Marine scientists stepped onboard the Schmidt Ocean Institute's research vessel Falkor to take part in a 12-day expedition that ran from July 26th to August 6th off the coast of Southern California. Their goal was to survey the biodiversity of deep-sea areas rich in minerals that are of interest to deep sea mining developers around the world. But they ended up discovering much more than expected.

The aim of the expedition was to establish mineral and biological baselines in the area covering 5,310 square miles known as the southern California Borderland, which has the potential for deep sea mining. The area contains rare earth marine minerals such as ferromanganese and phosphorite that are used in the manufacture of electronics, electric car batteries, solar panels, and other green technologies.

Scientists collected more than 300 samples of seafloor rocks, sediment, seawater, and marine invertebrates to better understand the ecology, mineral and microbial makeup of the relatively unexplored deep-sea system. In collecting samples, researchers also hope to evaluate the therapeutic or drug discovery potential of deep-sea microbes found in mineral-rich areas.

A barrel thought to contain DDT waste products rests on the bottom of the ocean floor off of the coast of Los Angeles. Many of the barrels, which were dumped between 1947 and 1982, are surrounded by light-colored bacterial matte halos. The halos indicate a change to the microbial community in the sediment and the scientists hope to learn what bacteria are there and what chemicals they are breaking down. (Image credit: Schmidt Ocean Institute)

The expedition explored nine deep sea sites, including the offshore site where possibly hundreds of thousands of barrels of toxic waste from the production of the insecticide DDT were dumped from 1947 to 1982.

With an underwater robot, the team of scientists from UC San Diego’s Scripps Institution of Oceanography and the United States Geological Survey collected sediment and biological samples around six barrels. Building on previous expeditions to the area, the data will later help to understand potential ecological effects of the dump site and to determine the levels of DDT present in the ecosystem after more than 50 years.

“Establishing ecological baselines in the deep sea allows us to track changes over time and better understand the consequences of human actions,” said Chief Scientist Dr. Lisa Levin, a professor of biological oceanography at Scripps Institution of Oceanography. “The DDT dump site provides evidence of a large human footprint in the deep ocean, but we are just starting to identify the effects on local marine communities.”

The information the team collected at the DDT barrel disposal site will be compared to animals and microbes at more distant sites in order to assess the current concentrations and effects of DDT in the region. The samples will return to Scripps Institution of Oceanography where scientists will conduct further analysis and DNA sequencing.

During one of the 12 expedition dives to explore the DDT site, scientists discovered a whale fall--the seafloor location where the remains of a whale come to rest. When a whale dies, it becomes a source of food for a host of other animals. If the dead whale’s carcass makes it to the bottom of the ocean, their death can give life to a new, extreme type of ecosystem.

Researchers unload and sort sediment cores - samples of the sea floor and sediment - after the samples were brought to the surface from known DDT dumping sites by Remotely Operated Vehicle (ROV) SuBastian. The study took place on and was operated from the Schmidt Ocean Institute's research vessel Falkor. (Image credit: Schmidt Ocean Institute)

Scientists also identified a new area of methane seepage. Methane seeps transfer carbon, which is the primary element in methane, from below the seafloor to the ocean. Seeps therefore play a critical role in moving older carbon stored in the seafloor into the ocean, where the carbon can be consumed by organisms. Furthermore, rising methane bubbles from natural seeps can either dissipate in the water column, or “survive” up to the water surface and be released into the atmosphere.

Marine biologists consider both areas a focus of specialized research because of the unique habitat they create.

“We are just beginning to understand the valuable resources of our ocean ecosystem,” said Wendy Schmidt, co-founder of Schmidt Ocean Institute. “We can’t protect what we don’t know and understand, and the human impact on our ocean over the past 75 years has had a detrimental effect on its health and on the many ocean systems that support life on land. We expect the knowledge gained from this expedition will inform policy, management and stewardship of the deep sea, so that episodes of dumping toxic waste, such as this one, will not happen again”

This feature appeared in Environment, Coastal & Offshore (ECO) Magazine's 2021 Autumn edition, to read more access the magazine here.