A "blob" of unusually warm sea water in the Pacific Ocean was responsible for the deaths of about 1 million seabirds in 2015 and 2016, a study released Wednesday said.

The birds — a species known as the common murre — likely died of starvation due to the warm water, which severely disrupted the birds' food supply.

Scientists say the mass die-off was unprecedented — both for murres, and across all bird species worldwide.

"The magnitude and scale of this failure has no precedent," said study lead author John Piatt, a research biologist at the U.S. Geological Survey's Alaska Science Center, in a statement. "It was astonishing and alarming, and a red-flag warning about the tremendous impact sustained ocean warming can have on the marine ecosystem."

From May 2015 to April 2016, about 62,000 murre carcasses were found on beaches from central California north through Alaska. Citizen scientists in Alaska counted numbers that reached 1,000 times more than normal for their beaches.

The 'Blob': Ocean heatwave is warming up the West Coast – and endangering animals

Scientists estimate that the actual number of deaths was likely close to 1 million, since only a fraction of birds that die will wash to shore, and only a fraction of those will be in places that people can access.

An ocean heat wave, which first began in 2013, created the blob of warm water, which significantly affected marine life up and down the West Coast over the next couple of years. A number of other species experienced mass die-offs during this period, including tufted puffins, sea lions and baleen whales.

At one point, the blob of ocean water was 2 to 7 degrees above average and about 1,000 miles across and 300 feet deep. It covered some 4.5 million square miles of ocean.

The warming was due to a persistent ridge of high atmospheric pressure that kept winds calm. A high-pressure ridge features sinking air, which also prevents clouds from forming and precipitation from falling.

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Warmer water isn't as nutrient-rich as the colder water that wells up from the bottom. So it doesn't support the same tiny plants and animals that sustain marine life.

"We believe that the smoking gun for common murres – beyond the marine heat wave itself – was an ecosystem squeeze: fewer forage fish and smaller prey in general, at the same time that competition from big fish predators like walleye, pollock and Pacific cod greatly increased," said study co-author Julia Parrish, a University of Washington professor in the School of Aquatic and Fishery Sciences.

As the largest mass die-off of seabirds in recorded history, the common murre event may help explain the other die-offs that occurred during the northeast Pacific marine heat wave, and also serve as a warning for what could happen during future marine heat waves, study authors said.

University of Washington scientists recently identified another marine heat wave forming off the Washington coast and up into the Gulf of Alaska.

While these blobs of unusually warm seawater are uncommon, scientists say that global warming is making them more of a regular occurrence. Overall, the world's oceans have warmed by about 1 degree because of human-caused global warming.

Wednesday's study was published in the journal PLOS ONE.

Contributing: Elizabeth Weise, USA TODAY

This article originally appeared on USA TODAY: Pacific ocean blob of warm water killed 1 million seabirds, study says