About 500 miles east of New Zealand's South Island, near the Chatham Islands, ocean temperatures have risen to nearly 10 degrees Fahrenheit (6 degrees Celsius) warmer than average.
Normally, surface temperatures in that part of the Pacific are around 59 degrees Fahrenheit (15 degrees Celsius), but it is 68 degrees Fahrenheit (20 degrees Celsius), according to James Renwick, a scientist at Victoria University in Wellington, New Zealand.
"It's the largest patch of above-average warming on the planet right now," Renwick told The Guardian.
In satellite images, this 386,000-square-mile (1,000,000-square-kilometer) patch looks like a menacing red spot.
A NOAA map from December 25 shows high-risk areas for corals in the South Pacific. These high-risk areas are correlated with spikes in sea temperature. NOAA Coral Reef Watch
"Sea temperatures don't really vary that much, and one degree or so is pretty big, and this area is probably 4 degrees [Celsius] or more than that above average and that's pretty huge," Renwick said. to The New Zealand Herald.
He added: "I don't have an explanation for that."
A little history about the "hot spot"
In 2014, a marine heat wave plagued the Pacific Ocean between Hawaii, Alaska and California. It caused seal and seabird populations to die, algal blooms to spread, and coral to bleach. Scientists dubbed it the "hot spot."
Four years later, a similar heat wave flourished in the same waters. That blob bleached coral in the Hawaiian Islands and stranded sea lions and whales off the coast of California. Ocean temperatures were nearly 6 degrees Fahrenheit (3 degrees Celsius) warmer than average.
Those two drops, like New Zealand's current hot spot, represent a disaster for marine life. Warmer temperatures cause the coral to expel its algae food sources and turn ghostly white. This bleaching increases the risk of coral death and threatens the species of fish that a reef supports.
Other underwater ecosystems are also at risk as the waters warm. Higher sea temperatures make it difficult for larger, more nutritious species of cold-water zooplankton to grow, which feed fish and other predators. Fish and sharks leave their traditional habitats in search of cooler waters; In 2018, a rare grouper fish from Queensland, Australia, was spotted nearly 2,000 miles away in northern New Zealand.
A 2019 study showed that higher temperatures from a Pacific heat wave caused the local extinction of a species of bull algae in New Zealand waters, which then allowed an invasive species of seaweed to take over.
High ocean temperatures could also lead to an increase in algal blooms that poison shellfish. In 2015, during the first "hot spot," a huge bloom swept across the west coast of the US, contaminating local seafood. The governments of Oregon, California and Washington closed the commercial Dungeness crab harvest for months to protect people from contaminated shellfish.