Extended Data Fig. 6: Sea ice-loss amplifying the decrease in surface water Revelle Factor (RF) in the Canada Basin.

Black dots represent the initial condition for RF and DIC at -1.6 °C. The arrows indicate the processes of warming (red), CO₂ uptake from the atmosphere (purple), dilution by ice meltwater (cyan). Sea ice reduction from 95% to ice-free is accompanied by a salinity decrease of 3.5 (Supplementary Table 4). The yellow shaded areas indicate the possible seasonal variations of RF, which are amplified by the synergistic effect of ice melt, warming and CO₂ uptake. To estimate the change of RF, we allowed 2 °C and 3 °C warming, and 10 and 50 µmol kg⁻¹ DIC perturbations due to air-sea CO₂ exchange in 1990s and 2010s, respectively, which are consistent with the long-term warming rate of 0.5 °C per decade³⁴ and the estimated increase in sDIC by 2.3-2.6 µmol kg⁻¹ per year (Table 1 and Fig. 4d). Note that higher RF indicates lower acid-base buffer capacity.