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Abstract Volcanic arcs are chemical weathering hotspots that may contribute disproportionately to global CO₂consumption through silicate weathering. Accurately modeling the impact of volcanic‐arc landscapes on the Earth's long‐term carbon cycle requires understanding how climate and physical erosion control weathering fluxes from arc landscapes. We evaluate these controls by examining the covariation of stream solutes, sediment geochemistry, and long‐term physical erosion fluxes inferred from cosmogenic³⁶Cl in magnetite in volcanic watersheds in Puerto Rico that span a ca. 15‐fold gradient in specific discharge. Analysis of this data using power‐law relationships demonstrates that CO₂consumption from arc‐rock weathering in the humid tropics is more strongly limited by physical erosion and the supply of primary minerals to the weathering zone than by temperature or the flux of fresh, chemically reactive waters through the critical zone. However, a positive correlation between long‐term physical erosion fluxes and specific discharge is also observed. This indicates that fresh mineral supply in arc environments may ultimately depend on precipitation rates, which may maintain a coupling between arc‐rock weathering fluxes and climate under principally supply limited weathering conditions.