Deep-SeaResearch, VoL 36, No. 11, pp. 1621-1634, 1989. 0198-0149/89 $3.00+ 0.00 Printedin GreatBritain, © 1989 Pergamon Press plc. Primary production in the North Pacific gyre: a comparison of rates determined by the 14C, Oz concentration and 1SO methods KAREN D. GRANDE,* PETER J. LEB. WILLIAMS,t JOHN MARRA,~ DUNCAN A. PURDIE,§ KRISTINA HEINEMANN,~ RICHARD W. EPPLEYII and MICHAEL L. BENDER* (Received August 1988; in revised form 26 June 1989; accepted 15 June 1989) Abstract--Primary production was measured at 28°N/155°W, north of Hawaii, during the late summer of 1985, using three independent in vitro techniques: (1) the 180 method, in which gross oxygen production is determined from the rate at which 1SO-labelled O2 is produced from 18D- labelled H20, (2) the O2 light/dark bottle method, and (3) the H14CO~ assimilation method. For samples incubated in situ, rates of gross 02 production, determined with 180, are similar to rates calculated by oxygen changes in light/dark bottles, 14C productivities range from -60 to 100% of 180 gross production. Assuming PQ i> 1, this implies that t4c production is ~>65% of gross C assimilation. However, in samples incubated on board ship (with neutral density filters at 35% of incident light intensity, and at surface seawater temperatures), the rates of gross oxygen production measured with 180 were up to two times the rates measured with light/dark bottles, and 2-3 times the rates of 14C production. We believe that the increase in 02 cycling and carbon cycling implied by these data is an artifact reflecting the response of metabolism to some condition of shipboard incubation, possibly the spectral quality of light. INTRODUCTION UNDERSTANDINGand characterizing the nature of biological activity in the oligotrophic ocean require accurate estimates of the rates of gross and net photosynthetic production and community respiration. Unequivocal determination of these rates, however, has proven difficult. Virtually all estimates of primary production have been generated using one technique: assimilation of 14C bicarbonate during incubation of seawater in bottles. Recent work has led to important improvements in the 14C methodology. These improvements include the introduction of trace metal clean techniques (FITZWATER et al., 1982), the use of filters with small enough pore sizes to collect the pO14C incorporated into picoplankton, and the more common determination of DO14C as well as pO14C. (POC and DOC refer to particulate and dissolved organic carbon, respect- ively.) It is now generally believed that the 14C method gives a good approximation to the rate of primary production. Support for this view comes from a number of studies where comparative productivities have been measured using 14C and other methods (WILLIAM et al., 1979, 1983; PLATr, 1984; DAVIES and WILLIAMS, 1984; BENDER et al., 1987). *Graduate School of Oceanography, University of Rhode Island, Kingston, RI 02881, U.S.A. t School of Ocean Sciences, Marine Science Laboratories, Menai Bridge, Anglesey LL59 5EH, U.K. ~: Lamont Doherty Geological Observatory of Columbia University, Palisades, NY 10964, U.S.A. § Department of Oceanography, The University, Southampton SO9 5NH, U.K. II Institute of Marine Resources A-018, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, U.S.A. 1621