the Expedition ARKTIS-XIX/4 of the research vessel POLARSTERN ...

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Preliminary results
Along profile 200 and 300 (Fig. 2-1), part of the instruments were not released until
getting on site, to insure good recovery within ice fields. As extremely good ice
conditions were encountered (ice cover always well below 30%, often below 10%),
instruments were recovered without any major time delay. The first quality check of
the data were performed on the vessel and showed that the data quality is quite
variable. In the oceanic part of the profiles the signal range is large enough that
mantle arrivals can be identified. On the shelf, the northernmost profile has the worst
quality in terms of signal range. This partly due to a reduced air gun volume of 45 l
since some technical problems prevented the operation of the large volume Bolt air
gun. The maximum signal range of 40 km at maximum might also be due to a high
attenuation/scattering of the shelf sediments. This explanation is supported by the
signal ranges in the oceanic part, which are similar to the more southern profiles. The
profile off Shannon Island is the first one, which crossed the pronounced negative
magnetic anomaly along the East Greenland margin. Here, the seismic energy is
strongly scattered/attenuated. In some OBS recordings no signals are visible across
this complex geological structure. In total 6 RefTek recording instruments were
placed on Shannon Island and on the mainland. They provide signal ranges up to
150 km, and show a clear onset of the mantle phase around 100 km. An example of
a land station recording is shown in Fig. 2-2. The first arrivals show strong
undulations (Fig. 2-2; 50 km offset), which indicate the presence of large sediment
basins east of Shannon Island. Similar results are observed on the two southern
profiles 20030400 and 20030500. A summary of the observed signal range for each
recording station is provided in table 2-3.
Fig. 2-1: Location of the deep seismic sounding profiles. The triangles mark the position of the
OBH/OBS and RefTek stations. All lines together have a length of almost 1500 km.