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

Meanders of the shelf break front in the Mid-Atlantic Eight (MAE) during Ap ril and May of 1997 were associated with chlorophyll enhancement along a hy drographic and a topographic feature. The hydrographic feature was the surf ace outcrop of the front, which ranged from similar to 10 to >100 km seawar d of the shelf break owing to the meanders. The topographic feature was the shelf break (100-m isobath). Chlorophyll enhancement was observed by a sat ellite instrument, the ocean color and temperature sensor, and by a fluorom eter in situ. It developed in near-surface waters typically nutrient deplet ed during late spring, thus local nutrient enrichment of near-surface water s was probable. Observations of sufficient resolution to define processes w ere available only for the region of shelf break chlorophyll enhancement. A long two meander troughs (shoreward extremities near the shelf break), we o bserved shoaling of cold shelf water. Shelf water shoaled >20 m along front al isopycnals, and phytoplankton absorption maxima coincided directly with the shoaled water. Thus local nutrient enrichment by along-isopycnal upwell ing was the supported mechanism of chlorophyll enhancement at the shelf bre ak. The basis for along-isopycnal upwelling was seaward flow of shelf water forced by meander circulation near the shelf break. Strong cross-isobath f low and mixing developed as these meanders propagated along the shelf break front of the MAB at a relatively constant rate of similar to 9 km day(-1).