Temporal Changes in the Causes of the Observed Oxygen Decline in the St. Lawrence Estuary

Abstract

Over the last decades, many coastal and estuarine environments have experienced a dramatic decline in dissolved oxygen concentrations (

Ocean Regime Shift is Driving Collapse of the North Atlantic Right Whale Population

“…Heat flux from the atmosphere can lead to the development of marine heatwaves in the surface waters (Chen et al, 2015;Schlegel et al, 2021), and Gulf Stream warm core rings can intrude onto the shelf in the Mid-Atlantic Bight and Georges Bank regions (Gawarkiewicz et al, 2018). However, the recent, decade-long warming event observed in the Gulf of Maine/ western Scotian Shelf slope water can be attributed primarily to the subsurface advection of slope water comprising a relatively large component of Gulf Stream water and a relatively small component of Labrador Current water (Figure 1b; Jutras et al, 2020;Neto et al 2021;Seidov et al, 2021). These warmer and more saline slope water intrusions enter the deep basins and troughs of the Gulf of Maine and the western Scotian Shelf through various deep-water channels, Number of whale icons → Mean SPUE category 0 → 0.0 ≤ SPUE < 0.5 per 100 km 1 → 0.5 ≤ SPUE < 2.5 per 100 km 2 → 2.5 ≤ SPUE < 5.0 per 100 km 3 → 5.0 ≤ SPUE < 7.5 per 100 km 4 → 7.5 ≤ SPUE < 10.0 per 100 km 5 → 10.0 ≤ SPUE < 12.5 per 100 km 6 → 12.5 ≤ SPUE < 15.0 per 100 km FIGURE 3.…”

The Gulf of St. Lawrence Biogeochemical Model: A Modelling Tool for Fisheries and Ocean Management

“…The GSL is also impacted by climate variability and change. Long term trends in physical and chemical conditions have been recorded in the GSL, such as warming of surface and sub-surface waters (Galbraith et al, 2012;Loder et al, 2013), deoxygenation (Gilbert et al, 2005;Claret et al, 2018;Jutras et al, 2020), and acidification (Mucci et al, 2011) of the deep Laurentian Channel waters. These trends are similar to those obtained with Earth System Models near the mouth of the Laurentian Channel and are projected to continue in the future (Lavoie et al, 2019).…”

Dissolved Methane in the World's Largest Semi‐Enclosed Estuarine System: The Estuary and Gulf of St. Lawrence (Canada)

“…According to Jutras et al. (2020), water between 150 and 300 m depths in the LC comprises ∼75% NACW and ∼25% LCW, yielding −37.5‰ (i.e., −35‰ × 0.75 + (−45‰) × 0.25) for the lower‐bound δ 13 C CH4 in the sub‐CIL layer based on water mass mixing only. This value lies at the lower end of the δ 13 C CH4 values determined for the sub‐CIL layer (range: −38.3‰ to −30.0‰; mean: −33.7‰).…”

“…The residence time of surface water in the LSLE is ∼4 months (Silverberg & Sundby, 1990), while it takes 3-5 years for a water parcel in the deep layer to travel from the mouth of the LC at the continental slope outside the GSL to the head of the LC (Bugden, 1988;Gilbert, 2004). The 100-m thick bottom layer in the LSLE has been under increasingly hypoxic conditions (dissolved oxygen concentration <62.5 μmol L −1 ) since the mid-1980s due to the permanent water column stratification combined with an increased biological oxygen demand and a reduced inflow of the cold, oxygen-rich LCW relative to the warm, oxygen-poor NACW (Gilbert et al, 2005;Jutras et al, 2020).…”