Research Document 2019/046

Physical Oceanographic Conditions in the Gulf of St. Lawrence during 2018

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

Abstract

An overview of physical oceanographic conditions in the Gulf of St. Lawrence (GSL) in 2018 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 above normal. Sea-ice maximum volume was 9^th lowest since 1969, but the winter mixed layer volume was near-normal. The August cold intermediate layer (CIL) showed warmer than normal minimum temperature (+1.6 SD) and less than normal volume of water colder than 1°C (-1.7 SD), and the seasonally averaged minimum temperature index was also warmer than normal. Near-surface water temperatures were at a record low in November, below normal in spring and fall and only above in August and September. The May to November average was near-normal, but the coldest since 2002. The timing of summer onset and post-season cooling of the surface layer were respectively later than normal (+0.8 weeks) and near normal. Deep water temperatures have been increasing overall in the Gulf, with inward advection from Cabot Strait. Gulf-wide average temperatures at 150 and 200 m are lower than the 2015 record highs but remain above normal at 3.0°C (+0.5°C, +1.0 SD) and 5.0°C (+0.6°C, +1.5 SD). New series record highs (since 1915) were set at 250 and 300 m, at 6.1°C (+0.8°C, +3.1 SD) and 6.4°C (+0.9°C, +5.8 SD) respectively. The bottom area covered by waters warmer than 6°C remained quite high in 2018 in Anticosti Channel and Esquiman Channel and Central Gulf, and increased sharply in and the northwest Gulf to reach a series record.

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