Introduction to Marine Oil Spills

706 million gallons: the amount of waste oil that enters the marine environment per year. Oil can enter the oceans through many different passages, but the majority of oil that enters the ocean originates from "land based sources and from unregulated recreational boating" (Oil Spills: Impact on the Ocean). Other forms of oil entering the marine environment include drainage of storm water that contains components of oil and improper treatment of waste disposal. Tanker crashes and other transportation accidents accommodate for 5.2% of oil that exists in the oceans, routine repairs and maintenance of ships make up 20%, and 13% of the oil within the oceans come from "hydrogen particles from online air pollution", and 8% is due to the natural uplifting of oil from the ocean floor (Oil Spills: Impact on the Ocean).

The gravity of marine oil spills relies on many factors. Factors that influence the severity of marine oil spills include "the type and quantity of oil spilled, the season and weather, the type of shoreline, and the type of waves and tidal energy in the area of the spill" (Effects of Oil Spills on Wildlife and Habitat). Because the density of oil is less than 1g/mL (the density of water), oil floats on the surface of the ocean and coats the water as a sheen. The intensity of waves, currents, and winds can expand the coverage of oil to larger areas in the marine environment. 

The way oil affects the environment physically, chemically, and biologically is called weathering, and weathering can actually reduce the harmful toxins in oil over time. Other forms that diminish oil from the marine environment include evaporation, decomposition by sunlight (photolysis), and decomposition by microorganisms (biodegradation). Biodegradation relies on the availability of nutrients and oxygen, the type of microorganism, and the temperature.  In addition, small amounts of waste oil dissolve in the ocean waters. 

Sources: 

http://alaska.fws.gov/media/unalaska/Oil%20Spill%20Fact%20Sheet.pdf

http://www.waterencyclopedia.com/Oc-Po/Oil-Spills-Impact-on-the-Ocean.html