Abstract

High-resolution δ13C records of bulk organic matter (OM) from three loess-paleosol successions from the central Chinese Loess Plateau document systematic fluctuations in C3 and C4 plant abundance for certain intervals during the past 620 k.y. Measured δ13C values of OM in paleosols are less negative by 0.5‰–4‰, and total organic carbon (TOC) contents are higher by up to 0.5 wt% relative to corresponding values in loess deposits. The δ13COM and TOC decrease from peak values in paleosols progressively into overlying and underlying loess deposits. Integrated δ13COM, TOC, and magnetic susceptibility rec ords indicate an increase in C4 vegetation to ≥50% during peak paleosol formation and a decrease in C4 vegetation to ≤30% during loess deposition for three of the past glacial-interglacial cycles. These results indicate that C4 plant abundance declined during glacials in this mid-latitude region driven primarily by a shift to enhanced winter precipitation and lower temperatures, and further contribute to the rapidly growing body of evidence that low pCO2 during Pleistocene glacials was insufficient to trigger C4 plant expansion without coincident favorable climatic conditions.

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