The Pacific Ocean hides chemical weapons, such as mustard gas, dumped after World War II. The Monterey Bay Aquarium Research Institute (MBARI) recently documented one of these dumps using diving robots.

The MBARI mission found rusting 55-gallon drums filled with unknown substances, but no artillery shells. Instead of instruments of death, the chemical weapons dump sites harbored life, including sponges, crabs and anemones. The animals clung to the sides of the barrels filled with unknown substances.

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The survey mission started in March of 2012 when a aquatic drone, known as an autonomous underwater vehicle, discovered 754 objects embedded in the muddy sea floor south of Santa Cruz Island and west of the Los Angeles coast. The deepsea drone used sonar to map the location of the objects, but couldn’t provide detailed information about their identity. In May, a remote-operated vehicle, named Doc Ricketts, videotaped the seafloor, which allowed identification of the barrels and other items.

The MBARI exploration found sea shells, as opposed to artillery shells, but that doesn’t mean marine chemical weapons dumps don’t threaten humans and wildlife. Nautical charts identify 32 chemical weapons dumping grounds in U.S. waters. Some of these areas cover vast expanses of seafloor and provide few details about the nature or exact location of the munitions, according to MBARI researchers who presented their findings at this week’s meeting of the American Geophysical Union.

In 1997, the Chemical Weapons Convention banned the production, storage and use of horrific chemical agents in 188 nations. Prior to 1997, many nations had already condemned and abandoned the use of chemicals such as blister-causing sulfur mustard or the nerve poison sarin. After World War I and II, large numbers of toxin-filled artillery shells and other weapons were dumped into the sea.

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Now however, the discarded weapons cause injuries when fishermen dredge up decades-old munitions. For example, the Centers for Disease Control noted three cases from the Atlantic Coast in the past decade:

For example, in 2010, commercial fishermen pulled munitions from the Atlantic while dredging for clams off Long Island, New York. Two crew members were hospitalized after a black tarry substance oozed from the weapons.

In 2012, workers found a 75 millimeter artillery shell at a clam processing plant in Delaware. A munitions disposal team identified mustard agent in the armament. No one received injuries in the incident.

When an artillery shell turned up in a Delaware driveway paved with crushed clamshells, two members of a U.S. Air Force Explosive Ordnance Disposal team received chemical burns. One serviceman was hospitalized with large, pus-filled blisters on his hands and arms. Analysis of the shells identified the chemical culprit as sulfur mustard.

IMAGE: Still image from video captured by MBARI’s ROV Doc Ricketts shows one of many 55-gallon drums that were lying on the seafloor in the area marked as a chemical munitions dump. Credit: (c) 2013 MBARI