Illustration by Adriana Heldiz

Around 11:50 a.m. on June 19, a whale watching tour captured drone footage of dolphins swimming through a 50-mile stretch of rainbow-colored oily mess about 70 miles from San Clemente Island, according to Gone Whale Watching Captain Domenic Biagini, who posted the video to his Instagram page.

That same day, only about an hour earlier, the Coast Guard had received another call reporting another slippery-looking sheen off Point Loma in San Diego, according to a press release. No dolphin casualties were reported in that case and the slick was much smaller, about three miles long and a half-mile wide. A Coast Guard helicopter did a fly-over.

The San Diego spill was also rainbow-colored, and since the Coast Guard actually had eyes on it, it hypothesizes the spill came from light fuel, like diesel – not the thick, black sludgy oil that renders pelicans flightless. There was no clean-up. If it was diesel, the fuel would disappear within half a day or so, Adam Stanton, a spokesman for Coast Guard San Diego, told Voice of San Diego.

With no witnesses, it left me wondering where all that mess goes and whether there’s hope of finding a culprit. It turns out the business of solving who may have dumped something bad into the ocean is much like solving any big crime – it takes good detective work.

So I called Chris Reddy, who I’m calling a marine detective. But the world knows him as a geochemist at the Woods Hole Oceanographic Institution that investigated where the 200 million gallons of crude oil released into the Gulf of Mexico during the 2010 Deepwater Horizon disaster went. He’s not involved in the investigation of the California spills in question, but he works on oil spills all over the world.

In Deepwater Horizon’s case, it was pretty easy to figure out who done it. An offshore oil rig exploded near New Orleans, killing 11 crew members and dumping 12 times more oil than the Exxon Valdez spill of 1989, according to National Geographic.

Reddy, an expert science communicator who’s testified before Congress, said oil is the collective term for a soup of different molecules.

“You could think of these molecules as teenagers at a mall given $10. They have an option to do something. Some will say I’m going to evaporate, others are going to dissolve and mix downward in the ocean. Some may hang out on the surface and get eaten by microbes or sunlight,” Reddy said.

Each substance has a personality, Reddy said. Diesel is volatile because it contains compounds that are quick to evaporate, but it can be pretty toxic if the circumstances are right – like if it’s spilled in a small, contained space like a pond, he said.

The June 19 spill near Point Loma was three miles long and a half-mile wide, floating 11 miles offshore, according to the Coast Guard.

“That’s a lot of elbow room for the diesel to mix and evaporate, be attacked by sunlight and diluted,” Reddy said.

One hundred gallons of diesel, with the right water and atmospheric temperatures, can become 50 gallons in half a day, he said.

Cargo ships usually burn either diesel fuel or fuel oil, which is a petroleum product made at a refinery and generally considered to be dirtier than diesel. There’s a chance the liquid could have been a mix of other liquids a ship carries called bilge, which might include lubricants.

Still, Reddy said a human eye alone is not a very good at deciphering what was spilled.

If you want to be certain, that takes forensics. Marine detectives analyze samples of suspected spills through a mass spectrometer, a relatively old technology that can identify the types of molecules in a sample by blasting it through heat and magnets.

But once you know what was spilled you have to match it with a suspect, otherwise known as the responsible party, for a case to hold up in court. (BP Exploration and Production paid $8.8 billion in natural resources damages for Deepwater Horizon, for instance.) That’s where the Coast Guard comes in. Marine traffic is closely tracked (you can watch it on this public website), and once you know who was near the spill site, it’s much like picking suspects out of a lineup.

Ocean cops  should be able to locate all the  ships within a certain range of the spill. Then it’s a matter of contacting them and physically taking a sample from their fuel tanks. Apply the same chemical analysis of the boat samples as scientists did to the spill sample, and find a match.

Stanton, from the Coast Guard, said the branch is in the investigation stage and checking vessel traffic. But Stanton confirmed the Coast Guard didn’t take any or receive any samples from the spill itself. So, there’s likely nothing to compare with a ship sample. He said Coast Guard could still possibly identify the culprit(s) by contacting operators of the vessels in their suspect pool and simply asking.

There’s also a chance the spill was from a natural source. The Earth’s surface is made up of a bunch of gigantic plates, like puzzle pieces, that move around at a slow geologic pace. Along the California coast, the Pacific plate slides along the North American plate, where sit massive oil deposits from  millions of  years ago.

Sometimes that oil gets hot enough and squeezes its way through cracks and fissures in the ocean floor to the water’s surface, creating what are known as natural seeps, said David Valentine, a geochemistry and microbiology researcher at University of California-Santa Barbara.

Oil may seep year-round from of those fissures in areas where those ancient deposits lie, from northern Orange County to Monterey County. San Clemente is known for having some natural seeps, but when they spout it’s usually a pretty substantial “belch,” Valentine said.

Over half the oil that enters the ocean naturally. But natural oil is a lot less toxic than spilled oil because heat and microorganisms have already eaten away at it before it leaves the ocean crust. It’s still a challenge identifying natural oil versus spilled oil or another fuel and still requires a chemical analysis, Valentine said.

“With spills, the real smoking gun is not these chemical signatures you’re trying to interpret, but having something to compare it to,” he said. “Try and disprove your hypothesis.”

I asked if witnesses to ocean spills should try and capture a sample themselves to help aid the investigation. Valentine said that could help, but there are a lot of factors that could mess up the quality of the sample, like using a plastic container.

The possible spillers seem to have also evaded big brother in the sky, satellites that capture images of ocean spills tracked by the National Oceanic and Atmospheric Administration or NOAA. Satellites pick up spills all the time, like a May 23 spill off the coast of San Clemente Island. The image shows an angular black streak, like a painted brow, which NOAA analysts deemed with high confidence as a bilge dump 10 nautical miles long.

NOAA satellite analyst Matt Coverdale told me satellites didn’t pick up any good images of the June 19 spill, as far as he could tell. That could have been due to the fact that the satellite, which rotates the Earth, simply didn’t pass over that area or the day was cloudy.

Coverdale said it’s fairly easy to tell a natural spill versus one from a ship. The May 23 spill’s sharp angle is synonymous with the way a boat maneuvers a turn through the water. How dark the streak is can add confidence it’s a spill that needs looking into. Plus NOAA can toggle on a map over the satellite image showing known oil wells and natural seeps.

Stanton, from the Coast Guard, said it’s unclear when investigators will finish their case. NOAA’s Fish and Wildlife Service and the California Department of Fish and Wildlife are also looking into the case.

If you see marine pollution, report it to the National Response Center at (800) 424-8802, or the Joint Harbor Operations Center at (619) 278-7057.

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