By Janet Raloff
Every few years, a major tanker accident releases huge masses of oil into the sea. As catastrophic as such events are, they account for only a small fraction of the oily pollution in marine waters, according to a new study released by the National Research Council (NRC). Indeed, nearly all oil in seawater traces to natural seeps or to human activities creating diffuse releases.
On May 23, the NRC issued its third report in 27 years tallying sources and impacts of oil at sea. Though getting better, data remain spotty, the council finds. It calculates that some 76 million of the 380 million gallons of oil and related hydrocarbon products that enter marine water globally are located in U.S. coastal waters.
Focusing on these waters, the new report notes that 61 percent of the oil seeps from natural deposits. Another 21 percent comes from diffuse runoff that results from land-based transportation and marine recreational vehicles, such as small boats and jet skis. Releases from tankers, pipelines, and other oil-transport vessels contribute 9 percent more, about a fifth of which comes from ocean-going ship spills. Those large marine spills release about the same amount of oil as recreational outboard motors and jet skis do.
Little is known about how diffuse, chronic releases affect coastal ecosystems. One reason for the knowledge gap, according to the NRC report, is that research funding remains scarce for anything but analyses of catastrophic spills.
