Coral Reefs Are Still Growing Atolls Despite Sea Level Rise


Ailinglaplap Atoll, of which Jeh Island forms a part. Reinhard Dirscherl / The Image Bank / Getty Images

Sea level rise caused by the climate crisis is considered a major threat to low-lying Pacific atolls. Despite this, however, some of these islands are actually growing.

Now, a recent study published in Geophysical Research Letters Nov. 20 has figured out why. The coral reefs that give these islands their structure are continuing to produce sediment.

“The big picture with this is the modern day coral reef can build an island even though the sea level is rising,” study coauthor and University of Auckland senior lecturer Dr. Murray Ford told Stuff.

Atolls are islands situated on top of rings of coral, with a lagoon in the center. Past studies have indicated that several of these islands have actually been growing, despite the threat of rising sea levels. A 2018 analysis of 30 Pacific and Indian Ocean atolls including 709 islands found that none of the atolls had lost land area in the preceding decades and that 88.6 percent of the islands had either increased their size or stayed the same.

“That started a bit of a goldrush in terms of studies,” Ford told CNN. “The signal was kind of consistent — there’s no widespread chronic erosion of atoll islands in the Pacific.”

To understand what was going on, Ford and his team focused on Jeh Island in the Marshall Islands, where sea levels have risen by 0.3 inches a year since 1993. They used aerial photographs to confirm that the island had increased in size by 13 percent between 1943 and 2015. In fact, sediment had actually caused two separate islands to merge and a spit at the island’s western end to grow longer, Stuff explained.

The researchers also used radiocarbon dating to confirm that much of the new sediment was deposited after 1950. This is an important finding, because scientists had previously been unsure if the islands were increasing in size because of new material or recycled reef pieces.

“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 told CNN. “It’s entirely the skeletons of the reef and the organisms that live on it.”

Ford told Stuff that more research was needed to discover if the same process was taking place on other growing atolls. Further, it isn’t certain if coral reefs will continue to protect the atolls from sea level rise in the future. Increased flooding could still damage fresh water supplies, CNN pointed out. A 2018 study found that the contamination of fresh water supplies with salt water could make atolls uninhabitable by 2050. And the climate crisis threatens reefs themselves with coral bleaching and ocean acidification.

“It’s all about the reef health, being able to produce sand and gravel to help make these islands and maintain them,” Ford told Stuff.

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