DECADAL VARIABILITY OF HYDROGRAPHY IN THE UPPER NORTHERN NORTH-ATLANTIC IN 1948-1990

We investigate the variability of the North Atlantic subarctic gyre in recent decades from time series of station temperature and salinity. Decadal variability stronger at the surface is identified, which exhib its vertical coherence over a layer deeper than the late winter mixed layer. In the northwestern Atlantic, it corresponds to the layer with a component of water from the Arctic Ocean or from the Canadian Arctic . The spatial coherence of the signal is investigated. An empirical or thogonal function decomposition of lagged time series indicates that a single pattern explains 70% of the variance in upper ocean salt conte nt, corresponding to a propagating signal from the west to the northea st in the subarctic gyre. The most likely interpretation is that the s alinity signal originates in the slope currents of the Labrador Sea an d is diffused/advected eastward of the Grand Banks over the near weste rn Atlantic. In the northwestern Atlantic, temperature fluctuations ar e strongly correlated to salinity fluctuations and are aligned along t he average T-S characteristics. This signal suggests large variations in the outflow of fresh, cold water in the slope current, and is stron gly correlated with ice cover. A basin scale atmospheric circulation o f weakened westerlies at 55 degrees N, weaker northwesterlies west of Greenland and weaker southerlies over the central and eastern North At lantic is associated with the high salinity and warm water phase of th e first principal component. This circulation pattern leads fluctuatio ns in the northeast Atlantic and lags those in the northwestern part o f the basin. The wind indices also suggest that the fluctuations of th e fresh water outflow occur during intervals of anomalously northerly winds, either east of Greenland (1965, 1968-1969) or off the Canadian Archipelago (1983-1984).