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

Abstract

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 18 O labeling, yielded integrated production (0–100 m) that was on average 1.5 times the 14 C 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 ∼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.