During April and May GEOFLAMME oceanographic campaign took place in the vicinity of Mayotte Island in the western Indian Ocean, where nearly 70 scientists from different institutes and laboratories board N/O Pourquoi pas? to study the interactions between volcanism, the water column and ecosystems on the largest submarine eruption ever observed, off the island of Mayotte. The multidisciplinary scientific research study of this major eruption was performed by carrying out in-situ observations and sampling (ROV, CTD, dredges and corers) and analyzes (petrology, chemistry, biochemistry) of rocks, pure fluids and the water column combined with high resolution maps, and reconstructions of volcanic, tectonic structures and fluid outlets (with ROV and AUV). ESR6 and the Ifremer LBCM Nantes mercury team participated in the campaign to investigate mercury dynamics associated to volcanic and pelagic processes. On-board analysis of Total Hg and Dissolved gaseous Hg, as well as suspended particles (McLane pump), water and fluids samplings (for MMHg analysis on land) were performed in order to acquire a baseline (dissolved / particulate) Hg data for the water column and for the acquisition of new knowledge on the volcano-mercury link from contents in pure fluids, diffusions, and the near and distal plume.


Fig1. ROV operation for the detection of fluid outlets and CO2 hydrates sites

Later this year during July, ESR6 and the Ifremer LBCM Nantes mercury team also participated in a sampling campaign for PoNutELA project at Étang du Prevost, a model lagoon where the sediment constitutes the main reservoir of nutrients and chemical pollutants brought by the watersheds. The main objective of this project is to study the impact of hypoxia on the fate of pollutants and nutrients in sediments in Mediterranean Lagoon ecosystems. For this campaign, an upgraded SUSANE sampling device was used to sample more accurately the gradient of dissolved Hg speciation and particulate data in the water column during the minimum and maximum oxygen concentrations in order to characterize the impact of variations in oxygen concentrations in the water column on transfers of chemical species at the water-sediment interface.

Fig 2. Ponutela sampling campaign at Étang du Prevost

By Isabel Garcia (ESR 6)