Surface salinity in the Atlantic Ocean (30 degrees S-50 degrees N)

Abstract

Sea surface salinity (SSS) data in the Atlantic Ocean is investigated between 50 degrees N and 30 degrees S based on data collected mostly during the period 1977-2002. Monthly mapping of SSS is done to extract the large-scale variability. This mapped variability indicates fairly long (seasonal) time scales outside the equatorial region. The spatial scales of the seasonal anomalies are regional, but not basin-wide (typically 500-1000 km). These seasonal SSS anomalies are found to respond with a 1-2 month lag to freshwater flux anomalies at the air sea interface or to the horizontal Ekman advection. This relation presents a seasonal cycle in the northern subtropics and north-east Atlantic indicating that the late-boreal spring/summer season is less active than the boreal winter/early- spring season in forcing the seasonal SSS variability. In the north-eastern mid-latitude Atlantic, SSS is positively correlated to SST, with SSS slightly lagging SST. There are noticeable long-lasting larger-scale signals overlaid on this regional variability. Part of it is related to known climate signals, for example ENSO and NAO. A linear trend is present during the first half of the period in some parts of the basin (usually towards increasing salinities, at least between 20 degrees N and 45 degrees N). Based on a linear regression analysis, these signals combined can locally represent up to 20% of SSS variance (in particular near 30 degrees N/60 degrees W or 40 degrees N/10-30 degrees W), but usually represent less than 10% of the variance