222Rn and226Ra: indicators of sea-ice effects on air-sea gas exchange

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Abstract
222 Rn and 226Ra distributions beneath the sea ice of the Barents Sea revealed that ice cover has varied effects on air-sea gas exchange. Twice, once in late summer and once in late winter, seawater samples from the top meter below drill holes had 222Rn activities that were not lower than their 226,Ra activities, indicating the existence of secular equilibrium and a negligible net exchange of 222Rn and other gases with the atmosphere. However, seawater in the upper 20-85 m usually exhibited at least some 222Rn depletion; 222Rn-to-226Ra activity ratios tended to have ‘ice-free’ values (0.3-0.9) in the summer and values between 0.9 and 1.0 in the winter. Integrated 222Rn depletions and piston velocities in both seasons typically fell in the lower 25% of the ranges for ice-free seawater, suggesting that a moderate but far from total reduction in gas exchange is normally caused by ice cover and/or meltwater. The results demonstrate that sea-ice interference with the oceanic uptake of atmospheric gases such as CO, is not well understood and needs further investigation.