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  1. Rapid climate warming and sea-ice loss have induced major changes in the sea surface partial pressure of CO2 ( pCO2I). However, the long-term trends in the western Arctic Ocean are unknown. Here we show that in 1994–2017, summer pCO2I in the Canada Basin increased at twice the rate of atmospheric increase. Warming and ice loss in the basin have strengthened the pCO2I seasonal amplitude, resulting in the rapid decadal increase. Consequently, the summer air–sea CO2 gradient has reduced rapidly, and may become near zero within two decades. In contrast, there was no significant pCO2I increase on the Chukchi Shelf, where strong and increasing biological uptake has held pCO2I low, and thus the CO2 sink has increased and may increase further due to the atmospheric CO2 increase. Our findings elucidate the contrasting physical and biological drivers controlling sea surface pCO2I variations and trends in response to climate change in the Arctic Ocean. 
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  2. Abstract

    To examine seasonal and regional variabilities in metabolic status and the coupling of net community production (NCP) and air‐sea CO2fluxes in the western Arctic Ocean, we collected underway measurements of surface O2/Ar and partial pressure of CO2(pCO2) in the summers of 2016 and 2018. With a box‐model, we demonstrate that accounting for local sea ice history (in addition to wind history) is important in estimating NCP from biological oxygen saturation (Δ(O2/Ar)) in polar regions. Incorporating this sea ice history correction, we found that most of the western Arctic exhibited positive Δ(O2/Ar) and negativepCO2saturation, Δ(pCO2), indicative of net autotrophy but with the relationship between the two parameters varying regionally. In the heavy ice‐covered areas, where air‐sea gas exchange was suppressed, even minor NCP resulted in relatively high Δ(O2/Ar) and lowpCO2in water due to limited gas exchange. Within the marginal ice zone, NCP and CO2flux magnitudes were strongly inversely correlated, suggesting an air to sea CO2flux induced primarily by biological CO2removal from surface waters. Within ice‐free waters, the coupling of NCP and CO2flux varied according to nutrient supply. In the oligotrophic Canada Basin, NCP and CO2flux were both small, controlled mainly by air‐sea gas exchange. On the nutrient‐rich Chukchi Shelf, NCP was strong, resulting in great O2release and CO2uptake. This regional overview of NCP and CO2flux in the western Arctic Ocean, in its various stages of ice‐melt and nutrient status, provides useful insight into the possible biogeochemical evolution of rapidly changing polar oceans.

     
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