Intrusions of outer shelf and slope water within the nearshore zone off Long Island, New York1,2

From 1974 through 1978 studies were made of temperature, salinity, and water velocity, by hydrographic surveys and from moored instruments, in the waters within 15 km of the southern Long Island coastline. Data of late summer reveal frequent intrusions of anomalous water which appear to be of slope or outer shelf origin. Three intrusions of notably differing character are described. Two occurred at middepth, within the pycnocline. Concurrent hydrographic and current meter data suggest that these water masses were transported shoreward due to circulation forced by wind stress and by longshore density gradients. The third intrusion was initially observed near the surface and was of anomalously high temperature. Its T/S relation was similar to a warm and salty bolus detected 12 days earlier in the midshelf region. Hydrographic data suggest that this bolus may have been a detached parcel of slope water. Such intrusions may commonly occur during summer and fall and may be related to the appearance of tropical fish in the Long Island vicinity during these seasons.