Freshening of the western Arctic negates anthropogenic carbon uptake potential

As human activities increase the atmospheric concentration of carbon dioxide (CO 2 ), the oceans are known to absorb a significant portion. The Arctic Ocean has long been considered to have enormous potential to sequester anthropogenic CO 2 , and mitigate emissions. The frigid waters make CO 2 more soluble, and as sea ice melts, greater surface area is exposed to absorb CO 2 . However, sparse data have made quantifying the amount of anthropogenic CO 2 in the Arctic difficult, stimulating much debate over the basin's contribution to CO 2 sequestration from the atmosphere. Using three separate cruises in 1994, 2005, and 2015 in the Canada and Makarov basins, we analyze the decadal variability in anthropogenic CO 2 uptake in the central western Arctic. Here we show, from direct carbon system measurements spanning two decades, that despite increased atmospheric CO 2 , total dissolved inorganic carbon has actually decreased, with minimal anthropogenic CO 2 uptake. The reduction in dissolved CO 2 results from a dilution of total alkalinity by increased freshwater supply, particularly river water. Changes in the freshwater budget of the western Arctic override its uptake potential, resulting in a weak sink, or possibly source of CO 2 .