The effects of a deep-sea mining test on organic matter in seafloor sediments were still evident more than 40 years later, according to research by the University of Liverpool published in Elementa: Science of the Anthropocene. Organic matter provides food and nutrients for organisms living on and within the seabed, so changes to its amount and quality could affect deep-ocean ecosystems.
In 2023, researchers with the SMARTEX project studied a site in the Pacific Ocean’s Clarion-Clipperton Zone where the Ocean Minerals Company tested deep-sea mining in 1979. Tracks left by the 100-ton mining machine remained visible. The team collected sediment from about 4,800 metres below the surface, both in and around the disturbed area and at an undisturbed control site.
The researchers measured the amount and composition of particulate organic matter, using indicators including carbon and nitrogen content, lipid biomarkers and stable isotopes. They found that the historic mining site had less organic matter, as well as differences in its composition and particle size, compared with the control area.
Images from the site also showed fewer larger animals and single-celled organisms in sediments affected by the test mining. The study links these lower abundances to the depleted organic matter, raising questions about how mining disturbance may affect the recovery and resilience of deep-sea life.
The Clarion-Clipperton Zone, located in the eastern and central Pacific between Hawaii and Mexico, is of interest for its polymetallic nodules, which contain metals used in electronics and manufacturing. The researchers say environmental assessments should account for long-term changes in the availability and quality of organic matter. They also call for long-term monitoring and further research into how these changes vary across the region and affect ecosystem recovery.
Sources: Phys.org.