Researchers on the Ocean Census Arctic Deep–EXTREME24 expedition discovered Freya hydrate mounds at a record depth of 3,640 meters beneath the Arctic, where crystallized methane structures form a “frozen reef.” These gas hydrate cold seeps emit methane plumes up to 3,300 meters and undergo cycles of collapse and reformation. Chemosynthetic organisms—some shared with hydrothermal vents—colonize the mounds, and scientists call for protections against potential deep-sea mining.
Frozen 'Reef' of Methane Mounds Discovered 3,640 m Beneath the Arctic
UiT / Ocean Census / REV Ocean
Far below the Arctic Ocean surface, scientists have found an unexpectedly active and strange seafloor ecosystem. Off Greenland, towering formations of crystallized methane and other gases—known as the Freya hydrate mounds—stand like a frozen reef, providing habitat for organisms adapted to life without sunlight.
A paper in Nature Communications reports the deepest-known occurrence of these gas hydrate mounds at 3,640 meters (about 2.26 miles). The discovery was made during the Ocean Census Arctic Deep–EXTREME24 expedition, which used remotely operated vehicles and other robotic tools to map, film, and sample these remote habitats.
These features, also called gas hydrate cold seeps, emit methane flares that rise roughly 3,300 meters into the water column—currently the tallest such plumes ever recorded. The researchers observed that the mounds are dynamic: they collapse and rebuild over time, a process that helps reveal how deep Arctic seafloor systems respond to tectonics, heat flow, and environmental change.
“These are not static deposits. They are living geological features, responding to tectonics, deep heat flow, and environmental change,” said Giuliana Panieri, a co-author and professor at the Arctic University of Norway.
Colonizing the mounds are chemosynthetic organisms that gain energy from chemical reactions rather than photosynthesis. Some species documented at the Freya mounds are also known from hydrothermal vents—separate seafloor systems where heated, mineral-rich fluids flow out—suggesting ecological connections between what were thought to be isolated deep-sea habitats.
“The links that we have found between life at this seep and hydrothermal vents in the Arctic indicate that these island-like habitats on the ocean floor will need to be protected from any future impacts of deep-sea mining in the region,” said Jon Copley, co-author and professor at the University of Southampton.
Beyond biological interest, these findings raise questions about the role of deep Arctic seeps in regional carbon and methane cycles, though the study focuses on ecosystem discovery and habitat dynamics rather than quantifying atmospheric impacts. The team emphasizes that these unique communities deserve protection as interest in deep-sea resources grows.
