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Marine Techs from Scripps Oceanography deploy a Deep SOLO for testing off the coast of La Jolla, California, November 2020. Photo courtesy of UC San Diego's Scripps Institution of Oceanography.
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Survey of seafloor finds thousands of munitions, explosives

REGION — A second sweeping survey of the seafloor off the Southern California coast by researchers from UC San Diego’s Scripps Institution of Oceanography revealed thousands of aging military munitions and explosives littering the bottom of the ocean.

The survey, conducted in April 2023, was a follow-up to one completed in 2021, which found thousands of barrel-sized objects organized in lines across 135 square miles of the San Pedro basin – between Santa Catalina Island and Long Beach.

Led by Scripps oceanographers Sophia Merrifield and Eric Terrill, the 2023 survey used a deep-water autonomous underwater vehicle with sonar and a remotely operated vehicle with an HD video camera, both capable of working up to full ocean depth of 6,000 meters or 19,600 feet, a statement from UCSD read.

The expedition took place with support from the U.S. Navy’s Supervisor of Salvage and the Office of Naval Research.

The researchers wanted to identify the barrel-like objects in the basin, a known location for industrial dumping between the 1930s and 1970s – including dumping of byproducts from the manufacturing of the pesticide DDT.

While industrial waste is indeed confirmed to be on the seafloor, a surprising number of the objects identified were munitions now nearly 80 years old.

These munitions are likely a result of World War II-era disposal practices,” a statement from the Navy reads. “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 DOD guidance for the appropriate disposal of munitions that aligns with state and federal rules and regulations.

“The Navy is reviewing the findings and determining 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,” the statement read.

During the 2023 survey, barrels from the legacy of industrial dumping and several old fishing vessels were also found on the seafloor. The barrels of industrial waste were found to be concentrated in two locations, and barrels were not pervasive across the dump site, the researchers said.

“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.

The survey data follow ongoing studies by UC Santa Barbara’s David Valentine, who in 2011 and 2013 discovered concentrated accumulations of DDT in the sediments and visually confirmed 60 barrels on the seafloor. Valentine is mapping DDT in sediments collected across the San Pedro Basin as part of the same project as the seafloor survey.

“Our preliminary findings of our analysis of sediments are showing that bulk dumping of DDT acid waste was the norm, that DDT immediately entered the environment and was likely not in barrels,” said Valentine, who in a 2019 study characterized the disposal of DDT waste as “inherently sloppy.”

“Once dumped, DDT spread at the seafloor, expanding its footprint to at least the base of the Catalina slope,” Valentine said. “We are finding that original DDT remains abundant in the seafloor today, in both absolute and relative terms.”

The Environmental Protection Agency has also stated that the majority of DDT found at offshore dumpsites was likely deposited through bulk-dumping rather than containerized barrels, according to the UCSD researchers.

Additionally, in the 2023 survey, scientists mapped whale falls, which are sunken whale carcasses. A total of seven whale falls were confirmed with video imagery, but the sonar data suggests more than 60 may exist in the footprint of the survey data collected by the AUV.

“The number of whale falls seems quite high relative to previous models of how many may occur on the seafloor off California,” said Scripps Oceanography marine biologist Greg Rouse. “However, the skeletons were mainly in very low-oxygen water that likely slowed decomposition markedly and the burial rate by sediment may also be very slow there. This would mean the whale falls may have accumulated over many decades.”

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