Upper ocean salinity balance in the western equatorial Pacific

The upper ocean salinity balance in the western equatorial Pacific warm pool was evaluated using up to 2.5 years of data (September 1991 through April 1994) from the Coupled Ocean‐Atmosphere Response Experiment's enhanced monitoring array of moorings. At the central mooring site (0°, 156°E), precipitation had a record‐length mean of 4.5 m yr−1, while evaporation had a mean of 1.4 m yr−1. This excess surface freshwater flux was balanced primarily by vertical mixing (estimated as the residual of a salt budget calculation) and by zonal advection. For timescales between a month and 2.5 years, surface salinity variability was dominated by zonal advection and only weakly correlated with precipitation, consistent with the concept of a zonally migrating “fresh pool.” The effects of precipitation on local surface salinity variations were more apparent for timescales shorter than a month. Shallow rain “puddles” tended to form in a matter of hours. However, owing to the combination of mixing and advection, these precipitation‐generated freshwater puddles were typically short‐lived.