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Sediment samples, except those for macrobenthos studies, had
been collected by multiple corers. After comparing the sampling ability of
multiple and box corers, it had been concluded that the multiple corer was
better for the meiobenthos study.
According to preliminary results, 87 percent of meiofauna were
distributed in the upper 3 centimetres at this site. Therefore, the study had
analysed the top 3 cm. Among the various sizes of benthic organisms, the
megafauna had been identified by video recorder, macrofauna had been
categorised as larger than 300 microns and smaller than 4 millimetres, and
meiofauna as larger than 32 µm and smaller than 300 µm.
As JET had been designed to ascertain disturbance impacts, the
experimenters had tried to determine the amount of redeposition. Since
deposition thickness was not easy to measure, several approaches were
necessary. The study had taken five approaches: (1) video observation, a
simple way to learn about sediment-deposition conditions; (2) colourintensity
analysis, for the same purpose as video observation; (3) the kriging
method; (4) stereo photoanalysis, and (5) numerical modelling. Colourintensity
analysis was an image-analysis technique that examined the
colour-intensity ratio between manganese nodules and sediment on the
seafloor, making it possible to recognise resedimentation and draw maps
(see figure 14 above). The kriging method addressed resedimentation
conditions using sediment-trap data (see figure 15 above). Stereo
photoanalysis of a disturber tow track had produced a diagram showing the
width of a track (see figure 16 above), in which the highest point of
sediment moved was about 15 cm.
The JET experimenters had written a simple scenario that had to be
carefully studied to confirm the theory. The environmental impact study for
manganese nodule development of Japan had been carried out during 12
years, generating a great deal of knowledge. That knowledge had been
accumulated systematically, with much trial and error. Moreover, the
knowledge had been disseminated through international symposia and
journals. Mr. Fukushima hoped it would greatly contribute to the guidelines
of the International Seabed Authority.
INTERNATIONAL SEABED AUTHORITY 217