Microphotometric characterization of phytoplankton and detrital absorption properties in the Sargasso Sea

Abstract

Microphotometric techniques were used to characterize the spectral absorption properties of individual phytoplankton cells and detrital particles from two sites in the Sargasso Sea during spring 1985. Direct determinations of the absorption efficiency factor, Qa(X), geometric crosssectional area, G, and particle type were made for about 50 individual particles for each water sample analyzed. Large intrasample and intersample variations of Qn(X) spectra for both phytoplankton and detrital particles were observed. For the mesotrophic northern station, mean values of Q=(x) and G for phytoplankton cells showed insignificant vertical variations. For detrital particles, however, the mean geometric cross-sectional area decreased with depth while their mean Q,(X) values increased. For the oligotrophic southern station these same relationships were observed, although more small-scale variability was apparent.The statistical comparison of the mean Q,(X) values with the total particulate absorption coefficient spectrum, a,(X), enabled quantification of the contributions phytoplankton and detrital materials made to a,(X). Results showed that phytoplankton abundances accounted for -X)-70% of the particulate absorption at 440 nm, although instances were observed where phytoplankton cells accounted for > 90% of a,(440 nm). The reconstructed particulate absorption spectrum, dp(X), compared favorably with the total a,(X) indicating that nearly all of the optically relevant absorbing particulate material was sampled with the microphotometric technique.

Variability in near-surface particulate absorption spectra: What can a satellite ocean color imager see?

“…In summary, partitioning &(X) into &.,(A) and &(A) demonstrates the importance of accounting for the contribution of detrital materials. Detrital absorption contributes about half of the total particulate absorption, with the greatest contributions for low biomass waters, consistent with previous studies (Mitchell and Kiefer 19883;Iturriaga and Siegel 1989;Bricaud and Stramski 1990). Detrital absorption masks the photosynthetically relevant absorbed radiation by phytoplankton, and its removal is important for the accurate modeling of phytoplankton productivity.…”

“…In addition, other decomposition methods (e.g. Bidigare et al 1987;Iturriaga and Siegel 1989) provide good agreement with the Morrow et al (1989) model . The model partitions a,(X) into phytoplankton and detrital components by using values of spectral absorption at 675 and 570 nm.…”

“…pheopigment concentrations are observed near 4 16 nm and at 685. However, this seems only to occur preferentially deeper in the water column or for coastal environments due to the effects of grazing or photooxidation (Kiefer and SooHoo 1982;Iturriaga and Siegel 1989).…”

Contributions of phytoplankton and other particles to inherent optical properties in New England continental shelf waters

“…comm. ]) determined from analysis of the microphotometric data of Iturriaga and Siegel (1989) for particles between ϳ9 and 27 m in diameter from the Sargasso Sea. The difference between these two estimates may reflect differences in the composition of nonphytoplankton particles between our study site and the Sargasso Sea and between the size ranges of particles analyzed.…”

Long-Term Preservation of Microalgal Cells and their Optical Properties

“…In addition, they provide microalgae taxonomic identification, chlorophyll concentration per cell, photo-adaptive state and particle geometrical cross-sectional area [9][10][11][12]. These determinations are time intensive and difficult to perform in the field, therefore a technique capable of preserving cells without altering their optical properties during analysis and storage was developed.…”