Preprints
https://doi.org/10.5194/egusphere-2022-1090
https://doi.org/10.5194/egusphere-2022-1090
20 Oct 2022
 | 20 Oct 2022

Temporal and spatial evolution of bottom-water hypoxia in the Estuary and Gulf of St. Lawrence

Mathilde Jutras, Alfonso Mucci, Gwenaëlle Chaillou, William A. Nesbitt, and Douglas W. R. Wallace

Abstract. Persistent hypoxic bottom waters have developed in the Lower St. Lawrence Estuary (LSLE) and have impacted fish and benthic species distributions. Minimum dissolved oxygen concentrations decreased from ~125 µmol L-1 (38 % saturation) in the 1930s to ~ 65 µmol L-1 (21 % saturation) in 1984. Dissolved oxygen concentrations remained at hypoxic levels (< 62.5 μM = 2 mg l-1 or 20 % saturation) between 1984 and 2019 but, in 2020, they suddenly decreased to ~35 μmol L-1. Concurrently, bottom-water temperatures in the LSLE have increased progressively from ~3 °C in the 1930’s to nearly 7 °C in 2021. The main driver of deoxygenation and warming in the bottom waters of Gulf and St. Lawrence Estuary is a change in the circulation pattern in the western North Atlantic, more specifically a decrease in the relative contribution of younger, well-oxygenated and cold Labrador Current Waters to the waters of the Laurentian Channel, a deep valley that extends from the continental shelf edge, through Cabot Strait, the Gulf and to the head of the LSLE. Hence, the warmer, oxygen-depleted North Atlantic Central Waters carried by the Gulf Stream now make up nearly 100 % of the waters entering the Laurentian Channel. The areal extent of the hypoxic zone in the LSLE has varied since 1993 when it was first estimated at 1300 km2. In 2021, it reached 9700 km2, extending well into the western Gulf of St. Lawrence. Severely hypoxic waters are now also found at the end of the two deep channels that branch out from the Laurentian Channel, namely the Esquiman and Anticosti Channels.

Journal article(s) based on this preprint

24 Feb 2023
Temporal and spatial evolution of bottom-water hypoxia in the St Lawrence estuarine system
Mathilde Jutras, Alfonso Mucci, Gwenaëlle Chaillou, William A. Nesbitt, and Douglas W. R. Wallace
Biogeosciences, 20, 839–849, https://doi.org/10.5194/bg-20-839-2023,https://doi.org/10.5194/bg-20-839-2023, 2023
Short summary

Mathilde Jutras et al.

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1090', Anonymous Referee #1, 10 Nov 2022
    • AC1: 'Reply on RC1', Mathilde Jutras, 30 Nov 2022
  • RC2: 'Comment on egusphere-2022-1090', Anonymous Referee #2, 09 Dec 2022
    • AC2: 'Reply on RC2', Mathilde Jutras, 16 Dec 2022

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1090', Anonymous Referee #1, 10 Nov 2022
    • AC1: 'Reply on RC1', Mathilde Jutras, 30 Nov 2022
  • RC2: 'Comment on egusphere-2022-1090', Anonymous Referee #2, 09 Dec 2022
    • AC2: 'Reply on RC2', Mathilde Jutras, 16 Dec 2022

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
ED: Reconsider after major revisions (26 Dec 2022) by Emilio Marañón
ED: Reconsider after major revisions (02 Jan 2023) by Marilaure Grégoire (Co-editor-in-chief)
AR by Mathilde Jutras on behalf of the Authors (17 Jan 2023)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (18 Jan 2023) by Emilio Marañón
RR by Anonymous Referee #2 (24 Jan 2023)
ED: Publish as is (25 Jan 2023) by Emilio Marañón
ED: Publish as is (27 Jan 2023) by Marilaure Grégoire (Co-editor-in-chief)
AR by Mathilde Jutras on behalf of the Authors (31 Jan 2023)  Manuscript 

Post-review adjustments

AA: Author's adjustment | EA: Editor approval
AA by Mathilde Jutras on behalf of the Authors (16 Feb 2023)   Author's adjustment   Manuscript
EA: Adjustments approved (16 Feb 2023) by Emilio Marañón

Journal article(s) based on this preprint

24 Feb 2023
Temporal and spatial evolution of bottom-water hypoxia in the St Lawrence estuarine system
Mathilde Jutras, Alfonso Mucci, Gwenaëlle Chaillou, William A. Nesbitt, and Douglas W. R. Wallace
Biogeosciences, 20, 839–849, https://doi.org/10.5194/bg-20-839-2023,https://doi.org/10.5194/bg-20-839-2023, 2023
Short summary

Mathilde Jutras et al.

Mathilde Jutras et al.

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Latest update: 07 Oct 2023
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Short summary
The deep waters of the Lower St. Lawrence Estuary and Gulf have, in the last decades, experienced a strong decline in their oxygen concentration. Below 65 µmol L⁻¹, the waters are said to be hypoxic, with dire consequences on marine life. We show that the extent of the hypoxic zone increased by seven-fold in the last 20 years, reaching 9400 km2 in 2021. After a stable period at ~65 µmol L⁻¹ from 1984 to 2019, the oxygen level also suddenly decreased to ~35 μmol L⁻¹ in 2020.