Oil Particle Aggregation Model for the Gulf of Mexico Continental Shelf: Scenario Testing

Observations from the Deepwater Horizon event in the Gulf of Mexico showed that oil droplets, marine snow, and mineral grains combined and formed aggregates having a wide range of transport characteristics, which modified the dispersal and fate of oil. One type of these, Oil Particle Aggregates (OPAs), were composed primarily of a mixture of oil and mineral sediment. Though the Gulf of Mexico has some very turbid waters, to date, few numerical models have accounted for the range of aggregation processes likely to form OPAs. However, interactions between oil and mineral aggregates may be represented using techniques recently developed to account for sediment flocculation. As part of CSOMIO (Consortium for Simulation of Oil Microbial Interactions in the Ocean), we modified an existing, population dynamics-based flocculation model (FLOCMOD) to account for the formation of OPAs, which changes the vertical transport of both the oil and the mineral grains; modifying sediment settling, while increasing deposition of oil to the bed. The new module, OPAMOD, is used for investigations into how interactions between oil droplets and sediment impact their vertical transport, including settling of oil to the seafloor. Parameterizations gained from the one-dimensional (vertical) model are directly transferrable to a three-dimensional coupled oil – sediment – microbial model developed by CSOMIO. A one-dimensional (vertical) version of this water column model has been implemented in the Regional Ocean Modeling System (ROMS) and used to represent various scenarios from the Gulf of Mexico continental shelf including oil spills during energetic storms, or within turbid river plumes.