Ti content in Huguangyan maar lake sediment as a proxy for monsoon-induced vegetation density in the Holocene

Abstract

The provenance of element Ti in Huguangyan maar lake (HGY) sediment has been under debate since Yancheva et al. () proposed its eolian source from the Chinese Loess Plateau (CLP) and applied it as a proxy for Asian winter monsoon. We performed a comprehensive study on Ti-carrying minerals and Ti fluxes in lake sediments, wall rocks, and loess from the CLP. Here we show that the chemical compositions and morphological features of magnetite, the most important Ti carrier in HGY surface sediments, are identical to those in wall rocks around the lake, but substantially different from those in CLP loess samples. Our calculated modern eolian Ti flux from the CLP is negligible compared to the average total Ti flux to HGY, and Ti flux from catchment erosion can provide enough Ti, indicating Ti in HGY sediment are predominantly from wall rock erosion. Inverse correlation between total organic carbon (TOC) (vegetation density) and Ti/Ca ratio (terrestrial input) in the Holocene suggests monsoon-induced vegetation density predominates over runoff in controlling Ti input to HGY. S-ratio represents TOC directly mediated reductive diagenesis of iron oxides (magnetite preservation), rather than anoxic/oxic condition at the bottom water induced by winter monsoon. Our record shows a decreased vegetation density, increased Ti input and weakened reductive diagenesis through the Holocene driven by a weakened summer monsoon. Key Points Ti in HGY sediment are predominantly from wall rock erosion monsoon induced vegetation density controlls Ti input to HGY Decreased vegetation density, increased Ti input through the Holocene ©2013. American Geophysical Union. All Rights Reserved.