BEIJING, June 11 (Xinhua) -- Scientists have discovered the world's deepest and largest collection of whale remains on the ocean floor, a site they call a "whale necropolis."
Located in the Diamantina Zone of the southeastern Indian Ocean, at depths of up to 7,000 meters, the find includes both ancient fossils and active whale-fall ecosystems that have been forming for at least 5.3 million years.
The study, conducted by the Institute of Deep-sea Science and Engineering (IDSSE) of the Chinese Academy of Sciences in collaboration with the University of Pisa in Italy and Earth Sciences New Zealand in Wellington, has been published in the latest issue of the journal Nature.
Whale falls occur when dead whales sink to the seabed. These carcasses create rich, temporary habitats for deep-sea creatures, supporting everything from bone-eating worms to sea stars. Until now, most known whale falls were found at depths of less than 4,000 meters, with the deepest active site recorded at 4,204 meters. No active whale-fall ecosystem had ever been reported from hadal depths -- which are those deeper than 6,000 meters.
In 2023, a team led by the IDSSE carried out 32 dives using the manned deep-sea submersible Fendouzhe (Striver), aboard the research vessel Tansuo-1. They explored a 1,200-kilometer stretch of the Diamantina Zone and found five active whale falls and 476 fossil sites, ranging from 4,616 to 7,001 meters deep. The density of whale remains reached up to 759.5 individuals per square kilometer.
"If that number is extrapolated across the entire zone, it suggests there may be more than 10 million whale carcasses in the area," said Peng Xiaotong, a professor at the IDSSE.
Among the active whale falls, one site consisting of three beaked whale vertebrae at a depth of 6,789 meters represents the deepest active whale-fall ecosystem ever recorded.
Using strontium isotope dating, researchers confirmed that the fossils there date back at least 5.3 million years to the Early Pliocene. Among them are both living beaked whale species, such as Andrews' and strap-toothed beaked whales, and extinct ones, including a newly described species named Pterocetus diamantinae.
Why are there so many whale remains there? According to the study, the zone is a feeding ground for beaked whales, some of which may die during deep dives. The V-shaped seafloor funnels the carcasses into the trench, and very low sedimentation rates keep the bones exposed on the seabed for long periods, helping to preserve them.
The researchers also calculated the carbon impact. Assuming an average beaked whale weighs two tonnes and is 25 percent lipids, the roughly 10 million carcasses could represent about 6.7 million tonnes of sequestered carbon. That is equivalent to approximately 4,700 years of "marine snow," the slow rain of small organic particles from the upper ocean to the deep sea.
This suggests that whale falls are a major, previously overlooked source of carbon on the deep-ocean floor, capable of shaping the region's food web and biodiversity, said Zhou Peng, an assistant professor at the IDSSE.
"This study extends the known depth record of whale falls from 4,200 meters to nearly 7,000 meters. Its depth, scale and temporal span all push beyond existing knowledge, providing a unique window into the early evolutionary history, paleoecology and population dynamics of ancient whales," noted Song Xikun, an associate professor at the IDSSE.
The Diamantina Zone may constitute a previously unrecognized "whale-fall chemosynthetic life corridor" across the southeastern Indian Ocean, offering significant academic value for understanding the dispersal and connectivity of deep-sea chemosynthetic life systems, Peng explained.
The research effort was supported by several scientific programs, including the Global Hadal Exploration Programme, a ten-year United Nations Ocean Decade initiative led by the IDSSE. This program is dedicated to exploring the deepest regions of the global ocean and addressing fundamental questions about deep-sea geology, life and environmental evolution. ■
