ALBERT

Beschreibung: The 318 m thick lacustrine sediment record in Lake El'gygytgyn, northeastern Russian Arctic cored by the international El'gygytgyn Drilling Project provides unique opportunities allowing the time-continuous reconstruction of the regional paleoenvironmental history for the past 3.6 Myr. Pollen studies of the lower 216 m of the lacustrine sediments show their value as an excellent archive of vegetation and climate changes during the Late Pliocene and Early Pleistocene. About 3.50–3.35 Myr BP the vegetation at Lake El'gygytgyn, in nowadays tundra area, was dominated by spruce-larch-fir-hemlock forests. After ca. 3.4 Myr BP dark coniferous taxa gradually disappeared. A very pronounced environmental changes took place at ca. 3.305–3.275 Myr BP, corresponding with the Marine Isotope Stage (MIS) M2, when treeless tundra- and steppe-like habitats became dominant in the regional vegetation. Climate conditions were similar to those of Late Pleistocene cold intervals. Numerous coprophilous fungi spores identified in the pollen samples suggest the presence of grazing animals around the lake. Following the MIS M2 event, larch-pine forests with some spruce mostly dominated in the area until ca. 2.6 Myr BP, interrupted by colder and drier intervals ca. 3.04–3.02, 2.93–2.91, and 2.725–2.695 Myr BP. At the beginning of the Pleistocene, ca. 2.6 Myr BP, noticeable climatic deterioration occurred. Forested habitats changed to predominantly treeless and shrubby environments, which reflect a relatively cold and dry climate. Revealed peaks in green algae colonies (Botryococcus) around 2.53, 2.45, 2.320–2.305 and 2.175–2.150 Myr BP suggest a spread of shallow water environments. Few intervals (i.e. 2.55–2.53, ca. 2.37, and 2.35–2.32 Myr BP) with a higher presence of coniferous taxa (mostly pine and larch) document some relatively short-term climate ameliorations.

Beschreibung: In this study a radiocarbon-dated pollen record from Lake Kotokel (52°47´ N, 108°07´ E, 458 m a.s.l.) located in southern Siberia east of Lake Baikal was used to derive quantitative characteristics of regional vegetation and climate since about 15 kyr BP (1 kyr=1000 cal. yr) until today. Quantitative reconstruction of the late glacial vegetation and climate dynamics suggests that open steppe and tundra communities predominated in the study area prior to ca. 13.5 kyr BP and again during the Younger Dryas interval, between 12.8 and 11.6 kyr BP. The pollen-based climate reconstruction suggests lower-than-present mean January (~–38°C) and July (~12°C) temperatures and annual precipitation (~270–300 mm) values during these time intervals. Boreal woodland replaced the primarily open landscape around Kotokel three times at about 14.8–14.7 kyr BP, during the Allerød Interstadial between 13.3–12.8 kyr BP and with the onset of the Holocene interglacial between 11.5 and 10.5 kyr BP, presumably in response to a noticeable increase in precipitation, and in July and January temperatures. The maximal spread of the boreal forest (taiga) communities in the region is associated with a warmer and wetter-than-present climate (Tw~17–18°C, Tc~–19°C, Pann~500–550 mm) occurred ca.\ 10.8–7.3 kyr BP. During this time interval woody vegetation covered more than 50% of the area within a 21×21 km window around the lake. The pollen-based best modern analogue reconstruction suggests a decrease in woody cover percentages and in all climatic variables about 7–6.5 kyr BP. Since that time our results demonstrate gradual decrease in precipitation and mean January temperature towards their present-day values in the region around Lake Kotokel.

Beschreibung: In this study a radiocarbon-dated pollen record from Lake Billyakh (65°17'N, 126°47'E; 340 m a.s.l.) in the Verkhoyansk Mountains was used to reconstruct vegetation and climate change since about 15 kyr BP (1 kyr=1000 cal. yr). The pollen record and pollen-based biome reconstruction suggest that open cool steppe and grass and sedge tundra communities with Poaceae, Cyperaceae, Artemisia, Chenopodiaceae, Caryophyllaceae and Selaginella rupestris dominated the area from 15 to 13.5 kyr BP. On the other hand, the constant presence of Larix pollen in quantities comparable to today's values points to the constant presence of boreal deciduous conifer trees in the regional vegetation during the last glaciation. A major spread of shrub tundra communities, including birch (Betula sect. Nanae), alder (Duschekia fruticosa) and willow (Salix) species, is dated to 13.5–12.7 kyr BP, indicating a noticeable increase in precipitation toward the end of the last glaciation, particularly during the Allerød Interstadial. Between 12.7 and 11.4 kyr BP pollen percentages of herbaceous taxa rapidly increased, whereas shrub taxa percentages decreased, suggesting strengthening of the steppe communities associated with the relatively cold and dry Younger Dryas Stadial. However, the pollen data in hand indicate that Younger Dryas climate was less severe than the climate during the earlier interval from 15 to 13.5 kyr BP. The onset of the Holocene is marked in the pollen record by the highest values of shrub and lowest values of herbaceous taxa, suggesting a return of warmer and wetter conditions after 11.4 kyr BP. Percentages of tree taxa increase gradually and reach maximum values after 7 kyr BP, reflecting the spread of boreal cold deciduous and taiga forests in the region. An interval between 7 and 2 kyr BP is noticeable for the highest percentages of Scots pine (Pinus subgen. Diploxylon), spruce (Picea) and fir (Abies) pollen, indicating mid-Holocene spread of boreal forest communities in response to climate amelioration and degradation of the permafrost layer.

Beschreibung: The modern and fossil pollen data obtained under the framework of the multi-disciplinary international "El'gygytgyn Drilling Project" represent a unique archive that allows the testing of a range of pollen-based reconstruction approaches and the deciphering of changes in the regional vegetation and climate since ~3.58 Ma. In the current study we provide details of the biome reconstruction method applied to the late Pliocene and Quaternary pollen records from Lake El'gygytgyn. All terrestrial pollen taxa identified in the spectra from Lake El'gygytgyn were assigned to major vegetation types (biomes), which today occur near the lake and in the broader region of eastern and northern Asia and, thus, could potentially have been present in this region during the past. When applied to the modern surface pollen spectra from the lake, the method shows a dominance of the tundra biome that currently characterizes the Lake El'gygytgyn area. When applied to the pollen spectra from the middle Pleistocene to present, the method suggests (1) a predominance of tundra during the Holocene, (2) a short interval during the marine isotope stage (MIS) 5.5 interglacial distinguished by cold deciduous forest, and (3) a long phase of taiga dominance during MIS 31 and, particularly, MIS 11.3. These two latter interglacials seem to be some of the longest and warmest intervals within the past million years. During the late Pliocene–early Pleistocene interval (i.e., ~3.562–2.200 Ma), there is good correspondence between the millennial-scale vegetation changes documented in the Lake El'gygytgyn record and the alternation of cold and warm marine isotope stages, which reflect changes in the global ice volume and sea level. The biome reconstruction demonstrates changes in the regional vegetation which suggest a step-like transition from generally warmer/wetter environments of the earlier (i.e., Pliocene) interval towards colder/drier environments of the Pleistocene. The reconstruction of most of the species-rich cool mixed and cool conifer forest biomes is particularly noticeable prior to MIS G16, whereas tundra becomes a prominent feature after MIS G6. These results consistently indicate that the study region supported significant tree populations during most of the interval prior to ~2.730 Ma. The biomization results also suggest that the transition from mostly forested to mostly open landscape was not gradual, but rather occurred in step-like fashion. Thus, the cold and drought tolerant steppe biome first appears in the reconstruction ca. 3.298 Ma during the tundra dominated MIS M2, whereas the tundra biome initially occurs between ~3.379 and ~3.378 Ma within MIS MG4. Prior to ~2.800 Ma, several other cold stages during this generally warm Pliocene interval experienced a dominance of tundra and a great reduction of tree populations in the regional vegetation.