In vitro and in situ gross primary and net community production in the North Pacific Subtropical Gyre using labeled and natural abundance isotopes of dissolved O2 -: art. no. GB3009

[1] We measured gross primary productivity (GPP) in vitro and GPP and net community production (NCP) in situ on four cruises to the Hawaii Ocean Time series ( HOT) station ALOHA during 2002 - 2003. In vitro GPP, determined by O-18 labeling, yielded integrated production (0 - 100 m) that was on average 1.5 times the C-14 integrated production. Mean integrated productivity from two winter and two summer cruises was 575 mg C m(-2) d(-1) and 930 mg C m(-2) d(-1), respectively. In situ GPP, determined from the triple-isotope composition of dissolved O-2, averaged 910 mg C m(-2) d(-1) in the winter and 1225 mg C m(-2) d(-1) in the summer/fall, with an uncertainty of +/- 40%. The NCP/GPP ratio, determined using O-2/Ar gas ratio and oxygen isotope measurements, was around 0.1 in the summer, close to the canonical f-ratio for the open ocean, indicating station ALOHA is a net autotrophic system during summer months. The consistently higher gross carbon production measured by the in situ method, which integrates production over the similar to 2-week residence time of O-2 in the mixed layer, suggests that aperiodic bursts of production contribute significantly to time-averaged mean productivity at station ALOHA.