In:
Biogeosciences, Copernicus GmbH, Vol. 15, No. 8 ( 2018-04-27), p. 2525-2549
Abstract:
Abstract. In this study, ship- and autonomous underwater vehicle (AUV)-based multibeam
data from the German ferromanganese-nodule (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 coverage. 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 coverage and the
related hard substrate habitat. AUV imagery was also successfully employed to map the distribution
of resettled sediment following a disturbance and sediment cloud
generation during a sampling deployment of an epibenthic
sledge. Data from before and after the “disturbance” allow
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 h after
the disturbance. The visually detectable impact was spatially
limited to a maximum of 100 m 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 mineable 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 to
100 m. Terrain knowledge is also needed to determine the
scale of the impact by seafloor sediment blanketing during mining
operations.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-15-2525-2018
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2018
detail.hit.zdb_id:
2158181-2
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