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

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 approximate to 103 degrees 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 degrees S-42 degrees 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 mol kg(-1) yr(-1) at approximate to 200 m depth, attenuating to approximate to 2 mol 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 approximate to 1.8 moles C m(-2) yr(-1) from 30 degrees S to 45 degrees S, 2-2.5 moles C m(-2) yr(-1) from 45 degrees S to 52 degrees S, and 2.5-3.5 moles C m(-2) yr(-1) from 52 degrees S to 60 degrees S.