Microbialites of Great Salt Lake

March 20  “Microbialites of Great Salt Lake, Utah – tape recorders of lake hydrology and chemistry since the Pleistocene”, Presented by Dennis Newell, Utah State University.

Microbialites (also known as stromatolites) are calcium carbonate structures built by a consortium of microbial life, including photosynthetic “blue-green algae”, and represent some of the earliest life on Earth. Today these features are restricted to salty environments such as constricted marine environments (e.g., Shark Bay, Australia), and closed-basin saline lakes. In lakes, since these deposits grow in near-shore waters, the microbialite carbonate cements can incorporate and trap information about the past water chemistry, biochemistry, and hydrology. One of the Earth’s largest occurrence of lacustrine microbialite deposits exist along the shores of Great Salt Lake (GSL), Utah, and potentially preserve a rich continental paleoenvironmental record.

We report microbialite radiocarbon ages, and carbon and oxygen stable isotope ratios from carbonate cements. Surprisingly these deposits are not “modern”, and inform paleolake hydrological and biogeochemical changes from the latest Pleistocene through the Holocene (approximately 18,000 to 3600 calendar years before present). Positive correlations between carbonate oxygen and carbon stable isotope ratios in some microbialites are consistent with a holomictic (mixes at least once per year), hydrologically closed-basin lake with fluctuations in volume, chemistry, and associated changes in lake primary production. However, inverse isotopic correlations present in a number of microbialites are enigmatic, but may imply more arid periods with higher salinity and stable lake stratification (meromixis) similar to modern GSL conditions.

The GSL microbialite deposits capture the climatic transition from the end of the last ice age into the warmer and drier Holocene, which resulted in the drastic lake lowering from Pleistocene Lake Bonneville to the Great Salt Lakes stage. The record of how Holocene climate fluctuation impacted GSL volume and chemistry are sparse, and the microbialite isotopic record holds significant potential for capturing salinity and volume changes. Furthermore, these data will help inform how GSL may respond due to ongoing climate change in the intermountain west.