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Land-Ocean Systems in the Siberian Arctic: Dynamics and History
The Laptev Sea since the Last Glacial
Paleoceanographic investigations based on radiocarbon datings (AMS 14C) of bivalve shells in
sediment cores (up to 5 m) have provided new insights into the history of the Laptev Sea since
the last glaciaL The history of the Laptev Sea can be subdivided into various phases inherently
linked to sea level rise following the last glaciation.
During the last glaciation, large parts of the Laptev Sea Shelf were dry due to low global sea
leveL Sedimentation was probably governed by the deposition of syngenetic sediments (ice
complexes), although light planktic oxygen isotope ratios from the central Arctic Ocean may
indicate continuing river runoff during this time (N!,!rgaard-Pedersen et aL, 1998). During
deglaciation, records from the Laptev Sea continental slope reveal a major depletion in 0 18 0 at
11,000 years before present (yBP), which seems to correlate in age with the onset of the
Younger Dryas cold spell. A major change towards marine conditions on the shelf due to rising
sea level is noted at 9,500 yBP with increasing a l3 c values for organic matter and marine
biomarker concentrations. This is coeval with an onset in the lateral distribution of heavy
minerals from east to west on the shelf and along the continental slope. The outer parts of the
Laptev Sea Shelf (?70 m water depth) are marked by an abrupt decrease in sedimentation rates
at 9,000 yBP. In the inner-shelf areas, the sea level continued to rise until flooding of the shelf
terminated near 6,000 yBP, accompanied by a major drop in sedimentation rates between
paleodepth 30 to 50 m (Bauch et aL, in press).
The later Holocene (since 6,000 yBP) situation appears to be rather stable in that
sedimentation rates varied between 1.2 mm per year in the Lena Valley and 0.1 mm per year in
the Khatanga Valley (Bauch et a!., in press). This is about 5 times lower in comparison to the
continental slope. Surface sediments, freshwater diatoms, and chlorophycean algae dominated
the eastern shelf, whereas marine diatoms and dinoflagelate cysts are prominent on the western
parts of the shelf (Cremer, 1998; this volume; Kunz-Pirrung, 1998; this volume). Ice algae
species become more abundant particularly towards the north, along the average position of the
summer ice edge. Grounding ice contributed considerably to sediment transport on the Laptev
Sea Shelf. Side-scan sonar records and 30 kHz echograms indicate that at some locations (e.g.,
north of the Lena Delta) sediments are disturbed as a result of grounding ice (Benthien, 1995;
Lindemann, 1995). These plough marks can be as deep as ten meters. Such grounded icebergs
were actually occasionally observed between 15 and 25 m water depth in summer.
Another interesting feature of the Laptev Sea is the existence of offshore permafrost, which
was verified by ice-bonded Holocene sediments found in areas as shallow as 12 cm below
surface in the central Laptev Sea (Kassens and Karpiy, 1994; Romanovskii et aL, 1997). The
impact of offshore permafrost on the environmental system is unknown and will be a primary
goal during further investigations.
Modern processes in permafrost landscapes
In Arctic regions, hydrological, geochemical, and biological processes are directly controlled by
the presence of permafrost and the seasonal thawing of the active layer. Most of the processes
occur during the short summer season from May to August and cease during the winter. As the
active layer thaws with the progress of summer, the infiltration and storage capacity of the
ground are increased. Consequently, geochemical, biological, and hydrological activities in the
active layer are enhanced and influence the hydrology and geochemistry of surface and ground
waters.
Modern seasonal dynamic processes were studied on various scales in the different climatic
settings of the Levinson-Lessing and Labaz Lake catchments, and of northern Bolshevik Island,
Severnaya Zemlya (Figure 3). For example, pedological and biological studies were conducted
and replenished by seasonal measurements of C02 and CH4 fluxes. In addition, the temporal
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
The Laptev Sea since the Last Glacial
Paleoceanographic investigations based on radiocarbon datings (AMS 14C) of bivalve shells in
sediment cores (up to 5 m) have provided new insights into the history of the Laptev Sea since
the last glaciaL The history of the Laptev Sea can be subdivided into various phases inherently
linked to sea level rise following the last glaciation.
During the last glaciation, large parts of the Laptev Sea Shelf were dry due to low global sea
leveL Sedimentation was probably governed by the deposition of syngenetic sediments (ice
complexes), although light planktic oxygen isotope ratios from the central Arctic Ocean may
indicate continuing river runoff during this time (N!,!rgaard-Pedersen et aL, 1998). During
deglaciation, records from the Laptev Sea continental slope reveal a major depletion in 0 18 0 at
11,000 years before present (yBP), which seems to correlate in age with the onset of the
Younger Dryas cold spell. A major change towards marine conditions on the shelf due to rising
sea level is noted at 9,500 yBP with increasing a l3 c values for organic matter and marine
biomarker concentrations. This is coeval with an onset in the lateral distribution of heavy
minerals from east to west on the shelf and along the continental slope. The outer parts of the
Laptev Sea Shelf (?70 m water depth) are marked by an abrupt decrease in sedimentation rates
at 9,000 yBP. In the inner-shelf areas, the sea level continued to rise until flooding of the shelf
terminated near 6,000 yBP, accompanied by a major drop in sedimentation rates between
paleodepth 30 to 50 m (Bauch et aL, in press).
The later Holocene (since 6,000 yBP) situation appears to be rather stable in that
sedimentation rates varied between 1.2 mm per year in the Lena Valley and 0.1 mm per year in
the Khatanga Valley (Bauch et a!., in press). This is about 5 times lower in comparison to the
continental slope. Surface sediments, freshwater diatoms, and chlorophycean algae dominated
the eastern shelf, whereas marine diatoms and dinoflagelate cysts are prominent on the western
parts of the shelf (Cremer, 1998; this volume; Kunz-Pirrung, 1998; this volume). Ice algae
species become more abundant particularly towards the north, along the average position of the
summer ice edge. Grounding ice contributed considerably to sediment transport on the Laptev
Sea Shelf. Side-scan sonar records and 30 kHz echograms indicate that at some locations (e.g.,
north of the Lena Delta) sediments are disturbed as a result of grounding ice (Benthien, 1995;
Lindemann, 1995). These plough marks can be as deep as ten meters. Such grounded icebergs
were actually occasionally observed between 15 and 25 m water depth in summer.
Another interesting feature of the Laptev Sea is the existence of offshore permafrost, which
was verified by ice-bonded Holocene sediments found in areas as shallow as 12 cm below
surface in the central Laptev Sea (Kassens and Karpiy, 1994; Romanovskii et aL, 1997). The
impact of offshore permafrost on the environmental system is unknown and will be a primary
goal during further investigations.
Modern processes in permafrost landscapes
In Arctic regions, hydrological, geochemical, and biological processes are directly controlled by
the presence of permafrost and the seasonal thawing of the active layer. Most of the processes
occur during the short summer season from May to August and cease during the winter. As the
active layer thaws with the progress of summer, the infiltration and storage capacity of the
ground are increased. Consequently, geochemical, biological, and hydrological activities in the
active layer are enhanced and influence the hydrology and geochemistry of surface and ground
waters.
Modern seasonal dynamic processes were studied on various scales in the different climatic
settings of the Levinson-Lessing and Labaz Lake catchments, and of northern Bolshevik Island,
Severnaya Zemlya (Figure 3). For example, pedological and biological studies were conducted
and replenished by seasonal measurements of C02 and CH4 fluxes. In addition, the temporal