Science Advisory Report 2020/028

Oceanographic Conditions in the Atlantic Zone in 2019

Summary

• Monthly average sea surface temperatures were generally below normal to normal in ice-free months of 2019 until July, including record lows (since 1982) in March in NAFO Divisions 3P and 4V. They were normal to above normal for the seasonal maximum reached in August, but decreased remarkably along the track of tropical storm Dorian in early September. The 100+ km/h winds mixed the water column to as deep as 45 m, decreasing surface temperatures by as much as 8°C and increasing it equally at depth. September average surface temperatures were at record lows in the Gulf of St. Lawrence and well as on St. Pierre Bank and the Scotian Shelf (NAFO Divisions 3P, 4V and 4W). Surface temperatures remained stable in the thick mixed layer until air temperatures cooled to below water temperatures. Surface temperatures were above normal in November on the Scotian Shelf and Gulf of Maine-Bay of Fundy.
• Sea surface temperatures averaged over the ice-free months were normal to above normal on the Labrador Shelf and the northern Newfoundland Shelf, and varied from below normal to normal south and east of the Newfoundland shelf. In spite of regional disparities, the zonally averaged seasonal sea surface temperature was below normal for the first time since 1992. However, this average would have been near-normal had it not been for tropical storm Dorian.
• Winter average sea ice volumes were below normal on the Newfoundland and Labrador Shelf and near normal in the Gulf of St. Lawrence. However sea ice formed much earlier than normal in the coastal areas of the western and southern Gulf, and the November first occurrence of ice in the Upper Estuary was the earliest on record.
• Summer cold intermediate layer metrics indicated normal to warmer-than-normal conditions across the zone; there were no measurements of these metrics on the White Bay line because of limited ship availability.
• Bottom temperatures were mainly above normal across the zone except in NAFO Divisions 3LNO where they were near normal. This included a 100+-year record high in the deeper waters of the northern Gulf of St. Lawrence, a record high in Emerald Basin at 250 m, and second highest at 200 m in Georges Basin.
• At the high-frequency sites Rimouski and Shediac Valley, seasonal stratification was above normal and 0–50 m seasonal average salinity was below normal. They were both associated with the highest spring freshet of the St. Lawrence since 1974. At both stations, 0–50 m seasonal average temperature was above normal (record high at Shediac Valley). Rimouski station bottom temperature was also at a record high. Station 27 and Halifax 2 had below normal stratification.
• The Labrador Current weakened relative to 2018 on the NL slope, becoming close to normal.
• Deep nitrate inventories were above or near normal on the Newfoundland and Labrador Shelf and in the Gulf of St. Lawrence but mainly below normal across the Scotian Shelf. Record highs occurred along the Seal Island section and at Station Rimouski. The record high at Station Rimouski is a marked shift from the record low that occurred in 2018.
• Annual chlorophyll a inventories were above normal over most of the Newfoundland and Labrador Shelf and northern Gulf of St. Lawrence, but below or near normal in the southern Gulf of St. Lawrence and Scotian Shelf.
• The onset of the spring phytoplankton bloom was highly variable across the Atlantic Zone. An early onset occurred in the St. Anthony Basin, southeast Shoal and Eastern Scotian Shelf while delayed onset occurred on the Northeast Newfoundland Shelf, northeastern Gulf of St. Lawrence and Western Bank. The magnitude of the bloom was near or below normal throughout the Atlantic Zone, with a record low on Georges Bank. Bloom duration was generally near or above normal in the Newfoundland and Labrador Shelf, reaching records in St. Anthony Basin and over Southeast Shoal. Bloom duration was also longer than normal over the Magdalen Shallows and Eastern Scotian Shelf but shorter or near normal in the other Gulf of St. Lawrence and Scotian Shelf regions.
• The zooplankton community shift observed in recent years (2014–2018), characterized by lower abundance of the large energy-rich copepod Calanus finmarchicus, higher abundance of small copepods and non-copepods, persisted in 2019 despite the apparent shift toward normal conditions in 2018. Calanus finmarchicus remained near or slightly below normal across most of the Atlantic zone with the exception of the Eastern Gulf of St. Lawrence and Prince 5. The abundance of Pseudocalanus spp. was above or near normal throughout the Atlantic Zone. Non-copepods were near or above normal throughout the Atlantic Zone.
• Zooplankton biomass was generally below normal across most of the Atlantic zone. Exceptions occurred on the Bonavista section, Station Rimouski, the Northwestern Gulf of St. Lawrence and Prince 5.
• 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. Undersaturated bottom conditions were also observed in the Avalon channel on the Newfoundland shelf.
• New record lows of deep dissolved oxygen concentration were measured in the Lower St. Lawrence Estuary.
• In the Labrador Sea, convection reached the depth of about 1400 m in the western part of the Labrador Basin, and only about 1000 m in the central and eastern parts, contrasting the 2014 to 2018 period during which winter convection incrementally deepened from 1600 to 2000 m. Ocean temperature in the central Labrador Sea was above-normal, reversing a cooling trend observed since 2010 in the 15–100 m layer, and since 2011 in the 200–2000 m layer.
• In general, all biological indicators in the Labrador Sea were lower than normal, including a record of Hyperiidae. Notable exceptions were the positive anomalies observed in the central Labrador Basin for Clausocalanoidea and the delayed onset of the spring phytoplankton bloom on the Labrador Shelf/slope and central Basin.

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  This Science Advisory Report is from the Twenty-second Annual Meeting of the Atlantic Zone Monitoring Program (AZMP) held via video-conference April 20–21, 2020. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

  

  Science Advisory Report 2020/028 (PDF, 4,198 KB)

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