Millions of mystery holes at the bottom of the North Sea are not what scientists thought they were | Live Science
In the murky waters of the North Sea, shallow divots dot the seafloor. The pits are round or oval, and range in width from a few meters to more than 196 feet (60 meters), but are only 4.3 inches (11 centimeters) deep. Some pits appear to have merged, creating oblong Venn-diagram-shaped depressions.
Such pits usually form when fluids containing methane or other groundwater bubble out of the sediment. But new research published in Communications Earth & Environment suggests that thousands, and perhaps millions, of pits in the North Sea and elsewhere might actually be the work of foraging porpoises. The work showed that these and other megafauna may play a large role in shaping the seafloor.
For years, geoscientist Jens Schneider von Deimling of Kiel University was skeptical that the North Sea pits were made from leaking methane. The floor of the North Sea is made of porous sand and has strong currents, which aren t conducive to methane accumulating in sediment.
“I didn’t really see any mechanisms that accumulate methane,” Schneider von Deimling said. Out on the water during a research cruise, he and his colleagues confirmed his suspicion. Mapping studies designed to detect methane in the sediment using a subbottom echo sounder, which is a form of sonar that bounces sound off the seafloor to image the shallow subsurface, turned up nothing. “We mined thousands of miles of data for shallow gas, and simply didn t find that,” he said.
Ha. Indeed. Quite right.