Climate change has warmed waters off the coasts of Oregon, Washington and northern California each summer, and reduced oxygen levels over a much larger area of the Pacific Ocean than was previously known, a new study found.
This depletion could harm shellfish in the region, such as Dungeness crabs, and lead to the migration or mass die offs of groundfish such as sole and lingcod. Both are critical sources of revenue for the region’s multi-million dollar seafood industry.
The findings, published recently in the journal Nature, showed more broadly what was known piecemeal from other studies during the last 70 years, according to Jack Barth, lead researcher and an Oregon State University professor of marine studies.
“It’s bringing into focus this very blurry picture we had, and now we can actually point to areas off the coast that are more susceptible and less susceptible to ocean warming and hypoxia,” he said.
During the summer of 2021, Barth and scientists from Oregon State University, the National Oceanic and Atmospheric Administration and the Oregon Department of Fish and Wildlife deployed research ships and self-driving underwater gliders across the continental shelf of the northwest U.S.
They measured oxygen levels across 2,100 square miles of Pacific Ocean from Crescent City, California to the Strait of Juan de Fuca along the Canadian border. About half had areas that were “hypoxic,” meaning the concentration of oxygen in the water was so low that few organisms would survive for long.
Barth said the data, collected during a summer of record-breaking heat, gives a good snapshot of what climate change is likely to bring in the future. In 2021, there were mass die-offs of shellfish along the coasts of Washington and British Columbia, and Oregon’s crab catch was well below average, according to the Oregon Dungeness Crab Commission.
Doubling in three years
Historical data and maps from other research show summer hypoxia on the rise off the northwest coast during the past few decades. From 1950 to 1980, low oxygen levels were recorded in 2% of that part of the Pacific. It grew to 24% from 2009 to 2018 and then more than doubled by the summer of 2021.
Barth is currently reviewing 2022 and 2023 data, and said it appears that hypoxia was found across much of the same area, but was less severe during those slightly cooler and less windy summers.
The researchers estimate that the quantity of hypoxic water in the Pacific Ocean along the northwest coast during the summer of 2021 was five to ten times greater than the volume found annually in the infamous Gulf Dead Zone. That’s an area of low-oxygen water about the size of Rhode Island and Delaware, which is formed in late summer each year as vast amounts of farm fertilizers and animal manure flush down the Mississippi River to the Gulf of Mexico.
“People are familiar with the Gulf Dead Zone, and the problem of excess nutrients,” Barth said. “We’re trying to draw attention to a much larger area impacted by bigger changes in the ocean.”
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