Excess radiocarbon constraints on air-sea gas exchange and the uptake of CO2 by the oceans

[1] We re-assess the constraints that estimates of the global ocean excess radiocarbon inventory (I) place on air-sea gas exchange. We find that the gas exchange scaling parameter aq cannot be constrained by I E alone. Non-negligible biases in different global wind speed data sets require a careful adaptation of aq to the wind field chosen. Furthermore, aq depends on the spatial and temporal resolution of the wind fields. We develop a new wind speedand inventorynormalized gas exchange parameter aq N which takes into account these biases and which is easily adaptable to any new estimate of I. Our study yields an average estimate of aq of 0.32 ± 0.05 for monthly mean winds, lower than the previous estimate (0.39) from Wanninkhof (1992). We calculate a global annual average piston velocity for CO2 of 16.7 ± 2.9 cm/hr and a gross CO2 flux between atmosphere and ocean of 73 ± 10 PgC/yr, significantly lower than results from previous studies. Citation: Naegler, T., P. Ciais, K. B. Rodgers, and I. Levin (2006), Excess radiocarbon constraints on air-sea gas exchange and the uptake of CO2 by the oceans, Geophys. Res. Lett., 33, L11802, doi:10.1029/ 2005GL025408.