Preface The expedition ARK XIX/3 with the German icebreaking RV ...

particle flow, macro fauna and surface structures such as ripples or bumps have been
found.The upper part of the sediment layer has been sampled since it is the predominant
effect on the backscatter of the acoustic pulse. The cores were sampled in 1cm slices
(from 0 to 10cm depth) and every second 1cm slice was sampled below 10cm. The
description of the multicorer stations is given in Table A4.2.2-1.
Backscatter analysis
Angular backscatter data are difficult to display on bathymetric maps. Since the
backscatter strength is mainly affected by the sonar beam angle, the images show
artifacts parallel to the track lines. Therefore, the angular backscatter was processed and
the mean angular dependence has been removed from the data. As a result normalized
backscatter (grey level) is used for seabed analysis and represents the angular
backscatter data as approximate values.
The backscatter grey level of the area shows a range of 12dB. The background
sediments of the margin have backscatter grey levels of about -42dB. The area of the
"Belgica mounds" reaches higher backscatter levels up to -35dB. The highest value of -
30dB was found to exist at a strong slope of a depression area. The multicorer video
deployment indicated corals on this slope.
For a preliminary investigation two channels have been selected for studying sediment
(grain size, stratigraphy) and backscatter properties: channel 1 and the northern Gollum
Channel.
Grain size analyses were carried out using a binocular and a 0.1mm surgical sewing
thread as a reference scale. The classification of the sediments to sand, silt or clay was
made visually. The sediment grain size of the selected stations is given in Table A4.2.2-2.
The southern part of the area of investigation including the channels is displayed in
Fig. A4.2.2-2. The segmentation of the channels based on the backscatter grey level is
also indicated. In Table A4.2.2-2 backscatter levels and sediment properties are given at
the multicorer stations. At channel 1 we found that the higher backscatter in the eastern
(upper) part corresponds to a low penetration of the multicorer. The upper part of that
channel shows -36.6dB versus 26cm penetration compared to the western (lower) part
which shows -39.5dB versus 16cm penetration. This situation also exists if one compares
the background sediments with the mouth of channel area, i.e. -36.6dB / 28cm and -39.6 /
20cm, respectively.
The northern Gollum channel was subdivided into four segments which have an average
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