Variability in spectral and nonspectral measurements of photosynthetic light utilization efficiencies

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Abstract
The aim,of this study,was,to quantify the variability in and differences between,spectral and nonspectral measurements of light utilization efficiencies for natural phytoplankton communities, in order,to evaluate possible,consequences,for bio-optical models,of in situ primary,production,(P). Field samples were collected at 4 coastal stations during a 1 d transect (July 23, 1988) across the South- ern California Counter,Current (SCCC) at a time,when,phytoplankton,communities,were,dominated largely by picoplankton,(0.4 to 5 pm). Concurrent,determinations,were,made,of downwelling,spectral irradiance [C&-&z)], photosynthetica lly available radiation (C&J, spectral attenuation coefficients [K&z)], detrital-correc ted phytoplankton absorption [Q@,z)], white light photosynthesis-irradiance parameters (PmaX, a, &) and carbon action spectra a(A&,z). From these parameters, spectral estimates of jn situ phytoplankton absorbed radiation [AQph(AAi,z)] 1 maximum quantum yield [&ax (AAi,z)]f opera- tional quantum yield [ +(A&,z)], radiation utilization efficiency [ e(AAi,z)] and productivity P(AAi,z) were derived. Significant spatial variability in all bio-optical parameters,was,noted,for communities,in the surface waters and the chlorophyll maximum. For surface waters, there was significant variability in the 525 to 600 nm region of the spectral signatures of 4(AAifz) and p(AAi,Z) which was attributable to phycobilins,not resolved,in absorption,spectra. The importance,of light absorption,by photosyntheti,c pigments other than chlorophyll a (chl), and their associated impact upon absorption-based production parameters, increased with light depth. One consequence was a close correspondence between AC&h and P(AAi,Z) at depth which was not evident in surface waters. A second consequence was that while spectrally weighted,and,white,light estimates,of quantum,yield were,occasionally,similar in surface waters, spectral estimates for all chlorophyll maximum communities were 4- to 6-fold higher than white light measurements.,Results confirm,previous,observations,that white,light measures,of quantum,yield

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