In the face of the current ecological disaster in the Gulf of Mexico, it is important to remember: regardless of this or any other similarly catastrophic mishap, oil and the oceans will be linked for many decades to come. It is a fact of life; there are no instant energy alternatives. Offshore platform production and global transport of oil by tankers and seafloor pipelines will remain essential to supplying the world's energy needs.
There will always be spills, and even without them, there will always be hydrocarbons staining the Earth's oceanic realms. It is therefore useful to strive for some context regarding accidents such as the tragic BP Deepwater Horizon spill.
Compared to refined petroleum products such as fuels and lubricants, crude oil is a natural substance. Refined products have a wide variety of chemical additives that make them far more toxic in the case of spills. Crude spills do have toxicity, but to a much smaller degree.
The major damage from oil spills is to living things in the sea. Free-swimming animals are generally able to move away from contaminated waters. But fixed organisms such as clams and oysters cannot move. They are filter feeders that will concentrate toxic compounds in their tissues. In addition, heavier fractions of oil that may eventually settle to the seafloor can smother immobile organisms. While images of oil-covered birds, turtles, and other shore-dwelling species are heart-rending, the real damage to life in the ocean is generally out of sight.
Oil in the sea is removed by a combination of natural and man-made processes. Natural remediation is called "weathering." Crude oil has lighter volatile components that are essentially boiled away by solar energy. This diminution is aided when the seawater is warmer.
Eventually, the heavier oil fractions will tend to sink away from the surface and form tar balls. Some settle to the seafloor while others can float ashore. Those that have been in the sea for some time tend to collect colonies of marine life, which can hasten the oil-clusters' breakdown.
Nature provides an array of bacteria that feed on oil. Depending on the fraction and origin of the oil, different microbes will specialize in "eating" specific types of spilled oil. The process is relatively efficient but slow. Wind and wave actions help disperse the oil over larger areas to allow these natural processes to be more effective.
Man-made remediation activities are divided into three broad approaches: removal by skimming, dispersing chemicals and active bacteria, and erecting barriers between the oil slick and a shoreline. Most spills will have all three remedies applied.
Skimming operations can be quite effective where sea conditions are calm. Surface vessels use long booms to sweep the surface oil into concentrated areas where it can be pumped out of the sea. In some cases the oil can be simply burned.
Chemical dispersion (aircraft provide the usual delivery system) causes an oil slick to disaggregate, permitting natural microbes to be more effective. Commercially developed microbes targeted to specific types of oil have been used effectively to augment the natural microbes.
As oil slicks approach shorelines, barriers serve as the last resort. Their effectiveness is dependent on sea and wind conditions, not to mention the availability of barrier material in sufficient quantities. Barriers serve the dual function of protecting the shore and collecting the oil, which then can be pumped out of the sea.
Finally, what are the main sources of oil in the oceans Since 1975, the National Research Council has done three studies on this subject. Its most recent report (2003) found that spills from worldwide offshore exploration and production account for only about 3 percent of the annual total of oil entering global waters. For U.S. waters, this figure is closer to 1 percent.
In the illustration on the facing page, note the item "natural seeps." Found throughout the world, these are areas where crude oil and gas slowly percolate up through the seafloor.
As shown here, natural seeps contribute nearly 15 times more oil to the oceans than does offshore drilling.
The best-known seeps are found off Santa Barbara, California. From them, about 24 tons of oil leak into the ocean every day. It has been proposed to drill wells into these formations to reduce the reservoir pressure. Such a step would reduce the rates of seepage, but cultural and political constraints make this remedy unlikely.
Ocean-based oil production began off piers in California in 1896. Since then, worldwide activity has involved tens of thousands of platforms in water depths as great as 9,627 feet. Historically, it has been a relatively clean activity. Catastrophic events such as the BP Deepwater Horizon blowout, however, demonstrate that much more needs to be done in terms of operational safety, diligent regulation by governments, and development of better deepwater technologies.
