Analysis of endolithic biosphere pore network in basaltic glass using three-dimensional computer tomographic imaging.

SRISAWANG, B., MURR, A., HATZL, T., BÖHM, C., GEHLKEN, P.-L., KLENGEL, H., REITNER, J., PECKMANN, J. & BÖTTCHER, M.E. (2006):
Analysis of endolithic biosphere pore network in basaltic glass using three-dimensional computer tomographic imaging.

Computer Tomography (CT) was applied to assess the pore space and pore network of basaltic glass. The pore network delimits nutrient availability, which probably controls the distribution of chasmo- and endolithic microorganisms (Ketcham and Carlson 2001; Edwards, Bach, et al. 2005). CT is a non-destructive three-dimentional visualization technique. The samples were digitally analyzed with a resolution of 0.5 mm with conventional CT. The CT images reflect the variation of x-ray attenuation within samples, which relates closely to density. The density transitions usually correspond to boundaries between materials or phases of the sample (Ketcham and Carlson 2001). Individual CT images are referred to as slices, as they correspond to what would be observed if an object were sliced open along the scan plane (Ketcham and Carlson 2001). By acquiring a neighboring set of slices in different rotations, data for complete volume can be obtained (Ketcham and Carlson 2001). This provides information on porosity, pore volume, and distribution of pore radii. Besides this, length and connectivity of the pores are analyzed and the pore space is visualized 3-dimensionally.
The collected basalt samples are from the Mid-Atlantic Ridge, obtained during expedition ARKTIS-VII/1 of RV “Polarstern” in 1990. The CT images reveal that there is plenty of space for a chasmolithic biosphere in basaltic glass. The maximum pore size is 60 mm3, but pores smaller than 1 mm3 contribute most to the porosity. Abundant pores and a surprisingly high permeability favor the proliferation of chasmolithic communities.