Hot vents in an ice-covered ocean: the role of the Arctic as a connectivity pathway between ocean basins

Deep-sea hydrothermal vents (hot springs) are tiny, isolated habitats found on volcanic submarine mountain chains called mid-ocean ridges. These oases of exuberant life are sustained by microbes that produce food using chemical energy from the vent fluids, rather than sunlight. Four decades after hydrothermal vents were first discovered, exploration of these unique ecosystems continues to provide new knowledge to better understand our planet and, lately, it has stimulated exploration for life on other worlds in our solar system. In the depths of the Arctic Ocean lies one of the most unexplored ridges on Earth - the Gakkel Ridge. Here, in 2014, the first vents under ice were discovered on the Aurora mound, at 82°N and 4 km depth. But these vents were only glimpsed by a robotic vehicle for less than a minute before the expedition had to end. A group of over 50 scientists, engineers, communicators and vessel crew involved in HACON project have successfully conducted the first survey of the Aurora vent field and surrounding area in two cruises (2019 and 2021) on board the Norwegian icebreaker R/V Kronprins Haakon. As pioneer explorers, the HACON team has conducted the first ever ROV (Remote Operated Vehicle) dives to deep hydrothermal vents in the Arctic under permanent ice cover, pushing forward the frontiers of Arctic exploration and providing methods and guidelines for future deep-sea Arctic investigations. The team has surveyed in detail the Aurora Hydrothermal Vent, providing a unique new dataset on the geological, geochemical, oceanographic, microbiologic and biologic characteristics of this remote and pristine ecosystem. The ongoing analyses of the samples is providing novel information on the community composition, ecosystem function and environmental drivers of hydrothermal systems in the Gakkel Ridge. This new knowledge will provide the missing piece of the global biogeographic puzzle of hydrothermal vents, helping understand if the Arctic vent communities have evolved in isolation or are connected to other ocean basins. Initial results show that the Aurora Vent Field is composed of 3 black smokers colonised by amphipods and gastropods. The HACON team has also contributed to technological development, with projects working on miniaturising subsea equipment to used on complex expeditions. The collaborations with NASA-JPL have contributed to research related to the search of life in the moons of outer planet such as Jupiter. And collaborations with major documentary experts (National Geographic and a film company) are greatly contributing to raising awareness of these remote and fragile ecosystems when they are still pristine.

1) Proven methodology for ROV (remote operated vehicle) operations to the deep-sea floor under permanent ice cover, opening for future deep-sea research under ice. 2) First ever survey of an active hydrothermal vent field in the Gakkel Ridge, Arctic Basin, providing an environmental baseline of a pristine ecosystem from which to measure change caused by potential future stressors. 3) Greatly increased interdisciplinary and international (5 nations) collaborations amongst physical oceanographers, geologists, geochemists, micropaleontologists, microbiologists, biologists and astrobiologists, subsea engineers and communicators. This has enabled mentoring of the next generation of ocean professionals, contributed to technology development (miniaturised equipment), pushed forward the frontiers of knowledge of deep Arctic ecosystems and raised awareness of such remote systems in society (Nat Geo article and TV documentary).

Forty years after the discovery of hydrothermal vents, research of these unique ecosystems is still in a discovery phase. The findings have changed the way we understand life on Earth and are fuelling exploration for life in our solar system. The remote Arctic Gakkel Ridge remains largely unexplored and ecosystems in this under-ice region are largely unknown. First evidence of active venting in the Gakkel Ridge has been available since 2001, but visual confirmation was not obtained until 2014 on the Aurora seamount. HACON proposes to return to the Aurora seamount in 2019, using the most modern infrastructure for oceanographic and Arctic research, including the new Norwegian icebreaker Kronprins Haakon, ROV Ægir and hybrid AUV Nereus Under Ice (WHOI, USA). HACON will conduct the first full-scale multidisciplinary study of deep (4000 m) hydrothermal vents under permanent ice cover in the Arctic (82°N). HACON will unravel the processes that shape the Aurora communities and test the hypothesis that the Gakkel Ridge provides a connecting pathway for gene flow between the Pacific and Atlantic oceans. The project will provide empirical robust data of a pristine system prior to expected climate-change variations and increased human activities in the Arctic region. HACON integrates research in geology, geochemistry, physical oceanography, microbiology, micropaleontology, ecology, molecular biology and modelling to answer 3 questions addressed in 4 integrated work packages: 1) What are the geologic controls on the vent-site?s setting and how do chemical signatures evolve in the water column (WP1)? 2) What microbial and faunal communities are supported by such geochemical settings (WP2) and how do they function (WP3)? 3) What are the pathways and barriers to population connectivity between the deep Pacific, Arctic and Atlantic oceans (WP4)? The scientific excellence in HACON is ensured through the participation of first-class national and international partners.