanders of the shelf break front in the Mid-Atlantic Bight (MAB) during April and May of 1997 were associated with chlorophyll enhancement along a hydrographic and a topographic feature. The hydrographic feature was the surface outcrop of the front, which ranged from ∼10 to >100 km seaward of the shelf break owing to the meanders. The topographic feature was the shelf break (100-m isobath). Chlorophyll enhancement was observed by a satellite instrument, the ocean color and temperature sensor, and by a fluorometer in situ. It developed in near-surface waters typically nutrient depleted during late spiring, thus local nutrient enrichment of near-surface waters was probable. Observations of sufficient resolution to define processes were available only for the region of shelf break chlorophyll enhancement. Along two meander troughs (shoreward extremities near the shelf break), we observed shoaling of cold shelf water. Shelf water shoaled >20 m along frontal isopycnals, and phytoplankton absorption maxima coincided directly with the shoaled water. Thus local nutrient enrichment by along-isopycnal upwelling was the supported mechanism of chlorophyll enhancement at the shelf break. The basis for along-isopycnal upwelling was seaward flow of shelf water forced by meander circulation near the shelf break. Strong cross-isobath flow and mixing developed as these meanders propagated along the shelf break front of the MAB at a relatively constant rate of ∼9 km day-1. Copyright 1999 by the American Geophysical Union.

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Journal of Geophysical Research: Oceans