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4. Survey and Sampling Strategy for a Baseline Study
Based on the above results, a generic survey and sampling strategy
is suggested for baseline studies which takes account of observed trends
from our Peru Basin investigations and tries to minimise efforts to cover
natural variability:
I. Survey with acoustic methods
a) Acquire bathymetry of a survey area (a full-coverage bathymetric
map is needed) with sufficient resolution (approximately 10-m
contour lines).
b) Map sediment distribution and thickness using a high resolution
sediment echo-sounder system (profiles along and across are
required). (Bathymetric swath mapping and sediment echosounding
systems can normally be run in parallel.)
c) Deploy a (deep-towed) side-scan sonar system to define small
topographic features and acoustic reflectivity of the surface (e.g.
coverage with nodules, etc.).
d) Check and classify side-scan results using photo-sledge
runs.
II. Define facies types
Based on the results from the initial surveys, several facies types
should be defined, based on differences in morphology (basin, slope,
steep escarpment, ridge, plateau), sediment character (thickness of
sequence, stratification, acoustic transparency, reworked sediment,
erosion, etc.) and fine-scale surface features (nodule coverage, fault
steps, etc.). This approach also appears reasonable in the CCFZ,
where a variety of sedimentary facies zones have been reported 20 .
III. Characterise sediment-facies types by seafloor sampling
a) Sample different facies types adequately (taking account of their
distribution), using a box corer and multicorer.
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