A recent article in EOS Magazine from researchers at the Woods Hole Oceanographic Institution and Louisiana State University have shed new light on the role sunlight in substantially altering petroleum floating at the sea surface.

The article describes the findings of research following the Deepwater Horizon (DWH) disaster in the Gulf of Mexico that killed 11 people and caused hundreds of millions of gallons of oil to spill into the Gulf of Mexico.

When crude oil is spilled into the ocean, it undergoes a series of weathering processes, including dissolution, evaporation, emulsification, biodegradation, and photooxidation. Some of these processes relocate oil, whereas some transform it.  These oil weathering processes have wide-ranging implications for ecosystem and human health, as well as for spill response operations.

One finding from the study the DWH oil spill is that the photooxidation of oil floating on the sea surface is far greater than what had previously been considered.  Before the spill, the consensus perspective across many subdisciplines of oil spill science was that evaporation, emulsification, and biodegradation were the most important weathering processes influencing the fate of oil spilled at sea.  But several studies have have documented the rapid and extensive photooxidation of oil floating on the sea surface during the DWH spill.

The second major finding from the study of the DWH was how sunlight oxidized so much oil floating on the sea surface. There are two ways that oil photooxidation can occur: directly and indirectly.  Numerous field and laboratory studies have now documented the governing role that indirect photooxidation pathways play in cleaning up oil spills.