Reconstruction of limnology and microbialite formation conditions from carbonate clumped isotope paleothermometry: A test case from Pavilion and Kelly Lakes
Abstract
Quantitative tools for deciphering the environment of microbialite formation are relatively limited. For example, the carbonate-water geothermometer requires assumptions about the isotopic composition of the water of formation. We explored the utility of using 'clumped' isotope thermometry to study microbialites. We measured freshwater microbialites from Pavilion and Kelly Lake and determined the temperature of precipitation and the 18O/16O ratio of the waters they grew in. Microbialites are from 10-55 m water depth in Pavilion Lake, and 10-25 m in Kelly, spanning the thermocline in both lakes. At present there is a close association between photosynthetic communities and carbonate precipitation/microbialite formation and thus modern microbialites should record near surface temperatures. Their conditions represent an ideal test case to evaluate the application of clumped isotopes. Isotopic ratios were determined for each sample, and used to reconstruct limnology. Results were then compared to current limnological data from the lake in order to reconstruct the history of microbialite formation. Microbialites collected at shallow depths in Pavilion Lake and Kelly Lake yield clumped isotope-based temperature of formation that match the current measured temperature profiles. Air temperatures can be accurately inferred using published transfer functions relating shallow water temperatures to mean annual air temperature. Similar temperatures are also reconstructed for microbialites collected from deeper parts of both lakes. In contrast, the clumped isotope-based temperature estimates from the deeper microbialites do not match with present limnological characteristics, consistent with published radioisotope ages for the microbialites that suggest deeper microbialites are early Holocene in age. Given the deepest microbialites are receiving <1% of photosynthetically active radiation (PAR), it is likely that the deepest microbialites primarily formed earlier in the Holocene when pollen data and our reconstructed water 18O/16O ratios indicate a period of aridity, with lower lake levels resulting in these microbialites being located higher in the photic zone. Our results suggest that clumped isotope thermometry can be used to provide information on the environmental conditions during the time of microbialite formation, which is important to the fields astro and exobiology. Additionally, microbialites can be used to reconstruct past hydrology and climate.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMPP21D..04P
- Keywords:
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- 4914 PALEOCEANOGRAPHY Continental climate records;
- 0473 BIOGEOSCIENCES Paleoclimatology and paleoceanography;
- 0458 BIOGEOSCIENCES Limnology