Holocene Environmental Change in South-East Altai Evidenced by Soil Record

Abstract

The soils of Russian Altai highlands were used as a paleoenvironmental archive, as a source of dating material, and as a chronostratigraphic marker to describe Holocene environmental change in the studied area. Based on calibration intervals of 14C dates obtained for buried humus horizons (11 buried soils in 6 studied soil-sedimentary sequences) and some dates from pendants of contemporary soils, following stages of pedogenesis were recorded in studied soil-sedimentary systems and surface soils: 6.4 – 11.5 ky cal BP; about 4.9-5.3 cal BP; 2.5-3.8 cal BP; 0.6 – 1.2 cal BP. All studied surface soils in the basins nowadays develop in cold, ultra-continental water deficit conditions: Skeletic Kastanozems Cambic, Skeletic Cambisols Protocalcic, Skeletic Cambic Calcisol Yermic. The most extreme conditions of soil formation within Holocene were within the last 1-2 kyr. All buried soils were formed in better conditions, more balanced in water, with higher biological activity, mostly within steppe or forest-steppe landscapes. Cryogenic features had been insisting all over the Holocene till nowadays. Water demandant cryogenic features are met in buried soils up to the age of 1-2 ky cal BP. In the last millennia cryogenic processes are suppressed, water demandant features gave way to those which can be formed in contemporary water deficit conditions: simple fissures, frost sorting, and shattering. At lower levels (Kuraj basin) more or less arid cold steppe conditions insisted within the most part of Holocene. Initial stages of soil formation were often ground water affected, or at least shortly waterlogged. At the highest positions humid and relatively warm Early Holocene stage of forest pedogenesis is recorded for the beginning of Holocene, and a Late Holocene (last 3-4 kyr) cold humid phase, presumably under mountain tundra and/or alpines. Microsedimentary intra-soil record in carbonatehumus pendants imprints fine fluctuations of soil water regime at initial stages of soil formation, controlled by local topography, and climatic changes in the second half of Holocene. General trends of environmental changes in the region recorded in soil and soil sedimentary systems are in well correspondence with other records of paleonvironment.

Climatically Driven Holocene Glacier Advances in the Russian Altai Based on Radiocarbon and OSL Dating and Tree Ring Analysis

“…Probably, at that time, mountain forests formed a tree belt along the slopes of the Chikhachev and Sailugem ranges, and the Ukok high-mountain plateau united with the forests in northwestern Mongolia, where they were widespread until the middle of the Holocene [74]. The fossil forest soils of about 11-8 cal kBP and Larix sibirica charcoal fragments of about 9-7.8 cal kBP discovered within the eastern mountain periphery of the Chuya Basin also indicate a prolonged period of forestation of the now treeless landscapes [45,59].…”

“…Nevertheless, it could be stated that forest vegetation still existed at that time at the foot of the North Chuya Range. [45]; climate reconstructions on the base of palynological analysis for (1) the foot of Kurai range [69]; (2) the foot of North Chuya range [66]; (3) northern slope of the Chikhachev range [70]; (4) Boguty valley, Chikhachev range [67]. Chironomids-after [68].…”

“…In the Boguty river valley, buried charcoals of Larix sibirica of about 7.4 cal kBP (IGAN AMS 6525, Table 2) were found near the Upper Boguty lake at 2473 m a.s.l. Earlier, at the same altitude, the charcoals of larches aged 9.3-10 and 8.3-8.6 cal kBP (Table S1) were repeatedly found 10 km downstream the valley, within the mountain framing of Low Boguty lake [24,45,59]. Today, the Boguty valley, like other valleys of the Chikhachev and Sailugem ranges, is completely treeless.…”

“…Peats are presented in the central parts of the Chuya and Kurai intermountain depressions along the Chuya river and in the trough valleys of surrounding ridges. The soils were formed and buried repeatedly during the Holocene at different altitudes-from the basins' floor up to the head of trough valleys [43][44][45][46]. All those buried paleosols have mollic horizons, which are well developed and rich in organic carbon.…”

“…All those buried paleosols have mollic horizons, which are well developed and rich in organic carbon. Comparative analysis of the contemporary surface soils and the Holocene buried soils of different ages allowed for the conclusion that the last thousand years were, climatically, the most arid [45].…”