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Rapid coastal deoxygenation due to ocean circulation shift in the northwest Atlantic

Nature Climate Change volume 8, pages 868–872 (2018)Cite this article

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Abstract

Global observations show that the ocean lost approximately 2% of its oxygen inventory over the past five decades1,2,3, with important implications for marine ecosystems4,5. The rate of change varies regionally, with northwest Atlantic coastal waters showing a long-term drop6,7 that vastly outpaces the global and North Atlantic basin mean deoxygenation rates5,8. However, past work has been unable to differentiate the role of large-scale climate forcing from that of local processes. Here, we use hydrographic evidence to show that a Labrador Current retreat is playing a key role in the deoxygenation on the northwest Atlantic shelf. A high-resolution global coupled climate–biogeochemistry model9 reproduces the observed decline of saturation oxygen concentrations in the region, driven by a retreat of the equatorward-flowing Labrador Current and an associated shift towards more oxygen-poor subtropical waters on the shelf. The dynamical changes underlying the shift in shelf water properties are correlated with a slowdown in the simulated Atlantic Meridional Overturning Circulation (AMOC)10. Our results provide strong evidence that a major, centennial-scale change of the Labrador Current is underway, and highlight the potential for ocean dynamics to impact coastal deoxygenation over the coming century.

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Fig. 1: Schematic of the large-scale circulation in the northwest Atlantic.
Fig. 2: Warming, salinity increase and deoxygenation in the coastal northwest Atlantic.
Fig. 3: Two isopycnal depth anomalies at the Tail of the Grand Banks.
Fig. 4: Decomposition of the modelled oxygen decline with warming in the northwestern Atlantic.

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Acknowledgements

The authors thank A. Cogswell and R. Pettipas from Fisheries and Oceans Canada for providing hydrographic data in the central Scotian Shelf and C. E. Brennan for providing the data for the oxygen time series in the central Scotian Shelf. The authors also acknowledge many scientists at NOAA GFDL that configured and ran the climate model, without whose efforts this work would not have been possible. This project has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant no. 682602). E.D.G. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness through the Mara de Maeztu Programme for Centres/Units of Excellence (MDM-2015-0552). The Canadian Foundation for Innovation provided the computing resources for model analysis. D.B. acknowledges support from NOAA grant NA15NOS4780186.

Author information

Authors and Affiliations

  1. Joint Institute for the Study of the Atmosphere and the Ocean, Seattle, WA, USA

    Mariona Claret

  2. University of Washington, Seattle, WA, USA

    Mariona Claret

  3. Department of Earth and Planetary Sciences, McGill University, Montréal, Quebec, Canada

    Mariona Claret & Eric D. Galbraith

  4. Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain

    Eric D. Galbraith

  5. Institut de Ciència i Tecnologia Ambientals, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Spain

    Eric D. Galbraith

  6. Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA

    Jaime B. Palter

  7. Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA, USA

    Daniele Bianchi

  8. Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada

    Katja Fennel

  9. Maurice Lamontagne Institute, Fisheries and Oceans Canada, Mont-Joli, Quebec, Canada

    Denis Gilbert

  10. NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA

    John P. Dunne

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Contributions

E.D.G., J.B.P. and D.B. conceived the study. M.C., D.G. and K.F. assembled and analysed the observational data. M.C. and D.B. performed the model output analyses. J.P.D. and E.D.G. participated in the design of the CM2.6-miniBLING experiments. M.C., E.D.G., J.B.P. and D.B. wrote the first draft of the manuscript. All the authors discussed the results and provided input to the manuscript.

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Correspondence to Mariona Claret.

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Supplementary information

Supplementary Information Description: Supplementary figures 1–9, Supplementary Notes, Supplementary References, Supplementary Tables 1–3

Supplementary figures 1–9, Supplementary Notes, Supplementary References, Supplementary Tables 1–3

Supplementary Video 1

Time evolution of simulated O2 in the northwest Atlantic on isopycnal σθ = 27.25 kg m−3 over the last twenty model years (from 181 to 200) for preindustrial control (LEFT) and warming (1% annual pCO2 increase until doubled, RIGHT) scenarios. Climate model horizontal resolution is 1/10° and the time period between movie frames is five days. The movie shows that the oxygen supply to slope waters (white shading in Fig. 1) and the Laurentian Channel decreases significantly under warming due to a reduction in transport of ventilated Labrador Current waters west of the Tail of the Grand Banks. Isopycnal outcrop is shown in white

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Claret, M., Galbraith, E.D., Palter, J.B. et al. Rapid coastal deoxygenation due to ocean circulation shift in the northwest Atlantic. Nature Clim Change 8, 868–872 (2018). https://doi.org/10.1038/s41558-018-0263-1

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