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Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Methods
An inflatable boat was equipped with a portable "Chirp" sediment echo sounding system
(GeoChirp 6100A, Geoacoustics, UK) for continuous subbottom profiling during the Taymyr
expedition in summer 1996. The GeoChirp was modified at the Alfred Wegener Institute by
combining it with a digital delay box (for operation in deeper water), a GPS receiver (Trimble
Scoutmaster, for positioning) and a four-channel DAT tape recorder (Sony PC 204A, for data
storage of seismic trigger, seismic signal and GPS position). A detailed system description is
given by Niessen et al. (1997). The GeoChirp system offers the choice of two different modes:
sweeps of 2 to 8 kHz for deeper penetration and of 1.5 to 11.5 kHz for higher resolution. For
both modes, the sweep length is 32 ms. The returning sweep of signals is processed in the
Chirp Transceiver over a period of 130 ms during which a cross correlation of the received
echo pulses is performed. The profiles are plotted on a chart recorder in analog mode. We used
a P-wave velocity of 1500 m s-1 to calculate sediment depths from the two-way travel times.
A total of 11 profiles (103 km) and 42 profiles (ca. 59.1 km) were recorded in high resolution
mode on Lakes Taymyr and Levinson Lessing, respectively. On Levinson Lessing an
additional number of 24 profiles (about 38 km) were recorded in high penetration mode (Figure
2 and Figure 3). GPS positioning was optimised by combining the Trimble data output on the
lakes with GPS data received by a reference station on land (GPS-DAN linked to a power book
by PCMCIA-port). Data sampling rate and storage was 2 sec for both GPS systems. Since this
combination does not provide exact differential GPS data, post processing was carried out at
the Institut flir Geodasie der Universitat Dresden. The accuracy was improved from +/- 500 m
(unprocessed) to +/- 10 m (processed). If not stated otherwise, depths reported in this paper are
expressed in metres below present lake level (m b.p.I.!.).
The water content of sediments from core PG 1228 was determined from the wet and dry
weights of sub-samples. Water contents of PG 1227 are based on calculations from the wet bulk
densities assuming a constant grain density of 2.65 g cm- 3 . Wet bulk density is measured by a
gamma-ray absorption sensor installed on a Multi-Sensor Core Logger (Geotek Ltd., UK). The
of whole-core gamma-ray logging method and the calculation of water contents from logging
data are described in detail in Weber et al. (1997).
Description of seismic stratigraphies
Lake Taymyr
In Lake Taymyr, sound penetration is observed to a sediment depth of up to 25 m. Over large
areas of the central lake, however, there is strong backscatter from the sediment surface which
results in diffraction (no penetration) or a diffuse appearance of deeper reflectors (Figure 4,
below 21 m water depth). In many profiles strong reflectors can also be seen subbottom which
occur only locally and often terminate abruptly (profile 4 between 38 m and 45 m, Figure 5;
profile 10 between 20 m and 28 m, Figure 6). Therefore, lateral correlation of stratification and
seismic units over long distances is often not possible. This is particularly true for the deeper
part of the fill. Stratigraphic features and distinct variability in unit geometry are best seen in
profiles recorded from 15 to 21 m water depth (e.g. profile 11, Figure 4). A link to profile 4 in
the deepest part of the lake (Figure 5, location of sediment core PG 1127) can only be achieved
on the basis of seismic interpretation because there is a lateral gap in the data set over a distance
of about 1 km between profiles 10 and 4 due to technical problems in the field (Figure 2).
UnitTl
The topmost unit Tl is present in all areas observed. The unit is stratified although the reflectors
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Methods
An inflatable boat was equipped with a portable "Chirp" sediment echo sounding system
(GeoChirp 6100A, Geoacoustics, UK) for continuous subbottom profiling during the Taymyr
expedition in summer 1996. The GeoChirp was modified at the Alfred Wegener Institute by
combining it with a digital delay box (for operation in deeper water), a GPS receiver (Trimble
Scoutmaster, for positioning) and a four-channel DAT tape recorder (Sony PC 204A, for data
storage of seismic trigger, seismic signal and GPS position). A detailed system description is
given by Niessen et al. (1997). The GeoChirp system offers the choice of two different modes:
sweeps of 2 to 8 kHz for deeper penetration and of 1.5 to 11.5 kHz for higher resolution. For
both modes, the sweep length is 32 ms. The returning sweep of signals is processed in the
Chirp Transceiver over a period of 130 ms during which a cross correlation of the received
echo pulses is performed. The profiles are plotted on a chart recorder in analog mode. We used
a P-wave velocity of 1500 m s-1 to calculate sediment depths from the two-way travel times.
A total of 11 profiles (103 km) and 42 profiles (ca. 59.1 km) were recorded in high resolution
mode on Lakes Taymyr and Levinson Lessing, respectively. On Levinson Lessing an
additional number of 24 profiles (about 38 km) were recorded in high penetration mode (Figure
2 and Figure 3). GPS positioning was optimised by combining the Trimble data output on the
lakes with GPS data received by a reference station on land (GPS-DAN linked to a power book
by PCMCIA-port). Data sampling rate and storage was 2 sec for both GPS systems. Since this
combination does not provide exact differential GPS data, post processing was carried out at
the Institut flir Geodasie der Universitat Dresden. The accuracy was improved from +/- 500 m
(unprocessed) to +/- 10 m (processed). If not stated otherwise, depths reported in this paper are
expressed in metres below present lake level (m b.p.I.!.).
The water content of sediments from core PG 1228 was determined from the wet and dry
weights of sub-samples. Water contents of PG 1227 are based on calculations from the wet bulk
densities assuming a constant grain density of 2.65 g cm- 3 . Wet bulk density is measured by a
gamma-ray absorption sensor installed on a Multi-Sensor Core Logger (Geotek Ltd., UK). The
of whole-core gamma-ray logging method and the calculation of water contents from logging
data are described in detail in Weber et al. (1997).
Description of seismic stratigraphies
Lake Taymyr
In Lake Taymyr, sound penetration is observed to a sediment depth of up to 25 m. Over large
areas of the central lake, however, there is strong backscatter from the sediment surface which
results in diffraction (no penetration) or a diffuse appearance of deeper reflectors (Figure 4,
below 21 m water depth). In many profiles strong reflectors can also be seen subbottom which
occur only locally and often terminate abruptly (profile 4 between 38 m and 45 m, Figure 5;
profile 10 between 20 m and 28 m, Figure 6). Therefore, lateral correlation of stratification and
seismic units over long distances is often not possible. This is particularly true for the deeper
part of the fill. Stratigraphic features and distinct variability in unit geometry are best seen in
profiles recorded from 15 to 21 m water depth (e.g. profile 11, Figure 4). A link to profile 4 in
the deepest part of the lake (Figure 5, location of sediment core PG 1127) can only be achieved
on the basis of seismic interpretation because there is a lateral gap in the data set over a distance
of about 1 km between profiles 10 and 4 due to technical problems in the field (Figure 2).
UnitTl
The topmost unit Tl is present in all areas observed. The unit is stratified although the reflectors