Oxidation of petrogenic organic carbon and the net geological carbon budget of the Eastern Tibetan Plateau

The erosion and weathering exert a key control on the long-term carbon cycling between the earth's surface and crust, thus impacting Earth's climate. The net carbon budget of a tectonically active catchment is based on the superposition of several carbon sources and sinks, but certain processes, such as petrogenic organic carbon (OC_petro) weathering, still lack comprehensive quantitative research, hindering a full understanding of the net carbon budget of mountain building. In this study, we explored OC_petro weathering process within the Eastern Tibetan Plateau utilizing rhenium (Re) as a tracer to quantify OC_petro weathering rates and elucidate carbon fluxes. Detailly, we measured rhenium concentration, TOC, and the concentration of major ions of the river water as well as bedload sediments of the large river basins within and on the eastern margin of the Tibetan Plateau, including Yangtze, Mekong, Salween, Yellow and Brahmaputra Rivers. We then portioned the sources of major ions as well as dissolved rhenium by a Monte Carlo simulation. Lastly, we quantified the carbon transfer through several geological processes. The overall OC_petro weathering rate and net carbon budget of the Tibetan Plateau on time scales of 10⁴-10⁷ years are 1.95(±0.60)tC·km^-2·yr^-1 and 1.81 ^+0.34/_-0.49 tC·km^-2·yr^-1, respectively, indicating the Tibetan Plateau currently serve as a carbon source. This study not only refines our understanding of the OC_petro weathering but also reveals a dynamic transforming impact on the geological carbon cycle from mountain building at different stages.