Western boundary currents host some of the most intense air–sea CO₂ exchange in the ocean, yet what controls surface water partial pressure of CO₂ (pCO₂)  within their high-velocity jet cores remains unclear. The Kuroshio Extension (KE) jet — a warm-core, strongly stratified feature — suppresses the vertical exchange that drives carbon uptake at submesoscale fronts, leaving lateral advection as the dominant pathway shaping its surface biogeochemistry. Whether this advection enhances or opposes the jet's thermodynamic CO₂ outgassing has not been directly quantified. Here we show, from high-resolution underway pCO₂, dissolved inorganic carbon (DIC) and total alkalinity (TA) measurements collected on two independent transects across the KE jet during the 2022 R/V Tan Kah Kee cruise, that the jet axis sustains surface pCO₂ ~60 μatm below the surrounding subtropical gyre despite elevated sea surface temperature. A four-term Taylor decomposition shows that warming alone elevates pCO₂ by +74 to +85 μatm and reduced TA by a further +52 to +61 μatm, a combined outgassing tendency overwhelmingly offset by a −124 to −134 μatm DIC suppression intrinsic to the warm Kuroshio water mass. Counterfactual flux calculations show that this DIC signature converts a thermodynamically predicted CO₂ source (+2.7 mmol C m⁻² d⁻¹) into an observed sink (−3.2 mmol C m⁻² d⁻¹), enhancing regional carbon uptake by ~5–6 mmol C m⁻² d⁻¹. The KE jet thus acts as a thermodynamic carbon-sink amplifier — a mechanism likely operating in other western boundary currents and currently under-represented in regional carbon budgets.