A Lagrangian tracer study was performed on the west Florida shelf in April 1996 using a deliberately injected trace gases. Although such studies have been performed previously, this work is the first where the deliberate tracers, in conjunction with carbon system parameters, are used to quantify changes in water column carbon inventories due to air-sea exchange and net community metabolism. The horizontal dispersion and the gas transfer velocity were determined over a period of 2 weeks from the change in both the concentrations and the concentration ratio of the two injected trace gases, sulfur hexafluoride (SF6) and helium-3 (3He). The second moment of the patch grew to 1.6¿103 km2 over a period of 11 days. The gas transfer velocity, normalized to CO2 exchange at 20 ¿C, was 8.4 cm hr-1 at an average wind speed, U10, of 4.4 m s-1 for the duration of the experiment, which is in good agreement with empirical estimates. Remineralization rates exceeded productivity, causing an increase in dissolved inorganic carbon of about 1 &mgr;mol kg-1 day-1 in the water column. During this period of senescence, 80% of the increase in inorganic carbon is attributed to community remineralization and 20% due to invasion of atmospheric CO2.¿ 1997 American Geophysical Union