Long-term CO2 fluxes across erosional and lithological gradients in the Himalayas

The role of mountain building in regulating Earth’s climate remains unclear, as uplift and erosion can drive both CO₂ drawdown via silicate weathering and CO₂ release via carbonate dissolution by strong acids and oxidation of petrogenic organic carbon. Understanding how erosion rate, climate, and lithology influence these reactions is key for understanding the impact of the growth and subsequent erosion of the Himalayan Orogeny on atmosphere pCO₂. 

We present comprehensive long-term inorganic carbon budgets linked with millennial-scale cosmogenic denudation rates across 65 river tributaries of the Alaknanda, Bhagirathi, Tons, Yamuna, and Pabbar rivers, which together form the headwaters of the Ganges. These catchments span wide gradients in erosion rates, climate zones, and underlying geology. For each catchment, we combine basic geochemical measurements with δ³⁴S_SO4, δ¹⁸O_SO4, and δ¹⁸O_H2O analyses to quantify the proportion of sulfate derived from pyrite oxidation to the net inorganic carbon budget. We calculate long-term CO₂ fluxes from inorganic sources and combine these estimates with new and existing in situ cosmogenic ¹⁰Be measurements to independently constrain denudation rates. Denudation rates for unsampled catchments are extrapolated using a stream-power-law regression between discharge-weighted channel steepness and measured denudation.

Preliminary results reveal strong contrasts in both the magnitude and direction of net CO₂ fluxes across the High Himalayan Crystalline Sequence (HHCS), Lesser Himalayan Sequence (LHS), and Tethyan Sedimentary Sequence (TSS). The LHS catchments exhibit dominant silicate weathering and sustained long-term CO₂ drawdown, whereas for the TSS and HHCS catchments sulfide oxidation coupled to carbonate dissolution reactions are prominent and outpace CO₂ drawdown by silicate weathering reactions. Long-term denudation rates correlate with CO₂ fluxes, but subtleties exist between the differing morpho-tectonic units. These findings provide new constraints on the spatial controls of weathering processes in the Himalaya and their net impact on Earth’s long-term carbon cycle.