Department Seminar: Xiaomei Xu

Title: Radiocarbon as a Window into the Carbon Cycle: From Analytical Innovation to Discovery

Abstract: Radiocarbon ( 14 C) is a valuable tracer for studying carbon (C) in the Earth system. Because fossil C is 14 C-free and nuclear bomb testing produced a doubling of 14 C in the modern atmosphere, 14 C reveals the origins of the active C cycle on Earth. I will present analytical methods that have opened new windows into the C cycle, including 14 CO₂ time series from the NOAA Barrow Alaska Atmospheric Baseline Observatory and UCI. I will present an estimate of fossil fuel CO₂ emissions in the Los Angeles Basin, and evidence that Arctic lake methane emissions are dominated by young rather than ancient permafrost C. I will also present the penetration of bomb 14 C into the deepest ocean trenches, the surprising role of ancient and methane-derived carbon in supporting contemporary aquatic food webs, and 14 C-based forensic dating of seized ivory to constrain the illegal ivory trade. Collectively, these examples reflect how improvements in 14 C measurement capability have expanded the range of questions that 14 C measurements can address.