Examination of temperature and salinity data from the Scotian Shelf, Gulf of Maine, Gulf of St. Lawrence, and the adjacent continental slope has shown that the dominant low-frequency event over the last 45 years was a cooling and subsurface freshening of the water masses from 1952 to 1967, followed by a rapid reversal of these trends. The largest temperature and salinity changes (1952--1967) were 4.6 ¿C and 0.7, respectively, and occurred at about 100 m over the slope. Exchanges with shelf waters and vertical mixing gave rise to the surface manifestation of this variability. The westward transport of the Labrador Current was found to have similar variability, increasing from about 1¿106 m3 s-1 in the early 1950s to about 4¿106 m3 s-1 in the mid-1960s. A simple model that accounts for this variation of transport and has a constant entrainment of North Atlantic water indicates that changes of the westward flow of the Labrador Current could contribute significantly to the T-S fluctuations. ¿ American Geophysical Union 1993