World's largest graveyard of whales found

At nearly 7,000 meters below the surface of the southeastern Indian Ocean, an international research team led by Chinese scientists has discovered the deepest and largest whale graveyard ever recorded — a 1,200-kilometer stretch of seafloor littered with whale remains that have accumulated over at least 5.3 million years.

The discovery indicates that the region has been a vast resting place for whales since the early Pliocene epoch, about 5.3 million years ago. It contains both active whale falls, where sunken carcasses support communities of deep-sea organisms, and hundreds of fossilized whale skeletons.

The study was conducted by researchers from the Institute of Deep-sea Science and Engineering of the Chinese Academy of Sciences in Hainan province, the University of Pisa in Italy and Earth Sciences New Zealand. It was published in the journal Nature on June 10.

The researchers used the Fendouzhe manned submersible aboard the research vessel Tansuo 1 to conduct 32 dives in early 2023 in the Diamantina Zone, a seafloor fracture zone stretching about 1,200 km parallel to the Southeast Indian Ridge. They documented five active whale falls and 476 sites containing fossilized cetacean remains along the corridor.

A whale fall occurs when a whale dies and its carcass sinks to the seafloor. The remains can become the center of a rich ecosystem, providing food and shelter for deep-sea organisms for years or even decades.

The deepest known whale fall had previously been recorded at a depth of 4,204 meters in the southwest Atlantic Ocean. Little was known about whale-fall ecosystems below 6,000 meters, while the fossil record of whales that dive to such depths was largely unknown.

The deepest active whale fall identified by the team was found at 6,789 meters and consisted of three vertebrae from a beaked whale. The discovery extends the known depth range of whale-fall ecosystems by more than 2,500 meters.

The whale bones were covered with dense white mats of microorganisms and bone-eating worms, suggesting that they had remained exposed on the seafloor for a long time.

"We did not set out to find whale falls or fossils, so this discovery was a wonderful surprise," said Peng Xiaotong, a researcher at the institute and the study's first and corresponding author.

"But that is precisely the significance of hadal exploration — we are entering the most unknown ocean regions on this planet, and any extraordinary discovery could happen," Peng said.

The expedition was part of the Global Hadal Exploration Programme, a 10-year initiative under the United Nations Decade of Ocean Science for Sustainable Development. Led by the institute, the program focuses on the hadal zone, the deepest parts of the ocean, generally below 6,000 meters.

Analysis of 43 fossil specimens identified five species of beaked whales and one species of baleen whale. The specimens included two species that still live in the southeastern Indian Ocean today and two extinct genera previously known only from fossils collected by trawlers off South Africa.

The researchers said the unusually high concentration of whale remains may be linked to the region's importance as a habitat for beaked whales. Some species are known to make extremely deep dives and may die when they exceed their physiological limits.

Dating of 33 fossil bones showed that they ranged from 5.26 million to 120,000 years old, confirming that whale-fall events have occurred in the region since the early Pliocene era, about 5.3 million years ago.

The area's V-shaped seafloor may also help carcasses collect at the bottom, while the extremely slow buildup of sediment allows whale bones to remain exposed on the seafloor for long periods instead of being quickly buried.

Based on an observed density of 759.5 whale remains per square kilometer, the researchers estimated that the area could contain more than 10 million whale and other cetacean carcasses.

They estimated that the whale remains collectively store about 6.7 million metric tons of carbon, equivalent to roughly 4,700 years' worth of organic material that normally sinks from surface waters to the seafloor in the region.

Stephen Godfrey, a researcher at the Calvert Marine Museum in Maryland in the United States, wrote in a commentary accompanying the study that the discovery "can be compared to many milestone discoveries in the history of deep-sea exploration" and represents "a unique and major breakthrough".

Zhou Peng, an assistant research fellow at the institute, highlighted the important role of the Fendouzhe manned submersible in the research.

The manned submersible allowed scientists to observe the seafloor directly and make real-time decisions about which specimens to collect, Zhou said.

"The manned platform provided by Fendouzhe opened up unprecedented space for this research and served as the key support behind the breakthrough results," he said.

limenghan@chinadaily.com.cn