Carbon isotopes of lipid biomarkers in modern travertine deposits: Implications for biogeochemical dynamics in hot-spring systems (Yellowstone National Park, USA)
Abstract
The goal of this study was to understand carbon cycling pathways in the context of changing depositional environments in modern travertine deposits. Microbial mats were collected for lipid and carbon isotope studies along a temperature gradient in four depositional facies at Angel Terrace, Mammoth Hot Springs, Yellowstone National Park. Bacterial phospholipid fatty acids (PLFA) appeared to be responsive to temperature variation. The vent facies (71°C) was dominated by unsaturated 20:1 (32%) and 18:1 (17%) fatty acids and saturated 18:0 (22%) fatty acid, which reflect bacterial adoption to high temperature. The down-gradient facies (the pond, 51°C; the proximal slope, 47°C; and the distal slope, 24°C) were dominated by saturated fatty acid 16:0 (30-55%), which exceeds that in the vent (10%). On the other hand, 20:1 was less than 1% in these relatively low-temperature environments. Total organic carbon (TOC) and PLFA in vent facies were significantly enriched in C-13 compared to those in the down-gradient facies. For example, the carbon isotope ratio in the vent was -13.7 per mil for TOC and -18.7 per mil for 16:0. In the pond and proximal slope, these values were about -27 and -36 per mil, respectively. The distal slope saw a slight increase in C-13 with TOC of -23.5 per mil and 16:0 of -28.9 per mil. The more positive C-13 values are consistent with isotope fractionation pathways performed by thermophilic sulfide-oxidizing Aquificales, which are primary producers in the vent. The more negative C-13 values in the pond, proximal slope and distal slope are typical of cyanobacteria and other autotrophic bacteria predominant in these low-temperature settings. These results may provide insight into biogeochemical dynamics in ancient travertine deposits with varying depositional facies.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.B11B0744Z
- Keywords:
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- 1030 Geochemical cycles (0330)