Understanding Mn-nodule distribution and evaluation of related deep-sea mining impacts using AUV-based hydroacoustic and optical data .

Peukert, Anne, Schoening, Timm, Alevizos, Evangelos, Köser, Kevin, Kwasnitschka, Tom and Greinert, Jens (2018) Understanding Mn-nodule distribution and evaluation of related deep-sea mining impacts using AUV-based hydroacoustic and optical data . Open Access Biogeosciences (BG), 15 (8). pp. 2525-2549. DOI 10.5194/bg-15-2525-2018.

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Abstract

In this study ship- and AUV-based multibeam data from the German Mn-nodule license area in the Clarion-Clipperton Zone (CCZ; eastern Pacific) are linked to ground truth data from optical imaging. Photographs obtained by an AUV enable semi-quantitative assessments of nodule coverage at a spatial resolution in the range of meters. Together with high resolution AUV bathymetry this revealed a correlation of small-scale terrain variations (< 5 m horizontally, < 1 m vertically) with nodule abundance. In the presented data set, increased nodule coverage could be correlated with slopes > 1.8° and concave terrain. On a more regional scale, factors such as the geological setting (existence of horst and graben structures, sediment thickness, outcropping basement) and influence of bottom currents seem to play an essential role for the spatial variation of nodule abundance and the related hard substrate habitat. AUV imagery was also successfully employed to map the distribution of re-settled sediment following a disturbance and sediment cloud generation during a sampling deployment of an Epibenthic Sledge. Data from before and after the "disturbance" allows a direct assessment of the impact. Automated image processing analyzed the nodule coverage at the seafloor, revealing nodule blanketing by resettling of suspended sediment within 16 hours after the disturbance. The visually detectable impact was spatially limited to a maximum of 100m distance from the disturbance track, downstream of the bottom water current. A correlation with high resolution AUV bathymetry reveals that the blanketing pattern varies in extent by tens of meters, strictly following the bathymetry, even in areas of only slightly undulating seafloor (< 1 m vertical change). These results highlight the importance of detailed terrain knowledge when engaging in resource assessment studies for nodule abundance estimates and defining minable areas. At the same time, it shows the importance of high resolution mapping for detailed benthic habitat studies that show a heterogeneity at scales of 10 m to 100 m. Terrain knowledge is also needed to determine the scale of the impact by seafloor sediment blanketing during mining-operations.

Document Type: Article
Funder compliance: info:eu-repo/grantAgreement/EC/FP7/603418
Keywords: Ferromanganese nodules, nodule abundance, deep-sea mining, environmental impact, seafloor mapping, sediment re-settling, seafloor blanketing, seafloor photographs
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems > DeepSea Monitoring
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.5194/bg-15-2525-2018
ISSN: 1726-4170
Related URLs:
Projects: JPIO-MiningImpact, MIDAS
Contribution Number:
ProjectNumber
DSM33
Expeditions/Models/Experiments:
Date Deposited: 08 Dec 2017 08:41
Last Modified: 10 Sep 2018 13:43
URI: http://oceanrep.geomar.de/id/eprint/40454

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