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Controls on sinking velocities and mass fluxes of size-fractionated marine particles in recent U.S. GEOTRACES cruises
  • Yang Xiang,
  • Phoebe J. Lam,
  • Adrian B. Burd
Yang Xiang
Department of Ocean Sciences, University of California at Santa Cruz

Corresponding Author:yaxiang@ucsc.edu

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Phoebe J. Lam
University of California, Santa Cruz
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Adrian B. Burd
University of Georgia
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Particle composition is an important parameter that influences sinking velocity of marine particles. Most current studies, however, are limited by either a lack of routine measurements of particle composition or low sampling resolution in the water column. Here, we compile full ocean-depth size-fractionated (1-51 and >51 μm) particle concentration and composition of suspended particulate matter from three recent U.S. GEOTRACES cruises to calculate their corresponding sinking velocity and mass flux. Our model is based on Stokes’ Law and incorporates a newly updated power-law relationship between particle size and porosity. The integration of the porosity-size relationship decreases the power applied to size in Stokes’ Law to 0.8. The medians of average sinking velocity in total particles are 15.4, 15.2, and 7.4 m/d, in the North Atlantic, Southeast Pacific, and western Arctic Ocean, respectively. We examine the relative importance of particle concentration, composition, size, and hydrography on sinking fluxes. Particle concentration is the major control of the variability and magnitude of mass flux, while particle composition is the second most important term. Increasing porosity with aggregate size and a dominance of smaller particles diminishes the importance of the size dependence in mass flux, elevating the relative importance of composition and thus density. Viscosity of seawater can result in up to a factor of two difference in mass flux between polar and tropical oceans. This work serves as one of the first studies to offer quantitative perspectives for the contribution from different factors to mass flux in field observations of marine particles.