|MadSci Network: Environment|
The most common oil spills are small ones that are set free by rinsing the tanks of oiltankers while they are at sea (several hundred tons per spill). Dozens of these spills happen every day worldwide. Additionally, a lot of spills happen when normal cargo ships rinse their fuel tanks to get rid of the slurry that build up in the respective tanks. The second huge source of spills is leaks and small accidents during the operation of oil platforms (drilling for oil in the sea). These give a normal day by day background of oil pollution in the sea. Only recently there have been international agreements to restrict washing of tanks in certain areas of the sea (Marpol special areas) to these belong huge parts of the North Sea, and I think the Baltic, and the Australian Great Barrier Reef.
The huge spills from tanker accidents add to this day by day pollution. Of course, these cause grave regional effects, which last for years. For example, the accident at the french Britanny coast happened to hit an area that had just recovered from a major spill 20 years ago. Reasons for these spills include old equipment, old ships, as well as low security standards in operation and in construction. Most vessels still operate as a single skin ship, meaning the oil is just separated by one layer of steel from the sea. Following the huge spill in Alaska, the US has decided that only double skin ships may enter US waters.
You can check the homepage of the WWF Oceans network: http://www.ngo.grid a.no/wwfneap/overview/overfset.htm additionally there is some sophisticated literature on remote sensing of oil films check: http://www.ifm.uni-hamburg.de/
Try the links in the MadSci Library for more information on Environment .