Student: Dominique Tobler
Supervisors:
Liane G. Benning (Earth Sciences, Leeds)
Jerry Knapp (Microbiology, Leeds)
Project start: 2004
Photo: A waste water pool from Svartsengi Power Station (Iceland), one of 5 sampling locations where Dominique followed in-situ silica precipitation experiments (see grey tray with glass slides).
Silica deposition (formation of silica sinters) occurs in active geothermal systems around the world, yet the chemical and biochemical controls for this process are not well understood. Recent studies have shown that a strong link between inorganic and biogenic silicification exists. However, the understanding of the overall process is largely dependent on knowledge of the mechanisms of the reactions that occur at a molecular level at the organic-inorganic interface between microorganisms and the reacting solutions. This project consists of a multidisciplinary study based around complementary field and experimental methodologies, with the main goal to quantify the silicification processes involving microbial activity and to determine the kinetic rates and mechanisms of silicification. The selected field areas (Iceland and Taupo Volcanic Zone, New Zealand) are well-characterized geologic features where silica deposition is actively occurring.
Solid, fluid and bacterial samples collected from various geothermal areas in Iceland and New Zealand will be characterized using geochemical, microbiological, spectroscopic and genetic methods. The use of synchrotron-based spectroscopic methods combined with dynamic light scattering measurements will help quantify nucleation rates of silica nanoparticle formation in inorganic and organic systems and help ascertain the changes in chemical and biochemical characteristics in the precipitates in the absence and presence of thermophillic microorganisms. Phylogenetoic analyses of the sinters from Iceland and New Zealand will improve our understanding of microbial diversity and functions in these geothermal environments and will be complemented by measurements of the distributions and isotopic compositions of bacterial and archaeal biomakers. The aim is to provide a first insight into prokaryotic community structure and fucntion.
Photo: SEM picture taken from a sampled glass slide showing a silicified microbe
These findings will help build a new model for biogenic silicification and serve as an indicator for understanding the formation of modern and ancient siliceous sinters. This is a multidisciplinary project, which allows the student to develop expertise in experimental (bio-) geochemistry, microbiological and genetic analyses, organic biomarker chemistry, and synchrotron-based spectroscopic and scattering techniques (Daresbury, and Diamond UK; ESRF, France).
Further reading:
(1) Benning, et al. (2003) Geochim Cosmochim Acta. 67
(2) Phoenix, et al. (2001) Geology 31
(3) Pancost, et al. (2000) Geology 28