Interannual to interdecadal variability of sea surface salinity in the Atlantic and its link to the atmosphere in a coupled model

Abstract

The interannual to interdecadal variability of sea surface salinity (SSS) in the Atlantic is investigated using 200 years of a control simulation of the Bergen climate model. After verifying that the model behaves realistically, we show that most centers of SSS variability are located near the mouths of the main rivers of the basin. This variability is due primarily to anomalous runoff, except in the St. Lawrence area, and to anomalous Ekman and geostrophic currents, while fluctuations in the freshwater flux play a somewhat lesser role. Away from the coast, SSS variability is strong in the northern tropics, due largely to anomalous advection and freshwater exchanges. Regression analysis and a Lagrangian technique show that the SSS anomalies are advected by the mean oceanic circulation and can be followed along the gyres for several years. The link between SSS anomalies and the dominant modes of variability of the atmosphere is also investigated. The SSS response to the North Atlantic Oscillation (NAO) is dominated by relatively small scales that are forced by anomalous Ekman currents, but the relative influence of the large‐scale freshwater fluxes increases at long timescales. The NAO‐induced SSS anomalies are also strongly advected and distorted by the mean currents, so that their pattern at the interannual timescale only reflects in part that of the atmospheric forcing. The link between SSS anomalies and the East Atlantic pattern is similar.