The Cold-Water Pathway during an Upwelling Event on the New Jersey Shelf

Abstract

A comprehensive dataset obtained in summer of 1996 on the New Jersey shelf off Atlantic City is analyzed to determine the pathway for cold water during a period of sustained upwelling. The data include shipboard CTD/ADCP surveys, time series from three across-shelf lines of moorings, and remote sensing. An upwelling event that occurred from 30 June through 10 July 1996 is studied. The event comprised three stages: first, the cold water was upwelled through the bottom layer; second, the onshore flow concentrated in the pycnocline; and third, mesoscale eddylike features developed. During the first upwelling-favorable wind pulse, which lasted approximately 2 days, a northward alongshelf current was generated and the pycnocline outcropped at the surface approximately 5 km off the coast. The northward current occupied the whole water column, and cold water was brought to the coast through the near-bottom layer, in the manner of Ekman dynamics. After that, an alongshelf pressure gradient was set, which was associated with the bending coastline approximately 100 km to the north at the corner formed by the intersection of the New Jersey coast and the southern coast of Long Island. The onshore flow was now maintained through the pycnocline, with maximum velocities at 10?12-m depth. At the same time, the temperature anomaly transport (pathway for colder water) was centered at 14?17-m depth, corresponding to the lower part of the pycnocline. This onshore transport was primarily balanced by alongshelf pressure gradient; the acceleration of alongshelf current was less important. Approximately 6 days after the onset of upwelling, mesoscale currents began to dominate the study area, establishing a three-dimensional flow field with spatially localized (in the alongshelf direction) onshore currents.