Determination of Persian Gulf Water transport and oxygen utilization rates using SF-6 as a novel transient tracer

Sulphur hexafluoride (SF6) has potential as a transient tracer of recently ventilated water masses, as its atmospheric burden continues to increase. Northern Arabian Sea hydrography was examined using measurements of atmospheric and dissolved SF6, CFC-11, CFC-12 and CFC-113. Persian Gulf Water (PGW) was characterised by its SF6 signal, and the time elapsed since its formation was evaluated by two approaches. Four ventilation age estimates were derived from SF6/CFC-11, SF6/CFC-12, CFC-113/CFC-11 and CFC-113/CFC-12, and their agreement at the oceanic stations confirms the validity of SF6 as a transient tracer. A second approach, of correcting SF6 partial pressure for PGW dilution by an optimal mixing model and referencing to the atmospheric SF6 chronology, provided a relative tracer age. This indicated a PGW flow of 0.016 (+/−0.003) m/s across the northern Arabian Sea, with an associated oxygen consumption of 10.1 µmol/l p.a. that exceeds tracer-derived estimates but confirms rates derived from export flux.