Marine heat wave off west coast has eased, scientists say

Despite the good news, ‘offshore warming’ still threatens ocean life

VANCOUVER— Scientists say a marine heat wave that blanketed a large area of the west coast has weakened, but the potential disruption to ocean life isn’t over yet.

Nate Mantua of the U.S.-based National Oceanic and Atmospheric Administration (NOAA) said the “good news” is that the area of exceptionally warm water is substantially smaller now than it was earlier this year.

And while the area about1,500 kilometres offshore between Hawaii and Alaska is still seeing high temperatures by historical standards, it is “simply not nearly as large as it was and it is no longer strong in areas near the west coast,” he said.

Scientists have been watching a marine heat wave that developed around June this year and resembled a phenomenon that was nicknamed “the blob” which disrupted ocean life between 2014 and 2016.

The heat wave, which resembles a wedge this time, stretched from south of Vancouver Island to Baja, Calif., and offshore towards Hawaii. It raised temperatures by up to four degrees Celsius.

Mantua said “many energetic storms and unusually strong winds from the north off the west coast” have cooled surface waters back to near normal temperatures for much of the region.

“On the other hand, the offshore warming is still in place, and by historical standards, it is still a large marine heat wave,” he said in an email.

The latest climate model forecasts from NOAA’s Climate Prediction Center suggest that the offshore warming will gradually weaken over the next seven months, but even by spring will still be warmer than normal, Mantua said.

Prof. Andrew Trites at the University of British Columbia’s Institute for the Oceans and Fisheries said the marine heat wave is caused when there is not enough wind to churn and cool the water. “This past summer winds were very, very light — not strong enough for ocean to be mixed the way it used to be in the past. As a result the ocean didn’t cool down the way it was supposed to and it’s holding its heat,” he said in a phone interview.

“It’s not that the ocean got warmer, it’s really that the ocean did not get cooler.”

As a result, some species of tropical fish that are usually seen in tropical waters were found off the west coast, he said.

“One of the fish that I saw a lot of this summer was the sunfish and presumably they are here in higher numbers because the water here was unusually warm this summer and they can tolerate warm temperatures,” Trites said.

Mantua said the most obvious impacts included a pattern of unusually low plankton production from July through September from Vancouver Island to northern California.