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The western Arctic Ocean is rapidly acidifying due to sea ice loss. 

Abstract The acidification of coastal waters is distinguished from the open ocean because of much stronger synergistic effects between anthropogenic forcing and local biogeochemical processes. However, ocean acidification research is still rather limited in polar coastal oceans. Here, we present a 17‐year (2002–2019) observational data set in the Chukchi Sea to determine the long‐term changes in pH and aragonite saturation state (Ω_arag). We found that pH and Ω_aragdeclined in different water masses with average rates of −0.0047 ± 0.0026 years⁻¹and −0.017 ± 0.009 years⁻¹, respectively, and are ∼2–3 times faster than those solely due to increasing atmospheric CO₂. We attributed the rapid acidification to the increased dissolved inorganic carbon owing to a combination of ice melt‐induced increased atmospheric CO₂invasion and subsurface remineralization induced by a stronger surface biological production as a result of the increased inflow of the nutrient‐rich Pacific water. 

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.