Impact of rapid sea-ice reduction in the Arctic Ocean on the rate of ocean acidification

[摘要] The largest pH decline and widespread undersaturation with respect toaragonite in this century due to uptake of anthropogenic carbon dioxide inthe Arctic Ocean have been projected. The reductions in pH and aragonitesaturation state in the Arctic Ocean have been caused by the melting of seaice as well as by an increase in the concentration of atmospheric carbondioxide. Therefore, future projections of pH and aragonite saturation in theArctic Ocean will be affected by how rapidly the reduction in sea iceoccurs. The observed recent Arctic sea-ice loss has been more rapid thanprojected by many of the climate models that contributed to theIntergovernmental Panel on Climate Change Fourth Assessment Report. In thisstudy, the impact of sea-ice reduction rate on projected pH and aragonitesaturation state in the Arctic surface waters was investigated. Reductionsin pH and aragonite saturation were calculated from the outputs of twoversions of an Earth system model with different sea-ice reduction ratesunder similar CO₂ emission scenarios. The newer model version projectsthat Arctic summer ice-free condition will be achieved by the year 2040, andthe older version predicts ice-free condition by 2090. The Arctic surfacewater was projected to be undersaturated with respect to aragonite in theannual mean when atmospheric CO₂ concentration reaches 513 (606) ppm inyear 2046 (2056) in new (old) version. At an atmospheric CO₂concentration of 520 ppm, the maximum differences in pH and aragonitesaturation state between the two versions were 0.1 and 0.21 respectively.The analysis showed that the decreases in pH and aragonite saturation statedue to rapid sea-ice reduction were caused by increases in both CO₂uptake and freshwater input. Thus, the reductions in pH and aragonitesaturation state in the Arctic surface waters are significantly affected bythe difference in future projections for sea-ice reduction rate. Our resultssuggest that the future reductions in pH and aragonite saturation statecould be significantly faster than previously projected if the sea-icereduction in the Arctic Ocean keeps its present pace.

[学科分类] 地球化学与岩石