Why Is the Gulf Oil Slick Red?

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The oil slick that's spreading atop the Gulf of Mexico looks nothing like the black gunk and tar balls that have washed ashore.

The reason for the reddish coloring of the oil slick has to do with how the oil mixes with water, but scientists are puzzled as to why the colors coating the Gulf water are so bright.

"We believe that the reddish brown color is indicative of the formation of a water-in-oil emulsion, called a mousse," said Edward Overton, professor emeritus at Louisiana State University. "These [oil slicks] typically have colors other than black, but with this oil, the colors are fairly vivid."

He added, "We still don't know the exact cause of the color change but it probably as something to do with the water/asphaltene interactions."

Asphaltenes are residues from chlorophyll, the green pigment in plants, and they make up a component of crude oil.

Over hundreds of thousands of years, as plants died and sank to the bottom of the sea, along with other organic matter, they (along with their chlorophyll) mixed with mud and sand of the surrounding area. As more and more sediment piled on top, the resulting heat and pressure transformed the organic layer into kerogen, a dark and waxy substance. Over time, kerogen molecules broke up into shorter and lighter molecules made mostly of carbon and hydrogen (hydrocarbons). Depending on the mixture of liquid and gas, the result can be either petroleum or natural gas.

"We are trying to see if we can find the chromophores, but this is not a priority project because it doesn't affect the ultimate weathering of the oil," Overton told Life's Little Mysteries. A chromophore is the light-absorbing part of a molecule responsible for its color.

The scientists hope to see if other oils in the area have the same reddish color when mixed with water.

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