The Tar Story

Every summer, sooner or later, the same question shows up on Santa Barbara’s beaches: is that tar on my feet from an oil spill, or is it just… the ocean? The honest answer is almost always “both, and it’s genuinely hard to tell which” — and understanding why takes a quick tour through geology, two of the more consequential oil spills in American history, and some fairly elegant chemistry.

The seeps were here first

Just offshore from Coal Oil Point, near UC Santa Barbara, sits one of the most active natural oil and gas seep fields on the planet. Cracks in the seafloor above the Monterey Formation — an oil-rich shale that underlies much of the Santa Barbara Channel — let crude oil and natural gas migrate up through fault lines and vents and bubble into open water. NOAA researchers have estimated the Coal Oil Point seep field alone releases somewhere on the order of 6,500 to 7,000 gallons of oil a day, along with far larger volumes of natural gas, day in and day out, with or without any human activity offshore. Some of that oil weathers into tar balls that wash up on beaches for miles around, from Isla Vista down through Santa Barbara and beyond. Long before anyone drilled a well in this channel, this coastline had a tar problem — indigenous Chumash communities are documented using seep asphaltum (“yop”) to caulk canoes and seal baskets, which is about as old a “beach conditions dataset” as exists anywhere.

Then people started drilling into the same reservoir

The Santa Barbara Channel has been an oil field since the 1890s (see Summerland’s own history, one tab over), and by the late 1960s that meant platforms standing in open water. On January 28, 1969, a blowout on Union Oil’s Platform A, about six miles offshore, ruptured the seafloor and released an estimated three million gallons of crude over the following weeks — coating 35 miles of coastline, killing thousands of seabirds and marine mammals, and becoming one of the direct catalysts for the first Earth Day the following year and the modern American environmental movement generally (NOAA’s incident archive covers it here: https://incidentnews.noaa.gov/). It remains, by volume, one of the largest oil spills in U.S. waters.

It happened again, smaller but still serious, on May 19, 2015: a corroded segment of the Plains All American Pipeline ruptured near Refugio State Beach, sending roughly 140,000 gallons of crude toward the coast, an estimated 100,000 of which reached the ocean. Oil and tar from Refugio turned up on beaches as far south as Los Angeles County in the following weeks (NOAA’s Office of Response and Restoration maintains spill response records: https://response.restoration.noaa.gov/).

Why you can’t always tell by looking

A tar ball from a 2015-vintage pipeline spill and a tar ball from last week’s natural seep can, after enough time in the surf, look and feel identical: black, sticky or hardened, smelling faintly of asphalt. Telling them apart is a job for chemistry, not eyeballs. Geochemists use “fingerprinting” — comparing biomarker ratios (like pristane-to-phytane), stable carbon isotope signatures (δ13C), and detailed hydrocarbon distributions measured by gas chromatography-mass spectrometry — to match a tar sample’s chemical signature against known source oils. Seep oil from the Monterey Formation has a fairly distinctive fingerprint; a specific pipeline or platform’s crude has its own. USGS geochemists have built out a reference library of exactly this kind of sample data for the Santa Barbara Channel specifically so a tar ball can, in principle, be traced back to its source (again: https://pubs.usgs.gov/of/2009/1225/).

The catch is time. The moment crude oil hits open water, it starts “weathering” — the lightest, most source-specific compounds evaporate or dissolve within hours, bacteria begin breaking down the rest within days, and sunlight photo-oxidizes the surface into a crust, all of which erodes the very chemical signatures that fingerprinting depends on. Within roughly a few days to a month, depending on conditions, a weathered tar ball’s fingerprint has degraded enough that confidently pinning it to one specific source — versus ruling it in as “consistent with regional seepage” — gets dramatically harder. Scientists sometimes call this the weathering window: the shrinking period after a release when attribution is still chemically tractable.

Why the timestamp matters as much as the sample

That weathering window is exactly why this site insists on a timestamp with every report, not just a photo. A tar ball logged with a precise observed-at time, on a specific stretch of beach, gives researchers something a bare lab sample can’t: a data point pinned to a moment in the weathering clock. Cross-referenced against wind, current, and swell data from that same window, a dense timeline of crowd reports can help narrow down when oil arrived on a beach — which is often the single most useful fact for deciding whether a given tar event traces back to the ancient seep field offshore, or to something newer that regulators need to know about right away. A crowd with good timestamps can’t replace a mass spectrometer. But it can tell the lab where, and when, to point one.