RN-222 AND RA-226 - INDICATORS OF SEA-ICE EFFECTS ON AIR-SEA GAS-EXCHANGE

Rn-222 and Ra-226 distributions beneath thc sea ice of thc 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 Rn-222 activities that were not lower than their Ra-226 activities, indicating the existence of secular equilibrium and a negligible net exchange of Rn-222 and other gases with the atmosphere. However, seawater in the upper 20-85 m usually exhibited at least some Rn-222 depletion; Rn-222-to-Ra-226 activity ratios tended to have 'ice-free' values (0.3-0.9) in thc summer and values between 0.9 and 1.0 in the winter. Integrated Rn-222 depletions and piston velocities in both seasons typically fell in thc 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 CO2 is not well understood and needs further investigation.