F.M. Phillips, D.B. Rogers, S.J. Dreiss, N.O. Jannik, D. Elmore

Water Resources Research 31 (1995) 3195-3204

Inspired by recently published chloride balance chronologies of closed-basin lakes in the Great Basin, researchers of the early 1960's attempted to estimate residence times of chloride in these lakes using ³⁶Cl. Unfortunately, the analytical methods of the period were not capable of measuring the ³⁶Cl levels found in these waters. About 20 years after the early research, advances in accelerator mass spectrometry permitted ³⁶Cl measurement at the required sensitivity. In this study we follow up on those pioneering efforts by remeasuring and reevaluating the ³⁶Cl content at several of the previously studied sites, focusing on Mono Lake in eastern California. Our data show that in general the streams in the region have ³⁶Cl/Cl ratios similar to those expected in present-day atmospheric fallout, but that the terminal lakes into which the streams flow have much lower ratios. These lower ratios could result from either a very long (>1 million years) residence time of the chloride in the basin sinks or from subsurface influx of low ³⁶Cl chloride. In the case of Mono Lake, a mass balance model based on the ³⁶Cl data and on independent estimates of chloride fluxes and reservoirs indicates major subsurface chloride input, presumably from volcanic sources, and an accumulation time in the range of 100-450 kyr. The upper bound of this range is similar to the timing of a shift from long-term humid to arid climate in the region and may indicate that hydrological closure of the basin was triggered by this event.