Stable Isotope Geochemistry

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ClaytonEAR-0439925Non-mass-dependent (NMD) isotope effects in sulfur and oxygen will be used to study two topics in the geochemistry and evolution of Earth's atmosphere. It has been proposed by others that the observed NMD effects in sulfur in Archean rocks are due to ultraviolet photochemistry in the stratosphere before the existence of an effective ozone shield. The underlying photochemistry will be studied in systematic laboratory experiments involving photolysis of sulfur dioxide. Determination of the timing and mechanism for the development of an oxygen-rich atmosphere is an important factor in biological evolution. The second study deals with the modern atmosphere, and consists of a search for NMD signals in tropospheric oxygen-bearing molecules, acquired from stratospheric ozone, and transported across the tropopause. Samples to be analyzed include ice cores from low-latitude, high-altitude glaciers, which may provide a millennial record of atmospheric dynamics. Both of these studies are of practical importance in understanding the chemical workings of our atmosphere. This work will constitute the doctoral theses of two graduate students.