Research Document - 2008/017

Physical Oceanographic Conditions on the Scotian Shelf and in the Gulf of Maine during 2007

By B. Petrie, R.G. Pettipas, W.M. Petrie and V.V. Soukhovtsev

Abstract

Maine and adjacent offshore areas during 2007 indicates that the annual average temperatures were generally lower than in 2006, one of the warmest years on record. This decline brought annual values to near normal at the mouth of the Bay of Fundy, Sydney Bight and eastern Scotian Shelf area. The central and western Shelf, the subsurface temperatures from the July groundfish survey and the spring and fall AZMP sections generally featured below normal temperatures by about 1oC, but with extreme anomalies as large as 6°C below normal over the upper continental slope. The St. Andrews annual sea surface temperature was normal in 2007, a marked decline from 2006, the warmest year in the 87 year time series. At 90 m deep AZMP fixed station site Prince 5, monthly anomalies varied from -1.3°C to +2.7°C. The annually averaged temperatures at 0 and 90 m were normal. Annual salinity anomalies were +0.3 (0 m) and +0.1 (90 m). The annual Halifax sea surface temperature was 1°C below normal, making 2007 the 10^th coolest in 82 years. At Halifax Station 2, temperature anomalies were generally 1°C below normal from 0 to 140 m; salinity anomalies were near normal from the surface to 100 m, and about 0.5 above normal from 100 m to the bottom. Misaine Bank had weak, annual temperature anomalies varying from -0.5 to +0.3°C in the upper 100 m; Emerald Basin anomalies were negative at all depths ranging from -0.1 to -1.8°C from 0- 250 m, with the larger anomalies from 30 m to the bottom. Lurcher Shoals annual anomalies varied from +0.6°C near the surface to a minimum of -0.8°C from 50 to 75 m. Georges Basin annual anomalies were quite uniform and about -0.9°C from 0 to 300 m. the eastern Georges Bank annual anomalies ranged from +0.4°C at 0 m to -0.7°C from 30 to 100 m. The outstanding feature of the observations from standard sections in April and October on the Scotian Shelf was the widespread negative anomalies over the shelf, particularly at the shelf break on the spring sections. Cabot Strait deep-water (200-300 m) temperatures were near normal. The overall temperature anomaly for the combined NAFO areas of 4Vn, 4Vs, 4W and 4X from the July groundfish survey was -0.8°C, a decrease of 1.5°C from the 2006 value and the largest decrease in the 38 year record. The overall stratification was above normal for the Scotian Shelf region in 2007. The Shelf/Slope front was about 30 km south of its long-term mean position; the Gulf Stream front was within 1 km of its mean position. A composite index for the region indicates that 2007 was the 7^th coldest overall of the past 38 years. This represents the largest single year decline of the composite index in the 38 year record.

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