The Arctic Ocean is currently undergoing rapid environmental change, with a decline in the summer extent of sea ice of >40% since 1979>40% since (Comiso et al., 2008 and further decreases over the next few decades predicted (Overland & Wang, 2013). Other changes, including increases in the sea surface temperature (SST; Steele et al., 2010), the freshening of surface waters (Timmermans et al., 2011), and increases in oceanic fluxes from the Pacific to the Arctic (Woodgate et al., 2012), have also been reported and have been attributed to global warming and climate change. Because sea ice limits air-sea gas exchange, its disappearance in summer enhances CO 2 exchange between the ocean and the atmosphere. In the Arctic Ocean, the surface partial pressure of CO 2 (pCO 2 ) is below the atmospheric level because of intense cooling, mixing with freshwater, and photosynthesis in summer (Bates et al., 2006;Gao et al., 2012). The increase in CO 2 uptake caused by the ice-free conditions decreases the pH of the surface waters. The enhanced uptake of CO 2 by seawater has decreased the pH values and the saturation state of calcium carbonate, a process known as ocean acidification (Orr et al., 2005). Models of the Arctic Ocean also predict that the decrease in calcium carbonate saturation resulting from water freshening and the enhanced absorption of atmospheric CO 2 caused by sea ice melting will lead to an undersaturation of aragonite in Arctic surface waters within the next decade (Steinacher et al., 2009;

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