Researchers still puzzled about mysterious sounds in Southern Ocean

Mysterious repeating sounds emanating from the depths of the Southern Ocean continue to baffle marine scientists since they were first heard by submariners in the 1960s, when they were dubbed “bio-duck” noises.

The ubiquitous sound has been recorded in Antarctic waters and off the Australian west coast. The 4 short bursts of quack-like sounds were also detected in the South Fiji Basin in July 1982 during one of the first experiments to study noise in the ocean.

A report in 2014, which identified the source of the noises, showed they were locally different.

“For example, bio-duck sounds from Dumont D’Urville, East Antarctica, as well as sounds reported in archived recordings made in the Ross Sea, exhibited three pulses per burst. In contrast, recordings of bio-duck sounds from West Antarctica, including the sounds described here, typically have five to six pulses,” the researchers said.

Emeritus Professor Ross Chapman of Australia’s University of Victoria became involved in the analysis of the 1982 data years later.

“Studying those data was like opening a book that nobody had ever read before,” Chapman said in a press conference for the Acoustic Society of America earlier this week.

“It was a very exciting time, because we learned something new about sound in the ocean every day.”

Chapman presented an online session on bioduck at the 187^th Meeting of the ASA on Thursday.

“The main feature of the experiment was the line array of hydrophones … towed behind the ship for about 3 weeks, collecting data continuously. In other words, listening to all the sounds in the ocean and all the time,” says Chapman.

“More than just listening, the hydrophone array is an acoustic antenna. So, we could know the direction the sounds were coming from.

“And that was unique even in today’s world, when most of the long-term recordings are made with single hydrophones, so you can hear but you can’t figure out where the sound is coming from.”

Chapman says the array resolved sound from at least 4 individual “speakers” at different locations, travelling in different directions in the ocean.

As there were no visual sightings from the boat, they couldn’t conclusively determine which animals were making the noises at the time. Since then, bioduck noises have been recorded at various locations in the Southern Ocean, including in waters off the west coast of Australia.

Their origin remained a mystery for decades until acoustic recording tags were attached to Antarctic minke whales (Balaenoptera bonaerensis) for the first time. The 2014 study analysed data from the 2 whales studied in Wilhelmina Bay on the Antarctic Peninsula and provided conclusive evidence the bio-duck sound was produced by the whales.

“The question is: when do they make the bio-duck sound and why do they make it?” asks Chapman.

“I wouldn’t say that the answer is really known even today.”