Searchers Cannot Tell Yet if Banging Sounds Are Clues to Missing Vessel

Underwater banging sounds, detected on Tuesday and again on Wednesday, might be an intriguing clue to the disappearance of a submersible on Sunday near the wreck of the Titanic — or they might just be unrelated noise. Searchers do not yet know which.

The U.S. Coast Guard issued a brief statement on Twitter Wednesday indicating that the origin of the noises had yet to be determined.

The sounds were detected by a sonobuoy, a floating device equipped with hydrophones to record noise underwater, and they seemed to be occurring at 30-minute intervals, according to a report in Rolling Stone. That raised the possibility that someone inside the vessel was making an “improvised signal for locating the vehicle by banging on the metallic part of the hull from the inside,” according to Jeff Eggers, a retired Navy commander with experience piloting compact submersibles.

“There’s lots of things in the ocean that will make noise and be heard on a sonobuoy, but there are few things that will sound like regular banging on metal,” Mr. Eggers said.

Limited information has been released to the public about the clanging sounds, making it difficult for outsiders to surmise what could be causing them.

What the sounds might signify “largely depends on what frequency, what rhythm, and what pattern” the sounds have, said Simone Baumann-Pickering, an acoustic ecologist at the University of California San Diego. Lower-frequency noises might be made by whales, for example, while higher-frequency whistles or echolocation clicks could come from dolphins.

The regularity of the sounds also matters, she said, because natural noise sources like animals or seismic and volcanic activity tend to generate sounds that are more variable than artificial sounds would be.

“I think it would be pretty straightforward to determine whether something is an Earth signal or a biological signal or a machine signal,” Dr. Baumann-Pickering said.

Search and rescue teams operating the aircraft that deploy the sonobuoys are expert in distinguishing faint sound signatures of submarines from other underwater noise sources, Mr. Eggers said. But to track down the precise origin of the banging sounds, he said, the teams will need to expand monitoring in the area with more sonobuoys. “Every bit of data and positional information helps,” he said.

Carl Hartsfield, a laboratory director at the Woods Hole Oceanographic Institute, spoke about the challenges at a news conference in Boston.

“From my experience with acoustics, there are sounds by biologics that sound man-made to the untrained ear,” he said. “But I can assure you that the people listening to these tapes are trained.”