Arctic Deep Life

Study extraterrestrial life in the Arctic. No, this is not the synopsis of the new version of the movie. The thing. These are particularly complex 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 an exploration of the Gakkel Ridge, which stretches between Greenland and western Russia. A ridge is a line of contact between two tectonic plates that are moving away from each other. Surprise: we got the characteristic hydrothermal pits – these are places on the seabed where underground magma interacts with seawater. “We didn’t think there could be hydrothermal pits there, because it’s the slowest ridge in the world,” said Chris German, a geophysicist at the Woods Hole Ocean Institute (WHOI) in Massachusetts. “Typically, magma is no longer hot when it goes into seawater.”

M. German was not done with astonishment. In Nature Communication, at the end of October, he describes how the Aurora hydrothermal pit, the one on the Gakkel Ridge in northern Greenland, was surrounded by 10 to 100 times more minerals than expected. “Hydrothermal pits on the slow ridge were thought to last only a few centuries. But Aurora has been around for a few thousand years, even 10,000 years. This means it has produced a lot of minerals like copper, which are found in the seabed around Aurora. And therefore underwater mining projects are more reliable than we thought. »

Another expedition to Aurora, by the Norwegian company REV Ocean in the summer of 2021, further demonstrated the extraordinary nature of this Arctic hydrothermal pit. “We have discovered a type of snail that has only been observed in Antarctica,” explains biologist Eva Ramirez-Llodra, from REV Ocean. “We wonder how they found themselves at the antipodes of the Earth. There are also species of animals and algae that are present further south, in hydrothermal vents in the Atlantic and Pacific. Because Aurora is isolated by many ranges of an underwater mountain, it is not clear how these species got there.REV Ocean was founded by a fisherman from Norway.

The a bc of hydrothermal springs

The first underwater hydrothermal vents were discovered in 1977, near the Galapagos. Unlike photosynthesis, which converts sunlight into energy, chemosynthesis living near these hydrothermal vents derives its energy from chemicals that escape from them, including sulfur. Hydrothermal vents owe their heat and their specific chemical composition to magma escaping from the joints of tectonic plates. In 2019, in the magazine Ecology and Evolution of Nature, researchers from the University College of London have shown that life on Earth could have emerged in these hydrothermal vents from the depths, then to the surface, with adaptations 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.

Europa and Enceladus

The satellites Europa of Jupiter and Enceladus of Saturn are covered by a layer of ice with a thickness of several tens of kilometers, in which oceans with a depth of 40 to 50 kilometers can have life based on chemosynthesis. “The study of Aurora allows us to understand what life would be like on Europa or Enceladus,” said German. Photosynthesis is impossible here. »

Since the Europa Clipper missions (planned for Europa in 2024) and the Enceladus Orbiter and Lander (toward Enceladus, proposed last spring by the American Academy of Sciences) will not be able to pierce this ice cap, it will be necessary determine the existence of extraterrestrial life others. “Gases cannot pass through the ice, but the ice itself moves and migrates over the surface,” explained Ms.^I Ramirez-Llodra. In addition, there are jets of ice on the surface of Europa and Enceladus that likely originate from fractures in the ice. NASA is therefore very interested in detecting evidence of chemosynthesis in ice. »

The drift of pack ice

The first pictures of the Aurora, in 2014, were barely taken. “We searched and searched for hydrothermal pits throughout the month-long campaign,” German said. But since we only have 20 minutes each time to explore a place, we can’t find it. On the last dive, we finally found it, and got less than a minute of photos. The problem with Aurora exploration is that the science vessel cannot hover, as it normally does when exploring at great depths in open water. “Using the motors to break the ice is too intense, we risk damaging the robot’s power cable under the sea,” Mr. German said. In open water, the motors can be gently used to maintain position. But to explore the Aurora, the ship shuts down its engines and drifts onto the ice. A second WHOI expedition, in 2019, is needed to perform Aurora measurements.

The semi-autonomous robot

The first two explorations of the Aurora pit, in 2014 and 2019, used a robot without autonomous propulsion, only towed by a 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 that give it an autonomy of about ten time. “This way, the only link needed on the ship is a communication cable to manipulate the robotic arm and the sampling equipment,” explains Michael Jakuba, the WHOI engineer who developed Nereid.

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

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 deviate to reach our goal because in a straight line the ice was too thick for the Norwegian icebreaker we were with,” German said.