616
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
the basis of presence of photosynthetic algae.
Nevertheless, relatively low rates of sedimentation in the deep Arctic basins (Stein et aI.,
1994) do not allow for more detailed paleoceanological reconstructions for Holocene. At the
same time, the restriction to the Eurasian Arctic shelf seas is very beneficial for studies of shortterm paleoceanographic changes of the Arctic Ocean. Different from the central Arctic Ocean
sedimentation rates proved to be very high during Holocene, for instance, sedimentation rates
were up to 70 cm/ky in the eastern Laptev Sea shelf (Bauch et aI., 1996) and about 50 cm/ky on
the eastern Laptev Sea continental margin (Spielhagen et aI., 1996).
The performed micropaleontological (mainly diatoms and foraminifers) investigations of the
bottom sediments of the Eurasian Arctic Seas (Polyakova, 1990; 1997a; 1997b; Saidova, 1994;
Dzhinoridze,1978; Samoilovich et aI., 1988; Khusid, 1989) allow us to draw the following
conclusions: (i) variations of the quantitative and qualitative composition of fossil assemblages
may be the basis for both: ecostratigraphical subdivision of the Holocene sediments of the
Arctic Seas and paleoceanological reconstructins; (ii) up to five diatom and foraminiferal
ecozones corresponding to the main stages of paleogeographical evlution of the Eurasian Arctic
Seas have been established in the Holocene sediments; (iii) the period of the most favorable
hydrobiological conditions for planktonic and benthic microorganisms ("hydrobiological or
marine optimum") has been established in all studied regions of the Eurasian Arctic shelf. It is
manifested by increasing number of organisms and appearance of several warm-water
species unknown in the modem flora and fauna of the Arctic Seas. However, age interpretation
of this paleoenvironmental event is different: (i) marine optimum of the Arctic Seas either
corresponds to the Holocene "climatic optimum", i.e. to the Atlantic period (according to
Saidova, 1982; 1994; Khusid, 1989), or (ii) has different age estimations in various regions
since changes in productivity and geographical distribution of species depend upon complicated
interactions between hydrochemical and circulation processes in oceans and seas (Polyakova,
1997a, 1997b).
The purpose of this paper is to analyze the downcore changes in the Eurasian Arctic shelf
sequences and to interpret variations of diatom assemblages and their abundance in terms of
regional changes of paleoceanological conditions, e.g., sea-level fluctuations, the extent of
various water masses and sea ice cover, changes in productivity through time. Most attention
has been concentrated on the examining paleoceanological conditions within the context of the
"hydrobiological optimum" (term suggested by Polyakova, 1997a, 1997b) or "marine
optimum" (term suggested by Andrews, 1972; Williams, 1992) and its correlation with
"climatic optimum" in the adjacent arctic regions of Eurasia. We used the terrestrial
chronostratigraphical scale of Mangerud et al. (1974).
The performed reconstructions are based on the study of the modem diatom flora and
distribution of diatom assemblages in the upper bottom sediment layer. It revealed strong
dependence of the species composition and the number of diatom valves upon hydrological,
hydrobiological and sedimentation conditions in the Arctic Seas (Polyakova, 1988, 1994,
1997b). This modem analogue approach has been used as the foundation for stratigraphical
subdivision of the Holocene deposits of the Eurasian Arctic shelf and paleoceanological
reconstructions.
Materials and methods
For the present study 45 sediment cores and 1 borehole from the Eurasian Arctic shelf were
selected (Table 1, Figure 1). The cores were obtained during the last 15 years scientific
expeditions of P.P. Shirshov Institute of Oceanology RAS and VNIIOceangeology through all
over Eurasian Arctic seas.
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
the basis of presence of photosynthetic algae.
Nevertheless, relatively low rates of sedimentation in the deep Arctic basins (Stein et aI.,
1994) do not allow for more detailed paleoceanological reconstructions for Holocene. At the
same time, the restriction to the Eurasian Arctic shelf seas is very beneficial for studies of shortterm paleoceanographic changes of the Arctic Ocean. Different from the central Arctic Ocean
sedimentation rates proved to be very high during Holocene, for instance, sedimentation rates
were up to 70 cm/ky in the eastern Laptev Sea shelf (Bauch et aI., 1996) and about 50 cm/ky on
the eastern Laptev Sea continental margin (Spielhagen et aI., 1996).
The performed micropaleontological (mainly diatoms and foraminifers) investigations of the
bottom sediments of the Eurasian Arctic Seas (Polyakova, 1990; 1997a; 1997b; Saidova, 1994;
Dzhinoridze,1978; Samoilovich et aI., 1988; Khusid, 1989) allow us to draw the following
conclusions: (i) variations of the quantitative and qualitative composition of fossil assemblages
may be the basis for both: ecostratigraphical subdivision of the Holocene sediments of the
Arctic Seas and paleoceanological reconstructins; (ii) up to five diatom and foraminiferal
ecozones corresponding to the main stages of paleogeographical evlution of the Eurasian Arctic
Seas have been established in the Holocene sediments; (iii) the period of the most favorable
hydrobiological conditions for planktonic and benthic microorganisms ("hydrobiological or
marine optimum") has been established in all studied regions of the Eurasian Arctic shelf. It is
manifested by increasing number of organisms and appearance of several warm-water
species unknown in the modem flora and fauna of the Arctic Seas. However, age interpretation
of this paleoenvironmental event is different: (i) marine optimum of the Arctic Seas either
corresponds to the Holocene "climatic optimum", i.e. to the Atlantic period (according to
Saidova, 1982; 1994; Khusid, 1989), or (ii) has different age estimations in various regions
since changes in productivity and geographical distribution of species depend upon complicated
interactions between hydrochemical and circulation processes in oceans and seas (Polyakova,
1997a, 1997b).
The purpose of this paper is to analyze the downcore changes in the Eurasian Arctic shelf
sequences and to interpret variations of diatom assemblages and their abundance in terms of
regional changes of paleoceanological conditions, e.g., sea-level fluctuations, the extent of
various water masses and sea ice cover, changes in productivity through time. Most attention
has been concentrated on the examining paleoceanological conditions within the context of the
"hydrobiological optimum" (term suggested by Polyakova, 1997a, 1997b) or "marine
optimum" (term suggested by Andrews, 1972; Williams, 1992) and its correlation with
"climatic optimum" in the adjacent arctic regions of Eurasia. We used the terrestrial
chronostratigraphical scale of Mangerud et al. (1974).
The performed reconstructions are based on the study of the modem diatom flora and
distribution of diatom assemblages in the upper bottom sediment layer. It revealed strong
dependence of the species composition and the number of diatom valves upon hydrological,
hydrobiological and sedimentation conditions in the Arctic Seas (Polyakova, 1988, 1994,
1997b). This modem analogue approach has been used as the foundation for stratigraphical
subdivision of the Holocene deposits of the Eurasian Arctic shelf and paleoceanological
reconstructions.
Materials and methods
For the present study 45 sediment cores and 1 borehole from the Eurasian Arctic shelf were
selected (Table 1, Figure 1). The cores were obtained during the last 15 years scientific
expeditions of P.P. Shirshov Institute of Oceanology RAS and VNIIOceangeology through all
over Eurasian Arctic seas.