Minimising impact of nodule mining

Saturday December 05, 2015 Written by Published in Weekend

The aspects of seabed nodule mining that require criteria of maximum-acceptable impact include:


(1) The seabed sediment plumes should be less than 2:1 (plume to nodules) to minimise the smothering of nearby seabed animals;

 (2) The uplifted nodules, water and sediment should be completely isolated from the water column to prevent any contamination or other effects of marine biodiversity;

(3) All nutrient-rich water, with or without sediment, taken to the surface production support vessel should be kept isolated and returned to the seabed to ensure that surface waters are not enriched to cause plankton blooms and to prevent sediment clogging filter-feeding mechanisms;

 (3) Mid and high-frequency noise intensity should be below that likely to interfere with toothed-whale echolocation and communication, and low frequency noise should be less loud than a humpback whale song (170dB in water @1m);

(4) White lights on seabed collectors should be downward pointing and minimised to reduce impacts on bioluminescent animals, and these impacts could be further reduced by the use of yellow, orange or red lights, which are invisible to almost all bioluminescent animals.

Biodiversity Preservation Areas?

The seabed collectors will remove nodules, which are the only hard substrate for microbes and animals, and they will mechanically damage the small benthic animals in the sediment.

The only way to ensure that no species becomes extinct is to fully protect parts of their populations. This will happen automatically to some extent, because the collectors will be unable to access steep areas. However, as a precautionary measure to achieve zero extinction, seabed Biodiversity Preservation Areas (BPAs) should be established.

BPAs can be established using the CBD Ecosystem Approach to identify an area that is ecologically equivalent to the mine site and up-current or distant, so that it is protected from sediment resettlement. Ecological equivalence can be established by morphological and genetic recognition that species in the mine area are also in the BPA, even though the international shortage of taxonomists means most species will not be identified with Latin names.

In the case of the Clarion-Clipperton Area, nine BPAs have been established using the extensive biological knowledge obtained by the industrialised countries with Exploratory Concessions.

In the case of the Cook Islands, where such research is very unlikely to be funded, it could be an obligation of the Exploratory Licence holders to undertake sufficient biological sampling within and near their concessions to enable ecologically equivalent areas to be found for the establishment of effective BPAs.

Working together;

The standards of best practice described in this feature are commonly incorporated in recent mining proposals, such as the Southampton system. They are not particularly difficult to achieve if the contractor knows in advance that these are the standards.

With prior knowledge of the standards, a contractor applying for Exploratory Licence would be confident of surpassing the criteria and obtaining a mining licence to recover the immense investment in exploration and technology development.


Agarwal B., Hu P., Placidi M., Santo H., & Zhou J.J. (2012) Feasibility Study on Manganese Nodules Recovery in the Clarion-Clipperton Zone. The LRET Collegium 2012 Series, vol.2., University of Southampton.

Hein J., Spinardi F., Okamoto N., Mizell K., Thorburn D., & Tawake A.  (2015) Critical metals in manganese nodules from the Cook Islands EEZ, abundances and distributions. Ore Geology Review. 68:97-116.


TEXT IN BOX: The Cook Islands Government has called for tenders for exploratory licences for polymetallic nodules, making this a good time to review the scientific information on the nodules and their environment to identify the possible negative impacts of mining, says Cook Islands Natural Heritage Trust director Gerald McCormack who wrote this final instalment in a three-part feature.

“Widespread knowledge of the possible impacts and effective mitigation could help to ensure that environmental damage is minimal and acceptable.”

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