North Atlantic Subpolar Gyre Surface Variability (1895-2009)

Surface temperature, salinity, and density are examined in the northeastern part of the North Atlantic subpolar gyre over the last 115 years of measurements. This region presents coherent variability in space but also between different seasons, with relatively small trends and large multidecadal variability. The most significant trend is a lowering in surface density. Multidecadal variability in T and S is large and is usually similar, with the largest difference between the two in the 1920s and a tendency of T to lead S. Multidecadal T and S are correlated with the winter North Atlantic Oscillation (NAO) index at 0 or 1-yr lag for T and 0 to 3-yr lag for S. This suggests a strong contribution of advection. The lag between T and S is also suggestive of a contribution of air-sea fluxes of heat or freshwater, but probably more so at high frequencies than at the multidecadal time scales. Salinity higher frequency is correlated with NAO at a 2-3-yr lag, whereas T higher frequency variability presents no correlation with NAO at any lag. This suggests different relations between seasonal NAO indices and air-sea heat fluxes patterns in this region before and after 1960; also the advective signal is more clearly identified in salinity in this region.