Interdecadal variability in Labrador Sea precipitation minus evaporation and salinity

Abstract

Changes in the air–sea freshwater flux (equivalently Precipitation minus Evaporation, P − E) over the interior of the Labrador Sea have been examined using the NCEP/NCAR and ERA40 reanalyses. A major increase in the net precipitation, equivalent to 9 cm yr −1, is observed in the mid-1970s, consistent with a recent study that reported a similar change in the eastern sub-polar gyre. The increase in the Labrador Sea is primarily driven by changes in the P component which occur in spring (and to a lesser extent summer). The seasonality of the change is markedly different to that found for the eastern gyre which had a strong winter increase in precipitation. Potential links between the Labrador Sea P − E increase and the NAO and other leading modes of atmospheric variability have been explored, but it has been found that the increase is not driven by long-term trends in these modes. The magnitudes of the increase in freshwater content for a range of depths (500, 1000, 1500, 2000 m) in the Labrador Sea are then calculated. Finally, it is suggested that the P − E increase must have played some role in causing the observed freshening of the Labrador Sea and the wider North Atlantic sub-polar gyre region in recent decades, although the exact impact can not be quantified.