The cross-shelf structure of wind- and buoyancy-driven circulation over the North Carolina inner shelf

Circulation and transport over the North Carolina shelf were studied as par t of an interdisciplinary CoOP study in 1994. Shipboard data and moored ins truments reveal two important influences on the density distribution. Winds in the area reverse every few days, driving upwelling and downwelling circ ulation alternately, and a low-salinity coastal buoyancy current from Chesa peake Bay is present only during downwelling. Empirical orthogonal function s reveal that variability in temperature and cross-shore circulation is dom inated by upwelling and downwelling, while patterns in salinity and along-s hore circulation are primarily due to the buoyancy current. The observed de nsity distribution goes through a cycle, showing each influence in turn. Af ter a period of equatorward winds, the thermocline bends downward at the ne arshore end, and a coastal wedge of low-salinity water is observed. When th e winds turn poleward, the thermocline bends upward and the low-salinity wa ter moves offshore. This cycle repeats four times during our study period w ith modest variations. (C) 2001 Elsevier Science Ltd. All rights reserved.