HR: 08:30h
AN: OS11C-03    [Abstracts]
TI: In Vitro and In Situ Primary Productivity in the North Pacific Subtropical Gyre as Determined by the Triple Isotope Composition of Dissolved O$_{2}$, $^{18}$O$_{2}$ Labeling, and O$_{2}$/Ar Gas Ratios
AU: * Juranek, L W
EM: juranek@ocean.washington.edu
AF: School of Oceanography, University of Washington, Box 355351, Seattle, WA 98195 United States
AU: Quay, P D
EM: pdquay@u.washington.edu
AF: School of Oceanography, University of Washington, Box 355351, Seattle, WA 98195 United States
AB: Marine organic carbon production rates are a fundamental property of marine ecosystems and are essential to an understanding of surface ocean carbon cycling. However, uncertainties inherent in the methodologies commonly used to determine marine primary productivity (PP) (e.g. $^{14}$C-labeling, O$_{2}$ light/dark changes) make interpretations of measured PP difficult. As a result, comparisons among various in vitro and in situ methods are useful. We used a relatively new technique, measurement of the triple isotope composition of dissolved O$_{2}$, to characterize the mixed layer gross primary productivity (GPP) in situ at the Hawaii Ocean Time-series station ALOHA on four cruises during 2002-2003. Winter and summer GPP averaged 90 and 120 mmol O$_{2}$ m$^{-2}$d$^{-1}$, respectively, with uncertainties of $\sim \pm 40%$. Concurrent in vitro measurements of $^{18}$O$_{2}$ enrichment and $^{14}$C-labelling yielded a mixed layer-integrated GPP that was always less than or equal to the in situ GPP ($^{18}$O$_{2}$: 45-70 mmol O$_{2}$ m$^{-2}$d$^{-1}$; $^{14}$C: 35-50 mmol O$_{2}$ m$^{-2}$d$^{-1}$). Ratios of net community productivity (NCP) to GPP, determined by pairing oxygen isotope measurements with dissolved O$_{2}$/Ar gas ratio measurements, averaged 0.1 in the summer, close to the canonical f-ratio for the open ocean. These results suggest that in vitro methodologies may miss infrequent productivity events that contribute to the time-integrated average measured by in situ techniques.
DE: 4806 Carbon cycling
DE: 4808 Chemical tracers
DE: 4820 Gases
DE: 4870 Stable isotopes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting