IGPP Seminar Series

Clumped isotopes for gas tracing and paleothermometry

by Edwin Schauble
ESS, UCLA

Abstract

Molecules like 13C16O18O, containing multiple heavy isotope substitutions, have generally not attracted much interest from geochemists. In part this is because they are so rare in nature. However, recent theoretical, experimental, and empirical studies are showing that the abundances of these molecules can help us better understand sources and sinks of important atmospheric gases. This follows from the temperature sensitivity of exchange reactions that form multiply-substituted – “clumped” – species, e.g.: 13C16O2 + 12C18O16O ?? 13C18O16O + 12C16O2 These reactions tend to favor formation of clumped molecules, in excess of what would be expected if the isotopes were distributed randomly. The lower the temperature of equilibration, the more clumpy the distribution. This provides a straightforward distinction between high-temperature CO2 sources, like combustion, and low-temperature CO2 sources like respiration and leaf-air exchange. Temperature sensitive isotope clumping is also observed in carbonates, for instance: 13C16O32– + 12C18O16O22– ?? 13C18O16O22– + 12C16O32– This has led to the development of a new paleo-temperature proxy, based on measurements of excess 13C18O16O22– in ancient carbonate minerals.
Tuesday, 28 October 2008
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM