A New Long-Term Atlantic Surface Salinity Record Reveals An Intensification Of The Mean Salinity Field

We present a new record of observed sea surface salinity (SSS) data, which has been compiled and processed to provide improved spatial coverage for the period 1896-2013. We discuss the characteristics of this data set and how we group the data in time series in 23 sub-regions from 20°S to 70°N, away from shelves. The low-pass (cut-off at 7.5 years) time series are then investigated as the combination of a regressed fit to major climate indices (NAO, AMO, IPO) and a residual. The regressed fit explains 20.6 % of the variance, with larger explained variance in the ITCZ region north of the equator and the North Atlantic subpolar gyre (NASG) north of 45°N. The residual presents a large positive salinity trend since the 1970s (except in the NASG), concurrent with the recent warming in global SST. The trend in the residual from 1970–2013 is markedly different from that of the initial series in the key regions of the ITCZ and the NASG, where most of the observed trend is attributed to the AMO trend during this period. Furthermore, the scatterplot of this residual trend as a function of average SSS shows a significant positive correlation, suggesting an intensification of the hydrological cycle. Interestingly, no Atlantic region shows a strong negative residual trend from the 1970s: the only negative trend is near 50-55°N, which also has a negative trend through the whole time series. The period of early 20th century global warming from 1912-1940 is also examined, but does not exhibit similar overall positive trends in the initial data or the residual.