A curious local surface salinity maximum in the northwestern tropical Atlantic

Sea surface salinity (SSS) measurements from the Aquarius/SAC-D satellite reveal the seasonal development of a local salinity maximum in the northwestern tropical Atlantic in boreal winter to early spring. This seasonal tropical SSS maximum, which is confirmed by comparison to in situ observations, is centered at 8°N, and is up to 0.5 psu saltier than the surrounding water despite its location in the latitude band of the highly precipitating Intertropical Convergence Zone. Its existence seems to be the result of the differing phases in the seasonal variations of Amazon discharge and ocean currents. In late boreal fall/ winter, when the discharge is at its minimum, but the North Brazil Current (NBC) and its retroflection are still present, a mixture of high-salinity water of equatorial and South Atlantic origin is transported along the shelf break by the NBC retroflecting into the western part of the North Equatorial Countercurrent (NECC). This salt transport produces the salty signature of the western part of the NECC, which is seen as a localized salinity maximum on satellite imagery, in contrast to the fresh signature present in summer-early fall. The seasonal slowing/reversal of the NECC in boreal spring stops this eastward salt transport, thus leading to the disappearance of this northwestern tropical SSS maximum.