Science Advisory Report 2018/039

Oceanographic Conditions in the Atlantic Zone in 2017

Summary

• Vessel breakdown and survey cancellation and delays resulted in important data gaps in the assessment of oceanographic conditions in the Atlantic Zone for 2017. Data gaps result in significant declines in the accuracy and precision of observational series and can limit our ability to detect shifts in environmental conditions in the future.
• Winter sea surface temperatures were above normal from the Scotian Shelf to the Bay of Fundy, including a record high (since 1985) on the central Scotian Shelf (4W) in February. Temperatures were also much above normal off of Nova Scotia in the fall including record highs in October and November on the Eastern Scotian Shelf (4X SS), in October and December in Eastern Gulf of Maine and Bay of Fundy and in November on the central Scotian Shelf (4W). Temperatures were typically below normal on the Southeast Grand Banks (3N) throughout the ice-free months, including a record low in June.
• Winter average sea ice extent was near normal on the Newfoundland and Labrador Shelf but was 6^th lowest since records began in 1969 in the Gulf of St. Lawrence. An unusual reappearance of very thick ice from the Labrador Shelf affected the northeastern Gulf from late May until mid-June.
• Summer cold intermediate layer conditions varied from colder than normal at the most northern sections (Seal Island and White Bay), to above normal on the Flemish Cap section and on the Scotian Shelf.
• Bottom temperatures were normal to above normal across the zone, including very high anomalies on the Scotian Shelf and in the deeper waters of the northern Gulf of St. Lawrence. Rimouski station bottom temperatures remained high but decreased from a series record high observed in 2016.
• Stratification was high at all high-frequency sites except Halifax 2. In the Estuary and Gulf of St. Lawrence, this was attributed to the highest April-May freshet on record (since 1948).
• Deep nutrient inventories declined considerably in 2017, reaching record lows across most of the Scotian Shelf. The only exceptions were the southern Grand Banks and the northern Gulf of St. Lawrence where inventories were near normal. The declines were modest across most of the Newfoundland Shelf but represent continuation of recent trends in the Gulf of St. Lawrence and the Scotian Shelf.
• Annual chlorophyll a inventories were below normal over the Grand Banks, Cabot Strait and eastern Scotian Shelf but normal or above normal in the Gulf of St. Lawrence.
• The onset of the spring phytoplankton bloom was delayed on the Newfoundland Shelf and normal or early in the Gulf of St. Lawrence and the Scotian Shelf; the magnitude of the bloom was generally below normal with the exception of the Northwestern Gulf of St. Lawrence which was well above normal; bloom duration was highly variable, with long blooms on the Newfoundland Shelf, Northwestern Gulf of St. Lawrence, Western Bank and Central Scotian Shelf, and near average in the remainder of the Zone.
• The zooplankton community shift observed in recent years, characterized by lower abundance of the large energy-rich copepod Calanus finmarchicus, higher abundance of small copepods, and higher abundance of non-copepods, persisted in 2017 although the intensity declined relative to 2016. Calanus finmarchicus increased on the southern Grand Banks and in the eastern Gulf of St. Lawrence while there were declines in Pseudocalanus sp. And non-copepods across much of the Zone.
• The biomass of zooplankton was below normal across the Zone, with the exception of the Halifax section. The strongest negative anomalies were on the Newfoundland Shelf and in the Gulf of St. Lawrence.
• The Labrador Sea continued to exhibit strong vertical mixing in the winter of 2017, exceeding 1,500 m in depth, and represents the fifth year of progressive intensification and deepening of convective mixing and production of Labrador Sea Water (LSW) since 2012. Both upper, 0-200 m, and deeper, 200-2,000 m, layers have been cooling since 2010 but the LSW formed in the winter of 2017 the densest since the mid-1990s. The Labrador Current was strong in 2016 and 2017 relative to the previous four years when it was in its near normal state. As a result of the cancellation of the spring research survey, it was not possible to neither update the rate of decline in pH nor assess the state of Calanus finmarchicus population, the dominant mesozooplankton in the Labrador Sea, in 2017.

This Science Advisory Report is from the Eighteenth Annual Meeting of the Atlantic Zone Monitoring Program (AZMP) held March 20-23, 2018. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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