National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2013

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

Sonnerup, R., S. Mecking, and J. Bullister

Deep-Sea Res. I, 72, 61–71, doi: 10.1016/j.dsr.2012.10.013 (2013)

Depth profiles of dissolved chlorofluorocarbon-11 (CFC-11) and sulfur hexafluoride (SF6) were measured during a September 2008 cruise in the Northeast Pacific Ocean. For each water sample, the two tracers were used in concert to estimate likely mean ages and widths of parameterized 1-D transit time distributions (TTDs). In shallow waters (<250 m), the TTDs’ mean ages were relatively loosely constrained due to the slow decrease of atmospheric CFC-11 since 1994. In the main thermocline (25.0–26.6 σθ, ~ 300–550 m), the CFC-11/SF6 tracer pair constrained TTDs’ mean ages to within ± 10%. Deeper than 26.8 σθ (~ 600 m), SF6 levels in 2008 were too low for the CFC-11/SF6 tracer pair to constrain the TTDs’ mean ages. Within the main thermocline of the subtropical North Pacific Ocean (20°–37°N along 152°W), the TTDs’ mean ages were used to estimate Oxygen Utilization Rates (OURs) of ~11 μmol kg−1 yr−1 on 25.0–25.5 σθ (~160 m), attenuating to very low rates (0.12 μmol kg−1 yr−1) by 26.8–27.0 σθ (~600 m). Depth integration of the in-situ OURs implied an average carbon remineralization rate of 1.7 ± 0.3 mol C m−2 yr−1 in this region and depth range, somewhat lower than other independent estimates. Along the 152°W section, depth integrating the apparent OURs implied carbon remineralization rates of 2.5–3.5 mol C m−2 yr−1 from 20°N to 30°N, 3.5–4.0 mol C m−2 yr−1 from 30°N to 40°N, and 2–2.7 mol C m−2 yr−1 north of 45°N.

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