Hydrographic Variability in the Waters of the Gulf of St. Lawrence, the Scotian Shelf and the Eastern Gulf of Maine (NAFO Subarea 4) During 1991-2000

Kenneth F. Drinkwater¹

Fisheries and Oceans Canada, Bedford Institute of Oceanography
P. O. Box 1006, Dartmouth, Nova Scotia, Canada  B2Y 4A2

Denis Gilbert

Fisheries and Oceans Canada, Institut Maurice Lamontagne
C.P. 1000, Mont Joli, Quebec, Canada  G5H 3Z4

DRINKWATER, K., and D. GILBERT. 2004. Hydrographic Variability in the Waters of the Gulf of St. Lawrence, the Scotian Shelf and the Eastern Gulf of Maine (NAFO Subarea 4) During 1991–2000. 2004. J. Northw. Atl. Fish. Sci., 34: 85-101. https://doi.org/10.2960/J.v34.m545

Abstract

This paper examines the hydrographic variability within the Gulf of St. Lawrence, the Scotian Shelf and the eastern Gulf of Maine, including the Bay of Fundy, during the decade 1991–2000. Comparisons are made with previous decadal means to place the 1990s into a longer-term perspective. The 1990s decadal means of the near-surface salinity were the lowest ever recorded for the northern Gulf of St. Lawrence, the Scotian Shelf and the Bay of Fundy. These low salinities were advected into these regions from the Labrador and Newfoundland Shelves and led to record or near record high vertical stratification in the upper layers of the water column. Also during the 1990s, the decadal means of the temperature of the intermediate layer waters (approximately 30–150 m) were well below normal throughout the Gulf of St. Lawrence and over much of the Scotian Shelf. Similar low temperatures were first observed in the late 1980s and were mainly caused by advection from the Labrador and Newfoundland Shelves, although local atmospheric cooling also contributed. In the deep channels and basins of NAFO Subarea 4, near-bottom decadal mean temperatures were high and linked to the persistence of Warm Slope Water along the shelf break. A notable exception occurred in 1998 when Labrador Slope Water moved southward along the continental slope as far as the Middle Atlantic Bight, pushing the Warm Slope Water offshore. This much colder water subsequently penetrated onto the Scotian Shelf and into the Gulf of Maine resulting in the coldest conditions in the deep basins since the 1960s.

Key words:  decadal variability, oceanography, salinity, stratification, temperature

¹ Present Address: Institute of Marine Research, P. O. Box 1870 Nordnes, N-5817 Bergen, Norway.

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