Ashley Quinn

Ashley Quinn

Ashley Quinn

Previous research has proposed the use of speleothem calcite growth rate as a proxy for paleoclimate. Observed seasonality of cave-air CO2 has implications on calcite precipitation and growth rate, and thus on the use of speleothems as paleoclimate proxies. It is important to understand what variables cause these seasonal changes because understanding individual shifts in CO2 production will allow a more precise quantification of how the combined seasonal effect will influence speleothem calcite growth rate and perhaps better characterize seasonal resolution. Endmembers that contribute to seasonal variations in cave-air CO2 concentrations are determined by analyzing δ13C values of cave-air samples collected from specific sites within several central Texas caves: Inner Space Cavern, Natural Bridge Caverns, Whirlpool cave, Maple Run Cave and District Park cave. The spread of the collected data is such that it encompasses seasonal changes.

Cave-air pCO2 v δ13C. Mixing curves between the known endmember, atmospheric values, and an unknown ‘cave-air’ endmember. Outside air is plotted to represent atmospheric values. Horizontal axes are on the same scale to show the shift to lower pCO¬2. Variation in the unknown endmember’s isotopic composition from heavier values in July to lighter values in September and October can be inferred from the plots.  Cave-air ventilation in the winter months (December and February) result in very large fractions of low pCO¬2 and heavy δ13C which mask any other sources to the cave-air.

Cave-air pCO2 v δ13C. Mixing curves between the known endmember, atmospheric values, and an unknown ‘cave-air’ endmember. Outside air is plotted to represent atmospheric values. Horizontal axes are on the same scale to show the shift to lower pCO¬2. Variation in the unknown endmember’s isotopic composition from heavier values in July to lighter values in September and October can be inferred from the plots. Cave-air ventilation in the winter months (December and February) result in very large fractions of low pCO¬2 and heavy δ13C which mask any other sources to the cave-air.

Speleothem Calcite Growth

Speleothem Calcite Growth

Honors Advisor:

Dr. Jay Banner