THE FATE OF RIVER DISCHARGE ON THE CONTINENTAL-SHELF .2. TRANSPORT OFCOASTAL LOW-SALINITY WATERS UNDER REALISTIC WIND AND TIDAL FORCING

A three-dimensional numerical simulation of shelf circulation is prese nted. We employ realistic forcing for the Southeast U.S. Continental S helf during the spring season. We show that the strongest offshore tra nsport of river-induced, coastal, low-salinity waters and associated m aterials occurs near the surface. The preferred mean pathway is in the northeastward direction, and it takes about 2 months to cross the ent ire shelf. Owing to the mean direction of surface transport and the to pography of the South Atlantic Eight shelf, the preferred location for springtime removal is off Charleston, South Carolina, and presumably in the vicinity of the Charleston Bump, The transport and fate of the river-induced, coastal, low-salinity waters during the spring season a re determined by (1) the stratification of nearshore waters, which is due to the high river runoff and causes the decoupling between ''near- surface'' and ''near-bottom'' layers; (2) the prevailing northeastward winds, which cause significant offshore transport within the shallow near-surface Ekman layer; and (3) the tidally induced bottom stirring (M(2) tides). Comparison of model and data time series of currents sho ws very good agreement, Standard deviations of the model and data-comp uted empirical orthogonal functions are almost identical, while the re spective variance-conserving spectra agree both in amplitude and phase .