A Visual Tour of Carbon Export by Sinking Particles

To better quantify the ocean's biological carbon pump, we resolved the diversity of
sinking particles that transport carbon into the ocean's interior, their contribution to carbon
export, and their attenuation with depth. Sinking particles collected in sediment trap gel layers
from four distinct ocean ecosystems were imaged, measured, and classified. The size and identity
of particles was used to model their contribution to particulate organic carbon (POC) flux.
Measured POC fluxes were reasonably predicted by particle images. Nine particle types were
identified, and most of the compositional variability was driven by the relative contribution of
aggregates, long cylindrical fecal pellets, and salp fecal pellets. While particle composition
varied across locations and seasons, the entire range of compositions was measured at a single
well-observed location in the subarctic North Pacific over one month, across 500 m of depth.
The magnitude of POC flux was not consistently associated with a dominant particle class, but
particle classes did influence flux attenuation. Long fecal pellets attenuated most rapidly with
depth whereas certain other classes attenuated little or not at all with depth. Small particles (<100
m) consistently contributed ~5% to total POC flux in samples with higher magnitude fluxes.
The relative importance of these small particle classes (spherical mini pellets, short oval fecal
pellets, and dense detritus) increased in low flux environments (up to 46% of total POC flux).
Imaging approaches that resolve large variations in particle composition across ocean basins,
depth, and time will help to better parameterize biological carbon pump models