Stable Isotope Ratios and the Dynamics of Caliche in Desert Soils

Abstract

Studies of the isotopic ratios in soil carbonates suggest that biota play a major role in the soil-forming processes of desert ecosystem. The isotopic composition of caliche forming in current conditions appears to be related to broad climatic patterns and to local conditions of vegetation. Many previous compilations of such data are uninterpretable because samples were collected from sites dominated by calcareous parent materials and from soil horizons that developed under unknown palaeoclimatic conditions. Gardner (1984) reported that Pleistocene age caliches contain lower values for delta 18O than Holocene samples. Such changes may suggest that the deposition occurred in a cooler climate, but changes in the evaporative removal of soil moisture may also be involved. Careful studies of the seasonal change in the delta 13C and delta 18O values of soil CO2 and soil H2O would help determine the mechanisms controlling the deposition of carbonate in desert soils.