Deepest and most extensive whale graveyard discovered in Indian Ocean

Some remains found in Diamantina fracture zone date back more than 5m years and reveal species and ecosystems unknown to science

The oldest, deepest and most extensive whale graveyard yet discovered has been found in the south-eastern Indian Ocean, with fossils dating back more than 5m years.

Whale falls – the term for dead whales that sink to the ocean floor – are not uncommon, but most have been found at depths of less than 4km (2.5 miles). By contrast, the newly discovered necropolis reaches depths of more than 7km, and extends hundreds of miles across the sea floor.

What’s more, researchers found decaying carcasses teeming with life.

Dr Giovanni Bianucci, a co-author of the study based at the University of Pisa, said: “This discovery demonstrates that these extreme and unexplored environments are home to species and ecosystems still unknown to science, and that we are therefore still far from understanding the true biodiversity of our planet.

“Furthermore, it shows us that life can adapt and evolve even in extreme environments where light is absent and pressure is extremely high.” He added that the study also provided unique information on creatures including the “mysterious and elusive” beaked whales.

In an article accompanying the study, Stephen J Godfrey of the Calvert Marine Museum in the US described the graveyard as “a truly unique discovery”, saying the site could yield many more exciting finds. “[The research] reminded me of a trailer for the first in a series of epic movies,” he wrote.

A team of researchers based in China, Italy and New Zealand used a submersible to explore an area of trenches and ridges in the south-eastern Indian Ocean, known as the Diamantina fracture zone. This formed between 60m and 50m years ago as the Australian and Antarctic continents drew apart.

The team, whose study was published in the journal Nature, discovered whale fossils at depths of up to 7,002  metres – near the deepest point of the Diamantina fracture zone. They subsequently carried out 32 dives to the sea floor, finding 485 whale-fossil sites, as well as five modern natural whale falls in an advanced stage of decomposition.

The team noted: “Aligned along a northwest-southeast axis for 1,200km, these falls may form a previously unrecognised ‘whale-fall community supercorridor’.”

The largest carcass discovered by the researchers was a five-metre long skeleton of an Antarctic minke whale. They also encountered remains of extinct species including a fossilised skull from a species of beaked whale called Pterocetus benguelae, which was dated to 5.3m years ago, and another fossilised skull from a new species the team have named Pterocetus diamantinae.

The decaying whale caracasses were home to a diverse array of life including crustaceans, molluscs, bone-eating worms and brittle stars, among other creatures. Many species, the researchers noted, may be new to science.

Jon Copley, a professor of ocean exploration and science communication at the University of Southampton, who was not involved in the work, said: “It’s an exciting and rare discovery – not only the world’s deepest known ‘whale-fall’ colony of deep sea animals, but also such an abundance of modern whale skeletons and fossils in this particular location.”

Copley said whale falls were island-like habitats for deep sea animals, including species related to those thriving at hydrothermal vents, which make a meal of their remains. But, he added, whale falls were harder to find than undersea hot springs as they cannot be detected remotely.

“Finding a ‘whale necropolis’ where there are nearly 800 skeletons per square kilometre is a surprise, and the mix of whale types is a puzzle,” Copley said, noting that it included some shallow-diving filter-feeding species such as Minke whales as well as many bones and fossils of beaked whales, which are very deep-diving hunters.

“As the researchers suggest, such a necropolis probably results from being on a migration route for filter-feeding species, while also a good place for the hunter species to dive deep for squid, but perhaps pushing them perilously close to their limits as they dive into this crack in the ocean floor,” he said.