Link between benthic oxygen isotopes and magnetic susceptibility in the red-clay sequence on the Chinese Loess Plateau

Abstract

Recent rock magnetic work on the red-clay sequence on the Chinese Loess Plateau (CLP) convincingly demonstrates that the enhancement mechanisms of low-frequency magnetic susceptibility (i.e., measured at 470 Hz; χ1f) in the red-clay sequence are similar to those in the loess-paleosol sequence. Therefore, χ1f in the red-clay sequence should indicate precipitation intensity received by the CLP, as is the case in the overlying loess-paleosol sequence. Based on this result, we compared χ1f in the red-clay sequence with benthic oxygen isotope records. We infer that the primary precipitation source on the CLP varies over time in three phases: during 8.1-4.5 Ma, the East Asian summer monsoon dominates; during 4.5-4 Ma, the Polar Westerlies dominate; during 4-0 Ma, the East Asian summer monsoon dominates. We attribute these precipitation source shifts on the CLP to the closure of the Panama Seaway around 4.5 Ma and the Tibetan uplift during the interval 4-2.6 Ma. Copyright 2008 by the American Geophysical Union.