The recent BP oil leak disaster has thrust the Gulf region into the international spotlight. Local residents and scientists alike are waiting to see how the damage impacts the area, as well as the long-reaching ramifications of this unprecedented environmental disaster. The immediate damage is obvious-the world has seen hundreds of images of once-pristine beaches slimed with tar balls, shimmering oil slicks miles across, and the heartbreaking images of oil-caked birds waiting to die. Local fishermen may be permanently out of business, just as many of them were gearing up for their most profitable time of the year.
Even the experts can’t agree on just how bad the long-term damage will be, or how many years it will take for the Gulf to recover. One way to evaluate the potential damage is by examining the weathering process of the oil. Several factors come into play-the type and amount of oil, weather, the sensitivity of the marine organisms to oil and other toxins, and type and effectiveness of cleanup efforts. There are eight main processes that cause oil on the ocean’s surface to weather.
Spreading
As soon as the oil spills, it begins to spread out. Thinner oils spread faster than thicker oils. Variations in the oil’s thickness are common. Within a few hours, waves, wind, currents and temperature cause the slick to break up into narrow bands known as windrows. More severe conditions such as a storm will cause the oil to spread and break up quicker.
Evaporation
The lighter and more volatile compounds of the oil evaporate, just like water does. Diesel and kerosene, which are lighter, can almost totally evaporate in a few days. Heavy fuel oils may have little or no evaporation. As the oil layer spreads and thins, evaporation may increase.
Dispersion
Wave action and turbulence causes the oil to break into fragments of varying sizes. The fragments spread throughout the upper layer of the sea’s surface, with smaller fragments remaining just below the surface. Larger fragments tend to rise back to the top. They may either spread and thin out, or combine with other large fragments and reform a slick. The oil that remains suspended has a larger surface area than before. This helps encourage natural processes of biodegradation and sedimentation to occur. Chemical dispersants can accelerate the process, but remain controversial as they may harm sea life and deoxygenate the water.
Emulsification
When two liquids combine, one ends up suspended in the other. The emulsification process that occurs when sea water mixes with oil is caused by physical mixing at the surface. The mechanical turbulence involved causes the mixture to become very viscous and often resembles chocolate mousse. The volume of pollutants can increase from three to four times.
Dissolution
The water-soluble compounds in oil may simply dissolve in the water. Most oil contains very small amounts of water-soluble compounds, making dissolution a negligible process.
Oxidation
The chemical reaction between oil and oxygen causes it to break down into soluble products or forming persistent compounds called tars. Sunlight speeds the process as thick layers of high viscosity oil oxidizes. Tarballs, which have plagued many areas, have a solid outer crust and a softer interior.
Sedimentation/Sinking
Sea water is very dense, and very few crudes are dense enough to sink in them. Sinking usually occurs when sediment particles or organic matter stick to the oil. In shallow waters near shore, suspended solids may mix with sand on shore. If this mixture is washed off the beach back into the ocean, it may sink. Also, oil which burns after being spilled can sometimes form dense enough residues to sink.
Biodegradation
Sea water is rich in microorganisms which can partially or completely degrade oil into water soluble compounds. The microbes tend to be very specialized in the type of compound they can degrade. This process requires oxygen and is more efficient when the oil is dispersed into droplets, increasing the surface area of the oil.
The end result of how well the oil is cleaned up depends on many variables, some of which are out of our control. Most likely, the final cleanup and its success or failure will depend on a combination of weathering processes and plenty of intervention from teams of scientists and other experts. It may be many decades before the area is completely recovered, if ever.
SOURCES:
International Tanker Owners Pollution Federation, Ltd. http://www.itopf.com/marine-spills/fate/weathering-process/
