Sea-ice loss amplifies summertime decadal CO2 increase in the western Arctic Ocean

Rapid climate warming and sea-ice loss have induced major changes in the sea surface partial pressure of CO 2 ( p CO 2 ). However, the long-term trends in the western Arctic Ocean are unknown. Here we show that in 1994–2017, summer p 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 CO 2 seasonal amplitude, resulting in the rapid decadal increase. Consequently, the summer air–sea CO 2 gradient has reduced rapidly, and may become near zero within two decades. In contrast, there was no significant p CO 2 increase on the Chukchi Shelf, where strong and increasing biological uptake has held p CO 2 low, and thus the CO 2 sink has increased and may increase further due to the atmospheric CO 2 increase. Our findings elucidate the contrasting physical and biological drivers controlling sea surface p CO 2 variations and trends in response to climate change in the Arctic Ocean. Surface CO 2 concentrations in the western Arctic Ocean differ due to local processes. During the period 1994–2017, the Canada Basin has shown rapid increases as warming and ice loss enhance air–sea exchange of CO 2 , whereas the Chukchi Shelf has strong biological activity, resulting in a CO 2 sink.