Calcite crystal growth orientation: implications for trace metal uptake into coccoliths

摘要

Inorganic calcite precipitation experiments were conducted to determine whether inducing specific orientations of calcite crystal growth can cause the enrichment of cations larger than Ca. Malonic acid (CH_2(COOH)_2), a di-carboxylic acid, was used to poison growth on acute kink sites, promoting growth on ohtuse kink sites, causing calcite crystals elongated along their c-axes to form in a mechanism similar to that seen in the growth of E. huxleyi coccoliths. Calcite was precipitated with a range of malonic acid concentrations (0 to 10~(-1) M), and 9 X 10~(-5) M of either SrCl_2 or MgCl_2. The results show that calcite crystals precipitated in the presence of large malonic acid concentrations show significant elongation along the c axis, and suggest that increasing malonate concentrations corresponded with increasing D_(Sr). Experiments with 10~(-1) M malonic acid caused elevated D_(Sr) comparable to that predicted for E. huxleyi coccolith calcite (Langer et al., 2006).