Air-Sea Ice-Water CO2 Balance: the Arctic Ocean

Climatic changes in the Northern Hemisphere have led to remarkable environmental changes in the Arctic Ocean, including significant shrinking of sea-ice cover in summer, increased time between sea-ice break-up and freeze-up, and Arctic surface water freshening and warming associated with melting sea-ice, thawing permafrost, and increased runoff. These changes are commonly attributed to the greenhouse effect resulting from increased carbon dioxide (CO2) concentration. The greenhouse effect should be most pronounced in the Arctic where the largest air CO2 concentrations and winter-summer variations in the world for a clean background environment were detected ( www.noaa.gov). Some increased seasonal variation may be a consequence of increasing summer CO2 assimilation by plants in response to higher temperature and longer growing season . The Arctic Ocean's role in determining regional CO2 balance has been ignored (Feely et al., 2001), because continuous sea-ice cover is considered to impede gaseous exchange with the atmosphere so efficiently that no global climate models include CO2 exchange over sea-ice.. However, measurements by Gosink and Kelley in the 1960-70s (Gosink et al., 1976) and our data (Semiletov et al., 2004) showed one year sea-ice was highly permeable to CO2 at temperatures above -15 o C through numerous tiny channels. Mechanism involved in this process has been roughly discussed. In this paper we show that sea-ice melt ponds and open brine channels form an important spring/summer air CO2 sink that also must be included in any Arctic regional CO2 budget; both the direction and amount of CO2 transfer between air and sea during open water season may be different from transfer during freezing and thawing, or during winter when CO2 accumulates beneath Arctic sea-ice.