Abstract
Marine surface waters are being acidified due to uptake of anthropogenic carbon dioxide, resulting in surface ocean areas of undersaturation with respect to carbonate minerals, including aragonite. In the Arctic Ocean, acidification is expected to occur at an accelerated rate with respect to the global oceans, but a paucity of baseline data has limited our understanding of the extent of Arctic undersaturation and of regional variations in rates and causes. The lack of data has also hindered refinement of models aimed at projecting future trends of ocean acidification. Here, based on more than 34,000 data records collected in 2010 and 2011, we establish a baseline of inorganic carbon data (pH, total alkalinity, dissolved inorganic carbon, partial pressure of carbon dioxide, and aragonite saturation index) for the western Arctic Ocean. This data set documents aragonite undersaturation in ∼20% of the surface waters of the combined Canada and Makarov basins, an area characterized by recent acceleration of sea ice loss. Conservative tracer studies using stable oxygen isotopic data from 307 sites show that while the entire surface of this area receives abundant freshwater from meteoric sources, freshwater from sea ice melt is most closely linked to the areas of carbonate mineral undersaturation. These data link the Arctic Ocean’s largest area of aragonite undersaturation to sea ice melt and atmospheric CO2 absorption in areas of low buffering capacity. Some relatively supersaturated areas can be linked to localized biological activity. Collectively, these observations can be used to project trends of ocean acidification in higher latitude marine surface waters where inorganic carbon chemistry is largely influenced by sea ice meltwater.
Highlights
The importance of the Arctic Ocean in the context of global carbon dioxide (CO2) uptake and ocean acidification is widely accepted [1,2,3,4,5,6,7,8,9]
Projections of the extent and rate of Arctic Ocean acidification and the associated ecosystem changes require models based on causal relationships and complex feedbacks among rapidly changing physical, chemical, and biological processes
Our baseline study significantly expands the body of data available for such work and provides the first high-resolution data from higher latitude waters
Summary
The importance of the Arctic Ocean in the context of global carbon dioxide (CO2) uptake and ocean acidification is widely accepted [1,2,3,4,5,6,7,8,9]. A large fraction of the global net CO2 uptake during recent decades (,2200 Tg C yr21) has occurred over the relatively small surface area of the Arctic Ocean. [8]), it is inferred that as much as 7.5% of global oceanic CO2 uptake may occur in the Arctic Ocean, which comprises only 3.9% of the global ocean’s surface. These figures may be even more noteworthy given that the uptake occurs predominantly in seasonally ice-free areas, which are a fraction of the Arctic Ocean surface. Multiyear sea ice has experienced the greatest decline [9] This loss of multiyear ice has exposed the surface mixed layer (typically#50 m thick), which is undersaturated with respect to atmospheric CO2; the result is oceanic CO2 uptake. Ice cover significantly inhibited CO2 exchange between this layer and the atmosphere [15,16,17]
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