Blue holes, the name for collapsed limestone caves filled with sea water, also serve as important repositories for storm data due to sediments captured with in their low-oxygen bottom layers.
A new study analyzed a sediment core from the Great Blue Hole in Belize and found that storms have steadily been increasing in region for the past 5,700 years.
However, recent sediment layers known as “tempestites” reveal that the dramatic uptick of storms in recent decades can be attributed to warmer ocean waters due to anthropogenic climate change.
Blue holes are some of the most fascinating geologic formations on Earth. As the name suggests, a blue hole resembles a kind of underwater well of dark water surrounded by coral reef, and these holes form from the interaction of limestone caves that’ve been slowly filled with water as the sea levels steadily rose following the past ice age. Apart from being breathtakingly gorgeous—as well as a scuba diver’s dream (or nightmare, depending on the blue hole)—they also serve as natural repositories of climate information as passing storms over the millennia deposit coarse particles that can be extracted and analyzed.
A new study led by scientists at Goethe University Frankfurt does just that by successfully retrieved a 30 meter (98-foot) sediment core from the “Great Blue Hole,” located off the coast of Belize. One of the most impressive blue holes on the planet (though the deepest rests off the coast of nearby Mexico), the Great Blue Hole descends some 125 meters (410 feet) and contains a diameter stretching 300 meters (984 feet). In the summer of 2022, the research term transported a drilling platform to the Great Blue Hole and extracted a 30-meter sediment core for laboratory research, and because of some unique marine conditions, this blue hole essentially kept a record of passing hurricanes and tropical storms for the past 5,700 years. The results of the study were published in the journal Science Advances.
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“Due to the unique environmental conditions—including oxygen-free bottom water and several stratified water layers—fine marine sediments could settle largely undisturbed in the ‘Great Blue Hole,’” Goethe University Frankfurt’s Dominik Schmitt, the lead author of the study, said in a press statement. “Inside the sediment core, they look a bit like tree rings, with the annual layers alternating in color between gray-green and light green depending on organic content.”
As storms moved coarse particles into the hole’s eastern reef edge, sedimentary layers known as “tempestites” formed and are distinctly different in both size, color, and composition compared to finer sediments typical of more fair weather. Using the sediment core, the researchers successfully identified 574 storms across more than 5,700 years. To put that into perspective, human instrumentation only documents storms in this region up to 175 years ago. So, this study not only provided an unprecedented look back at the Caribbean’s stormy past, it showed one undeniable truth: storms have been steadily increasing over the millennia.
“A key factor has been the southward shift of the equatorial low-pressure zone,” Schmitt says in a press statement. “Known as the Intertropical Convergence Zone, this zone influences the location of major storm formation areas in the Atlantic and determines how tropical storms and hurricanes move and where they make landfall in the Caribbean.”
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Although this sediment core stretches back into the Caribbean’s unrecorded past, the study also provides insight into the current anthropogenic causes of stronger and more frequent storms in the region. Nine storm layers detailing the past 20 years shows that the 21st century could far surpass the historical frequency of storms that passed over the great blue hole per century, which hover around four to sixteen storms.
“Our results suggest that some 45 tropical storms and hurricanes could pass over this region in our century alone,” Goethe University Frankfurt’s Eberhard Gischler, a co-author of the study, said in a press statement. “This would far exceed the natural variability of the past millennia.”
When it comes to storms in the Caribbean, it seems we ain’t seen nothing yet.
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Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.