Optically derived size distribution of particles from 20 nm to 20 mm in North Pacific Ocean

Xiaodong Zhang, University of Southern Mississippi, Division of Marine Science, Stennis Space Center, ND, United States, Yuanheng Xiong, University of North Dakota, Grand Forks, ND, United States, Lianbo Hu, University of North Dakota, Department of Earth System Science & Policy, Grand Forks, ND, United States, Yannick Huot, University of Sherbrooke, Remote sensing, Sherbrooke, QC, Canada and Deric Gray, US Naval Research Laboratory, Washington, DC, United States
Carbon export in the global ocean occurs over the entire dissolved-particulate size continuum and therefore depends on the size distribution of particles over an extended range from nanometer to millimeter. We deployed a suite of optical instruments using state-of-the-art inversion techniques to derive the size distribution of particles spanning 5 orders of magnitude of sizes from 20 nm to 20 mm. The volume scattering functions are measured with high angular resolution using a LISST-VSF an angles 0.08 - 150°, a LISST-100X at angles from 0.08 - 15°, a prototype MVSM at angles from 10 - 170°. Particle size distributions (PSD) from 2 – 200 µm are derived from LISST-100X following laser diffraction principle (Agrawal and Pottsmith, 2000). PSDs from 0.02 – 200 µm are derived from LISST-VSF and MVSM measurements using the VSF-inversion technique (Zhang et al. 2011). By tracking the thermal motion of suspended particles using three laser beams (at 450 nm, 520 nm, and 650 nm), the mean displacement of each particle is estimated and related to its size in the submicron range based on Brownian motion principle (Einstein, 1965). PSDs at sizes > 100 µm are estimated by direct imaging analysis using UVP. Finally, PSDs in the size range of 2 – 40 µm are measured using Coulter Counter. The optically-derived PSDs are further validated by comparing at size ranges where multiple estimates overlap.This approach was recently tested in North Pacific Ocean to estimate the variation of PSDs at various depths from the surface to twilight zones. Preliminary results showed that the PSDs derived from different instrument agree with each other very well, allowing us to investigate the dynamic changes of particles size distribution over an unprecedented size range from 20 nm to 20 mm.