Shipboard measurements of phytoplankton production and solar-stimulated fluorescence rates in the northwest Atlantic

We present results from a cruise to the Canadian sub-arctic and the Scotian Shelf designed to evaluate optical methods for bio-optical estimation of primary productivity. Vertical profiles of temperature and chlorophyll showed much variability from one station to the next, while primary production (normalized to biomass) ranged from 0.4 to 1 gC gChl(-1) h(-1) near the surface and decreased with depth. We used the linear model of Stegmann et al. (1992) (in Journal of Geophysical Research 97, 627-635) to examine the relationship between solar-stimulated fluorescence and primary production and to determine the variability of the ratio of the quantum yield of photosynthesis, Phi(c), to the quantum yield of fluorescence, Phi(f). We found that (1) there was a clear relation between production and fluorescence; (2) diurnal variations contributed. to the variability in Phi(c)/Phi(f); and (3) Phi(c)/Phi(f) ranged from 0.32 to 0.42 molC Ein(-1). The range of Phi(c)/Phi(f) found in this study is similar to the one from the equatorial Pacific (Stegmann et al., 1992, in Journal of Geophysical Research 97, 627-638), despite the fact that the environmental conditions in the two regions were very different from each other. We did not find an increase in Phi(c)/Phi(f) as temperature increased. (C) 1997 Elsevier Science Ltd.