Conditions océanographiques dans la zone atlantique en 2021

Abstract

Monthly and seasonal average sea surface temperatures were generally normal to above normal in ice-free areas, with many regional monthly records set in January, June, and September through December, and seasonal series records set in the northern Gulf and Estuary. Anomalies were weaker in parts of the Grand Banks. The spatially weighted zonal average was third highest of the time series. The Labrador Current transport remained near normal along the Newfoundland and Labrador Shelf break. The transport along the Scotian Shelf break has been weak since 2014. Winter average sea ice conditions were at a record low in the Gulf of St. Lawrence and third lowest of the time series on the Newfoundland and Labrador Shelf. The cold intermediate layer (CIL) was warm and of limited extent throughout the Zone, including series records in the Gulf of St. Lawrence. The CIL and sea ice index for the zone was the warmest of the times series, since 1980. Bottom temperatures were substantially above normal across the zone, including record highs in the northern Gulf of St. Lawrence and off southern Newfoundland. The zonal average index for CIL-influenced bottom temperatures tied for highest of the time series (since 1980). The zonal average index for below-CIL bottom temperatures was highest of the time series but is missing several of its components for 2021. At the high-frequency sampling sites, seasonal average 0–50 m and bottom temperatures were all above normal, including series records in one or both metrics at all stations except Halifax 2. Stratification was lowest since 2001 at Rimouski station and below normal to normal at other stations. Deep nitrate inventories were highly variable throughout the Atlantic Zone, with high inventories on the Flemish Cap, in the northeast and Central Gulf of St. Lawrence, and on the Central and eastern Scotian Shelf including a record high on the Halifax line. Surface chlorophyll inventories were generally below normal on the Newfoundland and Labrador Shelf and the Scotian Shelf, above normal in the Gulf of St. Lawrence. The reliability of interannual variations in this metric for 2021 from Newfoundland and Labrador and the Scotian Shelf is a concern because of limited sampling. The onset of the spring phytoplankton bloom was early throughout most of the Atlantic Zone, with the exception of the Grand Banks, southern Newfoundland and Georges Bank. The magnitude of the bloom was below normal on the Newfoundland Shelf and Gulf of St. Lawrence and above normal in the Labrador Sea, on the Labrador Shelf and the Scotian Shelf. The duration of the bloom followed a mainly latitudinal gradient from long in northern areas to short on the Scotian Shelf. Copepod abundance was below normal on the Newfoundland Shelf, the eastern Gulf of St. Lawrence and at Halifax 2, and above normal in the western and southern Gulf of St. Lawrence. Non-copepod abundances were close to normal on the Newfoundland Shelf, eastern Gulf of St. Lawrence and Halifax 2, and above normal in the northwestern and southern Gulf of St. Lawrence. The abundance of Calanus finmarchicus was generally normal or below normal throughout much of the Newfoundland Shelf, the Gulf of St. Lawrence, with a record low at Halifax 2. Pseudocalanus spp. abundance was below normal on the Newfoundland Shelf and eastern Gulf of St. Lawrence, and above normal in the western and southern Gulf of St. Lawrence and at Halifax 2. Zooplankton biomass was mostly above normal on the Newfoundland Shelf and below normal in the Gulf of St. Lawrence and at Halifax 2, reaching record or near record levels at several locations in each region. Zooplankton anomalies from the Scotian Shelf sections were not available as a result of limited sampling opportunities and delays in sample processing. Dissolved oxygen concentration generally declined in deep waters of the Gulf of St. Lawrence and was at a record low at Rimouski station, while pH remained at a near-record low value there. Labrador Sea convection reached 850 m, the shallowest since 2011 and 3rd shallowest in 32+ years. Sea ice area and extent were the lowest since 2011 and 2nd lowest in 42+ years. Biogeochemical metrics are not available for the Labrador Sea due to the cancellation of the survey in 2021.