Dive to a depth of nearly 4,000 meters aboard a scientific submarine to discover and feel a dark world revealing crazy biodiversity.
Long considered desert, cold and dark, the deep seabed, more than 500 meters deep, where sunlight no longer penetrates, can turn out to be true oases of life, close to emissions of fluids resembling geysers, which emerge from the bowels of the oceanic crust, then forming large chimneys: hydrothermal sources.
These hydrothermal sources, which are found for example along the mid-oceanic ridges which crack the oceanic crust at depth, were only observed for the first time in 1977, by geologists determined to do battle with the tectonics of the plates. At great depths, in the dark and therefore without light to ensure photosynthesis at the basis of life on Earth, geologists were very surprised to observe giant worms, shrimps or crabs. Indeed in these environments, life is possible not thanks to photosynthesis based on light energy, but thanks to microbial chemosynthesis, which uses the chemical energy available in the fluids emitted by hydrothermal sources (sulfide, hydrogen, iron, methane, etc.) in order to build the building blocks of life: sugars, proteins, lipids. Life has therefore adapted. Where does it come from? The question remains wide open!
2500 shrimps per square meter
It is in the middle of the Atlantic that a small 5 cm shrimp named Ricciaris ecolutawas discovered in 1986 in the middle of the Atlantic.
It lives in very dense and mobile aggregates along the walls of smokers, there are up to 2,500 per square meter! This shrimp quickly caught the eye of biologists with its large enlarged head, a bit like hamster jowls after a good meal. Let’s not talk about her behavior: she seems to eat stones! A few photographs of its shell later, we discovered a dense carpet of bacteria colonizing it.
This is how we met in 2001, during a discussion with a researcher who was ending his career and me, a microbiologist, passionate about geology and volcanoes, who was just starting out. How could this shrimp, with such densities, live and develop in such extreme, toxic environments (sulfides, methane, hydrogen, heavy metals, etc.), and what did it eat? That was all it took to pique my curiosity: I had to go and take a closer look at her way of life… But for that I have to go there: 3600 meters deep under the sea to meet her.
The nautilus, a scientific submarine
This is how I began to train myself to use a submarine, as valuable as it is rare. There are not even ten in the world, The Nautile, which can take us to the deep seabed up to 6000 m deep.
Provided by the author
A few medical aptitude tests and a hyperbaric chamber test later, I embarked on a scientific campaign and dived for the first time in 1999. Since then I have had the extreme privilege of diving 17 times, on a test mission. with the technologists who develop the machine, or on a scientific mission. Intrigued and with a desire to understand, I then did the exercise of becoming a scientific co-pilot!
A campaign at sea is a human adventure, of a modern explorer, and the desire to know more and understand how life develops, adapts, colonizes the deep seabed, far from the gaze of humans , hidden by thousands of meters of salt water. This is where I work halfway between the Canaries and the Antilles, for 45 days. The BICOSE3 campaign at the end of 2023 took us on site for 46 days with the ship called the “Why not? » and the Nautile for 27 dives, one per day.
Careful preparation
And there’s no question of forgetting anything before leaving… we stay at sea on board the ship in the middle of the Atlantic above the sites, so the preparation is long and meticulous.
Each crate, container and tool is prepared with all the laboratory equipment for working on board. The scientific team is made up of 31 people, including a filmmaker, 9 submarine operators and the ship’s 35 sailors. The three teams work together to bring maximum results, the mission leader must organize the diving days and the nights of operations such as dredging or coring.
Each dive is unique, prepared several days in advance. Pilots and scientists exchanging requests and possibilities. “No” followed by “maybe”, negotiations went well and then the dive plan was established between the pilot and the head of mission.
The day before the dive, the scientist then revises his dive plan, everything is timed. We have 6 hours on the ground, we must not waste time wondering what we should do, we must be active and indicate to the pilot the work, the measurements, the samples.
Tomorrow I dive to a depth of 3600 m to see my shrimp!
The evening arrives, light meal, early bed. The upcoming dive revolves in the head, the maps, the actions, the experiences to be done for the whole team, each dive is resolutely multidisciplinary.
Up at 6:30 a.m., very light meal, then the checklist begins. Everything is checked every morning, the operators test everything on the submarine, power, propulsion, computers, lights, arms, cameras, radio… 6 hours of work on the bottom, around 3 hours of descent and ascent, i.e. 9 hours in the machine.
8:30 a.m. we are ready, we change into a fireproof suit and here we are in front of the entrance to the sphere on the mezzanine. The co-pilot comes down and I go in, then the pilot gets into position, sitting on top of the submarine. The submarine moves backwards on the deck, we can hear the chains which allow it to move backwards with the rack.
I settle down, lying with my nose to the porthole on the right of the submarine. I install the chemistry analyzer control PC, the cards, notebook and pencil attached with its string, I prepare my fleece, socks and hat because the sphere will quickly cool down during the descent. We are about to launch, the pilot enters and closes the hatch of the sphere and sits on the left side of the submarine, lying down, the co-pilot is seated behind us.
“Portico to the sea” and here we are tilted above the ocean, then we go down and touch the water. The rear deck of the ship is before my eyes, the water is clear and the fish pass by, then we move away little by little.
The divers do the last checks, everything is OK we can take the dive. Let’s go for about 1h30 of descent, we sit down and quickly go over the dive and the actions to be done, contact with the surface every 30 minutes.
The bright blue exterior darkens little by little, 200m, it becomes gray, 300m, then black very quickly before 500m. Silence prevails, calm, the descent continues, 800m, 1000m, 1500m… We eat a meal prepared by the kitchen this morning. Then the bottom detection pings are heard on the depth sounder, we get into position: hat on, head resting on the edge of the cold porthole, fleece and socks.
And it’s gone for 6 hours on the bottom. The lights are on, and we are watching in front of us. The co-pilot ensures navigation and we head towards the chimney to study and its shrimps. Small white spots catch the eye, these are galathaea (crustaceans which have large claws in front and the abdomen folded under the belly) and anemones, proof that we are not far from the site. Then we begin to see the relief, the chimneys are in front of us with their swirling black plume reminiscent of a fiery cloud.
Bacteria that feed shrimp
And there thousands of shrimp swim between the cold but oxygenated sea water allowing them to breathe, and the fluids enriched with minerals and other chemical compounds allowing nutrient chemosynthesis to work. In fact, this shrimp harbors thousands of bacteria of several species in the shell of its head which feed it directly through its head! She still has a digestive system which seems functional but whose role we do not yet fully understand.
It is a wonder to see the behavior of these animals, perfectly adapted to these extreme living conditions. The deep seas are very colorful, red, black, gray, white, yellow, orange, even glittery with sulphide particles. Animals abound, not only shrimps but also anemones, crabs, fish, sometimes mussels: a real oasis of life. We walk around the site to find an area to work, you have to sit down and be stable for 15 minutes for the chemistry measurements. We land, a clever mix of propulsion and support on the chimney. We begin with chemical measurements, finely measured to the nearest centimeter around the shrimp aggregates, in order to characterize the living conditions.
Suddenly the submarine moves, lifted by a swirl of plume. We move and find another quieter area. New chemistry measurement. We take water from the pockets. We open the basket to grab a box called PBT (small insulated boxes), I ask for samples of rocks that the submarine manipulates thanks to the dexterity of the pilot.
The box is put away, the basket closed. We are making video with the co-pilot, 4K today, to share our discoveries! Then you have to grab the wildlife vacuum cleaner to take different samples of shrimp, the adults with large heads, mostly white, the almost fluorescent red juveniles, in order to better understand their adaptation capacities and the functioning of their symbioses with bacteria.
A myriad of shrimp pass in front of my window, it’s literally swarming. We move forward slowly, we step back, we bend a little to grab a last sample.
Time passes quickly, we go to the second site to collect fluids at high temperature. The site is in front of us, we must position ourselves gently. Temperature probe output, 322°C, 351°C, 375°C, 388°C, fluid at base is clear. The probe is stored, you have to open the basket and take the titanium syringe, place it in position on the fluid outlet, while holding the Nautile in place, the pilot is very concentrated. I have to monitor the purge and request the sampling trigger as soon as it is clear. Everything happens in a few seconds, you must not move so as not to dilute the precious fluid with sea water.
The bottle is put back in the basket after 35 minutes of battle with the elements, then we go down to the base of the chimney to make video and take chemistry measurements on the habitats. The 6 hours pass, the surface manager tells us that we must begin the ascent… Too short, we would like to stay, so many wonderful things before our eyes. We are humbled by this majestic nature, these ecosystems which seem far from us and yet so close that we would like to reach out our hand to touch them. This extraordinary capacity of life to colonize all biotopes, even the most improbable seen with a human eye!
Here we are on the surface, tossed by the swell, the divers are around us and reattach us. We are hoisted out of the water, then tipped onto the deck, placed on the cart. That’s it for this dive. The scientists run in front of the submarine to recover the precious samples and quickly leave for the laboratories. We can then leave the sphere, and there is a debrief with colleagues. What a day!
This article was published on the occasion of the 40th anniversary of Ifremer where you will be able to attend a film debate around the film “Abysses, the conquest of the seabed” on October 24 in La Seyne-sur-Mer.
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