Research Task 6 Autonomous voltametric and potentiometric sensors: toward long-term monitoring of sulphur biogeochemical dynamics at redox-interfaces

PhD position. Supervisors: R. Vuillemin, UPMC and Dr Nadine Le Bris, Ifremer.  Host: UPMC

Hydrogen sulphide is an important driver of biogeochemical processes and biodiversity settlement in various seafloor environments (hot and cold seeps, anoxic zones, etc). In addition to colorimetric flow analysers^(1,2) or amperometric microsensors⁽³⁾ widely used for short-term measurements, low energy cost and rugged potentiometric sensors have proven to be useful to assess sulfide variability in marine environments over days to weeks.⁽⁴⁾ Although more consuming in energy, voltammetry is an alternative electrochemical technique potentially suitable for autonomous measurements that offers additional advantages over potentiometry, including the ability to provide essential information on the in situ chemistry of sulphide.⁽⁵⁾ To optimise and test the performance of these sensors over duration of several months, in conditions relevant to seafloor sulphidic environments, in situ trials will be performed for potentiometric (total H_²S and pH) and voltammetry (free sulfide, polysulfide, thiosulfate, dissolved iron sulfide) sensors. The potential advantages of cleaning and internal standardization will be further explored, on the basis of preliminary work.⁽⁶⁾ Sensors will be integrated and deployed on modular experimental platforms, deployed at various depths at a test-bed station off the Observatoire Océanologique de Banyuls.

⁽¹⁾ Le Bris, N., et al., 2000. Mar. Chem. 72, 1-15. ⁽²⁾ Le Bris N. et al., 2006. Mar. Chem. (98) 167-182. ⁽³⁾ De Beer et al., 2006. L&O. 51(3). ⁽⁴⁾ Le Bris, N et al., 2008, Geophys. Res. Abstr., 10, EGU2008-A-11476. ⁽⁵⁾ Luther, G.W. et al., 2001. Nature 410, 813-816. ⁽⁶⁾ M. Lacombe, et al., 2007. Geophys. Res. Abstr., 10, Vienna, Austria.