628
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
favorable for the phytocoenoses development ("hydobiological or marine optimum"; ecozone
III). In all Eastern Arctic seas it was marked out by sharp increase (in 2-3 times) of the number
of diatom valves in sediments. Since lithological composition of sediments is unchanged, this
may be only caused by the burst of phytoplankton productivity. The area of the most warmwater diatoms considerably expanded, especially in the Chukchi Sea within the region
influenced by the Alaskan branch of the Bering Sea current. The surface water temperatures in
the Central Chukchi depression probably exceeded the modem ones by 2-4-. Notwithstanding
relatively stable paleotemperature conditions typical of the high latitudes, paleoproductivity
increase have been marked out in the East Siberian and Laptev Seas, together with invasion of
relatively warm-water Bering Sea species to the south-eastern regions of the East Siberian Sea.
The latter indicates strengthening of the Long branch of the Bering Sea current.
All these changes were apparently caused by increasing advection of the relatively warm and
highly productive Bering Sea waters. It is interesting to note that in the Holocene sequence of
the North-Western Pacific Jouse (1961) distinguished an interval (diatom assemblage B) which
had been characterized by significant changes in the structure of diatom assemblages
suggesting considerable northward migration of warm-water diatoms (not less than 1000 km).
The next short period (ecozone II) in the Eastern Arctic seas is characterized by
phytocoenoses production fall, elimination of the most warm-water species, and increase of the
cryophillic species abundance in several regions related to decreasing afflux of the Bering Sea
waters and severe ice conditions in the arctic seas. This period corresponds to the cooling
established in some Arctic and Subarctic regions at 2.5 Ka (so called neoglacial). In general,
environmental conditions during the last 1.5-2 thousand years were similar to the modem ones
with slight increase of paleoproductivity about 2 Ka due to cryophilic and ice-neritic species.
Similar paleohydrological changes were established in the Baffin Bay during the second half of
Holocene (Williams, 1990). While the first burst of productivity ("marine optimum") had
diachronous boundaries due to different termination of deglaciation of this area, the second one
was practically simultaneous (about 2 Ka) being related, like in the case with the Chukchi Sea,
to increasing abundance of cryophillic and ice-neritic diatoms.
Holocene paleoenvironmental changes in the Western Arctic seas had their own peculiar
features. In the Norwegian,Greenland, and Iceland Seas abundant diatoms appear at the end of
Pleistocene - beginning of Holocene. This boundary is diachronous and becomes younger in
the north-western direction during the time period ranging from 14 to 7 Ka in accordance with
the Polar front migration (Koc et aI., 1993; Koc Karpuz and Jansen, 1992). Further regional
variations of paleoproductivity and paleotemperatures were determined by the influence of
different water masses. About 9 Ka surface water temperatures in the Norwegian-Greenland
basin were close to the mordern ones, and during the interval between 8 and 5 Ka they exeeded
the mordern ones. Hydrobiological or marine optimum was the most pronounced in the western
and north-western coastal regions of Norway (Koc Karpuze and Jansen, 1992; Koc et aI.,
1993; Dzhinoridze et a!., 1981; Samoilovich et a!., 1988).
Intensive afflux of the North Atlantic waters to the southern regions of the Barents Sea which
began about 9-8 Ka caused northward and north-westward migration of the Polar front and
increasing productivity of waters. The main Holocene paleoceanographic event of the Barents
Sea, the so called hydrobiologic or marine optimum, corresponded to the last significant
intensification of the North Atlantic current. It was caused by the sharp increase of water
productivity and surface water temperature at the end of Atlantic - beginning of Subboreal
periods of Holocene.
Thus, the main Holocene paleoenvironmental event ("hydrobiological or marine optimum")
through all over the Eurasian Arctic seas was established at the end of Atlantic - beginning of
Subboreal periods. This rather short time period (about 2 - 2.5 Ka) with the most favorable
hydrobiological conditions for marine phytocoenoses was marked out by sharp increase of
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
favorable for the phytocoenoses development ("hydobiological or marine optimum"; ecozone
III). In all Eastern Arctic seas it was marked out by sharp increase (in 2-3 times) of the number
of diatom valves in sediments. Since lithological composition of sediments is unchanged, this
may be only caused by the burst of phytoplankton productivity. The area of the most warmwater diatoms considerably expanded, especially in the Chukchi Sea within the region
influenced by the Alaskan branch of the Bering Sea current. The surface water temperatures in
the Central Chukchi depression probably exceeded the modem ones by 2-4-. Notwithstanding
relatively stable paleotemperature conditions typical of the high latitudes, paleoproductivity
increase have been marked out in the East Siberian and Laptev Seas, together with invasion of
relatively warm-water Bering Sea species to the south-eastern regions of the East Siberian Sea.
The latter indicates strengthening of the Long branch of the Bering Sea current.
All these changes were apparently caused by increasing advection of the relatively warm and
highly productive Bering Sea waters. It is interesting to note that in the Holocene sequence of
the North-Western Pacific Jouse (1961) distinguished an interval (diatom assemblage B) which
had been characterized by significant changes in the structure of diatom assemblages
suggesting considerable northward migration of warm-water diatoms (not less than 1000 km).
The next short period (ecozone II) in the Eastern Arctic seas is characterized by
phytocoenoses production fall, elimination of the most warm-water species, and increase of the
cryophillic species abundance in several regions related to decreasing afflux of the Bering Sea
waters and severe ice conditions in the arctic seas. This period corresponds to the cooling
established in some Arctic and Subarctic regions at 2.5 Ka (so called neoglacial). In general,
environmental conditions during the last 1.5-2 thousand years were similar to the modem ones
with slight increase of paleoproductivity about 2 Ka due to cryophilic and ice-neritic species.
Similar paleohydrological changes were established in the Baffin Bay during the second half of
Holocene (Williams, 1990). While the first burst of productivity ("marine optimum") had
diachronous boundaries due to different termination of deglaciation of this area, the second one
was practically simultaneous (about 2 Ka) being related, like in the case with the Chukchi Sea,
to increasing abundance of cryophillic and ice-neritic diatoms.
Holocene paleoenvironmental changes in the Western Arctic seas had their own peculiar
features. In the Norwegian,Greenland, and Iceland Seas abundant diatoms appear at the end of
Pleistocene - beginning of Holocene. This boundary is diachronous and becomes younger in
the north-western direction during the time period ranging from 14 to 7 Ka in accordance with
the Polar front migration (Koc et aI., 1993; Koc Karpuz and Jansen, 1992). Further regional
variations of paleoproductivity and paleotemperatures were determined by the influence of
different water masses. About 9 Ka surface water temperatures in the Norwegian-Greenland
basin were close to the mordern ones, and during the interval between 8 and 5 Ka they exeeded
the mordern ones. Hydrobiological or marine optimum was the most pronounced in the western
and north-western coastal regions of Norway (Koc Karpuze and Jansen, 1992; Koc et aI.,
1993; Dzhinoridze et a!., 1981; Samoilovich et a!., 1988).
Intensive afflux of the North Atlantic waters to the southern regions of the Barents Sea which
began about 9-8 Ka caused northward and north-westward migration of the Polar front and
increasing productivity of waters. The main Holocene paleoceanographic event of the Barents
Sea, the so called hydrobiologic or marine optimum, corresponded to the last significant
intensification of the North Atlantic current. It was caused by the sharp increase of water
productivity and surface water temperature at the end of Atlantic - beginning of Subboreal
periods of Holocene.
Thus, the main Holocene paleoenvironmental event ("hydrobiological or marine optimum")
through all over the Eurasian Arctic seas was established at the end of Atlantic - beginning of
Subboreal periods. This rather short time period (about 2 - 2.5 Ka) with the most favorable
hydrobiological conditions for marine phytocoenoses was marked out by sharp increase of