Use of air-deployed drogued drifting buoys for oil spill tracking

The magnitude of the recent Gulf of Mexico oil spill resulting from the Macondo oil well blowout, catastrophic explosion, and subsequent sinking of the Deepwater Horizon semi-submersible offshore drilling rig is unprecedented. The complex oceanographic and environmental character of the spill location and the application of vast quantities of chemical dispersants combined to create greater challenges for those tasked with mapping the areal extent of the oil and the advective pathways by which the oil would eventually reach both the nearby shore or become entrained into the vigorous offshore currents of the deepwater Gulf. The action of the chemical dispersants combined with surface winds and wave action resulted in high loads of oil particles throughout the mixed layer and extensive surface slicks. In addition, the oil disaggregated into hundreds of small patches instead of remaining pooled on the surface. Under these unexpected conditions, the tracking and forecasting of the spill presents a challenge. Horizon Marine, Inc., an operational oceanographic monitoring and forecasting company, has been actively involved in the oil spill response efforts and supported the current monitoring program near the Deepwater Horizon incident site. One method employed to delineate the initial area of the oil patch and track its expanding perimeter was the use of air-deployable drifting buoys (Far Horizon Drifters). These buoys are equipped with GPS receivers, transmit new positions hourly via satellite, and were nominally drogued at 5m and 50m to provide coverage of the upper water column. Using these observations, we describe several major transport pathways resulting from physical mechanisms operating over different scales. The entrainment of several buoys into the Loop Current and associated frontal eddies provided early indication of potential pathways taken by both the visible surface and invisible subsurface oil.