After a voyage of 70,000 kilometres around the globe, the schooner Tara arrived in Brittany on Saturday. The scientists who took part in the two-year mission gathered thousands of samples of marine micro-organisms in a bid to better understand ocean plankton and the impact of pollution.
The survey was carried out from the 33-year-old Tara research schooner, which returned to her home port of Lorient on France's western coast at the weekend.
Nearly 25,000 samples were collected over the 70,000-kilometre route from Chile to Africa, via the Amazon and the Antarctic.
🔴 En direct de l’Armada pic.twitter.com/IsAZbHqTUm
— Fondation Tara Océan (@TaraOcean_) October 15, 2022
"All this data will be analysed. Within 18 months to two years we will start to have the first information from the mission," said Tara Océan Foundation director Romain Troublé.
At the base of the food chain, micro-organisms are the "invisible inhabitants of the sea", accounting for two-thirds of marine biomass, explains Troublé.
"They capture atmospheric CO2 and supply half of the oxygen we breathe."
Troublé said the mission sought to find out how it all works.
"How do all these marine viruses, bacteria, micro-algue manage to interact to produce oxygen? And how will that change tomorrow with climate change and pollution?"
Toxic algae
The Tara team paid particular attention to the impact on the oceans of the River Amazon, which has a water flow rate of 200 million litres per second.
They wanted to test a theory that deforestation and the spread of agriculture has increased nitrate fertiliser discharge, leading to an abundance of toxic algae along river banks and coasts, particularly in the Caribbean.
The 22-month odyssey also rounded South America.
Off the coast of Argentina, researcher Flora Vincent was interested in a bloom: a concentration of phytoplankton such that it gives the water a colour visible by satellite.
"Our aim was to understand how many cells, how many coccolitophores will be affected by viruses, how many will be eaten by predators, how many will die of natural causes ... a bloom is really a living organism," Vincent told RFI.
Plastic pollution
The expedition also sought to trace the sources of plastic pollution at river mouths, to understand the distribution and the types of material involved.
"In my lab we will extract a lot of DNA, we will try to see what life there is on these plastics... and at the same time we will chemically characterise each piece of plastic that has been collected," Jean-François Ghiglione, research director at the Observatoire Océanologique in Banyuls-sur-mer in the south of France told RFI.
The mission was Tara's 12th global journey and involved 42 research institutions around the world.
Next spring, Tara sets off to research chemical pollution off European coasts.
