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Research Document - 1999/052

Physical oceanographic conditions on the Scotian Shelf and in the Gulf of Maine during 1998.

By K. Drinkwater

Abstract

A review of physical oceanographic conditions on the Scotian Shelf and in the Gulf of Maine and adjacent offshore areas during 1998 is presented. The most significant change from 1997 was related to the appearance of cold, Labrador slope water along the outer edge of the Scotian Shelf. This subsequently penetrated onto the shelf through channels and gullies where it replaced the warm slope water remnants that were in the deep basins such as Emerald and Georges basins. The Labrador Slope water was located offshore of Emerald Bank in October of 1997, travelled soutwestward during late 1997, entered Northeast Channel at the entrance to the Gulf of Maine by January of 1998, moved onto the southern flank of Georges Bank in February and by March was at the entrance to Great South Channel. Cold slope waters lay along the shelf edge for the remainder of the year although there was evidence of slight warming by the end of 1998. Temperatures in the deep region of Emerald Basin dropped by 2°C between December 1997 and February 1998 and a further 1°C by April and were well below their long-term means. On the northeastern Scotian Shelf, waters continued to experience below normal temperatures. This pattern was established in the mid-1980s with maximum cooling in the early 1990s. In recent years, including 1998, there has been a slow but steady increase in temperatures in these regions. The presence of these cold waters is believed to be due to a combination of advection from the Gulf of St. Lawrence and off the Newfoundland Shelf and in situ cooling during the winter, although the relative importance has not yet been established. Also of significance was the establishment of increased stratification in the upper water column (between surface and 50 m) throughout the Scotian Shelf since the 1990s with maximum values in recent years. This high stratification was not observed in the Gulf of Maine, however.

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