Predominant East Asian summer monsoon control on clay-sized fraction lithium isotope ratios in Red Clay deposits on the Chinese Loess Plateau

Abstract

The Li isotope composition (δ⁷Li) of terrestrial sediments is a promising tracer for extracting past chemical weathering and environmental changes, but the relative importance of precipitation versus temperature effects on δ⁷Li remains poorly constrained. Here, we present bulk and clay-sized fraction δ⁷Li data for a Red Clay sequence from the Chaona section on the central Chinese Loess Plateau (CLP), and compare the results with magnetic parameter-based temperature and precipitation records. We find that, from the late Miocene onwards, the clay-sized fraction δ⁷Li record corresponds well with magnetic precipitation proxy records but not with temperature proxy records. This pattern suggests that changes in precipitation exert a primary control on clay-sized fraction δ⁷Li variations. Bulk δ⁷Li in the Chaona section shows an approximately similar decreasing trend to that of clay-sized fraction δ⁷Li from the late Miocene to mid-Pliocene, consistent with precipitation records. In contrast, bulk δ⁷Li variations display an inverse trend compared with clay-sized fraction δ⁷Li and precipitation records during the late Pliocene, which we attribute to intensified winter monsoon and provenance shifts. Our findings demonstrate that clay-sized fraction δ⁷Li in sediments can serve as a reliable indicator to reconstruct past precipitation changes on the CLP on million year timescales.