C3/C4 vegetation response to atmospheric CO₂ levels during the last 150 ka BP: Stable carbon isotopic evidence from soil carbonate

Zheng-Hua Li (1) (2), Claudia I Mora (1), Hua-Yu Lu (2)

1) Department of Geological Sciences, University of Tennessee, Knoxville, TN37996, USA

2) State Key Laboratory of Loess and Quaternary Geology, CAS, Xi'an 710054, China

The matrix carbonate δ¹³C profile for a loess-palesol sequence near Luochuan, China, preserves an ~150 kaBP record of soil ecology and paleoclimate. Minimum values of δ¹³C (-12.1‰) occur in the early part of the last interglacial, increasing to a maximum of -4.2‰ during the last glacial maximum. The d13C pattern is consistent with an ecosystem dominated by C3 vegetation during the last interglacial period, when the atmosphere had a higher pCO2. The fraction of C4 plants increased as the paleoclimate changed towards the drier/colder, lower pCO2 conditions of LGM. Soil carbonate δ¹³C in the upper Luochuan profile match very well with the Vostok ice core atmospheric CO₂ record, except for one portion of the profile where several prominent pCO₂ excursions are not clearly due to slower rates of loess accumulation. The results suggest that lower atmospheric pCO₂ during the last glaciation led to C4 expansion at Luochuan, despite lower temperatures.