Temperature dependent evaporite-sourced Li isotopic seasonality in the upper Yellow River

Abstract

Silicate weathering sustains the habitability of the Earth via regulating atmospheric CO₂ concentrations and nutrient supply over geological time scales. So far, it lacks an effective tracer for silicate weathering. Riverine Li isotopes are proposed as a promising tracer as silicate weathering intensity, but the evaporite contribution to riverine Li⁺ remains poorly constrained, shaking its root as a such tracer. Here, we collected river water samples weekly at the Toudaoguai hydrological station at the end of the upper Yellow River to address this issue. We found that more than 80 % (up to 100 %) of riverine Li⁺ is sourced from evaporite dissolution within the upper Yellow River catchment, where distributed a large amount of salt lakes and old marine stratum. Even though, the seasonal variation in the riverine Li isotopes still supports that the long residence time in large rivers facilitates the low temperature Li isotopic fractionation and thus temperature dependency. The sources and isotopic variation of terrestrial Li⁺ input to oceans should therefore be carefully reevaluated.