Variability in pigment specific particulate fluorescence and absorption spectra in the northeastern Pacific Ocean

-Variability in concentration and type of marine particles is the dominant source of optical variability in the oceans. As part of the Optical Dynamics Experiment (ODEX) spectral absorption coefficients and fluorescence excitation were measured for marine particles sampled at stations in the California Current and the eastern edge of the North Central Pacific Gyre. Chlorophyll a normalized fluorescence spectra [F* (k)] or chlorophyll a plus phaeopigment normalized absorption coefficients [a~ (~,)] were analysed with regard to their spectral shapes and magnitudes. Comparison of absorption samples indicates large variability vertically (mixed layer vs deep euphotic zone), horizontally (nearshore vs central gyre) and seasonally (autumn vs spring). When compared to spectra for detritus and for healthy cultures, it is apparent that a variable fraction of the particulate absorption in the ocean is due to detrital components. The effects of absorption by discrete particles may also result in variations in the magnitude and spectral shape of a~ (k). F*(~,) exhibited less variability than a~ (~,). Because F* (~.) appears to be a property of phytoplankton only, the principle causes of variability are photoadaptation and possible taxonomic changes in the phytoplankton crop. Because the origin of particulate organic material (POM) for these regions can be assumed to be derived from in situ biogenic processes, the deviation of field spectra from those observed for cultures must in large part be due to the previous history of biological dynamics within a particular water mass. Data presented here indicate that in situ or remote optical sensors may be capable of supplying information on algal physiology and ecosystem characterization including the extent of photoadaptation and the accumulation of small detrital particles derived from grazing. I N T R O D U C T I O N THE optical proper t ies o f suspended particles, including absorpt ion, scattering and f luorescence, are a m o n g the most fundamenta l and measurable propert ies that allow insight into phy top lank ton ecology. These three p h e n o m e n a are the basis of numerous techniques that are a m o n g the mos t rout inely applied analyses. They are also the focus of research on the deve lopment o f r emote sensing techniques and in situ optical systems. The f luorescence assay o f chlorophyl l and phaeop igment s is a m o n g the most useful and simple techniques to quickly assess algal biomass whether by extract ion in solvents (YENTSCH and MENZEL, 1963; HOLM-HANSEN et al. , 1965) or in v ivo (LORENZEN, 1966). The spectral diffuse a t tenuat ion coefficients and r emote sensing reflectance are determined directly by the absorpt ion and scattering proper t ies of the water and suspended * Polar Research Program A-002P, Scripps Institution of Oceanography, University of California, La Jolla, CA 92093, U.S.A. t Department of Biological Science, University of Southern Cahfornia, Los Angeles, CA 90089, U.S.A.