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 (SF 6 ) 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 SF 6 proved to be the most useful tracer for two reasons: the SF 6 measurements had a higher signal‐to‐noise ratio, and PFD showed some tendency to adsorb onto the surfaces of the sampling gear, whereas SF 6 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 SF 6 , which might be due to particulate transport.