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than the 200-metre depth distribution layer of the phytoplankton, where
photosynthesis took place. For this reason, vertical water samples had
been collected from seven layers at depths of 0, 20, 50, 75, 100, 140 and
200 m, using a rosette sampler. Observations in 1992 had indicated that,
at all stations, chlorophyll a concentration reached a subsurface peak
between 75 and 140 m, decreasing to zero near the depth of 200 m (see
figure 4 above).
Impact assessment study
An enrichment experiment had been carried out to understand the
effect of deep- seawater discharge on phytoplankton (see figure 7 above).
The finding was that the abundance and composition of the phytoplankton
community changed around concentrations of deep-sea water.
Impact prediction
A numerical model approach had been taken to predicting the
dispersion of a cold water mass at the surface of the ocean. To gather data
for this purpose, a field test had been conducted in the Japanese coastal
area, in which cold water had been pumped up from a depth of 300 m and
discharged at the surface. Temperature changes had been monitored by a
thermistor-chain system. The numerical model developed using the
experimental results predicted that cold water discharged in the Central
Pacific Ocean would sink quickly.
Benthic study
Mr. Tomohiko Fukushima, describing the benthic study, noted that
its results had been reported at the International Symposium on
Environmental Studies for Deep-Sea Mining held in Tokyo in 1997. 31
The goal in this study had been to evaluate the effect of deep-sea
mining. For purposes of the study, the effect had been defined as the
relationship between impact and damage, the impact was the redeposition
of sediment and the damage was the change in the benthic community.
The impact mechanism was assumed to be as follows:
1. The nodule collector discharged sediment, consisting less
of organic material than of sediment distributed on the
surface of the seafloor.
214 INTERNATIONAL SEABED AUTHORITY