GAS-EXCHANGE, DISPERSION, AND BIOLOGICAL PRODUCTIVITY ON THE WEST FLORIDA SHELF - RESULTS FROM A LAGRANGIAN TRACER STUDY

A Lagrangian tracer study was performed on the west Florida shelf in A pril 1996 using deliberately injected trace gases. Although such studi es have been performed previously, this work is the first where the de liberate tracers, in conjunction with carbon system parameters, are us ed to quantify changes in water column carbon inventories due to air-s ea exchange and net community metabolism. The horizontal dispersion an d the gas transfer velocity were determined over a period of 2 weeks f rom the change in both the concentrations and the concentration ratio of the two injected trace gases, sulfur hexafluoride (SF6) and helium- 3 (He-3). The second moment of the patch grew to 1.6 x 10(3) km(2) ove r a period of 11 days. The gas transfer velocity, normalized to CO2 ex change at 20 degrees C, was 8.4 cm hr(-1) at an average wind speed, U- 10, of 4.4 m s(-1) for the duration of the experiment, which is in goo d agreement with empirical estimates. Remineralization rates exceeded productivity, causing an increase in dissolved inorganic carbon of abo ut 1 mu mol kg(-1) day(-1) in the water column. During this period of senescence, 80% of the increase in inorganic carbon is attributed to c ommunity remineralization and 20% due to invasion of atmospheric CO2.