On board of Tara, a floating laboratory
In August 2021, the Tara schooner of the Tara Ocean Foundation began its one-year study of the Atlantic as part of the Mission Microbiomes. After a one-month technical stopover in Martinique, the schooner set sail for Brazil towards the first sampling stations.
To sample, the scientists on board use many tools, including the rosette to sample water down to 3000m deep, as well as the bongo and manta nets for surface water sampling. Once the samples are collected, they are transferred to three different labs: the wet lab on the deck, the sorting lab and the dry lab which are both located inside the boat.
The first scientific focus of this expedition was the study of the Amazon plume, the Amazon river and the open ocean waters between Martinique and Salvador de Bahia in Brazil. The group brought together researchers from Brazil, France, Spain, Canada, Argentine and the USA.
Studying the impacts of the Amazon on the global ocean and the world
The scientists on board of Tara studied three main topics:
First, they focused on one of the eddies, up to 300 km wide, that connects the Amazon plume to the Caribbean. As the water of the Amazon is warmer and less salty, it remains at the surface and therefore creates a very dynamic surface plume which affect the salinity and temperature of the tropical Atlantic. Scientists have been trying to understand how these eddies transport nutrient-rich water from the Amazon to the Caribbean islands, where the water is very clear and low in nutrients.
Secondly, they sampled open ocean water coming from the Amazon which travels over immense distances, all the way to the West coast of Africa and the Caribbeans. This is due to the North Brazilian current's retroflection, which happens at the mouth of the Amazon river. They dod so to understand how this process influences local ecosystems, including the effect on the sargassum that proliferates all around the tropical regions of the Atlantic basin.
Finally, the scientists sampled in the heart of the Amazon. This river, which runs through 40% of South America, carries a lot of plastics and chemicals. The scientific team looked for the presence of micro-and nano-plastics. Samples were taken upstream and downstream of cities to understand their contribution to plastic pollution.
Report from Paula Huber (UFSCar), chief scientist on board of Tara from Macapá to Salvador de Bahia
“The Amazon River is the world’s largest river and discharges a tremendous amount of freshwater into the Atlantic Ocean generating an extensive surface plume. This impacts not only all the communities inhabiting it, but also in the global biogeochemical cycles.
For two months and a half (August to October 2021) we navigated the Amazon River waters and its plume with the main aim to increase our knowledge on how the river affects the Atlantic Microbiome. On board Tara, we moved from the blue ocean, through emerald-green waters of the plume, to the immense brown-waters of the Amazon River.
If I had to describe this part of the expedition in a few words , I would say: extremely dynamic and innovative sampling campaign.
Each sampling station was particular in its challenges, difficulties, and wonderfulness. And we had to adapt to this dynamic, being part of the system, in order to better understand.
We explored the Amazon river plume taking a huge amount of samples, which will allow us to study the surface and deep microbiome combining cutting-edge molecular and microscopy techniques. Besides, we will quantify the plastics in this region and the microbes associated, the plastisphere.”