Variability in the average sinking velocity of marine particles

McDonnell, Andrew M. P., and Ken O. Buesseler

Limnol. Oceanogr., 55(5), 2010, 2085-2096 | DOI: 10.4319/lo.2010.55.5.2085

ABSTRACT: We used a new combination of sampling techniques involving in situ imaging of particles in the water column and the collection of particle flux in viscous polyacrylamide gels to estimate the average sinking velocities (Wi,avg) of marine particles ranging from equivalent spherical diameters of 70 µm to 6 mm at several locations, depths, and times along the west Antarctica Peninsula to explore the variability of Wi,avg. During the January 2009 deployments, Wi,avg ranged from about 10 to 150 m d-1, with the fastest velocities at the large and small ends of the sizes considered. A repeat occupation of one station in Marguerite Bay in February 2009 gave Wi,avg size distributions that were quite different from those of the previous month, with rapidly sinking small particles and very slow Wi,avg for the large particle classes. These results demonstrate the importance of diatom aggregates and krill fecal pellets with regard to the oceanÂ’s biological pump in this region. The observed variability in space and time indicates that global relationships between particle concentrations and fluxes, or simple theoretical formulations of sinking velocity as a function of particle size (such as a single parameterization of the StokesÂ’ Law), are unsuitable for yielding accurate estimates of particle flux from measurements of the particle size distribution. Combining measurements of Wi,avg with high-frequency sampling of the particle concentration size distribution would enable the estimation of particle fluxes at much higher temporal and spatial resolutions than is currently possible with conventional sediment trapping methods.

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