Houghton

Applications of diversity indices, geochemical models, and infrared imaging: two very different approaches to integration

J.L. Houghton¹* & L. D. Urbano²

Corresponding author: houghtonj@rhodes.edu
¹Rhodes College, Dept. of Biology, Memphis, TN, 38112
²University of Memphis, Dept. of Earth Sciences, Memphis, TN, 38152

Abstract:
Two lines of my current research interests can be applied to hydrothermal systems and are relevant to integration and synthesis of studies at mid-ocean ridges. The first is the application of statistical analyses to both microbial survey studies and geochemical models of subsurface hydrothermal environments. A test of these methods has been completed on two case studies of previously reported field work at 9˚N East Pacific Rise and will be submitted for review shortly. The results of the initial study show that diversity indicators such as the Shannon and Simpson’s indices can be used to broadly characterize differences even within zonation of a chimney wall. Such numerical descriptors of diversity can then be used in correlation statistics with geochemical model output to search for links between the microbial ecology and the environment.

The second line of research is a unique experimental technique in which we use a miniaturized Hele-Shaw cell design that is non-invasively monitored with infrared imaging to determine real-time fluid dynamics in porous media (subsurface) of the mixing between 2 fluids: in this case, hydrothermal fluid and seawater. Refinement of the experimental apparatus and technique is underway and we wish to present the initial test results to a wider audience to explore possibilities of collaboration on multi-discipline studies. Our intent with this apparatus is to be able to discern changes in patterns of fluid flow in pore spaces due to both abiotic and microbial precipitation of minerals and/or flocculent biomass itself. With a spot size of 10μm, our IR system should be capable of detecting clustered biomass (flocs).

Keywords:
Biogeochemical modeling, Hele-Shaw experiments, infrared imaging, statistical analysis

Contributions to Integration and Synthesis:
The statistical method described would be ideal for comparing large datasets of microbial surveys based on 16S rRNA analyses as well as on comparisons between geochemically distinct hydrothermal systems such as those chosen as ISS sites by RIDGE2000. This technique depends on the gathering of temporally and spatially correlated data (i.e., collection of mineralogical and/or chemical data concurrent with microbial subsampling). The goal is integration of multidisciplinary datasets from many places and across time to be able to identify patterns to pinpoint questions needing further field study.

The experimental method is ideal for conducting integrated studies on very small (mm) scales of fluid dynamics, geochemistry, and microbiology. Some possible outcomes of collaborative research: experimentally determine advection rates within chimney structures; determine subsurface biomass; examine ecological relationships between synergistic microbial species; quantify biogeochemical reactions and/or rates (both mineralogical and aqueous); examine feedbacks between mineral precipitation, biomass accumulation and geochemical mixing (advective and diffusive).