UC Irvine

Reconstructing the history of Earth's atmospheric radiocarbon (¹⁴C) through the detection limit has been a long term goal of the scientific community, because of the usefulness of ¹⁴C as a chronometer for records of Quaternary Earth history, and because variations in atmospheric ¹⁴C are, in part, recorders of changes in Earth's carbon cycle. This dissertation represents the result of work that aims to reconstruct the history of Earth's atmospheric ¹⁴C, both through studies of intervals of interest to the climate-carbon feedback cycle in the deglacial interval, and through attempting to develop speleothem records of atmospheric ¹⁴C in older intervals where knowledge of atmospheric ¹⁴C is currently lacking. The major results of this dissertation include a record of deglacial ventilation ages in the Santa Barbara Basin. This record demonstrates that the hypothesized "old water" mass thought to have been responsible for the deglacial atmospheric CO₂ rise and concurrent ∆¹⁴C decline is unlikely to have existed in the Santa Barbara Basin. Also included in this dissertation is the result of work to reconstruct atmospheric ¹⁴C during the Younger Dryas climate event based on New Zealand kauri. The remainder of the dissertation is composed of works that aim to develop speleothem-based records of atmospheric ¹⁴C, and to understand carbon incorporation in speleothems. These works demonstrate that there do exist some speleothems, most notably Hulu Cave H82, that have low and stable dead carbon incorporation and are are valuable sources of records of atmospheric ¹⁴C. Records speleothem ¹⁴C from Heshang Cave HS4 suggest that increases in precipitation drives increases in speleothem dead carbon incorporation through shifting carbonate dissolution to a more closed system regime, though decreases in precipitation do not appear to drive proportional decreases in speleothem dead carbon. Modern monitoring of cave carbon cycling at Heshang Cave and modeling of speleothem bomb peak records indicates that speleothem carbon is likely derived primarily from decomposition of down-washed soil organic matter in the deep vadose zone, and that organic matter in karst settings may be much older than organic matter in sites studied previously.