Research Document - 1999/039

Oceanographic conditions in NAFO Subdivisions 3Pn and 3Ps during 1997 and 1998 with comparison to the long-term (1960-1990) average.

By E. Colbourne

Abstract

Oceanographic data from NAFO subdivisions 3Pn and 3Ps during 1997 and 1998 are examined and compared to the long-term (1961-1990) average. The data are presented in several ways, as vertical transects across the major banks and channels, horizontal bottom temperature maps, time series of areal extent of bottom water in selected temperature ranges and as time-series of temperature anomalies at standard depths. Time series of temperature anomalies in the 3Ps St. Pierre Bank area show anomalous cold periods in the mid-1970s and since the mid-1980s, similar to conditions on the continental shelf along the east coast of Newfoundland. The most recent cold period, which started around 1984, continued to the early 1990s with temperatures up to 1^oC below average over all depths and up to 2^oC below the warmer temperatures of the late 1970s and early 1980s in the surface layers. Temperatures in deeper water off the banks show no significant trends. Since 1991, temperatures have moderated in some areas from the lows experienced from the mid to late 1980s and early 1990s but negative temperature anomalies continued over large areas of the banks into the spring of 1995. During 1996 temperatures started to moderate, decreased again during the spring of 1997 and returned to more normal values during 1998. An analysis of the areal extent of subzero ^oC bottom water covering the banks shows a dramatic increase since the mid-1980s, very low values in 1996 and 1998, while in 1997 it represented approximately 60% of the total area. The areal extent of bottom water with temperatures above 1^oC was about 50% of the total area of the banks in the 3Ps region during 1998 the first significant amount since 1984.

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