602
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
composition is studied in a sediment core from a shallow Siberian shelf and from the Central
Arctic Ocean. The purpose of this study is to document the occurrence of unusual species
which were up to now never known to occur in Holocene sediments from this region, and to
discuss various possibilities regarding the origin of these species.
Water masses and depositional environment
The modem oceanography of the Arctic Ocean is influenced by waters from three main sources.
Through Fram Strait and across the Barents and Kara seas high-salinty water of Atlantic origin
enters the Eurasian basin of the Arctic Ocean within the upper 600 m of the water column
(Rudels, 1995; Hanzlick, 1983). To a much lesser degree Pacific surface water flows in via the
Bering Strait (Coachman et aI., 1975). Besides these marine sources, the Arctic Ocean is also
fed by a vast fluvial freshwater runoff. This water mainly derives from large Siberian rivers
such as the Ob, Jenisey, and Lena rivers. Although the contribution of the total mass of this
river water to the Arctic Ocean is relatively low in comparison to the other two sources, it is of
major significance for the formation of a distinct halocline. Furthermore, increased cooling
processes on the shelf areas during fall season subsequently leading to sea ice formation
favours the release of brines (Aagaard and Carmack, 1989). This process is responsible for
much of the water mass transformation within the Arctic Ocean circulation system.
The bulk of Siberian shelves are rather shallow on average «50 m) whereas the continental
slope exhibits a steep break at -100 m water depth. The topography of the Laptev Sea is
marked by a gently northerly dipping plain cut by various submarine valleys (Holmes and
Creager, 1974). These channels are linked to the mouths of the major rivers and run along
preformed tectonic structures (Drachev et ai, in press). The freshwater from these rivers not
only reduces the salinity at the surface, it also influences the temperature of the surface water
during summer, which can reach 8-10 0 C or more (Baskakov et aI., 1987). Farther off the shelf,
temperatures within the halocline are - 1.8° C on average. Below the halocline Atlantic core
water with temperatures of _1.5° C is noted (Timokhov, 1994). The Atlantic water flows along
the continental slope of the Barents and Kara seas before reaching the Laptev Sea slope.
Nevertheless, the Atlantic water does not seem to flow onto the Laptev Sea shelf itself (Schauer
et aI., 1997). The fate of the Pacific surface water in the Arctic Ocean is not very well known.
This surface water has a distinct silicate signature (Walsh et aI., 1989) and may be used as a
suitable tracer (Bauch et aI., 1994).
Previous investigations on grain-size analyses in surface sediments from the Laptev Sea
showed that sediments are generally finer in the eastern part where silty clays dominate the
surface pattern (Lindemann, 1995; Rossak 1995). To some extent this pattern is due to different
amounts of suspended sediment material transported onto the shelf by the main rivers (Alabyan
et aI., 1995). Another source for sediment supply is coastal erosion (Are, 1988). By
incorporation into sea-ice these sediments can be transported far distances across the shelf
(Eicken et aI., 1997). Biogenic carbonate is rare in these sediments (Bauch et aI., 1995) as
compared to those Eurasian shelf areas which are under the influence of Atlantic surface water
(Hald and Steinsund, 1996).
Sample processing and counting technique
The studied gravity core (IK 9373-10) from the Laptev Sea shelf was taken on board RV Ivan
Kireyev during the Russian-German Transdrift I expedition in 1993 (Figure 1). Core IK 937310 was retrieved from a water depth of 47 m and has an overall sediment recovery of 109 cm
(Kassens and Karpiy, 1995). The site is located within the so-called Yana valley in the eastern
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
composition is studied in a sediment core from a shallow Siberian shelf and from the Central
Arctic Ocean. The purpose of this study is to document the occurrence of unusual species
which were up to now never known to occur in Holocene sediments from this region, and to
discuss various possibilities regarding the origin of these species.
Water masses and depositional environment
The modem oceanography of the Arctic Ocean is influenced by waters from three main sources.
Through Fram Strait and across the Barents and Kara seas high-salinty water of Atlantic origin
enters the Eurasian basin of the Arctic Ocean within the upper 600 m of the water column
(Rudels, 1995; Hanzlick, 1983). To a much lesser degree Pacific surface water flows in via the
Bering Strait (Coachman et aI., 1975). Besides these marine sources, the Arctic Ocean is also
fed by a vast fluvial freshwater runoff. This water mainly derives from large Siberian rivers
such as the Ob, Jenisey, and Lena rivers. Although the contribution of the total mass of this
river water to the Arctic Ocean is relatively low in comparison to the other two sources, it is of
major significance for the formation of a distinct halocline. Furthermore, increased cooling
processes on the shelf areas during fall season subsequently leading to sea ice formation
favours the release of brines (Aagaard and Carmack, 1989). This process is responsible for
much of the water mass transformation within the Arctic Ocean circulation system.
The bulk of Siberian shelves are rather shallow on average «50 m) whereas the continental
slope exhibits a steep break at -100 m water depth. The topography of the Laptev Sea is
marked by a gently northerly dipping plain cut by various submarine valleys (Holmes and
Creager, 1974). These channels are linked to the mouths of the major rivers and run along
preformed tectonic structures (Drachev et ai, in press). The freshwater from these rivers not
only reduces the salinity at the surface, it also influences the temperature of the surface water
during summer, which can reach 8-10 0 C or more (Baskakov et aI., 1987). Farther off the shelf,
temperatures within the halocline are - 1.8° C on average. Below the halocline Atlantic core
water with temperatures of _1.5° C is noted (Timokhov, 1994). The Atlantic water flows along
the continental slope of the Barents and Kara seas before reaching the Laptev Sea slope.
Nevertheless, the Atlantic water does not seem to flow onto the Laptev Sea shelf itself (Schauer
et aI., 1997). The fate of the Pacific surface water in the Arctic Ocean is not very well known.
This surface water has a distinct silicate signature (Walsh et aI., 1989) and may be used as a
suitable tracer (Bauch et aI., 1994).
Previous investigations on grain-size analyses in surface sediments from the Laptev Sea
showed that sediments are generally finer in the eastern part where silty clays dominate the
surface pattern (Lindemann, 1995; Rossak 1995). To some extent this pattern is due to different
amounts of suspended sediment material transported onto the shelf by the main rivers (Alabyan
et aI., 1995). Another source for sediment supply is coastal erosion (Are, 1988). By
incorporation into sea-ice these sediments can be transported far distances across the shelf
(Eicken et aI., 1997). Biogenic carbonate is rare in these sediments (Bauch et aI., 1995) as
compared to those Eurasian shelf areas which are under the influence of Atlantic surface water
(Hald and Steinsund, 1996).
Sample processing and counting technique
The studied gravity core (IK 9373-10) from the Laptev Sea shelf was taken on board RV Ivan
Kireyev during the Russian-German Transdrift I expedition in 1993 (Figure 1). Core IK 937310 was retrieved from a water depth of 47 m and has an overall sediment recovery of 109 cm
(Kassens and Karpiy, 1995). The site is located within the so-called Yana valley in the eastern