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ack-up camera, had also housed small baited traps in front of the camera,
permitting the researchers to spot unknown species.
The manganese nodules in the area had a cauliflower shape
composed of many different small sub-nodules that differed from most of
the nodules in the Clarion-Clipperton Fracture Zone (CCFZ). They had
crevices and holes with a lot of mud inside. When this material was
washed, special meiofauna had been found living within the nodules.
The researchers next had to think about how to produce an impact.
They had always emphasized that they were unable to simulate mining
because they did not have a miner and were unable to collect the nodules
on the surface, but they had wanted to create a comparable impact. One
September day, while Dr. Schriever and Professor Hjalmar Thiel had been
motoring through the countryside seeing farmers plough their fields, the
idea had struck them that they could do it the same way. They had wanted
to get rid of the nodules from the bottom surface, so they thought of
ploughing them under. They had then developed an instrument with
ploughs on both sides of a frame, shaped like the big iron spheres that were
used in fisheries. The entire device, 8 m wide and 2 m long, had been
towed over the sea bottom. As both sides of the frame had been equipped
with ploughs, it did not matter on which side it arrived at the sea bottom.
They had crossed the area 78 times. They had expected to find a
more impacted area in the centre and a less impacted area in the
peripheral grid. They had used the sidescan sonar system with a weight
and camera, which had been towed about 3-5 m above the bottom to get
images of the area behind the sonar device. A still camera and an online
video camera, making up the Ocean Floor Observation System (OFOS), had
also been towed over the area. They had regulated the impacts because
the equipment had had to be picked up after about 10-12 runs to replace
the ploughs. In the intervening periods, OFOS had been used to observe
the impact and see whether the plough-harrow had been working properly.
The impact had destroyed the top 10-15 centimetres of the sediment.
Photographs showed that the nodules had been totally removed, leaving
white calcareous structures that had been lying about 15 cm deep in the
sediment. No organisms were visible on the sediment surface.
X-ray examination of multiple-corer tubes from the various stations
showed differences in the resedimentation rate, which had been up to 2 cm
at the station centre southwest and less than 1 millimetre at the centre
northwest. These had been at different elevations. At 3 nmi north from the
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