CLUMPED-ISOTOPE THERMOMETRY OF PEDOGENIC CARBONATES: QUANTIFYING THE INFLUENCE OF CLIMATE, SEASONALITY, AND ALTITUDE IN THE SOUTH CENTRAL ANDES, ARGENTINA

Clumped isotope thermometry of paleosol carbonates is a potentially powerful tool for studies of paleoclimate and paleoelevation, providing independent estimates of the formation temperature and the δ¹⁸O of the water from which the carbonate grew, both of which reflect the local environmental conditions under which they form. However, interpretation of paleosol temperatures will remain problematic until the effects of site-specific environmental factors on carbonate formation temperatures are rigorously evaluated. To investigate how clumped-isotope thermometry reflects the above ground environment, modern pedogenic carbonates were sampled from 5-110 cm depth in soil pits along a transect spanning 2 km of relief with high seasonal variability in precipitation and temperature in the southern Central Andes of Argentina (33°S). Coherent pedogenic carbonate δ¹⁸O and δ¹³C depth profiles support the notion that all but the highest (3200 m) pit were excavated on stable geomorphic surfaces. Preliminary clumped-isotope soil temperatures vary between mean annual and hottest month mean air temperatures for the sample localities, possibly suggesting that, in some cases, pedogenic carbonate forms preferentially during the warm wet season. The maximum clumped-isotope temperature for each pit is correlated with elevation (R²=0.76), but temperatures do not vary monotonically with depth, and average soil temperatures are closest to maximum monthly mean air temperature at higher elevation sites but closer to mean annual temperature at lower elevations. These initial results suggest that environmental variables such as vegetation, snow cover, and seasonality of temperature and precipitation can produce significant (>5°C) variations in carbonate formation temperature. Therefore, assumptions that pedogenic carbonates record either mean annual or summer air temperatures may not be valid unless the influence of these factors can be determined.