Please join us for the AOS Seminar on Thursday, April 20 at 4:00PM in Spiess 330.
Daniel Koestner, Scripps Institution of Oceanography
"Experimental estimates of the contributions of different particle size-fractions to the optical scattering of seawater"
An understanding of the major sources of optical scattering by seawater constituents is limited because relevant knowledge has been acquired mostly from theoretical simulations based on oversimplifying assumptions about marine particle assemblages. Laboratory measurements on natural seawater samples have been conducted aimed at the determination of a scattering budget in terms of different particle size-fractions. The volume scattering function was measured with the LISST-VSF (Sequoia Scientific) at a light wavelength of 532 nm within the angular range from about 0.1 to 150°, and the particle size distribution was measured with a Multisizer 3 (Beckman Coulter) equipped with a 100 micrometer (um) aperture. Measurements were made on original unfractionated seawater samples and two size-fractionated samples that were obtained by filtering seawater through high precision mesh filters with mesh sizes of 5 and 20 um. Ancillary measurements of the particulate absorption coefficient and mass concentrations of particulate organic carbon, suspended particulate matter, and chlorophyll-a were made for each unfractionated sample. Mass concentrations of particulate organic carbon and suspended particulate matter were also determined for the 5 um filtrate. Samples from the Pacific Ocean were collected at several locations near San Diego County throughout Summer 2016. While small particles (<5 um) dominate scattering for all measured angles >1° for offshore seawater samples, the patterns of contributions of different particle size-fractions to scattering in nearshore coastal environments are highly variable and appear to depend on variations in the particle size distribution and composition. Large particles (>20 um) can play a greater role to scattering in these environments.