HR: 0800h
AN: B31D-0623    [Abstracts]
TI: Calcite Growth and Dissolution in Nonstoichiometric Solutions: A Site-Specific Role for Carbonate Control in Biomineralization
AU: * Arvidson, R S
EM: rsa4046@rice.edu
AF: Rice University, Department of Earth Science MS 126, PO Box 1892, Houston, TX 77251-1892,
AU: Davis, K J
EM: kjdavis@rice.edu
AF: Rice University, Department of Earth Science MS 126, PO Box 1892, Houston, TX 77251-1892,
AU: Davis, K J
EM: kjdavis@rice.edu
AF: San Jacinto College, North Campus 5800 Uvalde, Houston, TX 77049,
AU: Luttge, A
EM: aluttge@rice.edu
AF: Rice University, Department of Earth Science MS 126, PO Box 1892, Houston, TX 77251-1892,
AB: Biomineralization and crystal growth/dissolution studies typically express reaction kinetics as a function of the ion activity product (IAP) in saturation state expressions. However, there is increasing evidence that changes in the cation/anion solution ratio at constant IAP can influence mineral formation. This variation may thus be important in marine environments, where Ca²⁺/CO₃^2- activity ratio varies as a function of depth in the water column, as well as in biomineralizing systems, where organisms may manipulate Ca²⁺/CO₃^2- ratio at sites of mineralization as a vital effect. Lastly, the ratio in surface seawater may have varied in the geologic past, and may also likely change in response to anthropogenic forcing with rising atmospheric carbon dioxide levels. Here we investigate the role of Ca²⁺/CO₃^2- ratio, at constant saturation state, in determining calcite growth and dissolution using atomic force microscopy (AFM) and vertical scanning interferometry (VSI). These coupled techniques provide kinetic measurements across multiple length-scales. Our results indicate that changes in Ca²⁺/CO₃^2- ratio significantly affect the overall growth and dissolution rate as well as the distribution of growth and dissolution features on the calcite surface. Kinetic measurements of both calcite growth and dissolution suggest a more critical role for the CO₃^2- ion in governing calcite surface dynamics than previously thought. This finding broadens our understanding of the differential roles of specific species in calcite growth and dissolution, and also permits insight into the variable sensitivity of the surface with respect to trace components. Further, our results demonstrate that carbonate biomineralization cannot be understood in terms of bulk solution chemistry alone, but requires knowledge of both the structure of the biomineral surface and the specific interaction of solution species with surface sites on elementary steps. This study suggests that some of the complexity associated with understanding calcite precipitation and dissolution kinetics may reduce to site-specific interactions with carbonate ions.
DE: 0419 Biomineralization
DE: 0424 Biosignatures and proxies
DE: 1042 Mineral and crystal chemistry (3620)
DE: 1051 Sedimentary geochemistry
DE: 4854 Physical chemistry
SC: Biogeosciences [B]
MN: 2007 Fall Meeting