Beneath the icy surface of the Arctic lies a fragile and unique ecosystem that remains largely unexplored. The Ocean Census Arctic Deep Expedition, led by The Nippon Foundation-Nekton Ocean Census Alliance, UiT (The Arctic University of Norway), and REV Ocean, aims to change that by venturing into the deepest parts of the Arctic Ocean to document life in this extreme environment. While many of us imagine Arctic exploration as a tale of ice-bound ships and daring adventurers, the true frontier for biological science lies thousands of metres below the surface.

As the ice sheets receded at the end of the last Ice Age, roughly 11,000 to 15,000 years ago, they revealed an Arctic seafloor frozen in time. This untouched landscape, now exposed, offers scientists a rare opportunity to study how life adapts to extreme environments over short geological timescales. The emerging ecosystems present a living laboratory for understanding the past and the future of our planet’s biosphere.

This mission comes at a critical time. The Arctic deep sea, long considered a key indicator of the impact of climate change on the ocean’s biosphere, is also becoming a focal point for deep-sea mining. As countries like Norway sign treaties to explore extractive resources, the urgency to understand and protect these fragile environments has never been greater.

Despite the vastness of the world’s ocean, only about 240,000 marine species have been documented – a mere 10 percent of what scientists believe actually exists. The Ocean Census, launched in 2023, seeks to address this significant gap in our knowledge. It represents a collaborative effort among leading marine research organisations to accelerate the discovery of marine species worldwide, with a particular focus on underexplored regions like the Arctic deep ocean. “The Arctic deep sea is especially poorly studied,” says Alex Rogers, Ocean Census Science Director and co-principal investigator of the expedition. “There are only about 1,100 described species from this region, making it a key area of focus for the mission.”

Jan-Gunnar Winther, Pro-rector for research and development at UiT The Arctic University of Norway and Specialist Director at the Norwegian Polar Institute, underscores the global significance of this research: “The poles today stand out as extremely important for understanding climate change. Everything is connected. And that’s why if you study the polar regions, you also study the planet.”

In May 2024, a team of 35 scientists from 15 academic institutions set sail from Tromsø, Norway, aboard the 100-metre Norwegian Icebreaker RV Kronprins Haakon, one of the most capable polar research vessels in operation. Their destination: the Fram Strait passage west of Svalbard, near 80 degrees north, at depths ranging from 2,000 to 3,700 metres.

Given the scale and complexity of the mission, the team had to be highly selective in their focus. They targeted an intricate network of geological features associated with the mid-ocean ridge network west of Svalbard. This submerged mountain chain, stretching for 60,000 kilometres across the seafloor, is Earth’s largest geological feature. The discovery of these geologically active areas, where the Earth’s crust is pulled apart to form new seafloor, was pivotal in confirming the theory of plate tectonics – a revelation as significant to geology as the discovery of DNA is to biology. These ridges are not just geological marvels; they are also biological hotspots.

Life near these mid-ocean ridges continues to astonish scientists. The discovery of hydrothermal vents in the late 1970s, led by geologist Jack Corliss aboard the RV Knorr, revolutionised our understanding of life on Earth. These vents, where superheated, mineral-rich water flows from the Earth’s crust into the ocean, create ecosystems that thrive without sunlight, relying instead on chemosynthesis.

The Arctic Deep Expedition focused its first week on the Jøtul Hydrothermal Field, an area of vent activity discovered in 2022 during the RV Maria S. Merian expedition, led by Gerhard Bohrmann from the University of Bremen. Named after the frost giants of Norse mythology, the Jøtul field vents are stark and barren compared to their Southern Ocean counterparts, yet it is home to resilient species like the armoured isopods and amphipods.

One of the most intriguing finds was the ‘hairy’ decapod shrimp, discovered at a depth of 3,000 metres in the Jøtul Vent Field. The ‘hairs’ on this shrimp are actually bacteria that convert the vent’s toxic hydrogen sulphide into energy, much like plants utilise sunlight. Whether this relationship is a true symbiosis remains a mystery.

Further exploration at The Knipovich Ridge site revealed a unique interaction between a stalked crinoid and an octocoral – an observation never before recorded. Often called ‘sea lilies,’ these ancient marine invertebrates date back hundreds of millions of years. Anchored to the seafloor by a stalk, their feathery arms capture plankton. The octocoral, likely a new species, had grown around the crinoid’s stalk, marking a unique epizootic relationship.

Finding a cold seep is no easy task. The seafloor may appear flat and featureless, but beneath it lies a dynamic world. High-resolution mapping and data from CTD sensors, combined with sonar, help create detailed maps that guide the ROV to these elusive sites. Satellites help map the seafloor by measuring variations in the sea surface caused by gravitational anomalies from underwater features using radar altimetry. These variations are processed to infer the topography of the ocean floor, revealing large-scale features like ridges and trenches. However, knowing the seafloor with the precision needed to lower an ROV requires much more data. Data collected and shared through platforms such as the General Bathymetric Chart of the Oceans (GEBCO) and initiatives like Seabed 2030 have accelerated the process greatly. But for most regions, significant amounts of acoustic mapping are required before each dive.

CTD (Conductivity, Temperature, Depth) sensors, lowered and ‘yo-yoed’ through the water column, measure seawater’s physical properties, refining sonar data accuracy by accounting for variations in water density that affect sound speed. These data, combined with multibeam sonar, create high-resolution topographic maps and a flickering view of the water column, where bubbling methane can be seen like an underwater smoke signal. A detailed three-dimensional landscape is painted as each layer of data is overlaid. Without these layers, finding a cold seep or vent would be like jumping out of an aeroplane mid-flight, hoping to land on your house using only the flight tracker for reference. Yet even with all these data, the picture remains somewhat subjective until the ROV beams back the first images.

In the deep ocean, red coloration provides effective camouflage due to the absence of red light. Red light is absorbed and scattered by water, making red objects appear black and blend into the darkness. This energetically favourable trait is common among deep-sea organisms that continue from the twilight zone through to the abyssal plains, where there is no light at all.

One of the most striking images captured was of a threadfin snailfish. Found at a depth of 2,461 metres at the Jøtul Vent Field, the snailfish is one of the most common large fish found at these depths. Look closely to see a parasitic larva of the crustacean family Gnathiidae embedded in its cheek, highlighting the complex and often harsh interspecies interactions within the deep-sea ecosystem, where such adaptations are crucial for survival in the nutrient-sparse environment.