Hydrographic properties and circulation of the North Carolina shelf and slope waters

Abstract

Processes affecting the renewal of the North Carolina Shelf Waters are discussed on the basis of temperature, salinity, dissolved oxygen, nutrients, runoff and wind data collected during 1965–1967. These consist of horizontal advection near the coast from the north, meanders of the Gulf Stream, subsurface intrusion, cascading and runoff.The wind-driven Virginia Water transport past Cape Hatteras may markedly reduce the temperature and salinity, and accelerate the freshwater exchange. The runoff from the watershed north of Cape Hatteras, when driven south by northerly winds, especially during the peak period in early spring, has a much greater influence on the circulation in Raleigh and Onslow Bays that does that from the adjacent rivers south of Cape Hatteras. Meanders in the Gulf Stream may renew the shelf waters with warm, saline water. Intrusion of subsurface Caribbean Water on to the outer part of the shelf takes place most frequently during the late summer following a period of southerly winds. It is postulated that during the cold part of the year when the surface layers are only partly stratified, such an intrusion may lead to upwelling near the shelf break. Cascading from the shelf down the slope may occur during the cold season following periods of low air temperature. Intrusion of subsurface water replenishes nutrients in the area, while cascading reduces the available supply of nutrients.