Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements?

C.J. Sapart, P. Martinerie, E. Witrant, J. Chappelliaz, R.S.W. van de Wal, C. van der Veen, Peter Sperlich, S. Bernard, W.T. Sturges, Thomas Blunier, J. Schwander, D. Etheridge, T. Rockmann