Photo: A diver in an underwater cave

Photograph by Agnes Milowka, Wes/Karst Productions

See the Blue Holes Project in the August issue of National Geographic magazine.

About the Project

Submerged caves—found both on land and in the sea—are among the least studied and most threatened habitats on Earth. These systems, which hold the drinking water for many of the world’s inhabitants and influence the health of nearby marine ecosystems, also boast a unique biodiversity of microbial and multicellular life. In addition they provide a window into the distant past, as the cave’s geological formations can be analyzed to reconstruct past climate and the unique water chemistry of the blue holes has preserved skeletal remains of Paleo-Indian as well as extinct and still living species.

In 2008, Expeditions Council grantee Kenny Broad and his team, in collaboration with The National Museum of the Bahamas, began the Blue Holes Project, a comprehensive exploration of the biological, geological and cultural characteristics of anchialine caves (marine groundwater caves called inland blue holes) and submarine caves (known as ocean blue holes) of the Bahamas.

Blue holes can run extremely deep underground, with one Bahamian blue hole exceeding 600 feet (180 meters) below sea level, and contain a series of mazelike passageways going miles in many directions. These cave systems can transition from giant rooms to tiny holes that divers must remove all of their gear in order to squeeze through. To add to the challenge, currents reverse in the ocean caves, making timing of dives critical. All in all, a difficult place to explore and even more challenging to achieve the range of scientific and filming goals that the team has on their agenda.

The Bahamas in particular is one of the few places that afford the opportunity for original exploration and multidisciplinary science in one shot. The inland underground systems serve as aquifers that contain the rain water that percolates down through the porous limestone. In these geologic reservoirs, a thin lens of the lighter freshwater floats above the denser salt water. In addition to its critical role as a source of potable water, this underground world is home to dozens of new species, including a new class of crustaceans. The Bahamian archipelago spans almost 1,000 miles (1,609.3 kilometers), allowing the team to test theories of human and animal migration, and to reconstruct regional climate back hundreds of thousands of years. These reconstructions can help us understand the extent and rates of global sea level rise as well as occurrences of abrupt climate change, both important issues in the face of global warming.

Many of these cave systems are extremely vulnerable to current development plans. Information gathered during the Blue Hole Project will be integrated into a resource-management plan being developed by the agency charged with leading the protection of these resources: the Bahamian government's Antiquities, Monuments and Museums Corporation (AMMC).