A key objective of the CSOMIO project is to develop and evaluate the modeling framework for simulating oil in the marine environment, including its interaction with ecosystems and sediments. Modeling components for simulating oil, marine biogeochemistry, the marine microbial pool, and sediment transport have been developed previously by the consortium's lead investigators, and each of these components have been coupled to 3-D circulation models that have also been developed by members of the CSOMIO team.
CSOMIO will modify these components to include the interactions between each process, resulting in a coupled modeling system for simulating the fate of oil in the ocean and predicting where ecosystems may be affected. Critical novel interactions to be simulated in the coupled system include hydrocarbon biodegradation and flocculation. Biodegradation is typically included as a simple decay parameterization in oil models for removal of oil from the system, but in reality it is a complex process mediated by diverse microbial taxa that convert hydrocarbons into biomass, carbon dioxide, and more refractory forms of organic carbon. Similarly, flocculation is commonly included via parameterizations in sediment transport models, but the formulations used have rarely accounted explicitly for either the biological constituents of the water column or the presence of oil. Yet, flocculation is likely to be an important link facilitating transport between oil in the water column and the sediments at the seafloor, both in deep water and over the shelf. The role of flocculation may be especially important within turbid river plumes and during storms when significant resuspension occurs.
Central to CSOMIO's coupled modeling system is a module to simulate oil in the ocean. The oil model for CSOMIO is an adaptation of the Deep-C Oil Model (DCOM) that was developed as part of the GoMRI-funded Deep-C Consortium. The oil model simulates the 3-D movement of oil as a large number of Lagrangian elements (a so-called "mini-spill" approach), each representing a quantity of oil with various physical and chemical properties that can change in time. Oil is moved via spreading, advection by a velocity field (accounting for ocean currents, waves, and winds at the surface), and dispersed via submergence of droplets due to parameterized effects of wave breaking. Oil is input into the system via a deep blow-out or a source at the surface. Deep blow-outs are simulated using a jet/plume submodel to transport oil from the seafloor to the far field where it is then simulated using the mini-spill approach. As a stand-alone oil model, oil is removed from the system via parameterizations of settling, evaporation of volatile compounds, and biodegradation. Coupling with other model components involves modeling these processes to allow interaction with sediments and organisms (including microbes).
Microbial biodegradation of groups of hydrocarbons will be simulated with the Genome-based EmergeNt Ocean Microbial Ecosystem (GENOME) Model. GENOME is a novel model developed by Dr. Victoria Coles (UMCES) that simulates the microbial genes responsible for different metabolic functions. Since these genes encode for crucial microbial abilities (such as bacterial growth on methane or breakdown of oil) the model can realistically depict the microbial ecology of the unsung heroes of the Deepwater Horizon oil spill – bacteria. In collaboration with microbiologist Dr. Olivia Mason, Drs. Stukel and Coles will modify the GENOME model to incorporate hydrocarbon-degrading bacteria, then run it coupled to the other modeling components and validate it against in situ metagenomics and metatranscriptomic measurements made after the Deepwater Horizon oil spill.
Marine Biochemistry Model
Marine biogeochemistry (for trophic levels above microbes and ambient biogeochemical fields, e.g. O2) in the water column and sediment will be simulated using an “NPZD” model, so-called because it calculates the concentrations of nitrogen, phytoplankton, zooplankton, and detritus. The research group of Dr. Courtney Harris at the Virginia Institute of Marine Science (VIMS) has developed a model called HydroBioSed that couples hydrodynamics, sediment transport, and an NPZD biogeochemical model to investigate the roles of sediment and biogeochemical processes on dissolved oxygen. Combined with the DCOM oil modeling described above, HydroBioSed will be used to build a CSOMIO tool to improve our understanding of how sediment transport and biogeochemical processes influence dispersion and degradation of hydrocarbons. For example, links between the DCOM oil model and the sediment transport model will include estimates of the formation of oil-mineral aggregates.
Sediment Transfer Model
Sediment transport will be simulated by the Community Sediment Transport Modeling System (CSTMS) modified to include new parameterization of flocculation that will interact with the microbial and oil modeling components. Flocculation refers to the process by which fine particulates stick together into an aggregate, called a “floc.” The CSTMS accounts for sediment resuspension and transport when coupled with a hydrodynamic model. The model has previously been applied to the Texas-Louisiana continental shelf to characterize sediment resuspension during normal and storm conditions. Though the CSTMS includes multiple sediment classes that can be used to represent faster- and slower-settling particles, most implementations to date have neglected flocculation. The CSOMIO team will develop formulations for flocculation to provide settling velocities and settling fluxes of oil sediment aggregates (OSAs) and biologically mediated marine oil snow (MOS) flocs to investigate how oil dispersal is impacted by suspended sediment.