Estimating new production in the equatorial Pacific Ocean at 150°W

Abstract

A major goal of the WEC88 cruise of the R/V Wecoma to the equatorial Pacific (made in February‐March 1988), was to establish rates of new production along a meridional section at 150°W and to compare these measured rates with the relatively high values for the equatorial Pacific that had been reported previously using indirect methods and models. New production values were obtained from the traditional approach (in the sense of Dugdale and Goering (1967)) using 15N labelled nitrate uptake, and by using 14C fixation values multiplied by ƒ (proportion of new production) from various sources: from 15N data, from a 14C fixation versus ƒ relationship (Eppley and Peterson, 1979) or from a nitrate versus ƒ relationship (Platt and Harrison, 1985). The ratios of directly measured nitrate and carbon uptake and the ratios of nitrate to nitrate plus ammonium uptake, i.e., values of ƒ, agree well; values of ƒ calculated from carbon uptake or from nitrate concentration are overestimates for the equatorial upwelling region. Carbon to nitrogen uptake ratios measured with 14C and 15N, respectively, approximate the Redfield molar ratio, 6.6 C:N. The overall mean value of ƒ (0.17) helps confirm the view that the low primary production in the enriched eastern equatorial Pacific is due to failure of the nitrate uptake system.