Scientists discover ‘graveyard’ of whale skeletons in an ocean abyss off Australia
Deposited over millions of years, the whale necropolis is covered with deep-sea species, many of which are new to science.
On the barren seafloor, a sunken whale is like an all-you-can-eat buffet popping up on a deserted island. All manner of hardy deep-sea critters congregate at the carcass, turning a biological ghost town into a bustling ecosystem.
The often-isolated oases are called whale falls, consisting of just one fallen whale and its deep-sea groupies. However, researchers probing the depths west of Australia in a submersible recently discovered a sprawling cetacean cemetery containing nearly 500 individual whale remains. In a paper published June 10 in the journal Nature, the team analyzed bones from this “whale necropolis” and discovered that these skeletons were deposited over the last roughly five million years.
“This is the largest accumulation of fossil whale remains in the deep-sea of which I am aware,” says Craig Smith, a marine biologist at the University of Hawai’i who was not involved in the new paper. The staggering depths of the sites also make these finds “truly extraordinary,” he says. Some specimens lie more than four miles below the surface—nearly twice as deep as any other known whale fall.
This whale graveyard is crawling with denizens of the deep, many of which are new to science. The bones themselves belong to both modern and ancient whales, including one new species. Several are beaked whales, an elusive group of deep-diving marine mammals. “Beaked whales are rare in life, but they’re abundant in death at this site,” says Stephen Godfrey, a paleontologist at Calvert Marine Museum in Maryland who was not involved with the paper but wrote a perspective article on the finds for Nature.
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A trench of whale bones
Between February and March 2023, a team led by Xiaotong Peng, a researcher at the Chinese Academy of Sciences’ Institute of Deep-Sea Science and Engineering, ventured to the Diamantina Fracture Zone, a nearly 750-mile swath of seafloor in the southeastern Indian Ocean that is carved by trenches and ridges. The zone bottoms out nearly 4.5 miles below the surface, exposing a rare glimpse of some of the ocean’s deepest depths.
To explore this rugged abyss, team members boarded the HOV Fendouzhe, a deep-sea submersible equipped with video cameras, mechanical arms and vacuum-like devices to collect samples. Around 4.35 miles below the surface, the submersible stumbled across a smattering of ancient whale skeletons settled on the seafloor.
“We did not expect to find this massive graveyard for whales,” says Peng, who made multiple dives on the HOV Fendouzhe to see the whale remains up close. “Finding an isolated whale fall here or there would not have been surprising, but we have never seen anything on this scale before.”
Over the course of more than 30 dives, the team documented 485 individual sites containing fossilized whale bones. To determine when these ancient whales lived, the team examined levels of certain chemical elements preserved in some of the bones, and the oldest samples dated back nearly 5.3 million years.
The team also observed several modern whale skeletons strewn among the ancient bones, which makes the area unique. Most dense fossil sites “stopped growing millions of years ago, but whale bones are continuing to be added to this deep trench,” Godfrey says.
A biodiversity bonanza
All five modern whale falls were crawling with critters. One carcass covered an area less than 11 square feet and contained 2,840 individual deep-sea animals.
In total, the team observed 35 different types of animals snacking on the dead whales, including jellyfish, spindly brittle stars and deep-sea clams that contain symbiotic bacteria that convert sulfur chemicals from the whale carcass into energy. Bone-eating worms were another common inhabitant. The worms produce acid to dissolve the whale bone into organic material that their own symbiotic bacteria turn into food.
The team used the submersible’s vacuum-like sampling device to carefully collect creatures from the whale bones, which were coated with white microbial mats. The team took DNA samples from 21 of these animals and were only able to conclusively tie one to a previously described species.
The high diversity of creatures does not surprise Smith, who published a 2015 review article documenting both ancient and modern whale fall sites drive evolution in the deep sea. But “these trench depth communities are clearly different from those found at whale falls at shallower depths,” he says, revealing that depth impacts which species show up to chow down at a whale fall.
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A marine mammal morgue
The team used the submersible’s arms to pick up bones from several of the whale falls. Some of the larger remains were from baleen whales, including a sei whale and an Antarctic minke whale. But the majority of the skeletons belonged to beaked whales, a little-known family of cetaceans who sport a dolphin-like beak, or rostrum, that is packed with dense bones. The deep-diving whales, which can hold their breaths for more than an hour, use their re-enforced rostrums and tusk-like teeth to dispatch rivals.
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The density of their snouts meant several of the skulls were in remarkable shape despite their prolonged stint on the seafloor. Over the eons, many of the skulls were also covered in black crusts of ferromanganese, a mineral compound that precipitates out of seawater. Godfrey compares this mineral crust to a protective “sarcophagus” that preserves the skull.
Some of the skulls belonged to two species of modern beaked whales: the Andrews’ beaked whale and the strap-toothed whale. Among the extinct beaked whale specimens, the scientists identified and named one newbie: the prehistoric whale Pterocetus diamantinae that lived as early as 5.3 million years ago. In future studies, the beaked specimens could help researchers flesh out how this elusive group of deep-diving marine mammals evolved their extreme lifestyles, Godfrey says.
Why did so many whales die here?
The scientists think the Diamantina Zone’s rich record of whale falls is due to its location and depth. This part of the Indian Ocean sits along the migration routes of several species of baleen whales, and the squid and fish in its deep waters also entice beaked whales. Some of these animals likely died during hunting trips into the area’s trenches, which lie below their maximum diving depths. Once they succumbed to either exhaustion or decompression sickness, their skeletons sank and funneled into the V-shaped trenches over millions of years.
The team suspects that similar accumulations of ancient bones likely exist in other areas where beaked whales congregate, including deep ocean environments off the coast of South Africa and the Iberian Peninsula.
Godfrey thinks this discovery will inspire others to search these depths for more whale necropolises. “There’s no reason why there could not be similar whale falls in other trenches,” he says. And who knows how many new species those undiscovered cetacean crypts might hold.
