Seasonal salt budget of the northwestern tropical Atlantic Ocean along 38W

The western tropical Atlantic has a complex salt budget, with strong seasonal river discharge, precipitation, evaporation, and the confluence of different water masses all contributing. This paper addresses the atmospheric and oceanic causes of the seasonal budget of mixed layer salinity based on direct observations. Data sets include up to five years (September 1997 December 2002) of measurements from moored buoys of the Pilot Research Array in the Tropical Atlantic (PIRATA), ship-intake salinity observations, and near-surface drifting buoys. We analyze the mixed layer salt balance at four PIRATA mooring locations along the 38W (4N, 8N, 12N, and 15N). At 4N precipitation is primarily semiannual. Here there are also strong contributions from zonal and meridional advection. The sum of the three balances a strong annual cycle of local storage. The strongest seasonal cycle of precipitation occurs at 8N and is balanced by horizontal advection and local storage. At 12N the balance is mostly local, with only a minor contribution from horizontal advection. At 15N horizontal advection plays a key role in balancing a semiannual cycle of local storage.