Interactions between diatom aggregates, minerals, particulate organic carbon, and dissolved organic matter: Further implications for the ballast hypothesis

Correlations of particulate organic carbon (POC) and mineral fluxes into sediment traps in the deep sea have previously suggested that interactions between organic matter and minerals play a key role in organic matter flux to the deep. Here experiments were carried out in rolling tanks to observe the incorporation of suspended biogenic minerals ( calcium carbonate coccoliths or silica diatom frustules) into diatom aggregates and examine their influence on aggregate character. Addition of higher concentrations of suspended minerals to tanks resulted in a decrease in aggregate volume and mass and in an increase in aggregate number. POC to dry weight ratios also declined as mineral concentrations increased, saturating at 2-5 weight percent POC. Large amounts of suspended particulate material, consisting of miniscule aggregates of both inorganic material and organic matter, formed during the experiments. This suggested sizable scavenging of dissolved organic matter into the particulate phase during the experiment in general, and in particular associated with the presence of suspended minerals. Some of the increase in particulate inorganic matter may have been tied to cation crosslinking of the polymerized organic matter. The C to N ratio of this scavenged material was lower in the opal experiments than in the calcium carbonate experiments, suggesting differences in the compounds being formed.