Scientists have discovered 5,700 years of storm records hidden within sediments at the bottom of the Great Blue Hole in the Caribbean Sea.
Located off the coast of Belize in the Lighthouse Reef Atoll, the Great Blue Hole is a 125-metre-deep sinkhole formed when an ancient island cave collapsed – and subsequently flooded – after the last ice age.
Since then the underwater chasm has become a refuge for numerous marine animals, including Caribbean reef sharks, bull sharks and hammerheads, as well as sea turtles, parrotfish, angelfish and groupers. But that's not all that lurks in its depths.
In summer 2022, a team of German and Swiss scientists lowered coring equipment into the sinkhole and extracted a 30-metre sediment sample from its bed, uncovering a remarkably well-preserved archive of tropical storm activity that offers new insights into the Caribbean’s stormy past – and its potentially stormier future.
“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,” says Dr Dominik Schmitt, lead author of the study and researcher in the biosedimentology group at Goethe University Frankfurt.
- Hurricane causes epic explosion of life off Mexican coast
- "We nearly fell off our chairs!" Scientists find rare ocean bird that chases tropical cyclones
Hurricane evidence in the Great Blue Hole
Each year, thin layers of sediment build up like tree rings at the bottom of the hole, alternating in colour depending on organic content.
When storms hit, coarse sand and shell fragments from the reef edge are washed into the hole, creating distinct layers known as tempestites, says Schmitt. These pale bands stand out from the usual green-grey sediments and mark the passage of hurricanes and tropical storms.
What did they find?
The research team identified 574 individual storm events dating back 5,700 years. Until now, storm records in the Caribbean relied only on 175 years of human data, making this natural archive a vital new resource for understanding past and future climate trends.
Their findings show that storm frequency has gradually increased over the past six millennia. “A key factor has been the southward shift of the equatorial low-pressure zone,” explains Schmitt. Known as the Intertropical Convergence Zone, this belt influences where storms form and where they make landfall in the Caribbean.
The data also reveal that sea-surface temperatures and hurricane activity tend to rise and fall together. In recent decades, however, the pace has quickened dramatically.
What does this mean for the future?
“Our results suggest that some 45 tropical storms and hurricanes could pass over this region in our century alone,” says Professor Eberhard Gischler, who led the 2022 research trip. “This would far exceed the natural variability of the past millennia.”
The team links this dramatic increase to man-made climate change, with warmer oceans and more intense La Niña events fuelling frequent and powerful storms.
Find out more about the study: An annually resolved 5700-year storm archive reveals drivers of Caribbean cyclone frequency
Main image credit: Getty
More stories about the environment from around the world
