Oil Seeps: The Ocean's Largest Source of Oil Is Natural

The biggest source of oil entering the world's ocean is not tankers or drilling platforms. It is the seafloor itself. Natural oil seeps — leaks of crude oil and gas that rise up through the seafloor — account for nearly half of the oil released into the ocean every year.

A natural tar seep offshore of Gaviota in Santa Barbara County, California. Credit: Donna Schroeder/U.S. Geological Survey.

How a seep works

A seep forms when crude oil leaks from cracks in the seafloor or rises through seafloor sediment — much as a freshwater spring brings water to the surface.

A natural laboratory

NOAA's Office of Response and Restoration (OR&R) studies seeps because they are predictable places to watch how oil behaves. Around Santa Barbara, California, where there are many natural seeps, OR&R trains aerial observers, calibrates its trajectory models and studies how weather, wind, tides and currents move oil.

Seep or spill?

Where there are many seeps, responders to an oil spill can struggle to tell spilled oil from seep oil — and the difference matters. The damage oil does depends not only on how much is released, but also on the type of oil and how fast it disperses. Seeps release oil slowly, giving ecosystems time to adapt. Spills from human activity, such as commercial oil transport, can release so much so fast that an ecosystem is overwhelmed. To tell them apart, OR&R tracks seeps, helps distinguish them from production-platform leaks and other spills, and works with the U.S. Coast Guard and the U.S. Fish and Wildlife Service on techniques such as oil fingerprinting, which traces where oil came from.

Not harmless

Every seep affects the marine environment. Oil can be toxic to fish, sea stars, shrimp and seabirds, though the effects are mostly concentrated around the seep itself.

Sources

Based on "What is an oil seep?" from NOAA's National Ocean Service, a work of the United States government in the public domain.