Particle size distributions in the Eastern Equatorial Pacific

Abstract

Size distributions for particles larger than 2.22 μ were measured at selected depths in the eastern equatorial Pacific along with the standard hydrographic variables. The particle size distributions were approximately exponential in shape, but a better fit is provided by the Weibull distribution. Measured, particle concentrations at the surface averaged 5×103cc. Near-surface maxima were found in both number and mean size, especially in regions with sharp thermal gradients. Below the thermocline, the concentration decreased rapidly to a typical value of 5×102/cc. The volume scattering function at 45° and the particle size distribution as measured at several stations were combined to create an optical vector consisting of the specific light scattering of the average particle and the cross section of the mean particle. Plots of the optical vector show a characteristic form, with a decrease in mean area accompanying an increase in specific scattering in the water above the oxygen minimum and little change below the minimum. The change in the optical vector with depth appears to be directly related to the oxidation of the decomposable parts of the nepheloid material.