• Researchers investigating the southeastern Indian Ocean have uncovered one of the largest and deepest whale graveyards ever recorded, stretching roughly 746 miles.

• Fossils at the site have accumulated for at least 5 million years.

• Recently deceased whales at the location are sustaining deep-sea ecosystems, including species that may be previously unknown to science.

A team of scientists piloting a deep-sea submersible in a remote part of the southeastern Indian Ocean has identified an immense whale graveyard containing hundreds of fossils, including one belonging to a newly recognized species. Despite its reputation as a resting place for the dead, parts of this underwater expanse are teeming with life.

Thousands of feet beneath the ocean’s surface, the remains of whales have settled across a vast stretch of seafloor measuring about 746 miles (1,200 kilometers) in length. Ancient bones lie alongside more recent skeletons, indicating that whale carcasses have been accumulating in this area for at least 5 million years, according to findings published Wednesday in the journal Nature.

The majority of the fossils are from beaked whales, a group distinguished by elongated skulls that taper into narrow snouts resembling those of dolphins. These elusive mammals are known for their extreme deep-diving behavior and limited time at the surface, making them difficult to observe and poorly understood.

Among the skeletal remains, researchers documented several relatively recent whale falls — carcasses that had not fully decomposed and were still surrounded by scavengers. Such whale falls provide a crucial source of nutrients in the deep ocean, supporting specialized organisms including bone-eating worms, snails, brittle stars and bivalves that rely on chemosynthesis, a process that converts chemical energy into food. Scientists believe that some of these organisms could represent species new to science.

Olivier Lambert, a vertebrate paleontologist at the Royal Belgian Institute of Natural Sciences in Brussels who was not involved in the study, noted that whale falls have traditionally been associated with large baleen whales. He explained that this discovery demonstrates that beaked whale carcasses can play a comparable ecological role in certain deep-ocean regions.

Lambert added that while the existence of a long-accumulating whale graveyard is not entirely unexpected — given the diversity of beaked whales known from this region and fossil discoveries made in nearby waters — the scale of the find is nonetheless remarkable.

‘It came as a complete surprise’

The graveyard was discovered in the Diamantina Fracture Zone, a system of marine ridges and trenches southwest of Australia. This geological formation originated between 30 and 40 million years ago during the separation of the Australian and Antarctic continents and reaches depths of approximately 15,000 to 23,000 feet (5,000 to 7,000 meters).

According to co-lead author Peng Zhou of the Institute of Deep-Sea Science and Engineering at the Chinese Academy of Sciences, accessing the site posed significant technical challenges because of its extreme depth. The expedition formed part of the Global Hadal Trench Exploration Program, an international effort aimed at studying some of the least explored regions of the planet’s oceans. Zhou said the discovery astonished the entire team when they first observed the site.

The researchers conducted their exploration aboard the research vessel Tan Suo Yi Hao, deploying the submersible Fendouzhe (“Striver”), which previously reached the bottom of Challenger Deep in 2020. In the Diamantina Fracture Zone, the team photographed the graveyard and used the submersible’s robotic arm to retrieve 43 fossil specimens along with scavenging organisms collected using a suction device.

What most surprised the scientists was the density and continuity of the fossils across the region. In some areas, they recorded as many as 760 whale remains per square kilometer — far exceeding densities documented at other deep-sea sites.

Based on their calculations, Zhou and his colleagues estimate that more than 10 million whale remains may rest on the ocean floor within this trench. Even more could lie buried beneath layers of sediment.

During 32 dives conducted between February and March 2023, the team identified 485 fossil deposits in addition to five modern whale falls. The more recent carcasses hosted abundant scavengers; in one instance, up to 2,840 organisms were counted within a single square meter. One modern specimen was identified as a minke whale (Balaenoptera acutorostrata) measuring about 10 feet (3 meters) long. Nearby lay the remains of Andrew’s beaked whale (Mesoplodon bowdoini), alongside fossils from the extinct genus Pterocetus. The oldest fossils, attributed to Pterocetus benguelae, were dated to approximately 5.3 million years ago.

Zhou emphasized that finding extinct genera such as Pterocetus alongside living species across 1,200 kilometers of seafloor at such depths was entirely unexpected.

Funnel to a graveyard

Co-lead author Xikun Song suggested that the V-shaped topography of the Diamantina Fracture Zone may help explain why so many beaked whales ended up in this particular area. The region may serve as both habitat and migratory pathway for cetaceans.

Although beaked whales are capable of diving to great depths, descending beyond about 9,800 feet (3,000 meters) may push them to their physiological limits, increasing the risk of fatal exhaustion or decompression-related injuries. The trench’s shape could funnel deceased whales downward, while minimal sediment disturbance at these depths allows the skeletons to remain exposed. Over time, minerals such as ferromanganese oxides accumulate on the bones, forming protective crusts that aid fossil preservation.

Another notable discovery was a partial skull from a previously unknown species, which the team named Pterocetus diamantinae. Although its precise age has yet to be determined, the fossil provides valuable insight into the evolutionary history of beaked whales, indicating that highly specialized forms had already developed by the time these sediments were laid down.

Study co-lead author Giovanni Bianucci, an associate professor of Earth sciences at the University of Pisa, described the find as fortunate but suggested that many more fossilized beaked whales likely remain scattered across the seafloor of the Diamantina graveyard.