Fall AGU Meeting (Dec. 2002) COAST abstracts:

• Allen
  
• Bane et al.
  
• Barth et al.
  
• Carney et al.
  
• Couch et al.
  
• Cowles et al.
  
• Dale et al.
  
• Durski et al.
  
• Egbert et al.
  
• Gan et al.
  
• Hales et al.
  
• Kosro et al.
  
• Kuebel et al.
  
• Kurapov et al.
  
• Perlin et al.
  
• Pierce et al.
  
• Ruttenberg et al.
  
• Samelson
  
• Spitz et al.
  
• Wheeler
  

Abstracts should be cited as:

EOS Trans. AGU, 83 (47),
Fall Meet. Suppl.,
Abstract XXXXX-XX, 2002

OS62A-0225

Particle Size Distributions Over the Oregon Continental Shelf During
Upwelling: Relationship to Inherent Optical Properties

M A Carney, R M Letelier, and W S Pegau

Phytoplankton size is a significant factor in the flow of energy
within a pelagic community, whereby larger particles are often
indicative of regions with high nutrients, productivity, and
export. Particle size distributions have traditionally been
measured using a variety of techniques that require discreet
sampling (e.g. Coulter Counter), but may also be derived from
optical parameters, which provide the possibility of continuous
measurement. Several studies have shown theoretical and empirical
relationships between the slope of a particle size distribution and
the slope of light attenuation as a function of wavelength. The
exact relationship depends on the type of particles that make
up the size distribution, specifically their absorption and
scattering characteristics. Here we look at the variability of
particle size distributions and corresponding fluctuations in
spectral attenuation for natural assemblages of phytoplankton off
the Oregon coast during the upwelling season. Particle size and
optical data were collected during May-June 2002 as part of the
NEP GLOBEC program. Size distributions in the range of 2-60 ?m
were measured from discreet samples using a Coulter Multisizer
II (Beckman Coulter), and attenuation by particles was measured
continuously along the cruise track at nine wavelengths using
two ac9s (WET Labs). Size distributions varied substantially
over the study region in both the along-shore and cross-shore
directions. Distinct size populations were present in different
water masses as indicated by physical parameters. Optical properties
varied in a similar fashion, and were largely driven by chlorophyll
concentrations. The spectral slope of attenuation was related to both
chlorophyll concentration and size distribution. Optical modeling
using Mie Theory was consistent with the empirical observations,
and both suggest unique relationships between size distribution and
attenuation for sediment-dominated waters (previous studies) and
phytoplankton-dominated waters (this study), respectively. Given
the relationship for phytoplankton-dominated waters, we propose
that optical surveys may be used as a proxy to monitor spatial
and temporal variations in phytoplankton size distributions in
coastal regions, and therefore to study the dynamics and fate of
primary production.