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Ocean coughs up tarballs at the Shores

It’s common for me to walk the beach at La Jolla Shores and see flattish scraps of tar lying on the sand. I even see them under water, wafting back and forth above the sand before they wash in to the beach. Frequently, small or nascent hitchhikers like barnacles are attached. Called tarballs, though not spherical, they form in the ocean when blobs of oil combine with swirling debris like sand grains to form solid yet bendable chunks of tar. The pieces I see at La Jolla Shores are mostly sand-dollar size and look not unlike stones with somewhat ragged edges. If you’ve walked the beach many a time and haven’t noticed them, it may be because they blend in so well with the genuine article — well-worn, dark stones dredged up by tidal and wave action. Tarballs likely resemble each other in size and shape because all that rolling around beneath the waves, along with tidal thrashings, selects for such constraints.

Tarballs are not a new phenomenon at La Jolla Shores, or elsewhere, for that matter, as they plague coastlines throughout the world. Beach tar may originate from offshore oil rigs or from onshore bulk oil storage or production facilities. The tar may get a start from people who dump automotive oil into their neighborhood storm sewers, which ultimately drain into the ocean. Seafarers also do their bit when emptying boat or ship bilges, which are tainted with heavy crude oil. The extent of tarballs on any given beach varies widely. On some shores, they are rarely seen unless a significant oil spill has occurred nearby. For the most part, wind and current conditions control the likelihood of whether tar fragments sink to the sea bottom or drift.

Tar on the beach is not always human induced; natural seeps also leak from the ocean floor. In fact, the sticky stuff has played a role in human society dating as far back as 13,000 years. Local Native Americans used seep material as a kind of all-purpose adhesive to waterproof their oceangoing plank boats and to waterproof baskets and containers. In more modern times, say within the last 100 years, natural asphalt seeps have been mined to pave California’s roadways.

What, then, is the root of the tarballs I constantly see at La Jolla Shores? I spoke to Scripps Institution of Oceanography (SIO) emeritus biologist Pat Masters, and after conferring with her husband and SIO emeritus coastal oceanographer Doug Inman, she said, “Doug is unaware of any natural seeps in the [La Jolla submarine] canyon. Doug and I suspect you are seeing bilge tar being carried from off San Diego Bay or Mission Bay by southwest winds that cause an eddy in the lee of Point La Jolla [located off La Jolla Cove].”

Eddies are currents best described as rivers in the ocean that move contrary to the direction of the main current. Some flow close enough to the shoreline to have an impact on the beach. Here, the fast-moving current can and does quickly move tarballs onshore.

Thirty years ago, the National Oceanic and Atmospheric Administration published a report on the “tarball problem.” They determined that tarballs originate from three main sources: 49 percent hail from land (for example, automotive oils dumped into sewers and vehicles leaking petroleum products onto the roads) where storm drain pollution and runoff from rain washes oils into the ocean; 40 percent come from oceangoing vessels when bilges are pumped and tanks are cleaned; and a scant 11 percent arise from natural seepage from the ocean floor. The study further concluded how exactly tarballs form:

Once in contact with water, oils decompose, and as they do, the lighter fractions evaporate. The remaining substance is the heavy asphalt-like material I see washed up on the beach.

Small amounts of tarballs generally don’t pose a serious threat to public health or the environment. However, walk on a beach with tar and some tacky residue my end up stuck to the bottom of your feet or shoes. If beach tar makes contact with your skin, wash it off when you can, because it may cause an allergic reaction like a rash. State and federal policies don’t allocate governmental funds to clean up minimal tarballs, but the government will get involved if the quantity of tar threatens public safety or if taking action will mitigate environmental damage.


— Judith Lea Garfield, naturalist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. Send comments to