Abstract
The strong CO 2 sink in Arctic Ocean plays a significant role in the global carbon budget. As a high-latitude oceanic ecosystem, the features of sea surface p CO 2 and air-sea CO 2 flux are significantly influenced by sea ice melt; however, our understanding of p CO 2 evolution during sea ice melt remains limited. In this study, we investigate the dynamics of p CO 2 during the progression of sea ice melt in the western Arctic Ocean based on data from two cruises conducted in 2010 and 2012. Our findings reveal substantial spatiotemporal variability in surface p CO 2 on the Chukchi Sea shelf and Canada Basin, with a boundary along the shelf breaks at depths of 250-500 m isobaths. On the Chukchi Sea shelf, strong biological consumption dominates p CO 2 variability. Moreover, in Canada Basin, the p CO 2 dynamics are modulated by various processes. During the active sea ice melt stage before sea ice concentration decreases to 15%, biological production through photosynthetic processes and dilution of ice melt water lead to a reduction in DIC concentration and subsequent decline in p CO 2 . Further, these effects are counteracted by the air-sea CO 2 exchange at the sea surface which tends to increase seawater DIC and subsequently elevate surface p CO 2 . Compared to the p CO 2 reduction resulting from biological production and dilution effects, the contribution of air-sea CO 2 exchange is significantly lower. The combined effects of these factors have a significant impact on reducing p CO 2 during this stage. Conversely, during the post sea ice melt stage, an increase in p CO 2 resulting from high temperatures and air-sea CO 2 exchange outweighs its decrease caused by biological production. Their combined effects result in a prevailing increase in sea surface p CO 2 . We argue that enhanced air-sea CO 2 uptake under high wind speeds also contributes to the high sea surface p CO 2 observed in 2012, during both active sea ice melt stage and post sea ice melt stage. The present study reports, for the first time, the carbonate dynamics and p CO 2 controlling processes during the active sea ice melt stage. These findings have implications for accurate estimation of air-sea CO 2 fluxes and improved modeling simulations within the Arctic Ocean.