Tara sets out to explore the unicellular beings of the ocean

The 36-meter schooner set sail from Lorient on Saturday for a scientific mission lasting nearly two years.

With its new gray sails to match its aluminum hull, the schooner Tara looked great on Saturday when she left the harbor of Lorient (Morbihan) to set sail for Punta Arenas, in southern Chile.

In times of Covid, nothing goes as planned. The teams were tested and placed in isolation during the ten days preceding the departure and the new mission could last nearly two years, instead of the eighteen months initially planned. A lengthened duration as a precaution because of the virus, which knows no borders and could delay the rotation of crews and the arrival of the 80 researchers who will take turns on board. Even the blessing of the boat did not take place, as usual, on the island of Groix: the local deacon was replaced by the priest Antoine Le Garo, from Lorient. A small change decided this time because of the weather and “The direction of the wind which could have delayed us” to leave the Bay of Biscay for the first stopover in Cape Verde, explains Romain Troublé, Managing Director of the Tara Océan Foundation.

Objective: to probe the microbiome, an invisible world that populates the ocean. A mission that “Is in line with previous missions since Tara Arctic in 2007”, notes Romain Troublé. It will be a question of better understanding “The role of viruses, bacteria and unicellular beings, vital for the planet”. The samples taken during 21 stopovers will involve 42 research laboratories around the world and nearly 200 scientists for data analysis.

Two-thirds of the ocean’s biomass

These microscopic populations, invisible to the naked eye, are considerable. “There are 10 to 100 billion viruses per liter of seawater. They are 10 times more numerous than bacteria, 100 times more than archaea and 1000 times more than protists (unicellular beings that are neither animals nor plants, Editor’s note), explains Copan de Vargas, ecologist, research director at CNRS and one of the 3 scientific co-directors of the mission. “These invisible populations represent two thirds of the biomass of the oceans”, adds Chris Bowler, professor at the École normale supérieure, research director at CNRS and also scientific co-director of the mission. When leaving, the two researchers saw each other for the first time “in real life” since the start of the second confinement despite almost daily digital conferences. Stuck in Italy, the third scientific co-director Daniele Ludicone was absent.

What roles for these microscopic beings?

The modern notion of “microbiome” was born with the 21st century, explains Chris Bowler. But these organisms remain very difficult to cultivate in laboratories. Even though many genes have been deciphered, it is still unclear what their precise roles are. The scientific community therefore has a great deal of work ahead of it to try to understand the interactions and the distribution of these microscopic species which notably play a role in “the carbon pump. of the ocean. These microorganisms help sequester atmospheric CO2 in the depths of the ocean. But this biological role is around 1% of the 25% that is captured each year by seas around the world, especially in cold waters. Most of the CO2 dilution would be linked to “Physical mechanisms”adds Chris Bowler, also a phytoplankton expert.

Thus was born the idea of ​​the mission which will focus, in particular, on what is happening at ocean interfaces, where seas mix, especially near the Weddel Sea, in Antarctica, where d Huge icebergs help bring less salty water and nutrients. The plume of the Amazon and that of the Congo River, in particular, will also be studied. These fluctuations will be examined, in conjunction with numerous data such as the role of temperature, chemical pollution (mercury, microplastics, etc.) and the pressure on these invisible beings. Samples and direct measurements from the Tara schooner will be supplemented by measurements made by Argo beacons that crisscross the ocean around the world and satellite observations.


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