Arctic Deep Life

Study extraterrestrial life in the Arctic. No, this is not the synopsis of a new version of the film. The Thing. These are particularly complicated missions to a hydrothermal source located under five meters of ice and four kilometers deep, in the Arctic, north of Greenland.

Surprises

In 2001, there was exploration of the Gakkel Ridge, which stretches between Greenland and western Russia. A ridge is a line of contact between two tectonic plates moving away from each other. Surprise: we captured the characteristic signature of hydrothermal pits – these are areas of the seabed where underground magma comes into contact with seawater. “We did not think that there could be hydrothermal pits there, because it’s the slowest ridge in the world,” says Chris German, a geophysicist at the Woods Hole Ocean Institute (WHOI) in Massachusetts. “Normally, magma is no longer hot when it comes into contact with seawater.”

M. German had not finished being amazed. In Nature Communications, at the end of October, he describes how the Aurora hydrothermal pit, the one on the Gakkel Ridge in northern Greenland, is surrounded by 10 to 100 times more minerals than expected. “Hydrothermal pits on slow ridges were thought to last only a few centuries. But Aurora has been around for several thousand years, even 10,000 years. This means that it has produced an abundance of minerals like copper, which are found on the seabed around Aurora. And therefore that underwater mine projects are much more promising than we thought. »

Another expedition to Aurora, by the Norwegian company REV Ocean in the summer of 2021, further demonstrated the exceptional character of this Arctic hydrothermal pit. “We discovered a species of snail that had only been observed in Antarctica,” explains biologist Eva Ramirez-Llodra, from REV Ocean. “We wonder how they could have found themselves at the antipodes of the Earth. There are also species of animals and algae present much further south, in hydrothermal pits in the Atlantic and Pacific. As Aurora is isolated by numerous undersea mountain ranges, it is unclear how these species got there. REV Ocean was founded by a fishing magnate from Norway.

The a bc of hydrothermal springs

The first underwater hydrothermal vents were detected in 1977, near the Galapagos. Unlike photosynthesis, which converts sunlight into energy, the life-sustaining chemosynthesis near these hydrothermal vents draws its energy from the chemicals that escape from them, including sulfur. Hydrothermal vents owe their heat and their particular chemical composition to the magma escaping from the joints of tectonic plates. In 2019, in the magazine Nature Ecology & Evolution, researchers from the University College of London have shown that life on Earth could have appeared in these hydrothermal vents from the depths, then on the surface, with an adaptation to photosynthesis. Aurora is the only arctic hydrothermal pit. Previously, the northernmost hydrothermal pit was Loki’s Castle, discovered in 2008 in the far north of the Atlantic, between Greenland and Norway.

Europe and Enceladus

The Europa satellites of Jupiter and Enceladus of Saturn are covered in a layer of ice several tens of kilometers thick, under which oceans 40 to 50 kilometers deep could harbor life based on chemosynthesis. “Studying Aurora allows us to understand what life would be like on Europa or Enceladus,” says German. Photosynthesis is impossible here. »

As the Europa Clipper missions (planned for Europe in 2024) and Enceladus Orbiter and Lander (towards Enceladus, proposed last spring by the American Academy of Sciences) will not be able to pierce this ice cap, it will be necessary to detect the presence of extraterrestrial life other. “Gases cannot pass through the ice, but the ice itself moves and migrates to the surface,” explains Ms.^me Ramirez-Llodra. In addition, there are jets of ice on the surface of Europa and Enceladus which probably originate from fractures in the ice. NASA is therefore very interested in detecting evidence of chemosynthesis in ice. »

The drift of the pack ice

The first images of Aurora, in 2014, were almost never filmed. “We searched and searched for the hydrothermal pit throughout the month-long campaign,” says German. But since we only had 20 minutes each time to explore an area, we couldn’t find it. On the last dive, we finally found it, and managed to take less than a minute of images. The problem with exploring Aurora is that the science vessel cannot hover, as it normally does when exploring at great depths in open water. “The use of motors to break the ice is too intense, we risk breaking the power cable of the underwater robot,” says Mr. German. In open water, the motors can be gently used to maintain position. But to explore Aurora, the ship shuts down its engines and drifts with the ice. A second WHOI expedition, in 2019, was needed to take measurements on Aurora.

The semi-autonomous robot

The first two explorations of the Aurora pit, in 2014 and 2019, used a robot without autonomous propulsion, simply pulled by the science vessel. Last summer, the REV Ocean expedition used a motorized robot, also called Aurora, which extended the observation time above the hydrothermal pit to 40 minutes.

The WHOI cruise scheduled for next summer will take a big step forward with the Nereid UI, a robot equipped not only with autonomous propulsion, but also with batteries giving it an autonomy of about ten hours. “In this way, the only link needed with the ship is a communication cable to manipulate the robotic arm and the sampling equipment,” explains Michael Jakuba, the WHOI engineer who developed the Nereid.

“As it’s a lighter cable, we can have 20 km. This will allow the Nereid to stay two to three hours above Aurora. If necessary, the Nereid can even cut its communication cable and return to the ship on its own. Mr. Jakuba believes that Nereid UI’s technology could progress to a communications cable tens of kilometers long, which could make it possible to break through the ice sheet of Europa or Enceladus and directly explore their oceans.

five meters of ice

The thickness of the ice in this part of the Arctic does not change much with the seasons, because the arctic circular current causes the pack ice to accumulate there. The ice is always at least one meter thick and can reach five meters. “In 2019, we had to take a detour to reach our goal because in a straight line the ice was too thick for the Norwegian icebreaker that was accompanying us,” says German.