Research Document - 2014/062

Physical Oceanographic Conditions in the Gulf of St. Lawrence in 2013

By P.S. Galbraith, J. Chassé, D. Gilbert, P. Larouche, C. Caverhill, D. Lefaivre, D. Brickman, B. Pettigrew, L. Devine, and C. Lafleur

Abstract

An overview of physical oceanographic conditions in the Gulf of St. Lawrence in 2013 is presented as part of the Atlantic Zone Monitoring Program (AZMP). AZMP data as well as data from regional monitoring programs are analysed and presented in relation to long term means. St. Lawrence River annual mean runoff was near-normal but the spring freshet was above-normal. It began early, in March, consistent with early melt associated with the warmest March air temperatures since 1873, and persisted much longer than usual with peak runoff in May and an average runoff nearly as high in June. The seasonal maximal volume of sea ice was 6th lowest since 1969. A large portion of the winter mixed layer remained above-freezing by at least 0.6°C in early March, preventing further sea-ice formation. The August-September cold intermediate layer (CIL) had the third lowest volume (T < 1°C) since at least 1985. The CIL minimum temperature index for the Gulf in August-September was the third highest since 1985. The sea-surface temperature averaged from May to November over the Gulf was above-normal by +0.4°C. Deep water temperatures and salinities are increasing overall in the Gulf, with inward advection from Cabot Strait where temperature and salinity reached a record high (since 1915) in 2012 at 200 and 300 m, respectively. Temperature averaged over the Gulf at 300 m increased slightly in 2013 to reach the highest value since 1980. Temperatures at the depth of the temperature maximum (approx. 250 m) were above-normal in Esquiman Channel and central Gulf, exceeding 6°C, causing large areas of the sea floor to be covered by waters with temperatures > 6°C in these areas. Salinity at Cabot Strait at 300 m decreased to normal in 2013, accompanied by a decrease in temperature. While this could have signified an important change to cooler water masses entering the Gulf at depth, waters just as warm as the record of 2012 were observed again in Cabot Strait in March 2014, reaching 7.5°C. The 2013 near-normal conditions were therefore perhaps only a respite.

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