Effects of asphericity on single-particle polarized light scattering.

Polarized light scattering from individual particles has been analyzed to determine the effects of particle shape. Flow cytometric techniques were used on samples of spherical microspheres and naturally occurring marine algae. An analog of the depolarization ratio was obtained by using crossed polarizers in the source and detector of the flow cytometer. Results suggest that differences between the polarized light scattering of spheres and aspherical particles are not discernible unless the scattered intensities are normalized to the forward scattering, which is roughly equivalent to particulate cross section. This research indicates that polarized light scattering, when normalized to particle size, may provide an indication of the extent of asphericity of hydrosols.

Phytoplankton optical properties: flow cytometric examinations of dilution-induced effects.

Flow cytometry is used to measure dilution-induced changes in the optical properties of Dunaliella tertiolecta-light scatter, cell fluorescence, and refractive index. Observed changes in cell optical properties are compared to simultaneous measures of cell volume and count, extracted chlorophyll a concentration, and the (14)C uptake rate. Flow cytometric measurements reveal short-term dilution effects (within 1 h of dilution) that, are not evident in other morphological or physiological measurements such as cell volume, extracted chlorophyll a concentration, and (14)C uptake rate. Data are presented which suggest that these short-term changes in cell optical properties are the result of changes in the real component of refractive index, possibly due to a rapid and temporary rearrangement of the internal cellular structure. Long-term changes are observed in time series measurements of cell volume and count, extracted chlorophyll a concentration, and (14)C uptake rate.

Size and refractive index of individual marine participates: a flow cytometric approach.

Flow cytometric measurements of light scatter, near-forward light scatter (theta = 1.5-19 degrees ) and side scatter (theta = 73-107 degrees ), from individual marine particles is modeled using Mie theory. Particles are assumed to be homogeneous and nearly spherical in shape. Uniform polystyrene microspheres and oil suspensions are used to estimate model accuracy. Within the particle diameter range of 1-32 microm, the mean error for near-forward scatter and side scatter is 16.9% and 30.1%. respectively. The model is used to estimate size and refractive index of several nannoplankton species and the results are compared with microscopic measurements of cell size and published values of phytoplankton refractive index. Within the refractive-index range of 1.01-1.1, the model may be inverted to yield refractive index with an absolute error of between 0.01 and 0.003. Measurements of particle size distributions in clear ocean water indicate this range accounts for 99% of all nannoplankton and 39% of all particles within the size range from 1 to 10 microm.

Observations on the intra- and interspecific single cell optical variability of marine phytoplankton.

Phytoplankton occur as a wide variety of sizes, shapes, textures, and conformational inclusions. Optical reseachers, however, to date represent phytoplankton in models as uniform or varying by only a small amount. We give evidence here of changes in the distribution of light scatter for single cells of individual species. This observation is noted even within one species. Optical characteristics show ranges of intraspecific variability (as functions of physiological or nutritional state) comparable in magnitude to interspecific variability. Such variability may be attributed to changes in the cellular refractive-index distribution and the cell size and shape.

High Nitrite Levels off Northern Peru: A Signal of Instability in the Marine Denitrification Rate.

During February and March 1985, nitrite levels along the northern (approximately 7 degrees to 10 degrees S) Peruvian coast were unusually high. These accumulations occurred in oxygen-deficient waters, suggesting intensified denitrification. In a shallow offshore nitrite maximum, concentrations were as high as 23 micromoles per liter (a record high). Causes for the unusual conditions may include a cold anomaly that followed the 1982-83 El Niño. The removal of combined nitrogen (approximately 3 to 10 trillion grams of nitrogen per year) within zones of new or enhanced denitrification observed between 7 degrees to 16 degrees S suggests a significant increase in oceanic denitrification.

Volume scattering function of suspended particulate matter at near-forward angles: a comparison of experimental and theoretical values.

Narrow angle light scattering measurements were made for various sizes of spherical particles suspended in water. These were compared to calculated theoretical scattering values as derived from the theory of Mie (1908). Through measurements with different particle concentrations at angles between 0.2 degrees and 0.7 degrees the effect of the unscattered main beam light was removed. Results agreed well with Mie theory for these angles.