TMC held an open webcast on 11/21/23 where lead environmental manager, Michael Clarke, discussed data gathered from last year’s harvesting program. The data showed that benthic plume dispersion was heavily influenced by a gravity current such that the plume doesn’t spread upward to any great extent, but instead spreads laterally. Because the plume doesn’t spread upward it isn’t carried away by ocean currents and spread over a wide area. In general, the plume resettled within 1,000 meters of the harvester, with most sediment deposited within 500 meters. This is in contrast to the stories told by environmental organizations such as the Deepsea Conservation Coalition, which has advertised that these bottom water plumes could travel hundreds of kilometers.
As collector vehicles mine the seafloor, seafloor sediments would be resuspended, creating plumes which could disperse over tens to hundreds of kilometers beyond mining sites.
Deepsea Conservation Coalition, Link
The sedimentation plume from the harvester created a footprint that was smaller than expected vis a vis modeling. Within 500 meters of the harvesting operation, sedimentation levels of 1-2 millimeters were seen, resulting in nodules that had a light dusting of sedimentation but the nodules themselves remained clearly visible. Clarke noted that we would expect some impact from 2 millimeters of sedimentation, but the extent of that impact is not yet clear. As COMRC has noted elsewhere, Bryan O’Malley’s work indicated no impact to biodiversity levels or biomass levels to foraminifera in the plume zone.
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