The CO 2 flux () from lakes to the atmosphere is a large component of the global carbon cycle and depends on the air–water CO 2 concentration gradient (ΔCO 2 ) and the gas transfer velocity ( k ). Both ΔCO 2 and k can vary on multiple timescales and understanding their contributions to is important for explaining variability in fluxes and developing optimal sampling designs. We measured and ΔCO 2 and derived k for one full ice...