Slope water intrusions within the nearshore waters off Long Island, New York

Abstract

From 1974 through 1978 intensive measurements were made of the salinity, temperature and current structure of the waters within 12 km of the Southern Long Island coastline. The data were derived from two sources: a mooring array from which time series of temperature, salinity and water velocity were measured at four depths at each of four offshore distances; and high resolution, daily STD and current meter surveys. During August and September intrusions of slope or outer shelf water were often observed by the STD surveys. Three intrusions have been studied in detail. Two were observed at mid-depth following periods of upwelling favorable winds. Concurrent hydrographic and current meter data suggest that these water masses were transported shoreward by a combination of wind forcing and longshore density gradients. The third intrusion, initially observed near the surface, had coinciding salinity and temperature maxima. This water mass appears to have entered the shelf as a result of a shelf/slope water exchange, possibly induced by a warm-core ring near the shelf break. Such intrusions may commonly occur during the summer and fall and may be related to the appearance of tropical fish in the Long Island vicinity during these seasons.