Abstract
The effect of river fronts on oil slick transport has been shown using high resolution forcing models and a fully fledged oil drift model, OpenOil. The model was used to simulate two periods of the 2010 DeepWater Horizon oil spill. Metocean forcing data were taken from the data-assimilative GoM-HYCOM 1/50° ocean model with realistic daily river input and global forecast products of wind and wave parameters from ECMWF. The simulations were initialized from satellite observations of the surface oil patch. The effect of using a newly developed parameterization for oil droplet size distribution was studied and compared to a traditional algorithm. Although the algorithms provide different distributions for a single wave breaking event, it was found that the net difference after long simulations is negligible, indicating that the outcome is robust regarding the choice of parameterization. The effect of removing the river outflow was investigated to showcase effects of river induced fronts on oil spreading. A consistent effect on the amount and location of stranded oil and a considerable impact on the location of the surface oil patch were found. During a period with large river outflow (20–27 May 2010), the total amount of stranded oil is reduced by about 50% in the simulation with no river input. The results compare well with satellite observations of the surface oil patch after simulating the surface oil patch drift for 7–8 days.
Highlights
The synergy between shelf and open sea dynamics makes the Northern Gulf of Mexico (NGoM) a topographically and dynamically complex and interesting study area, in the presence of intense oil exploration [1,2]
Simulations were initialized from satellite observations of the Surface Oil Patch (SOP), and a continuous point source with a realistic spill rate at the sea floor
Our results indicate that the two different formulations for oil droplet size distribution give similar results for both vertical and horizontal distribution of the oil, when wind speeds are typically 5–12 ms−1 and breaking waves appear (Figure 4)
Summary
The synergy between shelf and open sea dynamics makes the Northern Gulf of Mexico (NGoM) a topographically and dynamically complex and interesting study area, in the presence of intense oil exploration [1,2]. The river induced, buoyancy-driven flows include a westward coastal current along the LATEX shelf (“downstream” plume regime, i.e. in the direction of Kelvin-wave propagation) and a northeastward flow toward the MAFLA shelf (“upstream”) The former is due to the geostrophic balance between Coriolis and cross-shelf pressure gradient (e.g., [9,10,11]) and is enhanced by downwelling-favorable winds; such conditions favor material entrainment and nearshore confinement due to mass balance considerations. The third important flow regime, the buoyancy-driven anticyclonic bulge, is often suppressed due to the Mississippi Delta proximity to a steep slope ([12,13]) and it is usually formed under high discharge conditions [3] These flow regimes induce well defined fronts that exhibit strong variability, depending on river discharge, winds and interaction with offshore flows [13]. Related transport pathways may have great impact on coastal ecosystems in the vicinity of GoM areas with river influence (especially over NGoM), and remote ecosystems that can be reached along the LC
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