After the Deepwater Horizon Oil Spill, the scientific community immediately realized that a system for tracking the discharged petroleum and associated contaminants, both at the surface and at depth, was needed for effective mitigation efforts. In the past years, largely within the framework of GoMRI, many efforts have been devoted to this, and significant progress has been made in tracking the petroleum via numerical models and satellite remote sensing resources. However, accurate oil tracking remains challenging. Among the challenges, tracking the subsurface hydrocarbons and other materials is particularly difficult, we, therefore, need to understand better the physical processes that are essential for the dispersal of subsurface materials, and to implement these understanding into oil tracking models. Also, approaching the end of GoMRI, it seems to be the right time to evaluate the existing numerical models in presenting the dispersal of subsurface materials in the Gulf of Mexico (GoM).
Among many oceanic physical processes that affect the dispersal of subsurface materials, mesoscale eddies likely play an essential yet overlooked role. Limited studies in the GoM and other regions of the global ocean show that mesoscale eddies can significantly influence the deep-ocean subinertial flows (horizontal dispersal), particularly near large topography. Also, these eddy-influenced deep-ocean currents, mainly subinertial, likely contribute to driving, dissipating and modulating internal waves, and consequently are expected to affect diapycnal mixing (vertical dispersal). Mesoscale eddies can thus affect both the horizontal and vertical dispersal of subsurface materials. Examining the likely impacts of mesoscale eddies on the subsurface low-frequency currents as well as vertical mixing can potentially improve our understanding of the three-dimensional dispersal of subsurface materials in the GoM, including the spilled oil and applied chemical dispersants after Deepwater Horizon Oil Spill.
The major objective of this proposal is to analyze, understand and quantify the roles of mesoscale eddies in the three-dimensional dispersal of subsurface materials. This will be achieved through three specific goals: 1) Characterize and quantify the subsurface impacts of mesoscale eddies in the GoM by synthesizing and analyzing multiple streams of data sets (e.g., satellite altimetry, historical in-situ deep-ocean current measurements); 2) Evaluate the existing state-of-the-art GoM circulation/oil tracking models (a synthesis of existing products within previous and ongoing research effort during RFP I to V) by focusing on the relationships between surface mesoscale features and subsurface currents and vertical mixing (if available); 3) Produce a semi-empirical formula to present the subsurface impacts of mesoscale eddies; conduct sensitivity experiments showing the impacts of this new formula in modifying the trajectory predictions with the existing GoM models.
The results gained from this study have numerous potential scientific and societal impact. Along with improving oil spill tracking capabilities in the GoM, the proposed study is also expected to yield useful information for harmful algae bloom prediction and tracking, fisheries ecology, dispersal of geochemical tracers, sediment transport, and so forth. This proposal will also support one graduate student, one postdoctoral associate, and two early career scientists.