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problematic; it would be better to decide these when specific schedules for
testing are submitted by contractors to the Authority.
2.3. Commercial mining
Many strategies for removing manganese nodules from the seafloor
and lifting them to the ocean surface have been tested. These range from
simple, towed dredges to self-propelled, highly manoeuvrable platforms with
hydraulic or airlift pumping systems (e.g. figure 1). Descriptions of the
concepts considered to date are presented elsewhere 6 . The expected
major throughputs of materials for commercial systems are presented in
Table 1.
Component Daily flux
Discharges
Benthic* Surface
Nodules (dry tons) 5,500 250 250
Sediments (dry tons) 54,000 52,000 1,000
Biota (kg) 783 760 23
Bottom water (m 3 ) 58,000 - -
Interstitial water (m 3 ) 42,000 - -
Total water** (m 3 ) 105,000 80,000 25,000
* Expected to be discharged within 20 m of seafloor.
**Includes entrained surface water.
Source: modified from NOAA 7 .
Table 1 Estimated mining system throughputs.
Each of these systems is likely to produce its own particular set of
environmental impacts. Hence, impact assessment will depend very much
on the specific designs used. Some consideration of the scale of impacts
that would be possible can be derived from table 1, but serious impact
analysis cannot be completed until specific development plans are
submitted to ISA.
Most important to the Workshop objectives, the specific sites for
initial mining operations have not yet been specified by the contractors.
Based on the predictions of NOAA scientists 8 , a commercial mining system
discharging into surface waters would generate a surface plume extending
as much as 85 kilometres down-current and 10-20 km cross-current; a
benthic boundary-layer plume is predicted to have dimensions of
approximately 160 by 40 km. These would be the largest areas potentially
affected by initial mining operations and would cover an area (6400 km 2 )
that is less than 0.5 percent of the areas currently claimed by the
INTERNATIONAL SEABED AUTHORITY 102