Seasonal rainfall patterns in stable carbon isotopes in the Mu Us Desert, northern China during the early and middle Holocene

Abstract

Intense Asian summer monsoon rainfall responds to high boreal summer insolation and environmental feedbacks in the early and middle Holocene. However, it is unclear what role of the Asian summer monsoon strength might have played for the heterogeneous wetness pattern in northern China. Here, we report two wet periods in the early and middle Holocene by paleosol, lacustrine, and peat stratigraphies in the southeast Mu Us Desert, and that early-Holocene wetness records are common and seen in valleys and missing from valley walls while mid-Holocene wetness records are found everywhere in the region. The preliminary analysis of the stable carbon isotopic composition (δ13C) of soil carbonate and organic carbon from a riverine dune–paleosol sequence in a river valley reveals that wet springs/falls with dry summers frequently prevailed in the early Holocene, while wet summers with dry springs/falls became predominant in the middle Holocene. Strong-wind and low-temperature springs and falls on valley walls and uplands cause eolian sedimentation faster than soil formation but weak-wind and warmer-soil temperature in valleys facilitate vegetation metabolism and thus soil formation. Warm summer rainfall with no strong northwesterly wind causes paleosol, lacustrine and peat formation either in valleys or on uplands. The early-Holocene heterogeneous and middle-Holocene uniform wetness records are indeed controlled by seasonal hydroclimate conditions but not a single factor of summer monsoon rainfall strength in the southeast Mu Us Desert.