HOLIVAR2006 Abstracts
Late Glacial and Holocene climatic and vegetation change in the mountain areas of the Altai and Tuva republics in southern Siberia (Russia) revealed by pollen data from lake sediments.
T.A. Blyakharchuk1, H. Wright2, P.S. Borodavko3 and B. Ammann4
1Institute for Monitoring of Climatic and Ecological Systems, 10/3, Akademichesky Ave. 634055, Tomsk, Russia
2University of Minnesota, Limnological Research Center, 310 Pillsbury Drive S.E., Minneapolis MN 55455, USA
3Tomsk State University, Problem Scientific Research Laboratory of Glacioclimatology, Lenina 36, 634050 Tomsk, Russia
4Institute of Plant Sciences, Altenbergrain 21, CH-3013 Bern, Switzerland
Contact: T. Blyakharchuk (tarun5@rambler.ru)
In central Eurasia, where moist Atlantic air meets the cold dry air of the Siberian Anticyclone, sediments from 5 lakes in the Altai and Tuva mountains (50°30'-50°23'N, 087°40'-089°37'E) were investigated using pollen and radiocarbon methods. In this area of Russia, forests are limited both by altitude and by moisture deficit. Precipitation today originates mostly from Atlantic cyclones.
Lakes along a gradient of decreasing moisture and increasing continentality from a west-east transect from Central Altai and forested by Siberian pine and larch, to grassy high mountain tundra (tundra-steppe) in south-west Tuva, were investigated. Pollen sequences cover about 13-14 kyr and reveal changes in the landscape. The most significant change, possibly caused by abrupt climatic changes, took place in the Early Holocene (8-9 kyr) when open treeless landscapes were replaced by forest-steppe and forest landscapes. In the Mid-Holocene, coniferous forests (taiga) spread in the south-west and northern Altai. From 9 to 7 kyr, taiga occupied its greatest extent since the last Glacial. It penetrated far to the south-east in the high mountain areas, where at present, only tundra-steppe and shrub lands are found. In south-west Tuva, pollen data give evidence of the increased role of forests from Siberian pine, larch, spruce, and fir at 9.5-5 kyr ago. It correlates well with data showing increased lake levels and with archaeological data from Mongolia.
Anomalously high summer insolation at 9 kyr ago is thought to have promoted the activity of Asian monsoons, which expanded into central Eurasia. Our pollen data show that during the Mid-Holocene, Atlantic cyclones were stronger and brought moisture to the mountains of Altai and Tuva, which are now treeless. The increased moisture and high summer insolation, raised the timberline and the forested areas were almost contiguous in central Eurasia. Forests of the Russian Altai were connected with modern islands of forest-steppe and forests of the Mongolian Altai.
After 5 kyr, decreasing summer insolation attenuated atmospheric circulation, and the amount of moisture brought to central Eurasia sharply decreased. A greater role was played by the Siberian anticyclone; increasing continentality and aridity. The tree-limit was lowered and forests retreated from the mountain areas of south-east Altai and south-west Tuva to the north and west. From 4 kyr ago increased continentality caused permafrost forms of relief in intermountain depressions. The extent of the forests considerably decreased giving way to open high mountain tundra-steppe vegetation. From this time the Mongolian Altai forests were separated from the Russian Altai forests. So the global change in atmospheric circulation over northern Eurasia caused change in moisture availability that influenced the forest-steppe relationship in central Eurasia.