Conditions océanographiques biogéochimiques sur le plateau continental de Terre-Neuve-et-Labrador en 2019 et 2020

Abstract

Biogeochemical oceanographic conditions in the Newfoundland and Labrador (NL) Region in 2019 and 2020 are presented and compared to long-term average conditions. Satellite observations indicated a general shift toward earlier onset of the spring phytoplankton bloom across the Region compared to the mid-to-late 2010s period with mixed effects on bloom magnitudes. The mainly near- or above-normal deep (50–150 m) nutrient inventories represented an increase compared to 2017 and 2018. Integrated (0–100 m) chlorophyll a (Chl a) biomass was mostly above normal across the region in 2019 continuing a trend that started in 2017, but declined to near-normal levels everywhere except on the Seal Island (SI) section in 2020. Total abundance of copepods and non-copepod zooplankton continued to be higher than normal in 2019 and 2020 with several record-high values for the Newfoundland Shelf in 2020. Total zooplankton biomass was below normal on the southeastern Grand Bank (SEGB) in 2019, higher than normal on the Newfoundland Shelf in 2020, and otherwise near normal elsewhere in both years. The abundance of large Calanus finmarchicus copepods decreased to below-normal levels on most of the Grand Bank in 2020 after having remained mostly near or above normal from 2017 to 2019. In contrast, the overall abundance of small copepod taxa remained high with several record-high values for Pseudocalanus spp. and Oithona spp., continuing a trend that started in the mid-2010s. Bottom dissolved oxygen saturation (O2 sat) on the NL Shelf and the Grand Bank was higher than average in both years and, overall, higher in 2019 compared to 2020. Localized near-bottom aragonite undersaturation (Ω<1) was observed on the Grand Bank and in the deeper slope waters off the Newfoundland Shelf, the Flemish Cap, and the tail of the Grand Bank in summer and/or fall for both years.