A submersible ride revealed a vast whale graveyard. And it holds more than just bones

Possible baleen whale ribs, pictured here, lie in the vast whale graveyard in the Diamantina Zone. (Global TREnD via CNN Newsource)

Scientists who recently piloted a submersible to a remote spot in the southeastern Indian Ocean have identified one of the largest and deepest whale graveyards containing hundreds of fossils, including one representing a previously unknown species. But not everything in this deep-sea necropolis is dead.

Tens of thousands of feet below the surface, dead or dying whales have drifted to the vast graveyard, their bones commingling across an area measuring approximately 746 miles (1,200 kilometres) long. Alongside the oldest bones are modern skeletons, suggesting that whale remains have settled on this spot continuously for at least 5 million years, based on the ages of the fossils, researchers reported Wednesday in the journal Nature.

Most of the remains belong to beaked whales, which have skulls that taper into slender snouts like those of dolphins. These whales are deep-diving and spend little time near the surface, so they are rarely seen and very little is known about their habits.

Researchers observed some sunken whale cadavers in the graveyard that were recent enough to still have scavengers attached to them; known as whale falls, these carcasses nourish diverse communities of deep-sea life, including bone-eating worms, snails, long-armed brittle stars and bivalves that survive through chemosynthesis — using chemical energy to produce their food. Many of these species may also be new to science, the study authors reported.

“Until now, whale falls were mostly based on large cetacean carcasses, mostly baleen whales,” Olivier Lambert, a vertebrate paleontologist at the Royal Belgian Institute of Natural Sciences in Brussels, told CNN in an email. “Here the authors show that beaked whale carcasses can play a similar role in some specific deep oceanic regions.”

It isn’t entirely surprising to learn that a graveyard full of whale bones has been accumulating for millions of years, Lambert added. This ocean region is known to host numerous species of beaked whales, and fossil skulls of such whales have been discovered nearby, snagged by trawlers or long-line fishing vessels in deep-sea regions off Iberia, South Africa and the Kerguelen Islands.

Nevertheless, “it is still really spectacular,” said Lambert, who was not involved in the discovery.

‘It came as a complete surprise’

Paleontologists found the graveyard in the Diamantina Fracture Zone, an area of marine ridges and trenches to the southwest of Australia. It formed between 30 and 40 million years ago during the breakup of the Australian and Antarctic continents, and reaches depths of about 15,000 to 23,000 feet (5,000 to 7,000 metres) below sea level.

“Although this is a truly massive whale graveyard, reaching it is extremely difficult due to the great depth,” said the study’s co-lead author Peng Zhou, a researcher with the ​​Institute of Deep-Sea Science and Engineering (IDSSE) at the Chinese Academy of Sciences in Beijing. The expedition was part of the Global Hadal Trench Exploration Program, an international collaboration to explore some of the least-known areas in the deepest parts of Earth’s oceans, Zhou told CNN in an email.

“That said, when we first observed this site, it came as a complete surprise to everyone,” Zhou added.

Zhou and his colleagues explored the zone from the research vehicle Tan Suo Yi Hao, using a submersible named Fendouzhe (“Striver” in Chinese), which had visited the bottom of Challenger Deep in the Mariana Trench — the deepest spot on Earth — in 2020. In the Diamantina Zone, they captured images of the necropolis and used the submersible’s robotic arm to collect 43 fossils as well as some of the scavenging animals, using a device called a slurp sampler.

What surprised the scientists most was the density of the fossils and the continuity of their distribution across the site, with some areas holding roughly 760 remains per square kilometre — “far higher than anything previously documented,” from similar sites, Zhou said.

“According to our estimate, there are over 10 million whale remains lying on the ocean bottom of this trench.”

As staggering as that number may seem, even more bones could be buried there under sediments on the seafloor, he added.

The researchers conducted 32 dives that took place between February and March in 2023 and found 485 whale-fossil deposits in addition to five modern whale falls. Scavengers were plentiful on the more recent remains, with one whale fall hosting up to 2,840 organisms in a single square metre. Scientists identified one of the modern cadavers as a minke whale, or Balaenoptera acutorostrata, that measured about 10 feet (3 metres) long. Remains of another modern species, Andrew’s beaked whale — scientifically known as Mesoplodon bowdoini — rested near fossils from an extinct genus called Pterocetus. The oldest fossils, belonging to Pterocetus benguelae, were 5.3 million years old.

“Finding both extinct genera like Pterocetus and living species like Mesoplodon bowdoini preserved together in the same region, across 1,200 kilometres of seafloor at such extreme depths — that was truly unexpected,” Zhou said.

Funnel to a graveyard

As for why many beaked whale corpses ended up on this one stretch of seafloor, the answer may lie in part in the Diamantina Zone’s V-shaped topography, said study co-lead author Xikun Song, a professor at the IDSSE.

“The area serves as a habitat or migratory corridor for cetaceans,” Song told CNN in an email. Beaked whales are deep-diving, but when they exceed depths of 9,800 feet (3,000 metres) they may reach their limit, “increasing the risk of fatal exhaustion or decompression sickness.”

The zone then funnels carcasses to the seafloor, and very little sediment movement at those depths means that the carcasses stay exposed to scavengers. Over time, deep-sea minerals, such as ferromanganese oxide, form crusts on the bones and preserve them as fossils, Song said.

Another unexpected find at the site was a partial skull belonging to a previously unknown species, which the scientists named Pterocetus diamantinae. Though the fossil’s age is not yet known, “its discovery helps document the evolutionary history of the group and shows that highly specialized beaked whales had already evolved by the time these fossils were deposited,” said study co-lead author Giovanni Bianucci, an associate professor in the department of Earth sciences at the University of Pisa.

“It was certainly a fortunate discovery,” Bianucci told CNN in an email, “but it is likely that many more fossil beaked whales remain on the seafloor of the Diamantina necropolis.”

By Mindy Weisberger, CNN