Oceanographers Gain A Tracer Compound

Oceanographers have traditionally injected kilogram amounts of sulfur hexafluoride gas into the ocean and followed the evolution of these spikes by gas chromatography of water samples to study mixing processes. The technique is useful because SF₆ can be detected at femtomolar quantities and tracked over large areas and long time periods. But researchers need a different tracer for localized studies because SF₆ must be reserved for global studies of ocean circulation and uptake of anthropogenic CO₂. Columbia University's David T. Ho and colleagues now report that the SF₆ analog SF₅CF₃ fits the bill (Geophys. Res. Lett., DOI: 10.1029/2007GL032799). The team conducted a two-year experiment in the Santa Monica Basin off the coast of Southern California that shows SF₅CF₃, which is not commercially available yet, can be detected almost as well as SF₆ and doesn't interfere with using SF₆ for simultaneous tracer studies. Both compounds are greenhouse gases, but the researchers write that the amounts of tracer gases used in ocean studies are insignificant and that SF₅CF₃ is an improvement because its atmospheric lifetime is one-fourth that of SF₆.