Abstract Rapid climate warming and sea-ice loss have induced major changes in the sea surface partial pressure of CO2 (\(p_{{\mathrm {CO}}_2}\)). However, the long-term trends in the western Arctic Ocean are unknown. Here we show that in 1994–2017, summer \(p_{{\mathrm {CO}}_2}\) in the Canada Basin increased at twice the rate of atmospheric increase. Warming and ice loss in the basin have strengthened the \(p_{{\mathrm {CO}}_2}\) seasonal amplitude, resulting in the rapid decadal increase.
