The freshest surface waters in the tropical Pacific are found at its eastern boundary. Using in situ observations, we depict the quasi‐permanent presence of a far eastern Pacific fresh pool with sea surface salinity (SSS) lower than 33, which is confined between Panama's west coast and 85°W in December and extends westward to 95°W in April. Strong SSS fronts are found at the outer edge of this fresh pool. We investigate the seasonal dynamics of the fresh pool using complementary satellite wind, rain, sea level and in situ oceanic current data at the surface, along with hydrographic profiles. The fresh pool appears off Panama due to the strong summer rains associated with the northward migration of the ITCZ over Central America in June. During the second half of the year, the eastward‐flowing North Equatorial Counter‐Current keeps it trapped to the coast and strengthens the SSS front on its western edge. During winter, as the ITCZ moves southward, the northeasterly Panama gap wind creates a southwestward jet‐like current in its path with a dipole of Ekman pumping/eddies on its flanks. As a result, upwelling in the Panama Bight brings to the surface cold and salty waters which erode the fresh pool on its eastern side while both the jet current and the enhanced South Equatorial Current stretch the fresh pool westward until it nearly disappears in May. New SMOS satellite SSS data proves able to capture the main seasonal features of the fresh pool and monitor its spatial extent.

We study mesoscale eddy characteristics in the Tropical Atlantic Ocean (TAO), using 23 years of daily altimetry sea level anomalies (SLA). Eddies are mainly generated in the eastern boundary upwelling systems (EBUS) and in the Brazil Current (BC) region. Their westward propagation speed reaches 20 cm.s^‐1 in equatorial areas, decreasing with latitudes. They present typical amplitudes of 1‐5 cm. The largest and most energetic eddies are observed in the equatorial region, especially in the North Brazil Current (NBC) retroflection. The seasonal cycle of the eddy characteristics shows higher amplitudes along the NBC retroflection and the western part of the North Equatorial Countercurrent (NECC). A new criterion, based on altimetry data, determines the probability that barotropic instability of mean surface currents is responsible for eddy generation. We find a strong likelihood that the later plays a key role along the NECC, whereas other mechanisms must be invoked for the NBC region.

Wind-driven coastal upwelling can be compensated by onshore geostrophic flow, and river plumes are associated with such flow. We investigate possible limitation of the northeast Gulf of Guinea upwelling by the Niger River plume, using regional ocean model simulations with or without river and dynamical upwelling indices. Here, the upwelling is weakened by 50% due to an onshore geostrophic flow equally controlled by alongshore thermosteric and halosteric sea-level changes. The river contributes to only 20% of this flow, as its plume is shallow while upwelling affects coastal temperature and salinity over a larger depth. Moreover, the river-induced mixed-layer thinning compensates the current increase, with no net effect on upwelling. The geostrophic compensation is due to an abrupt change in coastline orientation that creates the upwelling cross-shore front. The river nonetheless warms the upwelling tongue by 1°C, probably due to induced changes in horizontal advection and/or stratification.