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?? Baseline investigations in the selected polygons,
?? Disturbance of the benthic ecosystem, and
?? Monitoring of the disturbed sites and reference sites.
The first two polygons (BIE-I and BIE-II) were created in an American
licence site having low nodule density (on the border of the Russian site) at
coordinates 12 degrees 56 minutes north latitude and 128° 36' west
longitude. Polygon selection was done using methods such as echo-sound
survey, sonar survey, photo-video profiles, measurement of near-bottom
currents, and baseline biological, chemical and geological sampling.
All these investigations were carried out immediately after the
disturbance, one year later and seven years later. Resuspended sediment
plume was tracked using near-bottom CTD (conductivity-temperature-depth)
profiles. The thickness of the resuspended sediments was measured using
sediment traps, current-meter stations with transmissometers and X-ray
photos of sediment cores. The location of all underwater devices was fixed
with a global positioning system (GPS) based on navigational satellites and
an acoustic undersea navigation system, ASMOD.
The central place in the BIE experiment was occupied by the
disturber, which was designed by the United States firm Sound Ocean
Systems, Inc.
All cruises during the BIE experiment were carried out on the
Russian scientific vessel Yuzhmorgeologia.
1. Hydrophysical investigations
Eight bottom-current-meter stations with 13 current meters were
employed in the BIE experiment. Current meters were placed at intervals of
5-120 metres above the bottom. Near- bottom current velocity, current
direction and temperature were measured every hour. From the data sent
by these stations, it was established that the hydrodynamic regime of the
near-bottom area is characterised by low-energy currents with varying
directions and mean velocities of 3-4 m/second; maximum velocity was 10
m/s. Water temperature was about 1.5° Celsius and did not change.
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