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Grodsky, S., Johnson, B., Carton, J., and Bryan, F. (12-Nov-14)

Aquarius sea surface salinity (SSS) reveals the presence of interannual salinity variations in the Caribbean with about 0.5 psu change between salty and fresh events. Anomalous SSS propagates westward across the basin at an average speed of 11 cm/s. Fresh and salty events in the Caribbean are preceded by corresponding SSS anomalies east of the Lesser Antilles. These upstream SSS anomalies are produced by interannual changes in the Amazon/Orinoco plume. Their presence is verified using in-situ salinity measurements from the Northwest Tropical Atlantic Station (NTAS). In contrast to salinity, which displays the westward propagation patterns, SST changes almost immediately across the Caribbean, thus suggesting the primarily role of the atmosphere in forcing the interannual SST. A global 1/10 deg mesoscale ocean model is used to quantify possible origination mechanisms of the Caribbean salinity anomalies and their fate. Simulations confirm that they are produced by anomalous horizontal salt advection, which conveys salinity anomalies from the area located east of the Lesser Antilles towards the west across the Caribbean. Anomalous horizontal advection is dominated by mean currents acting on anomalous salinity. The model suggests that Caribbean salt anomalies propagate further, entering the Florida Current and reaching the Gulf Stream in about 6 to 12 months after crossing the central Caribbean. Previous studies link the origin of salinity anomalies in the Amazon/Orinoco plume to variations in the annual freshwater discharge from the continent. Despite the fact that model river discharge doesn't include interannual variations, the simulated SSS variability is in line with observations. This suggests that interannually forced ocean dynamics plays a key role in river plume variability and its spatial dispersion.