Sulfur hexafluoride as a transient tracer in the North Pacific Ocean

The atmospheric concentration of sulfur hexafluoride (SF6) has increased steadily during the past 30 years, making it potentially a valuable transient tracer of oceanic circulation and mixing processes on decadal timescales. Simultaneous measurements of dissolved SF6 with chlorofluorocarbons (CFCs), which have longer atmospheric histories but different growth rates, provides additional information over the use of each tracer alone. Concentrations of dissolved SF6, CFC11 and CFC12 were measured at the Hawaii Ocean Time-Series (HOT) site in 2005. Concentrations were highest in the upper water column, with pronounced CFC11 and CFC12 maxima at a depth of similar to 400 meters. Apparent water mass ages calculated from SF6 concentrations tend to be younger than those calculated from CFC12 concentrations. An isopycnal pipe model is used to estimate the effects of mixing on SF6 and CFC12 derived ages. Combining SF6 and CFC12 ages allows improved estimates of ideal ages and oceanic uptake of anthropogenic CO2.