This summer the North Pacific was hit with the second marine heatwave of the decade. Mirroring the first so-called “Blob” of 2014, scientists measured ocean temperatures as more than five degrees above normal, across millions of square miles stretching from Alaska to California.
The first “Blob” decimated fisheries, caused a mass seabird die-off and spurred toxic algal blooms up and down the coast. In the last year and a half, a second heatwave began brewing.
But then, it disappeared — at least for now.
NOAA research scientist Nate Mantua said they’re seeing surface ocean temperatures drop back to the 30 year average before the first “Blob.”
“Parts of the Bering Sea, the temperatures are a little below normal, which is nice to see for the first time for a few years,” he said. “And most of the area around the Aleutians and the coastal waters in Alaska are back to about normal — normal being the average from 1981 to 2010.”
But that’s not to say that the troubling long term warming trend that comes with climate change has slowed. Mantua says we may see short term warm and cold periods, but the warming trend will continue.
“It could go either way in the next few months and the next year. But the longer-term, next few decades, you’d expect that background warming is just going to continue to build up.”
University of Washington climate scientist Nick Bond said it’s important to note that the North Pacific never fully returned to “normal” temperatures after the first “Blob.” The second “Blob” just compounded the heatwave, warming waters at a greater depth and at higher temperatures than before.
This winter brought cold, northern winds and heavy storms to Alaska. Storms help to mix up ocean waters and release heat trapped below the surface, but Bond says deeper ocean layers are still hotter than normal.
“This winter, there has been some cooling of those sub-surface temperature anomalies, but they’re still well above normal,” he said. “There’s just some concern that even if these storms keep up, they won’t remove all that extra heat at depth.”
Kris Holdereid is a NOAA scientist who studies algal blooms in Kachemak Bay. She says it’s hard to tease out what the effects of this most recent heatwave are — and what’s just a hangover from the first “Blob.”
It’s not always easy to predict where toxic algal blooms will pop up, but recent rising ocean temperatures brought them to many parts of coastal Alaska, she said.
In the Gulf of Alaska, “there were some areas that actually had fairly high blooms and more paralytic shellfish poisoning, and then some that didn’t. And what we’re finding up in the Bering and Chukchi [Seas], in the Arctic, is that there’s some very high levels of these … cells that cause paralytic shellfish poisoning. And that, with the really warm temperatures that they had up there, was a big concern.”
But with these somewhat colder waters, Holdereid is hopeful that coastal ecosystems might start to bounce back.
“We’re going into this spring and summer with the water cooled off a bit. And you can imagine that the near coastal waters, the shallower waters, can cool off faster because they’re not as deep. And so we’re hopeful that for the near coastal ecosystems that will have you know, that’ll be an advantage,” she said. “But it remains to be seen.”
Monitoring over the next few months and fishery surveys this year will help give a clearer picture of the ecosystem impacts of the second “Blob.” But right now, scientists say, it’s just too soon to know for certain.