Influence of vegetation type and site-to-site variability on soil carbonate clumped isotope records, Andean piedmont of Central Argentina (32-34°S)

The clumped isotope geothermometer estimates the formation temperature (T(Δ₄₇)) of carbonates and has great potential to enhance the extraction of environmental data from pedogenic (soil) carbonate in the geologic record. However, the influence of vegetation type and site-specific conditions on carbonate formation processes and T(Δ₄₇) records remains poorly understood. This study examines the potential for variability in T(Δ₄₇) data between nearby, same elevation sites with different C₃/C₄ biomass. Pedogenic carbonates (undercoatings and nodules) were collected from five modern soil pits in the semi-arid eastern Andean piedmont of Argentina under a summer precipitation regime. Three pits were instrumented with temperature and moisture sensors to 1 m depth, and a fourth was instrumented with additional soil CO₂ and atmospheric (temperature, relative humidity, insolation, and rainfall) sensors. T(Δ₄₇) values (mean: 30±6°C (±1SE)) are invariant with depth and are statistically indistinguishable between the four instrumented sites, though a 10 °C difference between our T(Δ₄₇) values and those of a nearby Peters et al. (2013, EPSL) study suggests the potential for significant site-to-site variability, likely due to local soil hydrology. The results of this study suggest that deeper (≥40 cm) T(Δ₄₇) values are consistent with carbonate formation during the early part of soil drying immediately after large mid-summer rainstorms. Carbonate formation ≤ 40 cm depth may be biased to soil drying after small, frequent precipitation events occurring throughout the spring, summer, and fall months, averaging to shallow summer T(Δ₄₇) values and resulting in a near-isothermal T(Δ₄₇) profile.