Climatological coupling of the thermohaline decadal changes in Central Water of the Eastern North Atlantic

Abstract

Data collected at 42ºN, 10ºW in the intergyre region of the Northeast Atlantic show significant year to year variability in the T-S characteristics of the upper 800m of the water column. Taking salinity values on the sq = 27.1 kg m-3 isopycnal as representative of the Eastern North Atlantic Central Water mass it was found that the variability correlates well with the wind stress at 43ºN, 11ºW, with cumulative river discharge (which we take as an index of precipitation over the ocean) and with the NAO (which is an index of the strength and position of storm tracks and the state of the evaporation-precipitation balance). The covariation illustrates the close coupling between water mass formation and climate in the North Atlantic, where climate changes affect the deep ventilation by which ENACW is formed and the evaporation-precipitation balance from which the T-S signature results. Hints of a 20 year cycle in the ocean correlate with a 20 year periodicity in the NAO. It remains to be established whether there is a feedback mechanism by which water mass anomalies affect the climate and the intensity and variation of the NAO pattern, and the extent to which upper ocean observations can be used as an indicator of future climate trends.