The chemical composition of sinking particles and their vertical dynamics in the open ocean.

摘要

Sinking particles are one of the main vehicles for transporting chemical species, including carbon, from surface waters to the deep ocean and sediments. This process reduces the partial pressure of carbon dioxide in the surface mixed layer, and plays an important role in the oceanic carbon cycle. This thesis focuses on the vertical dynamics of sinking particles, and their chemical compositions and degradation trajectories.;A new method, based on fitting Fourier series to time-series data from sediment traps, was developed to estimate settling velocities (SV's) of sinking particles in the open ocean. The results showed that estimation of SV's is more reliable when single-elements, rather than element ratios, are used as tracers. Modal settling velocities estimated using single-tracer fluxes with good temporal resolution, averaged separately for each tracer, are 205+/-74 m/d. This new estimate is in essential accord with measurements made using Indented Rotating Sphere sediment traps in "setting velocity" mode at the same site.;Three-dimensional Principal Components Analysis (PCA) was applied to data on the organic composition of sinking particles collected in MedFlux. The results showed that constructing a 1-dimensional "degradation index" is oversimplified, and the trajectory from the first 2 or 3 axes is more informative.;Masses were summed with all the major chemical components, including organic matter (OM), opal, CaCO3, and lithogenic minerals, for sinking particles. The summed mass is often less than the mass that is directly measured. This mass deficit is also observed for sinking particles at the Ross Sea, but not for those collected from other US JGOFS deep ocean sites. OM was found to be directly related to mass deficit, especially in shallow water where OM content in particles is high. I hypothesize that water bound to organic molecules or minerals particles, especially in samples from shallow depths, may not be totally dehydrated after oven drying.