THE SANTA-MONICA BASIN TRACER EXPERIMENT - COMPARISON OF RELEASE METHODS AND PERFORMANCE OF PERFLUORODECALIN AND SULFUR-HEXAFLUORIDE

We describe the methods used to prepare and inject sulfur hexafluoride (SF6) and perfluorodecalin (PFD) for the Santa Monica Basin tracer experiment. The use of two tracers gave quasi-independent estimates of mixing rates in the basin, as well as a check on faults in the injection procedure. PFD was the easier substance to inject, but SF6 proved to be the most useful tracer for two reasons: the SF6 measurements had a higher signal-to-noise ratio, and PFD showed some tendency to adsorb onto the surfaces of the sampling gear, whereas SF6 was completely inert in this respect. This surface affinity suggests that PFD may be transported to some extent by settling particles. The PFD profiles obtained 6 months after injection show some enrichment towards the bottom relative to SF6, which might be due to particulate transport.