A 700-year macrophyte productivity record inferred from isotopes of macrophyte remains and bulk carbonates in Lake Koucha, northeast Qinghai-Tibetan Plateau

The isotopic composition of total organic carbon (TOC) in lakes has been widely used to interpret paleoclimatic changes and the depositional environments of lake sediments. However, the main factors that affect the carbon isotopes of TOC may vary in different lake sediment records, limiting the ability of organic carbon isotopes to explain biogeochemical and environmental changes, especially in lakes with a large number of aquatic plants. In this study, the δ13C values of macrophyte remains and bulk carbonate in a sedimentary core from Lake Koucha were investigated to evaluate their paleoenvironmental implications. We found that the bulk carbonate was dominated by authigenic carbonates formed in the lake and that their δ18O and δ13C values can be used to reconstruct environmental changes in the Lake Koucha area. The macrophyte productivity derived from the carbon isotopic offset between the macrophyte remains and the bulk carbonate (εremains-BC) in the Lake Koucha area agree well with total solar irradiance (TSI) records inferred from Δ10Be and temperature records based on tree rings from the Qinghai-Tibetan Plateau. Although the distribution of macrophytes is related to water depth according past studies and our observations in the field, our findings suggest that changes in macrophyte productivity may be primarily driven by temperature changes in the Lake Koucha area.