A 5.3-million-year-old whale necropolis found at 7,000 metres deep

In the south-eastern Indian Ocean, under nearly seven kilometres of water, an international team has uncovered a site with no known equivalent: a line of cetacean bones stretching over roughly 1,200 kilometres. Published in June 2026 in the journal Nature, the discovery yields both the deepest and the most extensive whale graveyard ever documented, and a series of still-living ecosystems that thrive on these carcasses.

An oceanic scar 1,200 kilometres long

The site occupies the Diamantina Fracture Zone, a feature of the ocean floor formed by the separation of Australia and Antarctica. Researchers recorded 476 fossil cetaceans there, together with five whale falls still active, spread between about 4,600 and 7,000 metres depth. Mean density stands at about 760 remains per square kilometre, which leads the institute to estimate that the area could hold more than ten million in all, the vast majority of them still to be explored.

The survey used the Chinese submersible Fendouzhe, deployed from the vessel Tan Suo Yi Hao, over 32 dives carried out between February and March 2023. The team brought together the Institute of Deep-sea Science and Engineering of the Chinese Academy of Sciences, the University of Pisa and Earth Sciences New Zealand.

Five million years of archives

Strontium isotope dating gives the oldest bones an age of at least 5.3 million years, the beginning of the Pliocene. In other words, whales have been dying and sinking in the same place for millions of years, with no apparent interruption. The site is not a snapshot but a continuous archive, which makes it a rare object for retracing the evolution of cetaceans.

Among the remains are present-day species, including Andrews’ beaked whale and the strap-toothed whale, but also a sei whale and an Antarctic minke whale. To these are added extinct genera, among them an entirely new species described on this occasion and named Pterocetus diamantinae, after the place.

Why so many carcasses in the same place?

The explanation lies as much in the geometry of the place as in the behaviour of the animals. The fracture traces a V-shaped valley that channels bodies towards the bottom, like a funnel more than a thousand kilometres long. The zone also serves as habitat and migration corridor for beaked whales, those unobtrusive odontocetes that specialise in deep diving.

Those extreme dives are not without risk: beyond three thousand metres, exhaustion or decompression sickness can be fatal. Lastly, sedimentation there is so slow that the bones stay exposed long enough to fossilise instead of being buried. Three conditions rarely met together, which account for the accumulation.

Oases of life on skeletons

In the food desert of the abyss, the carcass of a large whale amounts to several centuries of falling organic matter arriving all at once. Around the five still-active falls swarm bone-eating worms, snails, long-armed brittle stars, bivalves and bacterial mats, whose energy comes not from the sun but from chemosynthesis. At one of these sites, the measured density exceeds 2,800 organisms per square metre. The deepest of these still-living communities was observed at 6,789 metres depth, a record for this type of ecosystem.

Several of these species could be unknown to science. The comparison put forward by the authors is with the hydrothermal vents of the 1970s: a doorway onto a whole swathe of the living world that had not been suspected.

What to take away?

That large cetaceans go on feeding the deep long after their death, and that this transfer of carbon towards the ocean floor plays out on a scale that is poorly measured: the institute puts forward a figure of 6.7 million tonnes of carbon trapped by the site as a whole. That beaked whales, among the marine mammals hardest to observe alive, sometimes lend themselves better to study through their bones. And that a site that stayed invisible until 2023, for want of a craft able to descend to it, is a reminder of an uncomfortable truth: the deep sea is still, for the most part, a blank page.

Sources: study published in Nature (June 2026), Le Monde, The Conversation, Pour la Science, the IDSSE press release and Futura Sciences.