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

Abstract

[1] We re-assess the constraints that estimates of the global ocean excess radiocarbon inventory (I E ) place on air-sea gas exchange. We find that the gas exchange scaling parameter a q cannot be constrained by I E alone. Non-negligible biases in different global wind speed data sets require a careful adaptation of a q to the wind field chosen. Furthermore, a q depends on the spatial and temporal resolution of the wind fields. We develop a new wind speed-and inventorynormalized gas exchange parameter a q N which takes into account these biases and which is easily adaptable to any new estimate of I E . Our study yields an average estimate of a q 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 CO 2 of 16.7 ± 2.9 cm/hr and a gross CO 2 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 CO 2 by the oceans, Geophys. Res. Lett., 33, L11802,

Seasonal variability of the inorganic carbon system in the Amundsen Gulf region of the southeastern Beaufort Sea

“…The uncertainty associated with the air-sea flux term is relatively high (20%, or roughly 1.5 mmol kg 21 ) and is largely due to uncertainty in the parameterization of the gas transfer velocity (see Eq. 1 [Naegler et al 2006;Sweeney et al 2007;Watson et al 2009]). The uncertainty associated with the vertical diffusion term is quite high (100%), reflecting the range in estimates of K v , but the contribution from vertical diffusion is small, resulting in an error of , 2 mmol kg 21 .…”

Uncertainty of the global oceanic CO<sub>2</sub> uptake induced by wind forcing: quantification and spatial analysis

“…These studies have led to k dependencies on wind speed of quadratic (k 660 = c·U 10 ², Ho et al, 200610 ², Ho et al, , 2011Jacobs et al, 1999;, cubic (k 660 = a+d·U 10 ³ with a ≥ 0, Edson et al, 2011;Prytherch et al, 2010;20 Wanninkhof and McGillis, 1999) and linear-quadratic (k 660 = b·U 10 +c·U 10 ², Nightingale et al, 2000;Weiss et al, 2007) forms. Other studies have followed a distinct approach and constrained k-U 10 relationships for the global ocean on the basis of the global ocean bomb 14 C inventory (Broecker et al, 1985;Naegler et al, 2006;Sweeney et al, 2007) and global wind fields. The resulting relationships are all of quadratic form (k 660 = c·U 10 2 ), with different global values of c depending on the spatio-temporal resolution of the wind speed product used.…”

“…The resulting relationships are all of quadratic form (k 660 = c·U 10 2 ), with different global values of c depending on the spatio-temporal resolution of the wind speed product used. Therefore, in principle, values reported for c in Table 2 are 25 intimately associated to the specific wind product that was applied during the fitting procedure (Naegler et al, 2006). For further details regarding the different procedures, refer to Table 2.…”

“…In particular, Naegler et al (2006) have shown that the value of c is a function of the applied wind field but also of its spatiotemporal resolution. Hence, in principle, the selection of a given c value not only implies the use of the same wind speed product as the one originally applied, but also retention of the same spatio-temporal resolution and temporal coverage.…”

“…If 5 another wind product and/or different spatial and temporal resolutions are used to calculate FCO 2 , then the value of c has to be adapted accordingly. Naegler et al (2006) proposed different correction coefficients for c in order to account for the bias introduced by the choice of one wind product over another. These correction coefficients have been calculated for several sets of spatial and temporal resolutions (1° x 1°, daily or 5° x 4°, monthly for example).…”