'Porpoise-ful' mistake: Porpoises, not methane, may be responsible for mysterious pits in North Sea

In the North Sea's depths, small depressions, seemingly formed by leaking methane, have puzzled researchers for years. However, recent findings propose an unexpected explanation: these pits might be the handiwork of foraging porpoises, challenging long-held assumptions about the sea's geological features.

Methane pits no more

As per a Live Science report, Geoscientist Jens Schneider von Deimling of Kiel University initially doubted the methane theory, given the North Sea's porous, sandy floor and strong currents, which inhibit methane accumulation.

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"I didn't really see any mechanisms that accumulate methane," he said.

Subsequent research expeditions confirmed his suspicions. Mapping studies using a sub-bottom echo sounder — a form of sonar that bounces sound off the seafloor to image the shallow subsurface — led to the conclusion that the pits' formation was not methane-related.

"We mined thousands of miles of data for shallow gas, and simply didn't find that," explained Schneider von Deimling.

To investigate further, researchers employed a high-resolution multi-beam echo sounder, allowing detailed scrutiny of the pits' shape. They discovered that the pits were not conical, as expected with methane leaks, but rather maintained a consistent depth of 4.3 inches (10.92 centimetres), but of varying widths.

Why is this important?

Schneider von Deimling's collaboration with biologists studying harbour porpoises provided a breakthrough. These porpoises, known for scouring the seafloor for buried sand eels, overlapped with the pit locations. Subsequent oceanographic data analysis and echo sounder surveys confirmed this correlation, suggesting that the pits were porpoise-created and later shaped by ocean currents.

While photographic proof of porpoise digging remains elusive due to murky waters and the "pretty shy" harbour porpoise, the study's interdisciplinary approach sheds light on animal behaviour and its impact on seafloor morphology. Understanding the origin of seafloor pits is crucial for identifying submarine hazards, such as those related to tectonic activity, where methane seepage pits may indicate fault lines.

This study's results suggest that the potential long-term geological impact of large animals on seafloor evolution may be bigger than previous assumptions.

(With inputs from agencies)