Olivier Rouxel


September 2003 - December 2005

Using Heavy Stable Isotopes as Biogeochemical Tracers of the Deep Biosphere
Over the past few years, I have been working on the analytical development and biogeochemical applications of heavy or non-traditional stable isotopic systems such as metals (Fe, Cu) and metalloids (Se, Sb, Ge) stable isotopes. The research projects I have undertaken concern the study of these heavy stable isotopes in marine sediments (Black shales, Mn-nodules, biogenic opal) as tracers of past oceanic changes. I've also studied the chemical cycling and isotopic fractionation of various metals and metalloids during the alteration of the oceanic crust and in seafloor hydrothermal systems.

Recent findings have extended the biosphere to include the microbial life hosted in deep subsurface regions of the Earth's crust, such as the continental crust, terrestrial basalts, deep-sea sediments, deep oil reservoirs and at seafloor hydrothermal vents at mid ocean ridges and in deep oceanic crust. However, the study of the extent and nature of the active biosphere in the oceanic crust requires a new approach to overcome technical difficulties to recover and culture indigenous microbes and to develop new petrographic and geochemical tools to identify biogenic materials.

It is well known that crustal rocks react with oxygenated deep-sea water to form secondary minerals, including Fe-oxyhydroxides and clays minerals and the products of weathering reactions often persist for millions of years. Can we determine the extent to which microbes were involved in the alteration process though geological times?

To answer this fundamental question, I've joined the Deep Ocean Exploration Institute at WHOI to explore new tracers of the deep biosphere in seafloor hydrothermal systems and altered basalts. Recently, the role of neutrophilic chemolithoautotrophic Fe-oxidizing bacteria in weathering seafloor crustal materials, including basaltic glass and sulfide minerals has been identified (K. Edwards, WHOI) and I proposed to investigate Fe isotope systematic to provide new insights into the effects and extent of these bacteria in the oceanic crust. The approach involves the combination of contrasting experimental studies of mineral alteration with cultured microbial populations and sterile control and field studies in various environments (seafloor hydrothermal systems, altered basalts and coastal estuary systems).

I collaborate with Katrina Edwards, Wolfgang Bach, Ed Sholkovitz, Bernhard Peucker-Ehrenbrink (WHOI) and others.