Research Document 2018/050

Physical Oceanographic Conditions in the Gulf of St. Lawrence during 2017

By Galbraith, P.S., Chassé, J., Caverhill, C., Nicot, P., Gilbert, D., Lefaivre, D. and Lafleur, C.

Abstract

An overview of physical oceanographic conditions in the Gulf of St. Lawrence (GSL) in 2017 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. The annual average freshwater runoff of the St. Lawrence River measured at Québec City and its combination with rivers flowing into the Estuary (RIVSUM II) were both at the highest level since 1974. Above-normal January air temperatures led to late onset of sea-ice and the sixth lowest sea ice cover maximum volume since 1969, but the winter mixed layer volume was near-normal. The August cold intermediate layer (CIL) showed warmer than normal minimum temperature (+0.8 SD) and less than normal volume of water colder than 1°C (-0.6 SD), but the seasonally average minimum temperature index was near normal. Sea-surface temperatures averaged over the Gulf were near normal or above normal from May to November 2017, leading to an above-normal May-November average (+0.6°C, +0.9 SD). The timing of summer warming onset and fall cooling were respectively slightly sooner (-0.7 weeks) and later than normal (+1.7 weeks). Deep water temperatures have been increasing overall in the Gulf, with inward advection from Cabot Strait. Gulf average temperature decreased from 2015 record highs at 150 and 200 m, remaining above-normal (2.7°C, +0.5 SD and 5.0°C, +1.4 SD), decreased slightly at 250 m (6.0°C, +2.7 SD) from the 2016 record high but increased to a new record level at 300 m (6.3°C, +5.0 SD). The bottom area covered by waters warmer than 6°C decreased in 2017 in Anticosti Channel and Esquiman Channel, but increased sharply in Central Gulf and made its first appearance in the northwest Gulf.

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