Primary production estimates from recordings of solar‐stimulated fluorescence in the equatorial Pacific at 150°W

Abstract

Biological, optical, and hydrographical data were collected on the WEC88 cruise along 150 ø W and during a 6-day time series station on the equator during Februaxy/Maxch 1988. This axea was chaxacterized by a subsurface chlorophyll maximum (SCM), located at 50-70 m depth at the equator and descending down to 120-125 m at the north and south end of the transect. Highest primaxy production rates were neax-surface and confined to the equatorial region and stations between 7 ø and 11øN. To determine the relationship between solax-stimulated fluorescence (centered at 683 nm wavelength) and primary production, a production-fluorescence model based on phytoplankton physiology and maxine optics is described. Results of model calculations predict that there is a lineax relation between production and fluorescence. A compaxison between morning and midday measurements of the production-fluorescence relation showed that there was some difference between the two, whereas evening measurements, on the other hand, were distinctly different from the morning/midday ones. This seems to suggest that diurnal vaxiations contribute significantly to vaxiability in the quantum yield of photochemical processes. The ratio of the quantum yield of photosynthesis to the quantum yield of fluorescence (q)c/q)f), the paxameter which will determine how well production can be estimated from optical recordings, ranged between 0.24 and 0.44 molC Ein -1 (an Einstein equals a mole of photons) for all stations. The highest value for this ratio occurred at the equatorial stations, indicating that interstation (i.e., latitudinal) variability could have an effect on the production-fluorescence relation. Measured 14 (with C incubations) and predicted production compaxed qnite well, although high measured production rates for neax-surface samples were underestimated in most cases. Since both production and fluorescence were noulineax at high irradiance intensities, we recommend in the future that a nonlinear component be incorporated into our model to take this effect into account and thus allow us to refine our estimates of nonlineax data. validate appropriate models relating the measured optical properties with phytoplankton biomass and productivity.A method which shows substantial promise for the remote estimation of phytoplankton biomass and primary production utilizes the solar-stimulated fluorescence signal emitted by phytoplankton, which is centered at 683-685 nm wavelength [Neville and Gower, 1977; Gower and Borstad, 1981, 1990; Kishino et al., 1984a, b; Topliss, 1985; Topliss and Platt, 1986; Kiefer et al., 1989; Chainberlin et al., 1990; Stegmann, 1987a, b,c]. This method has several advantages which make it attractive over other passive methods. First, fluorescence emission is specific for chlorophyll a and its derivatives but not for other suspended matter co-occurring with phytoplankton [Linet al. , 1984]. This is particularly significant for measurements in estuarine or coastal regions, where there is usually a high suspended sediment load as ...

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