Where Does the Tar on Central California Beaches Come From?

Santa Barbara is a gorgeous little beachside town, one that I feel lucky to call home. But take a walk on our beaches and you'll likely take home a nasty surprise: tar.

Though tar can be found on beaches from Monterey to Los Angeles, you may have noticed it is especially bad in Santa Barbara county. Some may be surprised to learn that it seeps naturally from the ground, but even locals start to wonder how much of it is natural and how much of it is due to the various oil spill disasters.

Notice the background. The things that look like boats in the distance are actually oil rigs.

Notice the background. The things that look like boats in the distance are actually oil rigs.

Natural seeps are the highest contributors of petroleum hydrocarbons to the marine environment. Of the total load of petroleum hydrocarbons discharged into the sea, natural seeps account for the largest load, nearly 61 percent of the total. In southern California, natural seeps represent 98 percent of oil inputs to the offshore zone. In fact, the extensive system of natural seeps off Coal Oil Point accounts for nearly two thirds of the total load received by coastal and offshore waters of the Pacific seaboard, including Hawaii.
— National Research Council (NRC) of the U.S. National Academy of Sciences

The Santa Barbara Channel—which extends from Point Conception in the west to Hueneme in the east, from the mainland coastline in the north to the channel islands in the south—is home to the largest natural petroleum seep in the world.

Map credit: U.S. Geological Survey. USGS.com

Map credit: U.S. Geological Survey. USGS.com

Petroleum seeps occur across the world in areas rich in underground reserve of oil. Some seeps are located on land, like the famous La Brea Tar Pits, but Santa Barbara's seep is located underwater. As the oil reserve leaks through the seep conduit—at the rate of 100 to 150 barrels of liquid petroleum per day—the oil droplets merge on the surface to form oil slicks. Exposed to the elements, the oil slicks eventually degrade into tar, which gets carried to the beaches of the central coast with the tides.

It is due to the weather and ocean patterns that tar deposits are greater in the summer and fall when waves are smaller and the winds aren't as strong, thus allowing the oil slicks to degrade slowly in the calm waters and warm sun. In the winter months, bigger waves break up the slicks and prevent them from turning into tar. The high surf also tends to remove beach sand, causing the beaches to be narrower, steeper, and less likely to collect tar.

So unless there's a massive spill, the tar you find on the beach is most likely not due to the activities of the oil companies. In fact, it is stipulated that offshore oil drilling alleviates the pressure inside of the oil reserve and slows down the rate of seepage. Moreover, Venoco, a Santa Barbara oil company, even manages to capture some of the oil escaping from the seep conduits, thus further reducing the amount of tar finding its way to the beaches.

But don't go praising the oil companies just yet.  Due to the number of variables at play, there is a lack of proof that reduced pressure on the oil reserve really slows the rate of seepage. Either way, many argue that the risks far outweigh the benefits. Massive oil spills are far more destructive than the natural seep rates which many marine animals have evolved to tolerate to an extent.

The Santa Barbara oil spill of 1969 released between 80,000 and 100,000 barrels of oil into the ocean, and it is, to date, the third largest oil spill in U.S. history. To put things into perspective, 100,000 barrels is about 4.2 million US gallons. The Refugio oil spill of 2015 released an estimated 3,400 barrels. Despite the success of cleanup efforts after the Refugio spill—after two months, only 1 in 44 analyzed tar samples collected at various beaches from Santa Barbara to Los Angeles had originated with the spill—hundreds of animals perished in the aftermath. Only about one hundred affected birds and mammals were collected alive and saved.

So all things considered, we'd better off with renewable energy sources. But even when that day comes, Santa Barbarians and visitors will still be cleaning their feet after a walk on the beach. Thankfully, olive oil or dish soap work pretty well.