Partitioning of the global fossil CO2 sink using a 19-year trend in atmospheric O-2

O-2/N-2 is measured in the Cape Grim Air Archive (CGAA), a suite of tanks f illed with background air at Cape Grim, Tasmania (40.7 degrees S, 144.8 deg rees E) between April 1978 and January 1997. Derived trends are compared wi th published O-2/N-2 records and assessed against limits on interannual var iability of net terrestrial exchanges imposed by trends of delta(13)C in CO 2. Two old samples from 1978 and 1987 and eight from 1996/97 survive critic al selection criteria and give a mean 19-year trend in delta(O-2/N-2) of -1 6.7 +/- 0.5 per meg y(-1), implying net storage of +2.3 +/- 0.7 GtC (10(15) g carbon) yr(-1) of fossil fuel CO2 in the oceans and +0.2 +/- 0.9 GtC yr( -1) in the terrestrial biosphere. The uptake terms are consistent for both O-2/N-2 and delta(13)C tracers if the mean C-13 isotopic disequilibrium flu x, combining terrestrial and oceanic contributions, is 93 +/- 15 GtC parts per thousand yr(-1).