To better understand the extent of acidification in the Arctic Ocean, we present pH measurements collected along a shelf-slope-basin transect from the Chukchi Sea shelf to the Chukchi Abyssal Plain (CAP) in the western Arctic Ocean during the summer 2010 Chinese Arctic National Research Expedition (CHINARE) cruise. We observed low pH values in the Chukchi Sea shelf bottom waters (~30 m-bottom) and CAP upper haloline layer (UHL) (100–200 m). In the shelf bottom waters, the pH values were 7.66–8.13, about 0.07–0.68 pH units lower than the surface values of 8.20–8.24. In the CAP subsurface waters, the pH values were 7.85–7.98, about 0.08–0.31 pH units lower than the surface values of 8.20–8.24. Biogeochemical model simulations suggest that remineralized CO₂ driven by sea-ice loss is primarily responsible for the low pH values in the bottom waters of the Chukchi Sea (shelf) and the UHL waters of the CAP (basin). Recent sea-ice melt enhanced organic matter production in surface waters and subsequent supported the increased microbial respiration of organic matter in bottom waters. Moreover, low pH bottom waters were flushed into the UHL during winter to sustain the low pH characteristics in the subsurface basin layers. In addition, our simplified model suggests that the thermodynamic effect of pH is small. However, increasing temperature significantly increased aragonite saturation (Ω_arag) which slowed down the speed of acidification.