Researchers Discover the Deepest Whale Graveyard in the World in the Indian Ocean

The expedition with the Chinese submersible "Fendouzhe" in early 2023 examined a 1,200-kilometer-long section of the so-called Diamantina Zone in the Indian Ocean. The burial site lies at a depth of 4,200 to 7,000 meters. In total, the team documented nearly 480 whale remains, some of which are several million years old. Extrapolated to the total size of the area, there are likely to be around 10 million specimens.

According to estimates, more than 700 dead whales lie on every square kilometer of the seafloor. Five of the carcasses discovered were relatively fresh, but the majority are very old. The oldest was dated to an age of 5.3 million years. This was determined using strontium dating. Never before have whale fossils been discovered at anywhere near such a depth.

A Cemetery at 7,000 Meters Depth

The ancient finds are predominantly parts of the skulls of beaked whales, whose preservation is owed to a combination of fortunate circumstances. Beaked whale skulls naturally exhibit a very high bone density at the snout. Beaked whales in particular also had a very high bone density — meaning their skeletons decompose particularly slowly. They remained intact long enough to mineralize, which preserved their stability in the long term.

They were additionally protected by a layer of iron-manganese oxide that coats the fossils. For example, the V-shaped topography of the deeply incised zone contributes to the carcasses accumulating there. The trench-like terrain favors the sliding of the carcasses toward the deepest point, while at the same time hardly any sediment is deposited that could cover the carcasses.

Why Beaked Whale Skulls Were Preserved

The area belongs to the feeding grounds of beaked whales. The team found remains of species still alive today, such as Andrews' beaked whale and the strap-toothed whale, but also long-extinct species, for example representatives of the beaked whale groups Pterocetus and Izikoziphius. Some of the whale fossils found belonged to species that have since become extinct, and even a new species was among them, which was named Pterocetus diamantinae.

When a whale dies, the carcass usually sinks into the depths, lands on the seafloor and serves there as a food source for a large number of organisms. Most whales meet their end where they also spend their lives: on the open sea. When the carcass sinks to the ocean floor, the local ecosystem changes radically. The multi-ton whale bodies provide food for a wide variety of marine life over decades.

Life on the Carcass: 2,800 Animals per Square Meter

The research team found jellyfish, various species of worms, crustaceans, mollusks and starfish, in some cases up to 2,800 animals per square meter. Most of them are likely to be unknown species. How they track down the nearest carcass over hundreds of kilometers, however, remains unclear so far.

Overall, such so-called whale falls are indeed very common, the group writes, but so far only a little more than 70 such areas have been documented. It can be assumed that there are many other whale graveyards worldwide. Most finds come from depths of less than 4,000 meters.

Reactions from the Scientific Community

The whale carcasses transported around 6.7 million tons of carbon to the seafloor. The whale graveyard thus functions as a previously unknown carbon sink in the deep ocean. It is by far the deepest, largest and oldest known whale graveyard.

Stephen J. Godfrey of the U.S. Calvert Marine Museum speaks in an accompanying article to the Nature study of a "perfect storm" of special circumstances that made this discovery possible. "The article by Peng and his colleagues reminded me of the trailer for the first installment of an epic film series. I hope that many more such blockbusters will follow," says Godfrey.