Triple oxygen isotope composition of dissolved O2 in the equatorial Pacific:: A tracer of mixing, production, and respiration -: art. no. C12021

[1] As a contribution to the study of equatorial Pacific biogeochemistry, we measured the O-2/Ar ratio and the triple isotope composition (O-18, O-17, and O-16) of O-2 along six meridional lines in the equatorial Pacific (8 degrees N - 8 degrees S at 95 degrees W, 110 degrees W, 125 degrees W, 140 degrees W, 155 degrees W, and 170 degrees W). O-2/Ar ratios and delta O-18 were close to equilibrium values within the mixed layer and followed the general trend of increasing delta O-18 with decreasing O-2/Ar at greater depths. The (17)Delta (approximate to delta(17) O - 0.5 delta O-18) constrains the fraction of photosynthetic O-2; (17)Delta was slightly elevated with respect to equilibrium within the mixed layer due to local photosynthetic production. In aphotic zone waters above 250 m depth the average (17)Delta values were higher than in the mixed layer. There are four sources of this photosynthetic signal in the dark ocean: production in the euphotic zone prior to subduction in the distant source regions, production below the mixed layer during travel to the equatorial zone, diapycnal mixing with shallower waters bearing photosynthetic O-2, and accumulation of photosynthetic O-2 produced at very low rates below the 1% light level. Our results also constrain biological production rates within the mixed layer at several locations along 95 degrees W and 110 degrees W. Our average rate of C-14 production (53 +/- 34 mmol C m(-2) d(-1)) agreed well with other estimates in the equatorial Pacific, while our average rate of net C production (6.9 +/- 6.2 mmol C m(-2) d(-1)) and f ratio (0.12 +/- 0.11) were somewhat lower than other estimates. Adding delta O-18 and (17)Delta as tracers to three-dimensional biogeochemical ocean GCMs and comparing results with observations will extend our understanding of metabolic rates in the study region.