Deep-Sea Mining Threatens Nutrient Supply in Ocean's Twilight Zone

A new study from the University of Hawai'i at Manoa published in Nature Communications reveals that waste from deep-sea mining could significantly disrupt vital ecosystems in the Pacific Ocean's Clarion-Clipperton Zone.

Researchers found that sediment discharged during mining operations could adversely affect marine life in the midwater twilight zone, which is crucial for vast populations of zooplankton, the foundation of the ocean's food web.

The study indicates that 53 percent of zooplankton and 60 percent of micronekton, which rely on zooplankton for food, would be impacted by mining waste discharge. Lead author Michael Dowd states that mining activity releases waste that creates murky water, diluting the nutritious food particles that zooplankton consume.

This disruption could have cascading effects, ultimately impacting larger predators including fish, seabirds, and marine mammals. The research examined sediment plumes from a 2022 mining test in the CCZ, an area now targeted for the extraction of polymetallic nodules containing valuable minerals.

The findings highlight that mining particles contained far fewer amino acids compared to the natural particles that typically nourish marine organisms. Co-author Erica Goetze emphasizes that mining isn't just about extracting resources; it's about reducing the food supply for entire communities in the deep sea.

Currently, around 1.5 million square kilometers of the CCZ are licensed for deep-sea mining, driven by global demand for minerals used in renewable technologies. The mining process involves collecting nodules and surrounding sediments, which are then pumped to surface vessels while the waste is discharged back into the ocean.

Some companies propose releasing this waste within the twilight zone, with environmental consequences largely unknown until now. The twilight zone is home to a diverse range of life that contributes to the ocean's carbon balance.

Co-author Jeffrey Drazen warns that mining plumes introduce low-quality food into a system that has been finely tuned for centuries. The study raises alarms that large-scale mining could lead to long-lasting changes in ocean ecosystems.

As commercial fisheries could also be impacted, the authors stress the need for informed decision-making now that deep-sea mining has not yet begun at a commercial scale. Co-author Brian Popp calls for careful consideration of the discharge depth of mining waste to protect marine ecosystems.

The researchers hope their findings will guide policy discussions at the International Seabed Authority and inform environmental reviews by the National Oceanic and Atmospheric Administration. They underline the importance of developing international rules to safeguard marine ecosystems from surface waters to the deep sea.