A vast region of unusually warm water has formed in the northeastern Pacific Ocean, and scientists are worried that it could devastate sea life in the area and fuel the formation of harmful algal blooms.

The broad swath of warm water, now known as the Northeast Pacific Marine Heat Wave of 2019, was first detected in early June. Now data from weather satellites and buoys show that it measures six to seven times the size of Alaska, which spans more than 600,000 square miles.

Given its size and location, the marine heat wave rivals a similar one that arose in 2014 and persisted for two years. That heat wave, known simply as “the blob,” occupied roughly the same region of the Pacific and became known for triggering widespread die-offs of marine animals including sea birds and California sea lions.

“The moms were going out to get food, but when they couldn’t find anything, they swam off and the babies were just left dying,” Andrew Leising, an oceanographer at the National Oceanographic and Atmospheric Administration’s Southwest Fisheries Science Center in La Jolla, California, said of the sea lions and their inability to find enough squid and fish to feed on.

“This year is most similar to 2014, and that was just the beginning of that last big heat wave,” Leising said. “We saw the maximum impacts in 2015, so it’s possible that next year we’ll be in for some really strong impacts.”

The marine heat wave formed as a result of a stubborn ridge of high pressure that lingered over Alaska this summer, which in turn resulted in unusually light winds over the Pacific.

“When you don’t have too much wind, warm temperatures can build up near the surface as a result of just the sun shining down on it,” said Gregory Johnson, an oceanographer at NOAA’s Pacific Marine Environmental Laboratory in Seattle.

Leising and Johnson agreed that more research is needed to understand what role climate change may play in the formation of marine heat waves. But it’s unusual for two such big events to occur in a relatively short timespan, according to Leising. “We’ve never had this before,” he said. “This is new.”

It's likely that global warming will exacerbate heat waves in the future, given the excessive amounts of heat that oceans have absorbed in recent years, Johnson said. “From 1993 to 2018, the ocean has taken up heat at a rate of 350 terawatts — equivalent to five Hiroshima bombs a second exploding continuously from 1993 to the present,” he added.

With this trend of overall warming, climate change will likely make marine heat waves more intense and more frequent, said Nick Bond, a professor of atmospheric sciences at the University of Washington in Seattle.

"It's easier to have a heat wave if you're already starting with a higher base temperature," Bond said. "If the floor is raised, it's much easier to jump up and touch the ceiling."

The current marine heat wave extends to an average depth of about 65 feet, with some parts of the Gulf of Alaska having elevated temperatures as far down as 260 feet. In comparison, the blob reached depths of 1,000 feet in some areas.

The extent of the warm water and how deep into the ocean it penetrates have enormous implications for marine life. Sea birds and sea lions may have been some of the most obvious victims of marine heat waves, but the negative consequences of unusually warm water can be seen throughout the marine food chain — from plankton, the tiny organisms that form the foundation of the food chain, to whales.

“Plankton that live in colder waters are generally fattier and more nutritious, so when the water warms up and species composition shifts, creatures higher in the food chain — sea birds, salmon, marine mammals — that rely on that fatty base of the food chain all suffer,” Johnson said.

Marine heat waves can also trigger overgrowths of microscopic algae, and these so-called algal blooms can be harmful to humans and animals. In 2015, commercial fisheries along the Pacific Coast were severely affected by a bloom that rendered fish and shellfish in the area unsafe for human consumption.

Bond said there have already been reports of algal blooms off the coast of Washington state tied to the current heat wave.

Scientists will be closely monitoring how the heat wave evolves over the coming weeks and months, and Bond said there have been signs that it has backed off slightly over the past month.

"There's strong consensus in our climate models that it'll decrease some," he said. "What we're still trying to hash out is the ecosystem's response and what makes more of a difference: an extended, slightly warm period or an intense but shorter event."

Editor's note: This article was updated to correct the size of the marine heat wave, which is six to seven times the size of Alaska.

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