EPS mechanisms in aggregation and dispersion of oil: roller tank experiment using Chaetoceros and natural bacterial inoculum

This is an experiment of a series investigating the mechanisms driving the incorporation of oil into diatom aggregates using a water accommodated fraction (WAF) of oil. A culture of the diatom Chaetoceros sp. and natural bacteria inoculum was used, and WAF was prepared from Refugio oil (pipeline oil spill off California May 2015). Roller tank experiments mimic in situ conditions of the ocean where continuous sinking of particles is possible (infinity water column). Once aggregates > 1mm (operationally defined) have formed, they are harvested separately from the surrounding seawater, which contains non-aggregates cells or small aggregates. Both fractions are analyzed separately, so that the fraction of material incorporated within aggregates may be calculated. Samples were analyzed for cell abundance, particulate organic carbon (POC) and nitrogen (PON), the isotopes Carbon-13 and Nitrogen-15, estimated oil equivalent (EOE), and transparent exopolymer particles (TEP).