Across the globe, sea level rise is threatening island communities. But in the Pacific Ocean, some atolls—ring-shaped islands sitting on coral reefs—are actually expanding over time, posing a perplexing paradox: How can drowning islands also be growing?
In a new study published last month in the journal Advancing Earth and Space Science, a team of scientists studied Jeh Island, an atoll in the Marshall Islands, a Pacific nation located between Hawaii and the Philippines. They found that the island's area has grown by 13 percent since 1943, reports Julia Hollingsworth for CNN.
People who live on atolls have seen them change in size over time, but this is the first scientific paper to confirm how the process works, reports Michael Daly for Stuff, a New Zealand news media website. The scientists used satellite data and aerial imagery to study how the island grew over the decades. They also used radiocarbon dating to calculate the age of the sediment, most of which was found to have surfaced after 1950. Their findings suggest that newly minted material from coral reefs is fortifying the island.
"You can still see an island grow at a time when most people and most models would suggest they should be eroding," lead author Murray Ford, a coastal geomorphologist at the University of Auckland in New Zealand, tells CNN. "We have found islands are resilient in the face of rising seas and that sediment supply to some atolls is out-pacing sea level rise."
Previous research revealed that atolls weren't losing any land mass, but researchers weren't sure why this was happening. A 2018 study found that of 30 atolls and 709 islands, 88.6 percent of them had remained the same or grown in size, reports Oliva Rosane for EcoWatch.
"That started a bit of a goldrush in terms of studies," Ford tells CNN.
And that goldrush led to this discovery—the first to pinpoint how these islands grow. The study suggests that the island is built from sediment generated by the surrounding coral reef, such as from crushed up dead coral, weathered shells and dried-up microorganisms, reports EcoWatch.
"This is the first time we can see the islands form, and we can say the stuff making that island is modern...so it must be coming from the reef around the island," Ford tells CNN. "It's entirely the skeletons of the reef and the organisms that live on it."
But this growth doesn't mean Marshall Island atolls and the communities that live on them are immune to sea levels rising at a rate of 0.3 inches per year since 1993 in the area, reports EcoWatch.
Atolls are low-lying and usually sit at around six to seven feet above sea level, but sea levels are predicted to rise even more than that by the end of the century, reports CNN. Climate change is threatening the homes, cultures and communities of the more than half a million people who reside in the world's four atoll nations: the Marshall Islands, Tuvalu, Kiribati and the Maldives, which are named as the most vulnerable places in the world, according to a press release.
"For the atoll nations, climate change is not a distant threat for a future generation to face but an immediate emergency, with tropical storms and rising seas taking their toll on human lives, livelihoods and infrastructure," Takehiko Nakao, the president of the Asian Development Bank, said last year in the press release.
Plus, the threats to these atolls are exacerbated by coral bleaching and ocean acidification, which are predicted to wipe out 70 to 90 percent of existing coral reefs within the next 20 years, reports CNN. And without healthy, productive coral reefs, the atolls won't have the building blocks to grow their islands, though scientists are unsure how that will play out.
"What happens to the ecology of the reef in the future is a big driver in what happens to the ecology of the island in the future," Ford tells CNN. "If you turn off that engine room of sediment generation, then you potentially will see that effect the island."