Open AccessTriple oxygen isotope composition of dissolved O 2 in the equatorial Pacific: A tracer of mixing, production, and respiration
Author(s) -
Hendricks Melissa B.,
Bender Michael L.,
Barnett Bruce A.,
Strutton Peter,
Chavez Francisco P.
Publication year - 2005
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2004jc002735
Subject(s) - photic zone , mixed layer , new production , photosynthesis , subduction , stable isotope ratio , geology , oxygen , oceanography , isotopes of oxygen , atmospheric sciences , chemistry , phytoplankton , nutrient , physics , paleontology , biochemistry , organic chemistry , quantum mechanics , tectonics , geochemistry
As a contribution to the study of equatorial Pacific biogeochemistry, we measured the O 2 /Ar ratio and the triple isotope composition ( 18 O, 17 O, and 16 O) of O 2 along six meridional lines in the equatorial Pacific (8°N–8°S at 95°W, 110°W, 125°W, 140°W, 155°W, and 170°W). O 2 /Ar ratios and δ 18 O were close to equilibrium values within the mixed layer and followed the general trend of increasing δ 18 O with decreasing O 2 /Ar at greater depths. The 17 Δ (≈δ 17 O–0.5δ 18 O) constrains the fraction of photosynthetic O 2 ; 17 Δ 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 Δ 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°W and 110°W. Our average rate of 14 C 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 δ 18 O and 17 Δ as tracers to three‐dimensional biogeochemical ocean GCMs and comparing results with observations will extend our understanding of metabolic rates in the study region.