SEATTLE -- It looked big. It looked bad. But the marine heat wave that threatened much of the West Coast in the fall of 2019 has mostly dissipated, at least at the surface.
The Northeast Pacific Marine Heatwave of 2019, or NEP19, lasted 225 days and at its peak covered about 3.2 million square miles. It was the second longest-lasting and second-largest such event recorded in the northern Pacific Ocean over the past 39 years, according to the National Oceanic and Atmospheric Administration.
The disturbance decreased below the agency's classification threshold for a heat wave as of Jan. 5, said Chris Harvey, a fisheries biologist at the agency's Northwest Fisheries Science Center, on Tuesday.
But while NEP19 is mostly gone, it's not forgotten: Scientists caution that it is not clear the heat wave is entirely dissipated, or that it will not return. The deep ocean is still retaining significant amounts of heat. Monitoring of sea surface temperature readings from multiple platforms, including satellites, ships and buoys will continue.
The biggest marine-warming event ever was the original 2014-16 “Blob,” which resulted in unprecedented harmful algal blooms, invasive species, shifts in migratory ranges for animals, including humpback and gray whales, and changes in the marine food web that, among other things, depressed salmon returns for years.
Seabirds and marine mammals starved to death as a result of The Blob, as their marine food supplies collapsed and the heat wave barreled all the way to the shore, leaving them with nowhere to go. Warming water also stoked disease in starfish, wiping out sunflower stars, once a common species.
Salmon and steelhead runs crashed in part because of ocean conditions, hitting lows not seen since the 1990s. Many runs have yet to rebound. That in turn compounded the troubles of endangered southern resident orcas. Lack of regularly available, quality salmon is one of the factors driving them to extinction.
In both marine heat waves, the main driver was the atmosphere, said Andy Leising, research oceanographer with NOAA's Southwest Fisheries Science Center in San Diego. In the case of The Blob, an unusually large and persistent high pressure system stoked warm weather and killed winds that normally would have stirred up cooler water from below. The system stalled and reinforced itself, baking heat into the deeper ocean.
"The atmosphere failed to have its normal pattern of strong winds and storms that would come through and mix that warm water, Leising said. "What happened this winter was it kicked in late, but we got the change in wind and atmosphere patterns and storms that were able to mix the warm water in."
But scientists remain wary. The last event came and went, and came back again, partly because of heat still stored at depth.
"We are going to keep our eyes very peeled on this," Harvey said. "The Blob had a heartbeat to it, there were times when it was very strong and times when it backed off, then it resurged. ... We need to keep our guard up."
The ocean is still on the warm side and the climate models used for forecasting are unanimous in predicting warmer than normal water near the coast, said Nicholas Bond, the state climatologist and senior research scientist with the Joint Institute for the Study of Atmosphere and Ocean at the University of Washington.
The ocean has a memory. With so much lingering heat in the deep ocean, effects from the first Blob are still being seen and it doesn't take much to pile on new impacts.
The Pacific cod fishery in the Gulf of Alaska has collapsed as cod have fled north because heat is still stored in the deep ocean in the gulf, where the adult cod usually thrive. "Right now in that 100-to-200-meter layer, it is warmer than it was during the original Blob," Bond said.
Closer to home, the location of tuna that sport fishers delighted in catching close to shore in Oregon last year was a clue that the ocean was disrupted by the 2019 heat wave, said Nate Mantua, research scientist at NOAA's SW Fisheries Science Center.
Albacore typically are found in warmer water, but last year, Oregon anglers were nailing them right off the beach. Salmon catches, meanwhile, in the same area were dismal.
A bright spot looking ahead is the storms that broke up the 2019 heat wave also dumped enough snow in the mountains in Washington that the freshwater migration conditions for salmon -- at least where there isn't flooding -- should be favorable this year, Bond said.
“Our snow pack right now is right around normal, we are still in good shape.”