USC Earth Sciences has active programs studying processes in the current climate system and "proxy" archives of past climate variability, beyond the short reach of historical instrumental records. Studies of past climate using stable and radiogenic isotope geochemistry and biogeochemistry have revealed climate modes very different to our current climate. These terrestrial and marine records provide important insights into the nature and magnitude of climate shifts that we might expect in the future.
USC researchers and students in the Stott Laboratory are studying the oxygen and hydrogen isotopic composition of rainfall over California, Southeast Asia, and Africa, in efforts to document how atmospheric circulation and rainfall have responded to tropical influences such as El Nino. Climate archives include:
tree rings - Studies using the isotopic composition of tree rings from Bristlecone and Foxtail Pine, two of the world's oldest trees, are reconstructing atmospheric precipitation variations spanning several centuries in California.
speleothems - The oxygen isotope composition of calcium carbonate deposits that form speleothems in karst environments (caves) are being used to determine the isotopic composition of the original rainwater, information that can then be used to reconstruct a history of rainfall variability and atmospheric circulation.
marine samples of water and deep sea sediment cores - Studies of water and marine sediment from the deep sea are yielding information about ocean environmental change.
The Feakins Lab at USC uses biogeochemical techniques to reconstruct past climate and environmental change. Proxies include the carbon and hydrogen isotopic composition of various biomarker molecules for terrestrial and aquatic organisms. For example, long chain n-alkanes derived from plant leaf waxes, as well as various biomarkers for aquatic organisms e.g. alkenones. Isotopic techniques capture wet-dry paleoclimate variations through shifts in C3 versus C4 photosynthesis and the water isotopes in precipitation.
Current research in this area includes: