Temperature and salinity changes in the deep Labrador Sea, 1962–1986

Abstract

Multi-year variations in the potential temperature (θ) vs salinity (S) curve of Denmark Strait Overflow Water and Northeast Atlantic Deep Water are demonstrated in time series of θ on density anomaly ( σ 2) surfaces, constructed from all deep observations obtained in the western Labrador Sea between 1962 and 1986. The temperature of the densest Overflow Water ( σ 2 = 37.16 kg m −3) increased in the early 1960s by ≌0.15°C, decreased by about the same amount in the latter part of the decade, dropped a further 0.15°C in the late 1970s or early 1980s and rose between July 1985 and August 1986 back to the 1962 value. The variations are coherent through the two superposed water masses, but the range increases from ≌0.13°C at θ 2 = 36.96 kg m −3 in the upper layers of the Deep Water, to ≌0.36°C at θ 2 = 37.16 kg m −3 near the bottom, suggesting that the Overflow Water is the source of the fluctuations. The temperature decreases in 1968 and 1981 may be caused by the large low salinity anomaly that first appeared in the Iceland Sea in 1968 and that was observed to travel from Denmark Strait, through the Labrador Sea, across the North Atlantic and into the Norwegian Sea between 1968 and 1979. The temperature increases in the Overflow Water probably occur when the outflow of low salinity water from the Arctic is decreased.