In 2014, researchers conducting acoustic surveys in the Pacific Ocean recorded an unfamiliar sound from the deepest part of the Mariana Trench. The sound, which lasted a few seconds and had a five-part structure, was later named the “Biotwang.” Scientists could not identify its source at the time.

The Mariana Trench is the deepest oceanic location on Earth, with its lowest point, Challenger Deep, approximately 36,000 feet below the surface. The pressure there exceeds 1,000 times that at sea level, and sunlight never reaches the bottom. Fewer than two dozen people have visited the trench’s deepest point, fewer than the number of robotic rovers that have explored Mars.

For nearly a decade, the Biotwang remained unexplained. Researchers considered various possibilities, including unknown animal species or geological effects. In 2016, scientists from Oregon State University noted some similarities to the calls of baleen whales, but no known whale matched the sound completely.

A breakthrough came when the National Oceanic and Atmospheric Administration and Oregon State University applied artificial intelligence to the recordings. The AI system processed thousands of hours of underwater audio and compared the sounds with whale sighting records. In nine out of ten cases, the Biotwang was present when Bryde’s whales were observed near the trench. This established that the sound was the call of Bryde’s whales.

The call’s unusual structure may reflect regional behavior, similar to dialects in human populations. The function of the sound, whether for mating, navigation, or other communication, remains unknown.

Separate research into the trench’s microbial life has also yielded notable findings. A team from Shanghai Jiao Tong University and Lawrence Berkeley National Laboratory examined more than 1,100 sediment samples from the trench. They found that nearly 90% of the microbial species identified had never been documented before. These organisms survive without sunlight by drawing energy from chemical reactions in the Earth’s crust.

Studies of larger deep-sea animals have revealed patterns of convergent evolution. Snailfish and amphipods, which are not closely related, have both developed reliance on a compound called trimethylamine N-oxide to stabilize proteins under extreme pressure. This suggests that survival in harsh environments may follow a limited set of biological strategies.

Pollution has also reached the trench. Scientists studying amphipods living more than 11 kilometers deep found traces of industrial chemicals, including PCBs and PBDEs, inside their bodies. These substances, banned for decades, travel through the ocean via marine snow and microplastics. Contamination levels in some trench animals are higher than those found in species living near industrial zones.

The Mariana Trench continues to be a subject of scientific study, with ongoing research into its biology, geology, and the effects of human activity on its remote ecosystem.