The PMEL Chlorofluorocarbon (CFC) Tracer Program has been using dissolved CFCs as time-dependent or 'transient' tracers of ocean circulation and mixing processes. The concentrations of CFCs, along with a number of other anthropogenic compounds (e.g.CO2), have increased significantly in the global atmosphere during the past century. CFC concentrations in the surface ocean can be modeled as functions of location and time. Studies of the entry of CFCs from the atmosphere into the surface ocean, and the subsequent transport of these compounds into the ocean interior provides a unique description of the time-integrated circulation of the ocean on decadal time scales.
A key goal of the Chlorofluorocarbon Tracer Program is to document the transient invasion of CFCs and other tracers (including sulfur hexafluoride- SF6) into the thermocline and deep waters of the world ocean. This is done by means of repeat long-line hydrographic sections and time-series stations. The CFC observations are used to estimate the ventilation rate of water masses in the global ocean.
A second key goal of this program is to use information on the rates and pathways of the invasion of these compounds in the ocean to improve estimates of the rate of uptake of other gases including anthropogenic CO2 in the ocean and the rates of important biogeochemical processes such as the biological carbon export from the sea surface.
A third goal is to use the CFCs, in conjunction with other available ocean tracers, to constrain ocean circulation and carbon cycling models. Such tests are essential for evaluating and improving the models.
|This figure shows the concentration of dissolved CFC-12 in the ocean at the neutral density level 26.8. Black dots indicate the location of stations where dissolved CFCs were measured as part of the World Ocean Circulation Experiment (WOCE). Dissolved CFCs highlight regions of the ocean where gases in the atmosphere can be carried on decadal time scales.|
|NOAA | OAR | Pacific Marine Environmental Laboratory|