The impact of upwelling and river outflow on the mesoscale variability in the Caribbean Sea

The upper branch of the Atlantic Meridional Overturning circulation flows through the Caribbean Sea. In this basin, the mesoscale variability is dominated by anticyclonic eddies with a low salinity anomaly. They intensify on their path westward while they pass the coastal upwelling region along the Venezuelan coast. To predict the variability of the Caribbean Sea in a future climate, we need to understand the processes governing the life cycle of these anticyclones. In this study, we use a regional model to assess the impact of wind-driven upwelling and the river run-off of the Amazon and Orinoco River on the anticyclones. We show that their westward intensification is driven by the strength of the upwelling, which increases the horizontal density gradients, and consequently the vertical shear of the anticyclones along their propagation westward. The initial strength of the anticyclones is set by the horizontal density gradients induced by the river outflow. This implies that both upwelling and the advection of the river plumes affect the life cycle of mesoscale eddies in the Caribbean Sea. Taking the decreasing trend in upwelling strength and the increasing river run-off into account, we argue that this will alter the life cycle of anticyclones, and thus the mesoscale variability in the Caribbean Sea, in a future climate substantially.