Chinese, Italian and New Zealand scientists have discovered a vast whale necropolis at the bottom of the southeast Indian Ocean, in the Diamond Fracture Zone. The site extends for around 1,200 km, at depths ranging from 4,616 to 7,001 meters, and contains 476 cetacean fossils and five recent whale falls.
The expedition, carried out between February and March 2023 with the submersible Fendouzhe aboard the ship Tan Suo Yi Hao, recorded the largest and deepest accumulation of its type ever documented. The remains include current and extinct species of beaked whales (ziphiids), as well as Antarctic minke.
Living communities in whale bones
Five recent carcasses are in the sulphophilic phase, with bones covered in white microbial mats and bone-eating worms of the genus Osedax. These environments are home to more than 35 macrofaunal taxa, dominated by fragile sea stars, polychaete worms, and chemosynthetic bivalves such as Abyssogena southwardae.
In some points, densities reach thousands of individuals per square meter. Species such as sea stars of the genus Xyloplax have been recorded in the deepest location for the genus to date.
Fossils reveal evolutionary history
Analysis of 43 fossils identified five species of beaked whales and one species of baleen whale. Among them are Mesoplodon bowdoini and Mesoplodon layardii, still existing in the southeastern Indian Ocean, as well as extinct genera such as Pterocetus and Izikoziphius. A new species, Pterocetus diamantinae, was described.
Strontium isotope dating has shown that whale fall events have been occurring in the region since at least 5.3 million years ago, in the Early Pliocene. The oldest bones belong to extinct species.
Why does the site accumulate so many remains?
The V-shaped topography of the Diamantina Zone, combined with the low sedimentation rate and the deep-diving behavior of beaked whales, favors the concentration of carcasses. These species hunt squid at extreme depths, which increases the risk of natural mortality. Baleen whale migrations also contribute.
The hyperdense bones of beaked whales resist degradation better and accumulate iron-manganese oxides, which helps preserve them for hundreds of thousands of years.
What the discovery changes
Until then, most whale falls were recorded at a depth of around 4,200 meters. The new site extends that limit by more than 2,500 meters and reveals specialized communities possibly new to science.
The site functions as a biogeographic corridor for chemosynthetic fauna, connecting hydrothermal and cold vent ecosystems. Furthermore, it serves as a fossil archive to study the evolution, ecology and population dynamics of deep-diving cetaceans over millions of years.
Researchers estimate that similar sites may exist in other key areas for beaked whales, such as off South Africa and the Iberian Peninsula.