Oregon sees low-oxygen seasons in coastal waters

FILE -- Cannon Beach, Oregon. (KATU Photo)

The waters off Oregon's coast now have a season of low oxygen caused by warming ocean temperatures, according to scientists.

The coastal waters go through an annual season of hypoxia, a condition resulting in the deaths of sea organisms as dissolved oxygen decreases in water near the ocean floor, Oregon Public Broadcasting reported this week.

The low-oxygen season is much like the state's wildfire season, said Francis Chan, co-chair of the West Coast Ocean Acidification and Hypoxia Science Panel.

"Every summer we live on the knife's edge and during many years we cross the threshold into danger, including the past two years," Chan said. "When oxygen levels get low enough, many marine organisms who are place-bound, or cannot move away rapidly enough, die of oxygen starvation."

Some of the first signs of hypoxia appeared in 2002, when dead crabs were hauled up in crab pots. Hypoxia was rarely recorded last century, but it has been observed almost annually since 2002, Chan said.

Warmer ocean temperatures trigger excessive phytoplankton blooms, which take oxygen out of the water when they die and sink to the ocean floor. The problem has been exacerbated by the lack of mixing ocean waters. Changing wind patterns have led to the stratification of ocean layers.

"Scientists keep saying that the ocean is changing along with the climate, and people are beginning to get in tune," said Jack Barth, an Oregon State University oceanographer and co-chair of the Oregon Coordinating Council on Ocean Acidification and Hypoxia. "They see the heat waves and all the smoke from wildfires and are beginning to realize that this is something different."

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