Weathering Intensity Response to Climate Change on Decadal Scales: A Record of Rb/Sr Ratios from Chaonaqiu Lake Sediments, Western Chinese Loess Plateau

Abstract

The Rb/Sr ratio of lake sediments has been widely adopted as an indicator of weathering intensity in studies of past climate change, but the geochemical significance of this ratio varies with timescale. Here, we present Rb/Sr data for the past 300 years for sediments collected from Chaonaqiu Lake in the Liupan Mountains of the western Chinese Loess Plateau as a decadal-scale record of weathering intensity. To validate the application of this weathering proxy, we correlated the record with those of other major elements, rock-forming minerals, and paleoclimatic proxies. We found that Rb/Sr ratios are influenced mainly by Sr activity within the lake catchment (where Sr is likely sourced from albite). In addition, higher (lower) Rb/Sr ratios of bulk sediments from Chaonaqiu Lake are correlated with lower (higher) fractions of terrigenous detritus (SiO2, Ti, K2O, Al2O3, and Na2O). These indicate that the Rb/Sr ratios of bulk sediments in Chaonaqiu Lake are closely linked to terrigenous detritus input on decadal scales and also correlate well with TOC (a precipitation indicator) and other high-resolution paleoclimate records (e.g., tree rings and drought/flood index) in neighboring regions, with higher (lower) Rb/Sr ratios corresponding to more (less) precipitation. Lake bulk sediment Rb/Sr ratios are dominated by the input of terrigenous detritus over decadal timescales. Our data show that physical and chemical weathering in the Chaonaqiu Lake watershed have opposing influences on Rb/Sr ratios of bulk sediment, competing to dominate these ratios of lake sediments over different timescales, with ratios reflecting the relative importance of the two types of weathering.