standardization of environmental data and information - International ...

300 m deep basins alternating with ridges. These structural features are
from a few km to 10 km wide, and can be followed for tens of kilometres.
Some show relatively steep slopes, which appear controlled by block
faulting of the underlying basaltic basement 2 . Additionally, small volcanic
cones, 25 m high and a few hundred m wide, are scattered in the area.
Conclusion: A bathymetric map with complete coverage of the area
under investigation is essential, because the topographic variation is
greater than previously expected. Slope inclination places limits on
potential mining and is an important parameter for different environmental
settings.
1.2. Sediment echo sounding
Use of a parametric 4-kilohertz sediment echo-sounder system
made it possible to distinguish different sediment sequences and, where
the sediment cover was thin, to define the thickness of the entire sediment
cover above the volcanic basement. Besides an overall increase of
sediment thickness towards the north, the Quaternary sequence was found
to vary greatly: e.g. thinning of the sequence towards some of the larger
volcanic cones but thicker-than-usual deposits “behind” some hills,
erosional windows within the Quaternary cover (exposure of Tertiary strata
at some ridges), indications of downslope sediment transport at some steep
ridge flanks (slumping) 3 .
Conclusion: Sediment echo sounding reveals variability in the
thickness of the youngest sediment sequence. It shows (ongoing) natural
sediment redistribution or indications of a higher-than-expected dynamic in
this environment. Thus, neighbouring locations may differ in their long-term
“inherited” history. This variability of the substrate is an important
parameter likely to influence the character of the benthic communities.
1.3. Sea-floor reflectivity (side-scan sonar imaging)
Side-scan sonar profiling showed that the seafloor often displayed a
high acoustic reflectivity (relatively hard surface layer) that is occasionally
interrupted by irregular zones (50-400 m wide) of low reflectivity (soft
surface). This low reflectivity occurred at ridge crests and elevated
plateaus. It marks surface areas where the otherwise common manganese
nodule coverage at the seafloor surface was lacking 4 . Furthermore, small
(25 m high and 100-300 m wide) volcanic cones were detected that were
INTERNATIONAL SEABED AUTHORITY 149