Abstract
One of the most significant responses of arctic marine ecosystems to projected global changes of the coming decades will likely be an increased extent of ocean surface undersaturated with calcium carbonate minerals such as aragonite (CaCO sub(3)). Causes of this undersaturation in the Arctic Ocean are poorly quantified, but likely involve feedbacks with other environmental changes in the region, such as increasing atmospheric pCO sub(2), changes in surface temperature, increased freshwater inputs from terrestrial runoff, and reduction of the extent, thickness, and duration of sea-ice cover. We have documented changes in aragonite undersaturation over a 3-year, high-spatial-resolution study of surface waters in the Canada and Makarov basins in the western Arctic Ocean. We use stable oxygen isotope data to demonstrate that this area is also marked by increased freshwater content, with additional freshwater derived predominantly from sea-ice melt. The addition of freshwater reduces dissolved ion concentrations and thereby decreases aragonite saturation states. Comparison of these new high-spatial-resolution carbon and oxygen isotopic data with similar data from the western Arctic from 1997 shows that the undersaturation is recent, and occurs at unprecedented rates. Such high-resolution data will facilitate more accurate modeling of future undersaturation trends in areas such as the Makarov Basin where summer ice-free conditions are predicted in the near term. While the effects attributed to multiyear sea-ice melt may diminish, the consequences of increased runoff and direct precipitation on freshwater content may cause the observed trends to continue.