The Chukchi Sea shelf (CSS) is a highly productive region in the Arctic Ocean and it is highly efficient for absorbing atmospheric CO₂ and exporting and retaining carbon in the deep-sea. However, with global warming, the carbon retention time in CSS may decrease, leading to less efficient carbon export. Here we investigate the seasonal variability of carbonate chemistry in CSS using three sets of late- vs. early-summer reoccupations of the same transect. Our findings demonstrate substantially increased and rapid degradation of biologically-produced organic matter and therefore acidification over time in the southern CSS due to earlier sea-ice retreat, resulting in significantly shorter carbon retention time. In sharp contrast, no increased degradation has been observed in the northern CSS where photosynthesis has just commenced. In the future, climate change would further diminish the carbon export capacity and exacerbate seasonal acidification not only within CSS but also across other polar coastal oceans.

Sea ice loss,Carbon cycling,Ocean acidification,Seasonal extremes