490
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
relatively high temperature gradients (Ershov et aI., 1995). From above 2.4 m depth, the losslike silts showed a finer lattice-like cryostructure and a slightly lower ice content. Altogether,
sedimentary and cryogenic characteristics suggested that accumulation of these loess-like silts
occurred continually in a shallow lacustrine environment and that permafrost was formed by
freezing of water-saturated sediments shortly after their accumulation. The dominant frosted
sand-size quartz grains as well as the loess grain-size spectrum indicate the presence of material
subject to aeolian transport in the lacustrine environment.
The pollen diagram of the section LA06 (Figure 9) distinctly differs from the others
discussed above. Pollen assemblages in these lacustrine sediments indicated a strong
dominance of herbaceous plants while trees and shrubs as well as sporophytes were in the
minority. Within the herbaceous plants, Artemisia predominated and reaches a maximum of 54
- 59% of the total pollen sum. In addition, high amounts of Poaceae, and less Caryophyllaceae,
Compositeae and Cyperaceae, characterized the pollen assemblages. Shrubs were dominated by
Betula sect. Naneae, while Alnaster and Salix were continuously present in small amounts. A
generally low content of redeposited pre-Quaternary pollen in sediments of this site is important
and indicates that the erosion of glacial deposits was significantly diminished at this time. The
divided pollen zones had relatively small distinctions. Zones 1,3 and 5 were characterized by a
weak increase of both tree and shrub pollen percentages. For the herbs, the pollen percentage of
Artemisia clearly decreased in favour of an increase of Poaceae and some other taxa. In all, the
pollen assemblages suggest a wide-spread occurrence of grass-moss tundra and somewhat less
shrub tundra. Single larch populations with alder underbrush seems to have grown in the area,
but only sparsely distributed, probably similar to a gallery forest. The climate during these
periods was slightly more humid than that during the formation of pollen zones 2 and 4, the
pollen assemblages of which indicated distinctly cooler and drier climatic conditions. AP
percentages including shrub pollen (Betula nana, Alnaster, Salix) reached a minimum here.
Moss spores (Bryales) diminished. Other evidence for a significant change in the environmental
conditions during the accumulation of these loess-like deposits has not been found. In general,
the palynological data of section LA06 corresponded more closely with tundra-steppe
vegetation considered to be typical for non-glaciated permafrost areas of Northern Siberia
during the Sartan (Late Weichselian) glacial period (Kaplina, 1979; Tomskaya, 1981). With a
depth of 1.4 m upwards, the pollen diagram of the profile LA06 (see Figure 9) represents
typical assemblages for the beginning of Holocene climate warming similar to those presented
by Hahne and Melles (this volume) from two lake sediment cores drilled on the Taymyr
Peninsula.
According to the available radiocarbon datings, the lower part of the loess-like silts in section
LA06 accumulated at a time related to the middle warming phase of the Kargin Interstadial
(called the Malaya Kheta period by Kind (1974) and occurring about 35000 yr BP). That would
mean that they were formed during periods similar to those in which the sediments of profile
LA025 were formed. However, the significant differences between pollen assemblages of the
two sections contradict this concept. The following interpretations are possible: 1. we accept the
reliability of datings. This means that the lower part of the loess-like silts accumulated during
the second half of the Kargin Interstadial period. The occurrence of relatively high pollen
percentages for Larix (up to 10% of the total pollen and spore sum) as well as for Alnus trees in
this part of the section could argue for such an interpretation; 2. we assume that the radiocarbon
ages are not correct. This means that the dated fine plant remnants were mixed with redeposited
material. It is generally accepted that fresh plant remnants, and especially wood material, can be
very well preserved and repeatedly deposited under permafrost conditions, i.e. that plants
preserved in situ and redeposited plant material become very similar in appearance.
Sulerzhitsky (1982) was also concerned about the influence of such dating problems on the
study of permafrost sections from the lowland areas of Taymyr. Two datings in the upper part
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
relatively high temperature gradients (Ershov et aI., 1995). From above 2.4 m depth, the losslike silts showed a finer lattice-like cryostructure and a slightly lower ice content. Altogether,
sedimentary and cryogenic characteristics suggested that accumulation of these loess-like silts
occurred continually in a shallow lacustrine environment and that permafrost was formed by
freezing of water-saturated sediments shortly after their accumulation. The dominant frosted
sand-size quartz grains as well as the loess grain-size spectrum indicate the presence of material
subject to aeolian transport in the lacustrine environment.
The pollen diagram of the section LA06 (Figure 9) distinctly differs from the others
discussed above. Pollen assemblages in these lacustrine sediments indicated a strong
dominance of herbaceous plants while trees and shrubs as well as sporophytes were in the
minority. Within the herbaceous plants, Artemisia predominated and reaches a maximum of 54
- 59% of the total pollen sum. In addition, high amounts of Poaceae, and less Caryophyllaceae,
Compositeae and Cyperaceae, characterized the pollen assemblages. Shrubs were dominated by
Betula sect. Naneae, while Alnaster and Salix were continuously present in small amounts. A
generally low content of redeposited pre-Quaternary pollen in sediments of this site is important
and indicates that the erosion of glacial deposits was significantly diminished at this time. The
divided pollen zones had relatively small distinctions. Zones 1,3 and 5 were characterized by a
weak increase of both tree and shrub pollen percentages. For the herbs, the pollen percentage of
Artemisia clearly decreased in favour of an increase of Poaceae and some other taxa. In all, the
pollen assemblages suggest a wide-spread occurrence of grass-moss tundra and somewhat less
shrub tundra. Single larch populations with alder underbrush seems to have grown in the area,
but only sparsely distributed, probably similar to a gallery forest. The climate during these
periods was slightly more humid than that during the formation of pollen zones 2 and 4, the
pollen assemblages of which indicated distinctly cooler and drier climatic conditions. AP
percentages including shrub pollen (Betula nana, Alnaster, Salix) reached a minimum here.
Moss spores (Bryales) diminished. Other evidence for a significant change in the environmental
conditions during the accumulation of these loess-like deposits has not been found. In general,
the palynological data of section LA06 corresponded more closely with tundra-steppe
vegetation considered to be typical for non-glaciated permafrost areas of Northern Siberia
during the Sartan (Late Weichselian) glacial period (Kaplina, 1979; Tomskaya, 1981). With a
depth of 1.4 m upwards, the pollen diagram of the profile LA06 (see Figure 9) represents
typical assemblages for the beginning of Holocene climate warming similar to those presented
by Hahne and Melles (this volume) from two lake sediment cores drilled on the Taymyr
Peninsula.
According to the available radiocarbon datings, the lower part of the loess-like silts in section
LA06 accumulated at a time related to the middle warming phase of the Kargin Interstadial
(called the Malaya Kheta period by Kind (1974) and occurring about 35000 yr BP). That would
mean that they were formed during periods similar to those in which the sediments of profile
LA025 were formed. However, the significant differences between pollen assemblages of the
two sections contradict this concept. The following interpretations are possible: 1. we accept the
reliability of datings. This means that the lower part of the loess-like silts accumulated during
the second half of the Kargin Interstadial period. The occurrence of relatively high pollen
percentages for Larix (up to 10% of the total pollen and spore sum) as well as for Alnus trees in
this part of the section could argue for such an interpretation; 2. we assume that the radiocarbon
ages are not correct. This means that the dated fine plant remnants were mixed with redeposited
material. It is generally accepted that fresh plant remnants, and especially wood material, can be
very well preserved and repeatedly deposited under permafrost conditions, i.e. that plants
preserved in situ and redeposited plant material become very similar in appearance.
Sulerzhitsky (1982) was also concerned about the influence of such dating problems on the
study of permafrost sections from the lowland areas of Taymyr. Two datings in the upper part