The mystery of the mystical holes on the ocean floor has been revealed

Created by porpoises

Mysterious depressions discovered in the North Sea were previously thought to be the result of methane leaking from beneath sediments. But new research has shown that these mysterious phenomena are likely signs of life left behind by porpoises and sand eels that live in the region.

In a study conducted by geophysicist Jens Schneider von Deimling from the University of Kiel, it was proven that small depressions are the responsibility of representatives of underwater fauna. Porpoises (mammals similar to dolphins, but related to toothed whales) living in the North Sea forage on the bottom, and sand eels also nest there, which crawl out of their burrows, leaving holes behind them. The study was published in the journal Communications Earth & Environment.

“Our results show for the first time that these depressions arise in direct connection with the habitat and behavior of porpoises and sand eels and are not formed as a result of rising fluids, as previously thought,” says Schneider von Deimling. “Our high-resolution data provide new interpretation of the formation of tens of thousands of pits on the North Sea seafloor, and we predict that the underlying mechanisms occur globally.”

The previous interpretation of the holes was that liquid was escaping from the bottom. At the same time, many depressions—in fact, most—cannot be explained in this way.

The research team used a combination of high-resolution sonar mapping of the seafloor, behavioral biology, oceanographic analysis and satellite imagery to study the shape of the seafloor, look for traces of methane and find out what animals are active in the areas where the holes appear. Scientists have found that the depressions are often located in the foraging areas of porpoises, which are close to the habitats of sand eels.

New high-resolution data has shown that marine mammals leave shallow holes on the bottom, only about 11 centimeters deep, when they forage.

“The formation mechanism of these pits, as we call them, probably also explains the existence of numerous crater-like depressions on the seafloor around the world that have been misinterpreted as the result of methane gas leaks,” says Jens Schneider von Deimling.

The study, the team says, suggests that humanity is significantly underestimating the impact of marine vertebrates on the ocean floor environment.