The research team found a stalked jellyfish (Lucernaria quadricornis) during its 2024 Arctic Deep Expedition. Photo credit: The Nippon Foundation-Nekton Ocean Census Project, REV Ocean and University of Tromsø
Exploring the icy depths
The search for new species in the Arctic’s deep ocean ridges
The polar deep seas host a wealth of unique biodiversity. Despite the intriguing richness of the Arctic and Antarctic, much of the deep seafloor in these regions remains unexplored—but as ALEX DAVID ROGERS writes, a recent expedition to the Arctic’s deep ocean ridges revealed remarkable life in some of the most inaccessible places on Earth.
The polar regions are among the most difficult environments in the world to study because of their notoriously harsh weather, the presence of surface ice, and the polar night. Nonetheless, I fell in love with our high latitudes early in my career. The marine life is spectacular. Whales, seals and aquatic birds can be abundant at both poles. The scenery is breathtaking, with rugged mountains and glaciers tumbling into the sea when you are close to land. The light has an other-worldly, crystal-clear quality.
I also relish the challenge of running polar expeditions, juggling weather, wind, waves, equipment and fatigue to get the best science out of the precious time we have on ships. So it was with great anticipation that I set off for the Arctic Deep Expedition in April 2024.
The expedition was a collaboration involving the Nippon Foundation–Nekton Ocean Census programme, which aims to discover new species in the global ocean; Giuliana Panieri, a University of Tromsø expert on methane seeps; and REV Ocean, a Norwegian non-profit foundation dedicated to improving ocean health whose science director, Eva Ramirez-Llodra, specializes in chemosynthetic ecosystems. Eva had recently led an expedition to sample—for the first time—deep-sea hydrothermal vent communities under the Arctic ice from the same ship we would spend the next four weeks aboard: the Kronprins Haakon, a Norwegian ice-breaking research vessel.
Together, we joined an international team of early career ocean scientists and set out to explore the Arctic’s deep ocean ridges. The goal was to discover new species and better understand chemosynthetic ecosystems—places where microbes oxidize chemicals that emanate from below the seafloor (rather than using sunlight) to produce the energy that supports entire communities of specialized animals.
Dumbo octopus (Grimpoteuthis). Photo credit: The Nippon Foundation-Nekton Ocean Census Project, REV Ocean and University of Tromsø
Threadfin snailfish (Rhodichthys regina). Photo credit: The Nippon Foundation-Nekton Ocean Census Project, REV Ocean and University of Tromsø
Shrimp with filamentous bacteria. Photo credit: The Nippon Foundation-Nekton Ocean Census Project, REV Ocean and University of Tromsø
Broken basalt on the Knipovich Ridge, at a depth of 2,500 to 3,000 metres, covered with a variety of sponges. Photo credit: The Nippon Foundation-Nekton Ocean Census Project, REV Ocean and University of Tromsø
Encountering surreal geography
The Kronprins Haakon is one of the world’s most advanced multipurpose research vessels, and REV Ocean’s remotely operated vehicle (ROV), Aurora, is a robot that can dive to a depth of six kilometres to sample and survey the deep-sea floor.
Our main target was Knipovich Ridge, which lies in the deep waters west of Svalbard. It is along ridges like this that new seafloor is created when magma wells up from beneath the Earth’s crust. Underwater, this ridge presented a spectacular range of seafloor morphologies at huge scales. Within the middle of the ridge (what is known as the mid-axial valley) were craggy outcroppings of jagged basalt along with pillow basalts, formed when magma is extruded from the seabed into cold seawater—like toothpaste being extruded from its tube, only much larger.
These rocks were colonized by a variety of encrusting sponges, branching carnivorous sponges (yes, such things exist, and they capture and digest small crustaceans), and a very conspicuous, large-stalked sponge, Caulophacus arcticus. All these were shades of white to pale yellow and orange. Occasionally we would spot fish—mainly the beautiful red threadfin snailfish (Rhodichthys regina), but also the elongated and rather flattened glacial eelpout (Lycodes frigidus).
Moving away from the ridge centre, there were terraces and small volcanoes deeply buried in sediment, sometimes with abundant sea lilies, including Bathycrinus carpenteri, a living fossil that resembles a slender-stalked flower but is actually related to seastars and urchins.
Jotul black smoker vent. Photo credit: The Nippon Foundation-Nekton Ocean Census Project, REV Ocean and University of Tromsø
A hydrothermal vent field
The fauna in the Knipovich Ridge area were generally sparse and not particularly diverse. However, the Jotul hydrothermal vent field presented a very different perspective.
Here, at a depth of more than 3,000 metres, we encountered a white and grey mound of sulphide rubble topped by a crusty chimney emanating black hot fluids. Small crustaceans called amphipods were crawling about on the chimney surface, while around the vent, we found mats of bacteria with forests formed by the thin tubes of a worm called Sclerolinum contortum. This has symbiotic bacteria living in its tissues that oxidize chemicals in the vent fluids to provide energy for carbon fixation (the conversion of inorganic carbon into the organic compounds that form the base of the food web).
Among these tubes were other animals, including amphipods, small snails, sea spiders, anemones, and shrimps covered in threadlike bacteria.
But the greatest surprise was waiting for us at the end of our journey. North of the Knipovich Ridge lies the deepest part of the Arctic, the Molloy Deep. We knew that a column of gas had been detected to the northwest of this area using echosounders. Keen to find out where the gas was emanating from, we visited the site and sent Aurora down.
The seafloor was covered in deep, sandy brown sediment. Extruding from this were mounds of what resembled white or yellow ice. This was methane hydrate, which is formed under high pressure and at low temperatures when methane molecules are trapped by a cage of water molecules. The mounds were in various stages of decomposition, with some hollowed out to form arches and others completely collapsed to form pits. Methane also bubbled up in various places.
The hydrothermal vents and methane seeps we studied at similar depths hosted many of the same species—an overlap that seems to be unique to the Arctic
—Alex David Rogers Deputy Director, National Oceanography Centre, Southampton, England.
An alien landscape
The hard surfaces of the methane hydrates, as well as the sediments around them, were colonized by more worm forests that were home to amphipods, snails and anemones. Larger shrimps were scattered around, as were conspicuous stalked jellyfish, Lucernaria quadricornis, which spend their lives attached to the seafloor. It was a spectacular and alien landscape populated by abundant and strange life forms.
Examples of the animals we observed were collected during the expedition and are still being studied. Some are new species and are just now being formally identified and named. In fact, the new hydrate seep field, the deepest encountered at the time, was named after my daughter, Freya.
Vent and seep communities usually host different animals because these are distinct ecosystems with different chemistry and energy sources. But intriguingly, the hydrothermal vents and methane seeps we studied at similar depths hosted many of the same species—an overlap that seems to be unique to the Arctic. This raises intriguing questions about how these species evolved and how they survive in such chemically different worlds.
By Alex David Rogers
Deputy Director, National Oceanography Centre, Southampton, England.
ALEX DAVID ROGERS is a deputy director with the National Oceanography Centre in Southampton, England.
