Sea Surface pCO2 in the Beaufort Sea and Canada Basin during Marginal and Extensive Ice-cover, 2012 and 2013

Global warming and changing weather patterns have led to a dramatic decline in Arctic Ocean ice-cover. The warming and freshening of the Arctic Ocean are well-documented consequences of the loss of ice. Its effects on the carbon cycle and sea surface CO₂ levels are not so clear, however. Some studies have attributed increasing sea surface pCO₂ to reduced ice-cover that has opened up large expanses of the Arctic Ocean to air-sea exchange of CO₂ with the atmosphere. Sparse historical data is insufficient to confidently resolve a trend, however, especially because the natural seasonal variability is not well characterized. Two research cruises on the CCGS Louis S. St-Laurent in the Beaufort Sea and Canada Basin during 2012 and 2013 captured dramatically different conditions, with 2012 reaching a record minimum in ice cover and 2013 with a much greater ice extent. Shipboard pCO₂ measurements made on these cruises show that open water had pCO₂ levels near atmospheric saturation whereas ice-covered areas were typically ~100 µatm below atmospheric levels. Model calculations suggest that much of the difference is from air-sea gas exchange and heating of the sea surface. These processes are likely to reduce the effectiveness of the Arctic Ocean as a CO₂ sink as ice-cover continues to decline. The expected rapid increase in CO₂ levels will accelerate ocean acidification, with aragonite undersaturated (~0.9) when the sea surface reaches atmospheric saturation with CO₂.