NOAA/WDS Paleoclimatology - Mono Lake 150 Year Stable Isotope Data

The relationship between d18O and d13C in a closed-basin lake is a function of hydrological change, vapor exchange, lake productivity, and total CO2 (or carbonate alkalinity) concentration. Covariance of d18O and d13C usually occurs in lake sediments under the condition of hydrological closure for time periods of the order of 5000 yr or longer. On shorter time scales, however, certain subtleties in the use of the d13C-d18O covariance as a hydrology history indicator must be recognized. The covariant trend may not be found in hyper-alkaline lakes because of the insensitivity of d13C to lake volume changes. For less alkaline closed-basin lakes, covariance of d13C-d18O will result from relatively rapid increase or decrease of lake volume, with the rapid-decrease condition giving rise to heavy and narrow-ranged isotopic values for both d13C and d18O due to the coupled evaporation-productivity effect. When the lake volume remains stable (as is the case for an over-flowing open lake), poor d13C-d18O covariance will ensue, due to the effect of vapor exchange with the atmosphere. We have used the measured d13C-d18O covariance in carbonate sediments of Mono Lake, California, to deduce paleo-hydrological and lake-water alkalinity (and salinity) variations and found the results in consonance with Holocene lake-level history derived from the d18O and other information.