Footnote as

^asSee Tanhua et al. 2006, 2008.

Tanhua, T., A. Biastoch, A. Körtzinger, H. Lueger, C. Böning and D.W.R. Wallace. 2006. Changes of anthropogenic CO₂ and CFCs in the North Atlantic between 1981 and 2004. Global Biogeochem. Cycles GB4017, doi:10.1029/2006GB002695.

Tanhua, T., D.W. Waugh, and D.W.R. Wallace. 2008. Use of SF6 to estimate anthropogenic CO₂ in the upper ocean, J. Geophys. Res. 113, C04037, doi:10.1029/2007JC004416.