The legacy of industrial dumping off of the coast of Southern California has reared its ugly head once again. A new study from UC San Diego’s Scripps Institution of Oceanography performed a seafloor survey in which it revisited two industrial undersea dumpsites to identify objects discarded on the seafloor. What they found was that a large amount of objects previously documented on the ocean floor were in fact discarded military munitions.

The research was a followup to a 2021 survey, published in Environmental Science and Technology, that detected tens of thousands of barrel-sized objects strewn across the San Pedro Basin. The huge number of discarded objects was a result of the fact that, from the 1930s to 1970s, the site was a known location for industrial dumping, including of byproducts from the manufacture of DDT.

The new 2023 survey, led by Scripps oceanographers Sophia Merrifield and Eric Terrill, endeavored to identify the objects previously documented on the ocean floor. In order to do this, researchers employed a deep water autonomous underwater vehicle outfitted with synthetic aperture sonar and a remotely-operated vehicle with an HD video camera. The 2023 survey mapped 135 square miles and recorded more than 300 hours of video footage. “The resolution of the sonar provided by the U.S. Navy Supervisor of Salvage provides us an unprecedented map of the seabed which will take some time to fully appreciate and analyze,” said Terrill to UC San Diego.

What they found was that the majority of the objects were in fact multiple types of discarded military munitions and pyrotechnics. According to the Los Angeles Times, the findings included munition boxes, Hedgehog and Mark 9 depth charges and Mark 1 smoke floats, chemical smoke munitions used to conceal a ship’s movement or mark locations.

The study partnered with the U.S. Navy’s Supervisor of Salvage and the Office of Naval Research, who confirmed the findings. According to a statement from the Navy, “these munitions are likely a result of World War II-era disposal practices. While disposal of munitions at sea at this location was approved at that time to ensure safe disposal when naval vessels returned to U.S. ports, the Navy follows Department of Defense guidance for the appropriate disposal of munitions that aligns with state and federal rules and regulations.”

Scripps elaborated that the Navy will review the findings “to determine the best path forward to ensure that the risk to human health and the environment is managed appropriately and within applicable federal and state laws and regulations.”

Though this discovery is dramatic in its size and scope, the discovery of discarded military munitions offshore is not contained to Southern California. Last week, a WWII-era practice bomb washed ashore in Santa Cruz in the most recent swell to hit the region, prompting a response from the Santa Cruz Sheriff’s office bomb squad.


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