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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.

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.

Light transmission profiles have been used to study the optical properties of the suspended particles which are characteristic of the area of the Scotian Rise in the North Atlantic Ocean. This area is typified by very strong bottom currents and a highly variable bedform morphology. A good correlation (r = 0.96) has been found between the suspended volume and the light beam attenuation coefficient. This correlation is consistent with the fact that the cumulative slope of the hyperbolic particle size distribution is nearly constant throughout the region (slope = 3.1 ± 0.3). Numerical analysis of the optical data in conjunction with particle size analysis yields values of the index of refraction of the suspended particles of 1.20±0.07 relative to water. The conclusion drawn from these results is that the Scotian Rise benthic zone is characterized by suspended particles of high relative index of refraction and size distributions which do not vary much with altitude above bottom or over periods of time of more than a year in spite of the extensive fluctuations in activity of the region.

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