Unlocking seasonal climate records from modern and fossil tree-rings

The deep-time paleoclimate record is a reservoir of critical information on Earth System responses to CO₂-driven warming; however, few proxy systems offer the seasonal paleoclimate information that is relevant on human timespans. Ancient tree tissue is a unique substrate among paleoclimate archives, as annual growth bands serve as internal geochronometers and allow for dissection of sub-annual variations in local climate and environmental conditions. This talk will provide an overview of recent efforts to develop best-practices for analyzing and interpreting δ¹³C and δ¹⁸O values from fossil wood. New techniques for screening wood pieces for diagenetic alteration demonstrate that, in the absence of isotopic corrections, atmospheric CO₂ estimates can be substantially biased (e.g., by 2x for the Early Jurassic). This talk will also present a proxy system model case study, wherein seasonal rainfall is reconstructed using high-resolution, intra-ring analyses of δ¹³C on subfossil (mummified) trees from the late Oligocene of southern China. The results of this study provide clear evidence of summer-dominated rainfall that is consistent with strong East Asian Monsoon circulation prior to the Neogene, which supports predictions in recent general circulation model experiments.