Widespread and increasing near-bottom hypoxia in the coastal ocean off the United States Pacific Northwest

John A Barth; Stephen D Pierce; Brendan R Carter; Francis Chan; Anatoli Y Erofeev; Jennifer L Fisher; Richard A Feely; Kym C Jacobson; Aimee A Keller; Cheryl A Morgan; John E Pohl; Leif K Rasmuson; Victor Simon

doi:10.1038/s41598-024-54476-0

Widespread and increasing near-bottom hypoxia in the coastal ocean off the United States Pacific Northwest

Sci Rep. 2024 Feb 15;14(1):3798. doi: 10.1038/s41598-024-54476-0.

Authors

John A Barth¹, Stephen D Pierce², Brendan R Carter^{3

4}, Francis Chan^{5

6}, Anatoli Y Erofeev², Jennifer L Fisher⁷, Richard A Feely³, Kym C Jacobson⁷, Aimee A Keller⁷, Cheryl A Morgan⁶, John E Pohl⁷, Leif K Rasmuson⁸, Victor Simon⁷

Affiliations

¹ College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, 97331, USA. jack.barth@oregonstate.edu.
² College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, 97331, USA.
³ Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, WA, 98115, USA.
⁴ Cooperative Institute for Climate, Ocean, and Ecosystem Studies, Seattle, WA, 98105, USA.
⁵ Department of Integrative Biology, Oregon State University, Corvallis, OR, 97331, USA.
⁶ Cooperative Institute for Marine Ecosystem and Resources Studies, Oregon State University, Newport, OR, 97365, USA.
⁷ Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Seattle, WA, 98112, USA.
⁸ Oregon Department of Fish and Wildlife, Newport, OR, 97365, USA.

Abstract

The 2021 summer upwelling season off the United States Pacific Northwest coast was unusually strong leading to widespread near-bottom, low-oxygen waters. During summer 2021, an unprecedented number of ship- and underwater glider-based measurements of dissolved oxygen were made in this region. Near-bottom hypoxia, that is dissolved oxygen less than 61 µmol kg^-1 and harmful to marine animals, was observed over nearly half of the continental shelf inshore of the 200-m isobath, covering 15,500 square kilometers. A mid-shelf ribbon with near-bottom, dissolved oxygen less than 50 µmol kg^-1 extended for 450 km off north-central Oregon and Washington. Spatial patterns in near-bottom oxygen are related to the continental shelf width and other features of the region. Maps of near-bottom oxygen since 1950 show a consistent trend toward lower oxygen levels over time. The fraction of near-bottom water inshore of the 200-m isobath that is hypoxic on average during the summer upwelling season increases over time from nearly absent (2%) in 1950-1980, to 24% in 2009-2018, compared with 56% during the anomalously strong upwelling conditions in 2021. Widespread and increasing near-bottom hypoxia is consistent with increased upwelling-favorable wind forcing under climate change.