Download or read book Carbon Isotope Analysis of the Sources and Mechanisms of CO2 Input and Removal from Central Texas Cave Systems written by Ashley Elizabeth Quinn and published by . This book was released on 2010 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: Speleothem calcite growth rate is a commonly used paleoclimate proxy. Seasonal variations in cave CO2 concentration (P[subscript CO2]) are known to control speleothem growth. Thus, it is important to understand the mechanisms of CO2 input and removal from cave systems in order to better use speleothem calcite growth rate as a proxy. To this end, spatial and temporal variations in the atmosphere of several central Texas caves were studied over the course of a year. The stable isotope composition of the sources of CO2 in cave air were determined by measuring the [delta]13C values of cave-air CO2 samples collected from specific sites within the caves. Cave-air P[subscript CO2] consistently increased and [delta]13C values consistently decreased with distance from the cave entrance. The values along these spatial transects vary seasonally towards higher [delta]13C values and lower P[subscript CO2] in the winter months (October-March). The linear relationship between [delta]13C and 1/ CO2 suggests that CO2 in the cave atmosphere is a mixture between atmospheric air (~380ppm, -8% [delta]13C, V-PDB) and a cave-end-member with low [delta]13C and high P[subscript CO2]. The concentrations and [delta]13C values of cave-air CO2 were used to find the [delta]13C value of respired CO2 ([delta]13C[subscript r]) by correcting for atmospheric mixing and diffusion in the soil. The [delta]13C value of respired CO2 is generally higher in the summer and lower in the winter. The seasonal- and regionally consistent variations in P[subscript CO2] and the [delta]13C value of cave-air CO2 support density-driven ventilation controlled by seasonal surface temperature changes as the major influence on cave-air CO2. The calculated [delta]13C values suggest that C3 organic material is the primary source of cave-air CO2 and that seasonal variation in the magnitude of photosynthetic discrimination and/or seasonal changes in the relative productivity of C3 vs. C4 vegetation influence the [delta]13C value of CO2 entering the cave.