Heat Wave May 23

A new marine heat wave has formed in the northern Pacific Ocean that has been waxing and waning in size since shortly after the Northeast Pacific Marine Heat Wave of 2019 officially ended on Jan. 17, 2020.

After last year's heat wave dissipated, a large pool of warm water remained offshore, warming enough at the surface to become classified as a new marine heat wave from Feb. 21 to March 7, and again from March 14 until now, Andrew Leising, research oceanographer for NOAA's Southwest Pacific Science Center, told NW Fishletter.

By April 27, it had grown large enough to become the north Pacific's ninth-largest known marine heat wave, he said.

"That's actually a pretty big deal," Leising said. More than 400 marine heat waves have been identified in the north Pacific since 1982, when quality satellite images first became available. About half of those were tiny and didn't last long, he said, but "This is definitely a fairly large event."

Satellite images help determine ocean temperatures at the surface and the size of the marine heat waves, he said.

Last year's heat wave lasted 239 days, grew to 8.5 million square kilometers (five times the area of Alaska), and was the second-largest recorded in the north Pacific. It was second only to The Blob, a marine heat wave formed in 2013 that endured for more than two years, causing massive algal blooms and disrupting ocean food webs.

Leising said scientists aren't sure whether this year's heat wave is a continuation of the 2019 event—forming from warm water that persisted below the surface—or if it should be considered a new event.

It grew to 4 million square kilometers by late April, but has since dissipated somewhat, he said. The mass of warm water is also not as close to shore as The Blob or last year's heat wave, although a separate smaller heat mass is close to shore near Southern California, he said.

Climate scientists expect marine heat waves to occur more frequently and with growing intensity as the climate changes. Based on NOAA's criteria, the marine heat waves most likely to impact West Coast marine life are those that are roughly three times the area of Alaska, or 5.1 million square kilometers; come within 250 kilometers of the coast; and last at least three months.

K.C. Mehaffey covers fish issues for Clearing Up, and is editor of the NW Fishletter. She joined the NewsData writing team in February 2018. From lawsuits to scientific studies, she is enjoying the deep dive into the Columbia Basin's many fish topics.