Stable carbon isotopes, C3–C4 vegetation, and 12,800 years of climate change in central New Mexico, USA

A thick sequence of fine-textured alluvium in central New Mexico has provided an opportunity to reconstruct vegetation type and climate at the western edge of the Great Plains grassland. The analysis of thirty-eight AMS radiocarbon ages, δ13C values, and modern weather data has produced a 12,800 cal yr record of changing C3–C4 vegetation, temperature, and precipitation. The record begins with the Younger Dryas that was characterized by C3 plants and was about 2.4 °C cooler with over 100 mm rainfall than today. After 11,000 cal yrs BP, the climate became less cool and less wet, reaching present-day conditions by 9000 yrs. The middle Holocene was C4, warm, and dry although the δ13C record is incomplete for this interval. From 3300 to 1400 cal yrs BP, the climate was cool and wet with C3 plants, averaging 0.5 °C cooler and 22 mm greater rainfall than today, matching other records in the region for a wetter climate. After 1400 cal yrs BP, the local climate became warm and dry, shifting to C4 vegetation. The severe second century drought, first observed in tree-rings in southern Colorado, is supported by the δ13C data and occurred during the interval A.D. 40 to A.D. 180. Hiatuses in the local alluvial and δ13C record extend from 9000 to 6000 cal yrs BP and from 1000 cal yrs BP to present.