New Mexico Geological Society Annual Spring Meeting — Abstracts

Previous work on two opposing slopes at a Sevilleta field site inferred different paleoclimate conditions and vegetative patterns from measuring stable carbon isotope concentrations of pedogenic carbonate layers. However, calcium carbonate layers form over several thousands of years and thus represent an integrated climate signal over this time period. To better understand the short term variability we are conducting soil gas measurements periodically over at least four consecutive seasons.

By combining the seasonal trends of CO₂ flux and carbon stable isotope composition in the soil gas, we will be able to relate CO₂ production with the degree of vegetation respiration and carbonate deposition. Yearly variations will provide understanding to the degree of variability that can be expected in the more general determination of a paleoclimate condition. Differences in CO₂ production rates and concentrations within the soil on the two different slopes in the study provide information on their different vegetative growth patterns. Measurements started in spring 1998 and are planned to continue through 1999.

Results show that these two slopes with different vegetation patterns show different patterns of seasonal behavior with respect to surface CO₂ flux and subsurface CO₂ concentrations. Little variation is observed in the isotopic composition of the subsurface CO₂. Isotopic carbon values for both slopes favor C4 vegetation. This is inconsistent with the pedogenic carbonate which indicated one of the two slopes having a near equal distribution of C3 and C4 vegetation.