| Summary: | Changes in the quantities and proportions of various intermediate water masses in the eastern North Atlantic have important consequences for the climate of the region. Subarctic Intermediate Water (SAIW) is mostly found within the subpolar gyre and west of 20 degrees W. Small quantities of this water mass, however, are found on the 20 degrees W meridian at the southern end of the Rockall Channel and are observed to influence the vertical structure of the water column. Typically the comparatively fresh SAIW is a highly stratified water mass, and its subduction into the eastern North Atlantic over more saline Mediterranean waters results in a stable layer at intermediate depths that restricts the maximum depth of winter mixing by up to 150 m compared to stations north-west of the Rockall-Hatton Bank. Analysis of Ocean Weather Ship (OWS) data from this region shows temporal variability of the vertical structure during the 1960s and 1970s. During the 1970s the ''Great Salinity Anomaly'' (Dickson ct al., 1988) resulted in increasing quantities of comparatively fresh SAIW being present. This in turn resulted in a weakening of the stable layer instead of the expected strengthening. Changes in the stratification of the SAIW source are implied. By influencing the depth of maximum winter mixing, changes in the properties of the intermediate water masses of the eastern North Atlantic have more immediate consequences for ocean-atmosphere heat exchanges west of Europe than do longer term changes to the source waters of Labrador Sea Water (LSW) or Norwegian Sea Deep Water (NSDW). Such variations in the intermediate water column structure should therefore be taken into account in ocean climate models. (C) 1997 Elsevier Science Ltd.
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