If Oil Naturally Leaks From Underwater Sources Every Day, Then Why Are Man-Made Spills Such a Big Deal?

Literally tons of oil get released on a regular basis from natural underwater petroleum seeps around the world. Does that mean man-made spills like the ongoing one in the Gulf of Mexico are less problematic than most people think?

It's true that seeps located off the California coast release up to several thousand gallons of crude oil each day and that these leaks eventually amount to many times the amount of oil released in even the worst man-made oil spills, like the Exxon Valdez in 1989.

But there are also some important differences between these situations—and many reasons why the environmental impact of a man-made spill is hardly comparable to that of oil leaked from natural seeps.

For one, the biological communities around natural seeps have developed and adapted to the presence of oil over hundreds or thousands of years. When oil spills from a tanker or oil rig, on the other hand, biological communities that haven't had to deal with oil before are suddenly exposed to it at high concentrations. "At underwater seeps, you've already got luxuriant concentrations of microbes who depend on that seep as a carbon source and are very good at chewing it up in place, but you don't have any of that when a catastrophic release like [the one in the Gulf of Mexico] occurs," says Jeffrey Short, who spent decades studying oil spills as a chemist for the National Oceanic and Atmospheric Administration (NOAA) and is now Pacific science director at Oceana. "You're just exposing a naive biological community to an extraordinarily damaging change all at once."

As a result of exposure to an ill-prepared biological community, microbial degradation of man-made oil spills occurs much more slowly than degradation of oil from natural seeps, where the resident organisms literally make their living off of the oil that gets released. It's also important to note that natural seeps dribble oil at a rate that is much slower than most spills—so the flow is not nearly as overwhelming to surrounding organisms. The bottom line is that oil does indeed naturally seep from the seafloor in many places and that this seepage does, over time, add up to an awful lot of oil, rivaling some of the biggest human spills. But natural seeps have become part of the ecosystem (over long periods of time), while oil spills wreak massive ecological destruction.