Basin-wide photosynthetic production rates in the subtropical and tropical Pacific Ocean determined from dissolved oxygen isotope ratio measurements

We used the oxygen isotope anomaly ((17)Delta) to determine gross photosynthetic O-2 production (GOP) on Pacific Ocean transits of a cargo ship between United States and Australia and New Zealand in August 2004 and February, August, and November 2005. The (17)Delta approach yielded robust regional GOP averages of 98 +/- 8, 200 +/- 11, 115 +/- 7, and 182 +/- 32 mmol O-2 m(-2) d(-1) for the northern subtropics, tropics, southern subtropics, and South Coral and Tasman Sea, respectively. When converted to C-14 primary production (PP) rate equivalents, the (17)Delta-based rates compare favorably with prior field data and indicate that satellite algorithms (i.e., vertically generalized productivity model (VGPM) and carbon-based model (CBM)) underestimate in situ rates by a factor of 1.3-3, with greatest underestimation in the tropics. We determined empirical relationships between chlorophyll, nitrate, and GOP that explain 81% of variance in observed GOP rates. Integrating over the Pacific basin from 30 degrees N to 30 degrees S (excluding coastal areas) yields a gross production of 37.3 Gt C yr(-1) and a C-14 PP equivalent of 20.3 Gt C yr(-1), 1.3-1.8 x higher than the 11.4 and 15.9 Gt C yr(-1) estimated by the VGPM and CBM, respectively.