658
Land-Ocean SYstems in the Siberian Arctic: Dynamics and History
Modified from Holmes and Creager, 1974
... Paleo-River locations
t::. doubtful Paleo-River locations
J \ Late Pleistocene river valleys after Treshnikov et al. (1985)
- Cruise track ARK-XII 1
- Cruise track ARK -IXl4
Figure I: Bathymetry of the Laptev Sea modified from Holmes and Creager (1974), cruise tracks of the two RV
"Polarstern" expeditions ARK-IX/4 and ARK-XIII, and distribution of paleoriver channels identified in
PARASOUND profiles.
Methods
High resolution sub-bottom profiling
The hull-mounted PARASOUND echo sounder designed by STN Atlas Electronik GmbH
(Bremen, Germany) radiates simultaneously two primary sonic frequencies. A constant
frequency of 18 kHz and a second frequency, which can be selected by the operator between
20.5 and 23.5 kHz. As a result of the superimposition of the two primary frequencies in the
water column, known as the parametric principle, a secondary frequency is created. The latter is
equal to the difference between the two primary frequencies ranging between 2.5 and 5.5 kHz,
respectively (Grant and Schreiber, 1990). The secondary frequency is suitable for continuos
sub-bottom profiling of the uppermost unconsolidated sediment layers (Spiess, 1993). Because
the secondary frequency is only generated in the central part of the beam, where the highest
energy levels occur, the angle of the sounding cone is about 4° (Grant and Schreiber, 1990).
The narrow beam angle results in a small acoustic footprint diameter on the sea floor, which
Land-Ocean SYstems in the Siberian Arctic: Dynamics and History
Modified from Holmes and Creager, 1974
... Paleo-River locations
t::. doubtful Paleo-River locations
J \ Late Pleistocene river valleys after Treshnikov et al. (1985)
- Cruise track ARK-XII 1
- Cruise track ARK -IXl4
Figure I: Bathymetry of the Laptev Sea modified from Holmes and Creager (1974), cruise tracks of the two RV
"Polarstern" expeditions ARK-IX/4 and ARK-XIII, and distribution of paleoriver channels identified in
PARASOUND profiles.
Methods
High resolution sub-bottom profiling
The hull-mounted PARASOUND echo sounder designed by STN Atlas Electronik GmbH
(Bremen, Germany) radiates simultaneously two primary sonic frequencies. A constant
frequency of 18 kHz and a second frequency, which can be selected by the operator between
20.5 and 23.5 kHz. As a result of the superimposition of the two primary frequencies in the
water column, known as the parametric principle, a secondary frequency is created. The latter is
equal to the difference between the two primary frequencies ranging between 2.5 and 5.5 kHz,
respectively (Grant and Schreiber, 1990). The secondary frequency is suitable for continuos
sub-bottom profiling of the uppermost unconsolidated sediment layers (Spiess, 1993). Because
the secondary frequency is only generated in the central part of the beam, where the highest
energy levels occur, the angle of the sounding cone is about 4° (Grant and Schreiber, 1990).
The narrow beam angle results in a small acoustic footprint diameter on the sea floor, which