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Many researchers in recent years have noted the high degree of
local variability in the overall abundance, composition and surface
morphology of deep-seabed manganese nodules in the CCFZ. This high
local variability is attributed to such factors as the local seabed topography,
benthic current structure and sediment type 32 .
Investigators in the CCFZ have discovered persistent evidence of
active bedload transport, both with recent measurements of artificially
induced dispersion of benthic sediments 33 and through identification of
recent and ancient erosional surfaces using photography, acoustic subbottom
reflection profiling and direct sampling 34 . Recent Russian and
French studies cited above have shown (in the region defined by 133º 40'-
136º 40' W and 11-14º N) that these surfaces are arranged in a system of
erosional elements morphologically revealed as long, relatively flat valleys
(several hundred metres wide by several tens of kilometres long) with
depths of several tens of metres and flanked by steep (to 45º) slopes. The
valleys generally have southerly downslope directions.
The valleys are filled mostly by Pliocene to Pleistocene siliceous
clays, with the depth of recent sedimentation distinctly increasing from
north to south 35 . Because the regional bathymetry gets progressively
deeper toward the north-northwest, gravity-driven sediment transport is not
possible toward the southeast. Thus, the evidence strongly indicates a net
southward bedload transport by benthic currents.
5.4. Benthic community composition
This section summarises data for the Indian Ocean claim area and
the DOMES data for the CCFZ. Other collections, made in the Clarion-
Clipperton region 36 and in the Peru Basin of the South Pacific Ocean 37 ,
show similar taxa in similar relationships. It is beyond the scope of this
summary to resolve the differences and similarities among these studies,
but such an undertaking would greatly enhance our general understanding
of deep-seabed biological communities. (See also section 3.4 above.)
5.4.1. Benthic fauna in the Indian Ocean claim area
Sharma and Rao 38 present a qualitative description of the
megafauna observed in the Indian Ocean claim area, summarised in table
4. More recent assessments of infauna densities have been made from
examination of box cores 39 . These examinations indicate a dominance of
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