National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2015

Transit time distributions and oxygen utilization rates from chlorofluorocarbons and sulfur hexafluoride in the southeast Pacific Ocean

Sonnerup, R.E., S. Mecking, J.L. Bullister, and M.J. Warner

J. Geophys. Res., 120(5), 3761–3776, doi: 10.1002/2015JC010781 (2015)

Chlorofluorocarbons-11 (CFC-11), CFC-12, and sulfur hexafluoride (SF6) were measured during the December 2007 to February 2008 CLIVAR/Repeat Hydrography (RH) P18 section along ∼103°W in the Southeast Pacific Ocean. Transit-time distributions (TTDs) of 1-D transport that matched all three tracers were consistent with high Peclet number flow ventilating the subtropical mode water and the main subtropical thermocline (30°S–42°S, 200–800 m). In the subtropics, TTDs with predominantly advective transport predicted decadal increases in CFC-12 and CFC-11 consistent with those observed comparing 1994 WOCE with 2007/2008 CLIVAR/RH data, indicating steady ventilation in this region, and consistent with the near-zero changes observed in dissolved oxygen. The mean transport timescales from the tracer-tuned TTDs were used to estimate apparent oxygen utilization rates (OURs) on the order of 8–20 μmol kg−1 yr−1 at ∼200 m depth, attenuating to ∼2 μmol kg−1 yr−1 typically by 500 m depth in this region. Depth-integrated over the thermocline, these OURs implied carbon export rates from the overlying sea surface on the order of ∼1.8 moles C m−2 yr−1 from 30°S to 45°S, 2–2.5 moles C m−2 yr−1 from 45°S to 52°S, and 2.5–3.5 moles C m−2 yr−1 from 52°S to 60°S.

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