High resolution δ13CTOC and magnetic susceptibility data from the late Early Pleistocene southern margins of the Chinese Loess Plateau

On the Chinese Loess Plateau, stable carbon isotope values for total organic matter (δ13CTOC) from more than 10 loess/paleosol sequences since the last glacial/interglacial show generally consistent variations, with enriched values normally occurring in paleosol layers. The only exceptions are records from the westernmost and northwestern Chinese Loess Plateau. However, both Asian summer monsoon intensity and temperature have been suggested as the principal factor affecting these consistently similar δ13CTOC variations. Until now, δ13CTOC records covering the whole Quaternary have been relatively rare, with problems including low resolution and conflicts in both the C4 expansion history and with related climatic interpretations. In this paper, we report on high resolution, late Early Pleistocene low-frequency magnetic susceptibility (χlf) and δ13CTOC data from Yushan section on the southern margins of the Chinese Loess Plateau. Our δ13CTOC data present an abstruse relation with the glacial/interglacial cycles represented by loess/paleosol sequences, with δ13C-enriched excursions in some paleosol layers and δ13C-depleted excursions in others. Furthermore, our δ13CTOC data shows negative and positive correlations with χlf data, using a threshold χlf value of 70 × 10−8 m3/kg. If the χlf data are taken as an indicator of pedogenetic intensity, and therefore an indicator of Asian summer monsoon intensity, there are two possible relations between Chinese loess δ13CTOC and Asian summer monsoon intensity, i.e. the Chinese loess δ13CTOC cannot simply be adopted as the sole indicator of Asian summer monsoon intensity, at least during the late Early Pleistocene on the southern margins of the Chinese Loess Plateau. Our results demonstrate that C4 plants became a significant proportion of local vegetation cover only when Asian summer monsoon intensity exceeded a certain degree, for example, in the surface vegetation for the S15 and S16 paleosol layers of the Yushan section. The relation between climate and Chinese loess δ13CTOC requires further, detailed study.