The Dynamical Response of Salinity to Freshwater Discharge and Wind Forcing in Adjacent Estuaries on the Georgia Coast

Ten years of oceanic and meteorological monitoring data were collected in order to understand the spatial and temporal patterns of salinity distribution across three adjacent estuaries in the Georgia Coastal Ecosystems Long Term Ecological Research domain. Empirical orthogonal function analysis shows that 95% of the subtidal salinity variability can be explained by two principle modes. The first mode is dominated by river discharge, and causes system-wide freshening throughout the domain. The second mode, which explains 8% of the variability, is correlated with subtidal sea surface height and, hence, alongshore winds. The response in Sapelo and Doboy Sounds to this second mode, however, is out of phase with that of Altamaha Sound. During upwelling-favorable winds when coastal sea surface height decreases, Altamaha Sound freshens, and salinity increases in Doboy and Sapelo Sounds. On the other hand, freshening in Doboy and Sapelo Sounds and a salinity increase in Altamaha Sound accompany downwelling-favorable winds. A regional ocean model of a highly idealized coastal domain of three adjacent estuaries connected by the Intracoastal Waterway is consistent with the observations-river discharge and upwelling-favorable winds freshen the coastal domain so that when downwelling-favorable winds occur, the coastal freshwater originating in the Altamaha River is transported into Sapelo and Doboy Sounds. Model results suggest that the Intracoastal Waterway and the complex network of channels that connects the sounds play a dominant role in water exchange between the adjacent estuaries.