LATE QUATERNARY LOESS–PALAEOSOL SUCCESSIONS AND ATMOSPHERIC CIRCULATION, CENTRAL SIBERIA

Aeolian sediments and palaeosols represent the principal forms of sedimentation and hold the record of climate events in unglaciated central Siberia. Loess-palaeosol records in the Gorno-Altaisk, Biysk, and Krasnoyarsk regions indicate establishment of periglacial steppe-tundra during OIS 4 and OIS 2, replaced by parkland steppe and boreal forest during warmer intervals within OIS 3. The last interglacial maximum occurred ca. 125,000 BP, earlier than OIS 5e in Europe and North America. A gradual transition from parkland-steppe (OIS 5a) to moist tundra conditions (OIS 4) occurred ca. 75,000 BP. General cooling, punctuated by isolated short warm intervals, marked the period from ca. 75,000 to ca. 25,000 BP. OIS 2, ca. 25,000-18,000 BP, was marked by a sharp change to a dry tundra climate, followed by rapid warming ca. 15,000-8,000 BP. Mid- and latest Holocene conditions were warmer than those recorded during the OIS 5e maximum. Textural, magnetic susceptibility, and mineralogical analyses indicate that the OIS 4 and OIS 2 loess units were derived from different source areas. The mineralogy of the clay-rich OIS 4 loess indicates derivation from the Altai Mountains to the south, and is associated soft sediment deformation indicates niveo-aeolian deposition. The OIS 2 loess is coarser, distally derived from western sources, and was deposited under colder, drier conditions. The changes in loess mineralogy and texture thus record a shift from southerly winds during OIS 4 to western zonal/hemispheric circulation during OIS 2. OIS 2 was marked by an abrupt change in climate, in contrast to the gradual transition evident from OIS 5a through OIS 3. Each successive interstadial was marked by cooler and drier conditions than its predecessor. The similarity between climate successions in Siberia with those recorded in the central Russian Plain suggests that continental-scale changes in airmass circulation were ongoing during the Late Quaternary in northern Eurasia.