TITLE: The influence of biogenic ballast on the sinking speed of particles.

SUPERVISOR & CO-SUPERVISORS
Helle Ploug
Corinne Le Quéré, Erik Buitenhuis (UEA and BAS)

PROJECT DESCRIPTION

Certain classes of marine algae produce cell coverings of calcite (CaCO₃) and opal (SiO₂). When these algae die, the cell coverings end up in fecal pellets and marine snow that sinks from the surface ocean to the deep sea. The density of calcite and opal is higher than the density of seawater, while the density of organic matter is only slightly higher than of seawater. They have been shown to increase sinking of organic matter in a bloom of the calcite forming alga Emiliania huxleyi (Wal et al. 1995). Also on a global scale the sinking flux of organic matter has been shown to be associated with calcite and opal (Klaas and Archer 2002). Stokes' law predicts that sinking speed increases with the density of the particles. However, fecal pellets and especially marine snow are complex composites of particles, and the exact relationship between ballast and sinking speed is difficult to predict from Stokes' law, because the porosity and drag coefficient of these complex particles is not known. We therefore propose to measure the effect of ballast on the sinking speed of fecal pellets and marine snow. The student will also measure degradation rates of the particles. With this information it will be possible to represent the ballasting effect in a model of the ocean carbon cycle. The student will refine the Dynamic Green Ocean Model PlankTOM5 (Le Quere et al. 2005) to improve the representation of sinking particle flux, and explore the influence of climate change on changes in export production and air-sea CO₂ exchange.

Current status:
A similar project is now being carried out by Morten Iversen under the supervision of Helle Ploug at AWI in Germany. For more information please contact Erik Buitenhuis.

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