Collaborative Research: Interpreting clumped isotope temperatures and δ18O records from pedogenic carbonate: influence of climate, seasonality, and elevation

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A new isotopic measurement technique of a common geologic material, calcium carbonate, has the potential to reveal how continental temperatures and environmental conditions have changed throughout Earth history. The technique, called clumped isotope thermometry, exploits the temperature-dependent grouping of the heavy isotopes of carbon and oxygen in calcium carbonate. Calcium carbonate bearing soils are relatively common in the terrestrial geologic record and present attractive targets for reconstructing past earth surface environments. However, while the theoretical basis for clumped isotope thermometry is robust, exactly how environmental conditions are reflected in soil carbonate formation temperatures is not well understood. Thus, developing a framework for understanding the environmental factors that influence the timing of carbonate formation is the key to unlocking a potentially rich record of past surface temperatures and enhancing the understanding of Earth?s terrestrial paleoclimates. A team of researchers from Syracuse University and the University of Washington, in collaboration with researchers from the Pontificia Universidad Cátolica de Chile, and the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA) in Argentina will conduct a two-year study in and adjacent to the Andes near 30°S latitude to determine how the carbonate clumped isotope thermometer records temperatures in modern to 100,000 year old soils, with a focus on how these methods can be applied to understand Earth's past surface conditions on the continents. The primary research goals are to quantify: 1) the influence of seasonal precipitation, air temperature, and vegetation on the timing and temperature of soil carbonate formation; 2) how well clumped isotope temperatures of Holocene (11,500 year old) soil carbonates and calculated soil water oxygen isotopic values predict modern elevation and the isotopic composition of precipitation; and 3) the impact of signal integration over long (1000 to 10,000 year) timescales by exploring how clumped-isotope temperature varies with soil carbonate age and development stage. The Andean field site is ideal for this study because the 4 km of topographic relief in this area provides a wide range of mean annual and seasonal temperatures. The east and west sides of the Andes also have opposing rainy seasons and gradients in vegetation type and density, enabling this study to tease apart the influence of these factors on clumped isotope temperatures of soil carbonate. This study will support the education and training of two doctoral students in the Earth Sciences as well as foster collaboration among two US universities and their South American counterparts: Pontificia Universidad Catolica de Chile and Instituto Argentino de Nivologia. Components of this research will be used in University and high school teaching via the participation of the PIs in professional development programs for high school teachers in their respective states. The results of this study will be disseminated in scientific journals, professional conferences, the PIs' websites, university courses, and a hands-on activity for the UW's outreach program, Rockin' Out. The project will benefit the broader scientific community by developing a tool that can be applied in many places for paleoclimate and paleoaltimetry research, and potentially change the way researchers interpret stable isotope data for paleosols. Support of the international component is provided by the Office of International Science and Engineering.