An example of long-term variability for subsurface current and hydrographic patterns in the western North Atlantic
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An example of long-term variability along 55W, perhaps interannual, for current and temperature distributions during mid-1975-1977 is presented. The existence of significant energy in the 55W data set at time scales longer than mesoscale (50-150 days) has been clear for some time, but this is a first description of the latitudinal and vertical configuration of this low-frequency variability. The overall pattern observed may be described as a partial meander or lateral shift, associated with substantial changes in water mass properties. Perhaps we have identified a contraction of the subtropical gyre. Specific elements of the observed pattern include southward shifts and variations in intensity of abyssal currents, changes in the amount of vertical shear across the thermocline south of the Gulf Stream, along with southward shifts in current patterns at a variety of depths. The observed current variations are consistent with observed temperature changes from both moored instruments and hydrographic sections. There are also changes in the distribution of salinity anomaly, but these do not seem to be simply related to the changes in current and temperature patterns.