The Vitória-Trinidade chain: a unique area in the Atlantic ocean
The second part if the scientific adventure of Tara in Brazil was all about bio discovery. After studying the Amazon's impact on the Atlantic ocean, the scientific crew on board of Tara sampled a very special area between Salvador de Bahia and Rio de Janeiro. The main region studied during this leg was the underwater seamounts chain called Vitória-Trinidade and which is composed of 11 different seamounts.
These seamounts are particularly interesting to study because they are a shelter to a large biodiversity. Located in an area of the Atlantic that is the poorest in nutrients, these seamounts ate therefore an exceptional place bevies they enrich the water column with nutrients and allow a rich ecosystem to develop. Scientists will therefore seek to understand the impact of seamounts on the water column and biodiversity. Far from the coast this area is particularly protected from human activities. it is home to many species that don't exist anywhere else. In order to study this biodiversity in depth, the schooner Tara drifted for more than 12 days around the moutains.
To be as exhaustive as possible in their study, the scientific team set up a night station, from 7pm to 5am. The researchers sampled at 7 different depths to observe the nycthemeral migrations of the plankton, this refers to the way zooplankton moves up and down the water column on a daily basis. Every night they will rise up towards the surface to feed on smaller phytoplankton. This great migration stirs the water column up and creates an exchange of matter between the different layers of the water column.
Understanding the impact of seamounts on biodiversity
This was the first Biodiscovery leg of the mission, which is part of one of AtlantECO's case studies on Molecular bioprospecting. The three main objectives of the leg were to
augment plankton biodiversity discovery through replicated sampling and a higher vertical resolution, this means sampling more frequently, covering more depths in the water column.
enable the potential discovery of new bio products and chemicals for possible industrial applications with high socio-economic value. For examples, those enabling new ways of producing pharmaceutical products or natural enzymes which could be able to digest complex molecules such as plastics and other pollutants.
measure the impact of climate change on the Atlantic and notably on deep sea corals of the Vitória-Trinidade seamounts chain.
Report from Samuel Chaffron (CNRS, University of Nantes), chief scientist onboard Tara from Salvador de Bahia to Rio De Janeiro
“ Overall, this leg went very well and the whole team was very happy and satisfied by the work accomplished. The collected samples will allow to address both main objectives of this leg. First, replicated samples done at the surface will be particularly useful to augment the biodiversity discovery at these South Atlantic oligotrophic stations. Second, the fine-scale characterization of the observed deep chlorophyll maximum (DCM), the region below the surface with the maximum concentration of chlorophyll, in stratified waters at both long stations, which included 7 depths, as well as overnight samplings, will allow us to study the nutrient/light dynamics as well as the vertical biodiversity and ecology of a DCM.
The best memory I have from this leg : after sampling station 52 above Davis seamount, we had the opportunity to swim in the afternoon, while chasing seamounts reaching about 20m under sea level. After some time, some of us actually observed the top of one seamount “needle” reaching about 28m below the surface, surrounded by fishes at the bottom and at the surface, incredible vision at more than 600 km off the coast !”
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