Scripps researchers discover what lies within mysterious haloed barrels on the seafloor

When researchers discovered several eroding barrels on the seafloor off the coast of Southern California with an eerie, white halo encircling them, it wasn’t immediately clear what they held.

The barrels represent just a few of the thousands of barrels and barrel-sized objects that litter the seafloor in the San Pedro Basin, a stretch of ocean between Long Beach and Santa Catalina Island.

The area is significantly polluted with DDT, a chemical used as an insecticide that was banned in 1972. While researchers thought these haloed barrels may have carried DDT waste, they didn’t know for sure.

Until now. New research published Tuesday from UC San Diego’s Scripps Institution of Oceanography found that the barrels with halos contain caustic alkaline waste — a highly corrosive material that has been leaking out of the barrels for decades.

The leaked substance, which will take thousands of years to break down, has created an extreme environment surrounding the barrels where little to no life can survive — similar to deep sea hydrothermal vents, but not naturally found off the California coast.

“There shouldn’t be these extreme habitats out there in that part of the ocean, and that’s affecting not only the microbes, but the animals and all the way up the food chain, and who knows what else,” said Paul Jensen, retired marine microbiologist at Scripps and senior author of the study.

The work is part of a larger project with researchers across the region to assess the San Pedro Basin sites, where decades of dumping chemicals like DDT and other pollutants have raised environmental and human health risks.

The research has led to a range of discoveries. A few years ago, Scripps researchers found that most of the thousands of barrel-sized objects on the seafloor were discarded World War II-era munitions and pyrotechnics.

While the researchers didn’t identify the exact chemicals present in the barrels, alkaline waste was produced in DDT manufacturing, as well as oil refining — both prominent industries in the region in the mid-20th century.

“We only find what we are looking for, and up to this point we have mostly been looking for DDT,” Johanna Gutleben, a Scripps postdoctoral scholar and the study’s first author, said in a statement. “Nobody was thinking about alkaline waste before this, and we may have to start looking for other things as well.”

The presence of DDT in California and off its coast has had a lasting environmental impact: Significant amounts have been found in endangered California condors, and the chemical has been linked to cancer in sea lions.

But the newly-discovered alkaline waste, seeping from barrels 3,000 feet deep, could potentially affect the ocean even more than DDT. According to the study, it could take several thousand years for the effects of the material to resolve.

“We’ve discovered a new persistent pollutant in the bottom of the ocean that’s going to outlast the negative effects of DDT,” Jensen said. “That was so eye-opening for us.”

Jensen and Gutleben made their discovery by accident.

In 2021, the researchers and their team were on a research vessel off the California coast to study mineral-rich habitats for another project. But they were near the San Pedro Basin sites, so they decided to take a detour to collect some samples.

They focused on five barrels in the dumpsites, three of which had white halos around them — but it wasn’t easy to collect samples. The seafloor within the rings around the barrels had hardened like concrete, preventing them from collecting samples with a coring device that would be inserted into the seafloor.

They ended up breaking off a piece of the sediment with the robotic arm of a remotely-operated vehicle, then bringing it up to the surface to test it for DDT levels, microbial content and minerals.

The hardened sediment largely contained the mineral brucite — created through alkaline waste interacting with magnesium in the ocean water that resulted in the crust-like surface surrounding the barrels. When the high pH levels in the sediment interact with the water, it forms a chemical compound called calcium carbonate that deposits as a white dust, forming the halos.

Jensen says he would have expected the alkaline waste to dissipate in the ocean water soon after it was dumped. But by reaching the seafloor and interacting with the sediment — basically turning it to rock — the alkaline waste will now slowly dissolve.

Gutleben stressed that questions still loom over the widespread effects of the alkaline waste, as well as what mix of chemicals lie within the barrels that led them to be dumped into the ocean in the first place.

“We currently don’t know how many of those barrels are down there precisely,” she said. “We don’t know how many of them contain this alkaline waste, so we don’t know how big the problem really is.”