The Effect of Quaternary Climate Change on the Balance of Silicate Mineral Weathering and Eolian Input in Desert Soils

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9614875 Capo The interaction of atmospheric processes and terrestrial weathering is crucial to understanding global geochemical cycling and its relationship to climate change. The quantification of cation fluxes in the soil-atmosphere system is an essential part of this problem. Knowledge of the effect of climate change, time, parent material and other soil-forming factors on the development of desert soil and the storage and mobility of elements is also critical. The objective of this research is to quantify the effect of atmospheric input and silicate mineral weathering on Quaternary desert soil pedogenesis as a function of climatic regime. We will use a combination of field, mass balance and isotope tracer studies to examine the factors involved in soil formation in desert soils over the last 2 million years. Soil profiles from the Desert Soil-Geomorphology Project of the U.S.D.A. Soil Conservation Service, near Las Cruces, NM, and from Kohala Peninsula, Hawaii, will be studied to place constraints on the role of atmospheric addition of cations and in situ silicate weathering in arid to semiarid environments in an eolian-dominated and a silicate weathering-dominated system over Quaternary time. Strontium isotope measurements will be combined with micromorphologic studies, major and trace element analyses, and cation mass balance calculations in order to (1) determine the sources and quantify the relative contributions of cations into desert soil systems; (2) examine the locations, rates and mechanisms of silicate mineral weathering within the soil profile; and (3) identify shifts in the relative contributions of silicate mineral weathering and eolian input to the soil cation budget as a function of climate change. Well documented and preserved soil chronosequences at both locales permit detailed sampling of modern, relict, and buried soil profiles of known age and climatic history. The strontium isotopic and major and trace element composition of soil parent material, local atmo spheric inputs from dust and rain, and soil carbonate will be determined. Calcium provencance in the soil will be determined by Sr isotopic analysis. Mass balance analysis will quantify the gain, loss, and redistribution of cations in the soil system. These data will b correlated with existing radiocarbon, stratigraphic, stable isotope, pollen and paleohydrology records. The data will aid in reconstructing the history of desert soil formation over the Quaternary as a function of environmental change.