Deep-sea mining test from 1979 still alters seafloor food supply in 2023

A team led by the University of Liverpool has found that a deep-sea mining trial carried out in 1979 still leaves a measurable mark on the organic matter in seafloor sediments. Samples taken in 2023 showed lower quantity and quality of this material at the disturbed site than at an undisturbed control. The results were published in Elementa: Science of the Anthropocene.

A test site revisited after four decades

The work was carried out by researchers from the SMARTEX (Seabed Mining and Resilience To EXperimental Impact) project. They studied part of the Clarion-Clipperton Zone, a vast area of the Pacific between Hawaii and Mexico that is rich in polymetallic nodules. The nodules contain metals used in electronics such as rechargeable batteries and touch screens, which explains the commercial interest in the region.

In 1979 the Ocean Minerals Company used the site to test a mining machine weighing 100 tons. Its tracks remain visible on the seabed today. Over about a month, the team collected sediment samples at a depth of roughly 4,800 metres, from within and around the old disturbance and from a control area that had not been disturbed.

Measuring the quality of food in the sediment

The researchers focused on particulate organic matter, a key food source for animals and single-celled organisms living on and in the seafloor. It also supplies nutrients such as omega-3 fatty acids, which support growth, development and reproduction.

To judge both how much of this material was present and how nutritious it was, the team combined several approaches: carbon and nitrogen content, lipid biomarkers and stable isotope analysis. Together these give a picture of the origin and freshness of the organic matter, not just its volume.

Less food, fewer organisms

At the historic mining site, the organic matter differed from the control in composition and particle size, and it was lower in both quantity and quality more than four decades after the test. Still and video images collected by SMARTEX also showed lower abundances of larger animals and of single-celled organisms in the affected sediments.

The authors link the lower abundances to the depleted organic matter. The source describes this as a suggested connection with implications for recovery and resilience, rather than a demonstrated causal chain. The study is also based on one historic test site, so it cannot say how far the pattern holds across the wider zone.

Why it matters for research and regulation

Much of the debate about deep-sea mining has centred on the immediate removal of nodules and the plumes of sediment that mining stirs up. This study points to a slower consequence: changes to the food supply that sustains seafloor communities, which may in turn shape how well they recover.

Lead author Dr Rachel Jeffreys, a marine biologist at Liverpool, said the findings underline the need for long-term monitoring and for organic matter availability and quality to be considered in management and regulation of mining in the Clarion-Clipperton Zone. She noted that further research is needed on how organic matter varies across the region and how such changes affect ecosystem recovery.

For researchers, the study offers a rare long-term reference point. A single 1979 test is far smaller than the commercial operations now under discussion, so it is best read as evidence of how long disturbance can persist rather than a forecast of the scale of impact. Broader surveys of organic matter, repeated over time, would help establish baselines against which any future mining could be assessed.

The paper is Jeffreys et al., "Long-term impacts of deep-sea mining on sediment organic matter quantity and quality", Elementa: Science of the Anthropocene (2026), DOI: 10.1525/elementa.2025.00106.

Source: Impact of deep-sea mining on seafloor ecosystem still evident 44 years later (Phys.org, 3 November 2026).

Image: AI-generated illustration.