Discovery in the deep sea: Unique habitat at hydrothermal vents

Off the coast of Papua New Guinea, researchers discovered a novel type of hydrothermal field where two processes occur simultaneously: the release of hot hydrothermal fluids and unusually high amounts of methane and other hydrocarbons. This combination makes the system unique worldwide. It lies at a depth of around 1,300 metres on a flank of Conical Seamount in the western Pacific, off the island of Lihir in Papua New Guinea. A study presenting the discovery was published today in Scientific Reports.

ROV delivers the surprise
“We essentially have a hot vent bubbling right next to a cool gas seep – a combination that has never been described before,” says Dr Philipp Brandl, marine geologist at the GEOMAR Helmholtz Centre for Ocean Research Kiel. He served as chief scientist on the SONNE expedition SO299 DYNAMET, which explored the Tabar–Lihir–Tanga–Feni island chain in 2023 to study the region’s underwater volcanoes (seamounts).

Brandl continues: “No one really expected to find a hydrothermal field here, let alone one that is so exceptional.” Although previous expeditions had indicated minor hydrothermal activity, the field remained undetected during several research cruises. It was only through the use of the ROV Kiel 6000 that the peculiarities of this underwater landscape were revealed. “It was a real surprise,” says Brandl, “especially for those of us who had worked in this area multiple times.”

A hybrid system of hot and cool vents
Hydrothermal vents and methane seeps usually occur in different places on the seabed. In this case, however, they are in close proximity is due to the unique geology of Conical Seamount, where thick sediment layers containing organic material lie beneath the volcanic structure. Ascending magma heats these layers, generating methane and other hydrocarbons. At the same time, this magmatic heat also drives mineral-rich fluids upwards, where they emerge as hot vents at the seabed.

Both fluids – the hot water from depth and the cooler, methane-rich gases from the sediments – travel along the same pathways to the surface. Consequently, hot fluid and cold gas bubble up from the seabed just a few centimetres apart.

A habitat unlike any other
This direct neighbourhood creates an entirely new hybrid environment, providing a habitat for an extremely diverse range of animals. Dense fields of the mussel Bathymodiolus, tube worms, shrimp, amphipods, and striking purple sea cucumbers cover the rocks. “In places, you couldn’t see a single patch of rock because everything is so densely populated,” says Brandl. “We are confident that some of the species there have not yet been described. However, a dedicated expedition would be needed to fully study this unique habitat.”

Due to the abundance of mussels, the scientists, along with local observer Stanis Konabe from the University of Papua New Guinea, named the field ‘Karambusel’. In the local Tok Pisin language, this means ‘mussel’.

Traces of precious metals in the rock
The unusual gas composition at the Karambusel field influences both the communities of life and the geological features. The methane emitted is highly concentrated, exceeding 80 per cent, while hot fluids rise from the magma simultaneously, creating unique chemical conditions in the subsurface. Metals such as gold and silver, together with elements such as arsenic, antimony, and mercury, are deposited in the rock. Thus, the area bears the marks of an earlier, high-temperature phase involving precious metals, alongside present-day, cooler activity.

Threats from human activity
Despite its unique geology and biology, this site is under threat. Mining is already taking place in the region, for example, at the Ladolam gold mine on Lihir, where waste and residues are discharged into the sea. Exploration licences for minerals and hydrocarbons on the seabed also exist. This endangers the fragile habitat and its highly specialised fauna.

The researchers are therefore calling for urgent further study, targeted marine spatial planning, and effective protection measures to preserve this extraordinary ecosystem. Philipp Brandl: “We have discovered an unexpected treasure trove of biodiversity in the Karambusel field that needs to be protected before economic interests destroy it.”