Research Document - 2000/049

Oceanographic conditions in NAFO Subdivisions 3Pn and 3Ps during 1999 with comparisons to the
long-term (1961-1990) average.

By E. Colbourne

Abstract

Oceanographic data from NAFO subdivisions 3Pn and 3Ps during 1999 are examined and compared to the long-term (1961-1990) average. The temperature and salinity data are presented in several ways, as vertical transects across the major banks and channels, horizontal bottom maps, time series of areal extent of bottom water in selected temperature and salinity ranges and as time-series of temperature anomalies at standard depths. 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-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. Temperatures during 1999 continued to warm and were above normal over most of the water column and near bottom. 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 1998 and a complete disappearance in 1999. The areal extent of bottom water with temperatures above 1^oC on the banks was about 50% of the total area during 1998 the first significant amount since 1984 and it increased further to about 70% during 1999. The salinity data clearly shows a change in water mass characteristics during the last 2 years, compared to conditions that prevailed during the first half of the 1990s. The areal extent of the relatively saltier water (>32.5) on the banks increased by approximately 40% during this time, indicative of a shift from the cold-fresh conditions of the late 1980s and first half of the 1990s on the Newfoundland Continental Shelf to warmer-saltier conditions.

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