standardization of environmental data and information - International ...

discussed by Dr. Gerald Matisoff (chapter 12 above). How these
measurements should be distributed in space and time might be best
considered after a mining site was identified and the technology and mining
pattern were better known. Many of the parameters were geotechnical and
would be useful in a mining engineering survey, and thus were likely to be
measured independently of the environmental study.
Suboxic layer
One participant observed that the depth of the suboxic layer was
highly variable. In the Peru Basin, it was about 10 centimetres below the
seafloor, whereas in the western part of the Clarion-Clipperton Fracture
Zone (CCFZ) it was at least 10 metres below. He wondered whether it was
necessary to measure such thick sediments
Smith replied that he thought the intent was to determine whether
mining would lift up reduced pore water that might contain dissolved
metals. He suggested that the recommendation be reworded to conform
with others that called for measuring redox conditions down to a depth of
10 cm or to the depth of the change from oxic to suboxic conditions,
whichever was shallower.
Dr. Matisoff said the idea was that if the sediment was still oxic at
10 cm below the surface, there was no need to go deeper to look for
reducing activity. The problem could be resolved by specifying the depth at
which to measure pore water concentrations for flux and redox conditions.
One participant did not agree that measurement should be limited
to the anoxic depth, since a mining operation might go deeper. Smith
responded that the suggested depth of 10 cm was relevant to habitat
characteristics, while 10 m was not.
Another participant suggested that an easy solution might be to use
the 40-cm maximum depth of a box corer, one of the sampling instruments
that would probably be used. Smith responded that 40 cm was deeper
than one needed to go for redox conditions.
In situ measurement
A participant wondered whether in situ measurements should be
recommended, given the uncertainties that might be introduced if
measurement was done on board after cores were brought up. Smith
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