Stromatolites provide a terrestrial record of a ~35ka warming event in Walker Lake, a remnant of the Pleistocene Lake Lahontan (Western Nevada, USA)
Wednesday, 17 December 2014: 5:00 PM
Walker Lake is a closed-basin remnant of the large Pleistocene glacial Lake Lahontan that has experienced drastic changes in water level. Carbonate structures, such as stromatolites, precipitated from the lake and were studied as potential sources for historical climate change. A 16.7 cm long stromatolite was collected from a paleoshoreline approximately 58 meters above the present Walker Lake surface elevation. Radiocarbon dating revealed that the stromatolite spans approximately 2,000 years of growth, from 35,540 to 33,580 Calibrated YBP (IntCal13). Distinct laminae were drilled along the growth axis, and the resulting powders were collected for clumped isotope analyses, which uses the amount of heavy CO2 “clumps” (13C-18O-16O, or ∆47) generated from the dissolution of carbonate in acid to measure the temperature of formation of a rock. Using this method, we tracked the change in lake temperature and δ18Ofluid during stromatolite formation. Our results show that the stromatolite experienced an overall increase in temperature and δ18Ofluid values during the course of accretion. The resulting data were input to a Rayleigh distillation model for water evaporation in order to estimate the magnitude of lake level and volume fluctuations. Our modeling results show that, during the course of stromatolite accretion, the lake experienced a volume decrease of ~5 Km3, corresponding to lake level fall of ~14 meters. This study shows that lacustrine material (such as stromatolites or other tufas) can potentially be used to reconstruct the timing and magnitude of terrestrial climate change during important transitions in Earth history.