Arkashin (A) to Zavarzin (Z) Geochemical and Microbiological Characterization of Core Samples Collected at Two Thermal Pools in Uzon Caldera, Kronotsky Zapovednik, Kamchatka
Abstract
Sulfate-reduction by thermophilic prokaryotes may contribute to sulfide mineralization in volcanically-derived hydrothermal fields such as those found in the Uzon Caldera, Kamchatka, Far East Russia. In August 2005, core samples were taken from two chemically distinct thermal pools in Uzon; Arkashin Shurf which is ~1 m2, orange and enriched in arsenic (As), and Zavarzin II Spring which is ~10 m2, yellow and enriched in sulfur (S). Cores at both pools had distinct strata delineated by changes in color and texture. Subsamples of these strata were analyzed to examine changes in sediment and pore water chemistry, mineralogy, in situ sulfate-reduction rates (SRR), and prokaryote community structure with depth. We hypothesized that there would be a shift from oxidized to reduced species in the pore water samples with increasing depth. Although the concentrations of some oxidized aqueous species, such as arsenate, increased with depth, this trend was associated with changes in total arsenic concentration and may reflect of heterogeneous plumbing among thermal fields in the caldera. Mineralized elements precipitating with sulfide produced from sulfate reduction should exhibit decreasing pore water and rising sediment concentrations associated with increased SRR, in zones of mineralization. A dramatic increase in aqueous arsenic concentration with increasing depth in the upper strata in Arkashin dropped precipitously in the next stratum and had an associated increase in both SRR and sediment arsenic concentration. The As-S mineral realgar was identified in Arkashin samples by Raman spectroscopy. Only elemental sulfur was identified in Zavarzin samples from Raman spectra. The absolute value of SRR was higher in Arkashin, 2.0 nmol-cm-3hr^{- 1}, than in Zavarzin, 0.3 nmol-cm-3hr-1. Overall, SRR were much lower than anticipated. In Zavarzin, sulfate-reduction occurred at multiple depths. Sulfate-reduction in Arkashin may be restricted to a specific depth due to the presence of alternative terminal electron acceptors, such as arsenate. Changes in prokaryote community structure with depth were expected to reflect changes in abundance among different ribotypes under changing geochemical conditions. TRFLP analysis of environmental DNA extracted from different strata within the Zavarzin core revealed differences among Bacterial communities. The highest fragment richness occurred in the middle depths. These results suggest dynamic changes in geochemistry and microbiology with depth in both pools, even though their elemental compositions were different.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.B13C1100B
- Keywords:
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- 0419 Biomineralization;
- 0456 Life in extreme environments;
- 0465 Microbiology: ecology;
- physiology and genomics (4840);
- 0471 Oxidation/reduction reactions (4851);
- 0488 Sulfur cycling