Implications for Late Holocene climate from stable carbon and oxygen isotopic variability in soil and land snail shells from archaeological site 41KM69 in Texas, USA

Well-preserved fossil land snail shell collected in a 115 cm soil profile from archaeological site 41KM69 in Texas, USA, minimally span the past 2200 years and provide an opportunity to explore the paleoclimate implications of isotopic variability in shell carbonates, bulk soil carbonates, and soil organic matter. Carbon isotopic compositions (δ13C values) of modern and archaeological adult snail shell carbonates suggest significant (>60%) dietary input of C3 plants during all periods. Oxygen isotopic compositions of shells suggest that the isotopic composition of environmental water available at the time of shell growth has changed little over the period of the profile. A linearly decreasing trend in δ13C of soil organic matter from −22.8‰ at the bottom of the profile (115 cm below surface) to −25.6‰ for modern surface samples indicate an overall 20% increase in abundance of C3 plants. This implies a progressively wetter climate and less severe water stress conditions or decreasing summer rainfall that is in agreement with other studies on Late Holocene climate change in the southern Great Plains, USA. These results strongly suggest a stable climate that favored C3 vegetation in this portion of Texas during this period.