Polar desert chronologies through quantitative measurements of salt accumulation

We measured salt concentration and speciation in the top horizons of moraine sediments from the Transantarctic Mountains (Antarctica) and compared the salt data to cosmogenicnuclide exposure ages on the same moraine. Because the salts are primarily of atmospheric origin, and their delivery to the sediment is constant over relevant time scales, a linear rate of accumulation is expected. When salts are measured in a consistent grain-size fraction and at a consistent position within the soil column, a linear correlation between salt concentration and exposure age is evident. This correlation is strongest for boron-containing salts (R-2 = 0.99), but is also strong (R-2 > 0.9) for most other water-extracted salt species. The relative mobility of salts in the soil column does not correspond to species solubility (borate is highly soluble). Instead, the highly consistent behavior of boron within the soil column is best explained by the extremely low vapor pressure of boric acid at cold temperatures. The environment is sufficiently dry that mobility of salt species within the soil column is controlled by vapor phase effects. In other cold desert settings, topsoil salts, specifically boron, may be employed as a proxy for relative sediment exposure age.