Science Advisory Report 2019/034
Oceanographic Conditions in the Atlantic Zone in 2018
- Winter sea-surface temperatures were above normal from the Scotian Shelf to the Bay of Fundy, including multiple monthly record highs (since 1985). Temperatures there were also much above normal in August and September, including record highs for both months in the Bay of Fundy and eastern Gulf of Maine. Temperatures were typically below normal throughout the zone in June, November, and December, including multiple monthly record lows.
- Sea-surface temperature averaged over the ice-free months varied from below normal off the eastern coast of Newfoundland and Labrador, to near-normal south of Newfoundland and the Gulf of St. Lawrence, and to above normal off of Nova Scotia.
- Winter average sea-ice volumes were below normal on the Newfoundland and Labrador Shelf and in the Gulf of St. Lawrence.
- Summer cold intermediate layer metrics indicated warmer-than-normal conditions on the Newfoundland and Labrador Shelf and in the Gulf of St. Lawrence; there were no measurements of these metrics on the Scotian Shelf because of limited ship availability.
- Bottom temperatures were normal to above normal across the zone (with sampling gaps on the Scotian Shelf), including a record high in the deeper waters of the northern Gulf of St. Lawrence, where temperatures were at 100+-year record highs. Rimouski station bottom temperature was also at a record high, as was temperature at 200 m in Georges Basin.
- Stratification was below normal at the high-frequency sites Station 27 and Prince 5.
- Deep nitrate inventories were below normal across most of the Atlantic zone in 2018. Record lows occurred across parts of the Newfoundland and Labrador Shelf and at Rimouski Station. The exceptions were the Bonavista Bay section, the northwestern Gulf of St. Lawrence, and Shediac Valley, where inventories were near normal. Nitrate inventories were below normal throughout the Scotian Shelf but were mostly higher in 2018 relative to the record lows observed in 2017.
- Annual chlorophyll a inventories were above normal over most of the Newfoundland and Labrador Shelf, northwestern Gulf of St. Lawrence, and Cabot Strait, but near normal in the remainder of the Atlantic zone with the exception of Prince 5, where a record low was observed.
- The onset of the spring phytoplankton bloom was delayed or near normal on the Newfoundland and Labrador Shelf, early in the Gulf of St. Lawrence, and near normal on the Scotian Shelf. The magnitude of the bloom was generally below normal with the exception of the Gulf of St. Lawrence, where it was mostly above normal. Bloom duration was generally shorter than normal on the Newfoundland and Labrador Shelf, longer than normal on the Grand Banks and in the Gulf of St. Lawrence, and near normal on the Scotian Shelf.
- The zooplankton community shift observed in recent years (2014–2017), characterized by lower abundance of the large energy-rich copepod Calanus finmarchicus, higher abundance of small copepods, and higher abundance of non-copepods, started to break down in 2018. Calanus finmarchicus remained below normal across most of the Atlantic zone with the exception of the southeast Grand Banks. The abundance of Pseudocalanus spp. was above or near normal on the Grand Banks and Gulf of St. Lawrence and normal or below normal on the Scotian Shelf. Non-copepods were above normal on the Newfoundland and Labrador Shelf, reaching record highs on the Flemish Cap and southeast Grand Banks sections, but near normal or slightly above normal in the remainder of the Atlantic zone.
- Zooplankton biomass was below normal across most of the Atlantic zone in 2018, although not as low as in 2017 on the Newfoundland and Labrador Shelf and in the Gulf of St. Lawrence; differences were variable on the Scotian Shelf.
- Near-bottom pH and aragonite saturation are generally much lower in the Gulf of St. Lawrence than on the Grand Banks and Scotian Shelf. Near-bottom aragonite is under-saturated throughout most of the Gulf of St. Lawrence, including the shallow waters of the Southern Gulf. The occurrence of cold water on the Newfoundland and Labrador Shelf is coincident with near under-saturated conditions.
- New record lows of deep dissolved oxygen concentration were measured in 2018 in the Laurentian Channel, from Cabot Strait to the central Gulf of St. Lawrence.
- A continuation of the progressive intensification and deepening (down to 2000 m) of convective mixing and production of Labrador Sea water that started in 2012 was observed in 2018. The upper Labrador Sea (0–2000 m) has been cooling since 2010. The freshening trend that started in 2011 reversed in 2016. This resulted in increasing salinity and progressive densification that led to the densest Labrador Sea water in 24 years.
- The Labrador Current was strong in 2016–2018 relative to previous years, when it was near normal.
- In general, all biological indicators in the Labrador Sea were lower than normal in 2018, coinciding with the return of very deep winter convection that started in 2014. Notable exceptions were the positive anomalies located in the central Labrador Basin for Calanus spp., Pseudocalanus spp., and hyperiid amphipods while trends on the eastern and western shelves demonstrated declines in the abundance of these taxa.
This Science Advisory Report is from the Twenty-first Annual Meeting of the Atlantic Zone Monitoring Program (AZMP) held March 19-22, 2019. 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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