Increasingly Frequent Ocean Heat Waves Trigger Mass Die-Offs of Sealife, and Grief in Marine Scientists

Over the past several years, the temperature of the Earth’s oceans have been spiking high enough to trigger numerous die-offs of marine species, killing millions of corals, fish, mammals, birds and plants. Those mass die-offs also have sent a wave of emotional trauma washing over some researchers watching their life’s work vanish before their eyes. 

“We talk a lot about eco grief, that sense of being overwhelmed and feeling loss,” said Jennifer Lavers, who has been tracking how thousands of seabirds have starved to death during recent ocean heat waves off the coast of western Australia as coordinator of the nonprofit marine research Adrift Lab.

Right now the extreme ocean heat in her region is waning, but globally, marine heat wave conditions extend across nearly 30 percent of the planet’s oceans, a surface area equivalent to all of North America, Europe, Asia and Africa. The harms of long-term gradual ocean warming are well documented, but Lavers said the most recent studies show that increasingly frequent pulses of extreme heat are doing the most damage to marine ecosystems.

With even more mass die-offs of ocean species projected, “scientists are leaving in droves from the field,” she said. “Incredibly skilled, talented, qualified, very passionate people are leaving because no matter what they say, what they do, how many papers they publish … It doesn’t matter.”

The creatures many scientists hoped to help with their research are still in decline and often they are worse off than they were when they started their work, including the flesh-footed shearwaters that she studies, she said.

“That’s the case for me,” she said. “I have to literally say to people that my job is to describe the extinction of a species.” 

In the last few years, as the ocean off the west coast of Australia simmered for extended periods, Lavers, other researchers and volunteers documented increasing numbers of emaciated and plastic-stuffed shearwaters and other seabirds washing up on coastlines. 

“I’m supposed to go to work each day and inspire the next generation of young scientists,” she said. “They come to work with me and on day one, they’re bright eyed and bushy tailed. They can’t believe they’ve landed their dream job studying seabirds on remote, stunning islands. And by day four, they’re crying because they’ve just pulled 372 pieces of plastic out of the stomach of a seabird.”

Nearly Invisible, But Widespread Impacts

“I’m not sure I can come up with the right words to describe the global ocean situation at present, but it is pretty dire,” said Ben Noll, a climate scientist with New Zealand’s National Institute of Water & Atmospheric Research, who recently calculated that 78 percent of non-sea ice covered global ocean was experiencing marine heat wave conditions.

“It speaks to the critical, extreme nature of the warming that the planet has recently experienced,” he said, but the impacts on marine ecosystems are mostly hidden beneath the surface of the seas, except to researchers, divers, fisher people and other careful observers. “The impact of these warm seas may be difficult to grasp and comprehend, but the undersea world seems to be suffocating.”

“I’m concerned that these events are becoming normalized.”

Noll said the frequency, intensity and extent of marine heat waves has gradually increased in the last several decades across much of the globe, with a big spike in the last 5 years.

In New Zealand, the 2017-2018 ocean heat wave was the first to draw widespread public attention because it led to the country’s hottest month on record in January 2018. Another ocean heat wave in 2023 helped fuel the storm Gabrielle that flooded the North Island in February that year.

“I’m concerned that these events are becoming normalized,” Noll said. “At least in New Zealand, I’m not sure the term ‘marine heat wave’ is having the same impact it did seven years ago and may be regarded as a ‘normal’ summertime phenomenon now, given the increasing frequency.”

But the raw numbers suggest how deadly ocean heat waves can be. One research project estimated that 1 billion marine creatures died in the ocean off the northwest coast of North America where a so-called heat blob formed in 2021, and that the loss of so many organisms at once could potentially drive a long-term disruption to ocean ecosystems.

Ocean Heat Waves Fuel Tropical Storms, Deadly Algae Blooms

Researchers tracking marine heat waves in the tropical North Atlantic Ocean, where summer is now just starting, say that heat is a key ingredient in their projections for a very active hurricane season. 

In 2022 scientists published research suggesting that ocean warming doubles the chances of intense tropical storms in the oceans around the Southeastern United States and in the Gulf of Mexico and Caribbean Sea, so it’s no wonder that researchers like University of Miami climate scientist Brian McNoldy are closely tracking the current ocean heat wave conditions in the hurricane-spawning zone known as the Atlantic Main Development Region. 

A series of social media posts suggest that hurricane experts, including McNoldy, are anxious about the upcoming hurricane season.

“It just doesn’t end,” McNoldy recently posted on social media, noting that the sea surface temperatures in late April in that region are where they usually are in July, the start of the heart of the hurricane season.

New research also shows ocean heat waves contributing to a growing number of dangerous algal blooms like Florida’s red tide and other types of toxin-producing algae that can kill fish, birds and marine mammals everywhere. Studies published in the last few years warn about the rising risks of harmful algal blooms in the East China Sea and the fjords of Patagonia, both important areas for growing aquaculture operations. Besides harming marine life directly with toxins, increasing algae blooms also use up oxygen in the ocean, contributing to the growth of dead zones in many coastal areas.

Extremes Exceeding Projections

The extreme ocean heat currently spanning parts of the Atlantic Ocean are completely off the charts and those unexpected conditions have preoccupied ocean researchers around the globe, Lavers, the Australian marine ecologist, said. 

“I don’t think that scale of warming was expected,” she said. “It was so extreme that they considered it an anomalous model prediction and very unlikely to unfold, and yet here we are. I think the consensus is that the scale of warming has been so rapid and so intense that a lot of climatologists are kind of grappling with it, like, ‘What’s happened?’”

But the impact on seabirds is clear, she added. There are mass die-offs of many more species than occurred in marine heat waves just a few years ago, and they are happening in new unexpected ocean regions and in birds that until recently were considered less vulnerable to warming. Antarctica’s emperor penguins, for instance, were once somewhat buffered from warming by vast tracts of sea ice. 

But a study released April 25 by the British Antarctic Survey shows that 16 major emperor penguin colonies lost numerous chicks as Antarctic sea ice rapidly dropped to a record low. The threat to emperor penguins has been projected by models, and last year’s mortalities’ connection with the unprecedented sea ice decline shows how extremes, rather than steady warming, can suddenly drive spikes of seabird mortality.  

“It suggests to us that the ocean heat waves are reaching some kind of extreme threshold, because the birds are telling us they are really struggling,” Lavers said. “They’re having to try harder and further to find the things that they need.”

She said it doesn’t take a lot of warming to push their prey out range. 

“Fish and squid and other prey like krill can move if it gets too warm,” she said. “But birds are really constrained because, especially in breeding season, they can only go so far, and they can only dive to a certain depth.”

In the most recent monitoring in Australia, the fact that many of the dead birds were breeding adults is particularly concerning, because seabirds are slow to reproduce, and the loss of a generation of breeding-age birds can leave a big hole in the population.

“That is what we experienced between November and February in Australia,” she said. “Nearly 100 percent of all the birds that washed up dead and dying on the beaches were breeding adults.”

Ocean Heat Waves Could Hasten Mega-Extinctions

A 2022 study suggested that the current rate of warming, unchecked, could lead to ocean extinctions on an almost unimaginable scale, similar to catastrophic extinctions that have only been documented a handful of times in billions of years of Earth history, including the end-Permian extinction about 250 million years ago when almost 90 percent of marine organisms died in overheated, acidified and low-oxygen oceans.

Curtis Deutsch, a Princeton University oceanographer and co-author of the 2022 paper, said the extreme ocean heat waves in the last few years since those findings were published have intensified his sense of urgency about ocean warming.

“We think of climate change as being this kind of fairly steady progression of change in average conditions,” he said. “I think that we’ve learned, even since 2022, that there are also big changes in extreme events.”

Research the last few years, he added, is showing how important those extreme events can be for living things.

“The extremes may be the leading driver of change,” he said. “An extreme event typically only lasts a short time, but that doesn’t always mean that the system comes back from it.”

And in an alarming related trend, he said research in a well-studied ocean ecosystem in Panama shows that, accompanying the slow and gradual warming, there also have been more frequent low-oxygen periods with immediate impacts on marine life.

“When the frequency of those extreme events reaches a certain level, then things just stop living in the area altogether,” he said.

Lavers said that as the enormous consequences of global warming and ocean heat waves become more clear, she has become more determined to warn people.

“Even when you’re crying and you feel like there’s no hope and you just want to give up, our job is to give a voice to the voiceless,” she said. “Those animals that are dying, that are declining, that are losing their habitat to super-trawlers and everything else—I will not fly the white flag. I will fight on to the very end to give them the voice they so desperately deserve.”