Sea-ice loss amplifies summertime decadal CO 2 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.