Landscape development in response to climatic change during Oxygen Isotope Stage 5 in the southern Siberian loess region

Abstract

Toms, P. S. 2004 (May): Landscape development in response to climatic change during Oxygen Isotope Stage 5 in the southern Siberian loess region. Boreas, Vol. 33, Two high-resolution loess-palaeosol sections from the Ob Loess Plateau (Iskitim) and the Minusinsk Basin (Kurtak 33) provide new detailed information on the last interglacial climate variations and landscape development in the parkland-steppe zone of southern Siberia. The complete last interglacial sensu lato (130-74 ka BP) records of the two sites, documented by magnetic susceptibility, grain-size, CaCO 3 and organic carbon content as proxy climatic data, and supplemented by thin-section studies, indicate several short warm and very cold intervals correlated with OIS 5e-5a. A strongly continental warm climate culminated around the peak of the last interglacial sensu stricto (OIS 5e) and cooler conditions occurred during the following interstadial stages (OIS 5c and 5a), corresponding to shifts in palaeolandscape development with gradual replacement of parkland-steppe and mixed southern taiga by boreal forest. During stadial stages (OIS 5d and 5b), the palaeolandscape was transformed into a cold arid periglacial tundra-steppe. Evidence for a major cooling in Siberia during OIS 5d, corroborating the palaeolimnological record from Lake Baikal, is provided by deep frost-wedge casts distorting the OIS 5e chernozemic palaeosol, suggesting formation of permafrost shortly after the last interglacial climatic optimum. The pedosedimentary record, reflecting the effects of syndepositional pedogenic processes, attests to a dynamic climate pulsation during the last interglacial stage.

Weathering in the Lake Baikal watershed during the Kazantsevo (Eemian) interglacial: Evidence from the lacustrine clay record

“…In Southern Siberia, the last interglacial is characterized by a succession of loess-palaeosols: the landscape stabilization is indicated by the formation of distinct soil horizons formed during warm and humid intervals separated by thin loess units accumulated during dry, cold stages. At 125 kyr BP, chernozem formation requires warmer and more humid climate conditions (Chlachula et al, 2004), such as those inferred here by pollen analyses Tarasov et al, 2005).…”

“…Such trends could a priori suggest lower chemical weathering during interglacial than during glacial stages. But this interpretation is in contradiction with regional pedogenesis conditions favouring active hydrolysis and smectite formation during warmer conditions (Chlachula et al, 2004). According to the observed different relationships between smectites and illite (see above), the high values of S/I are most probably biased by the neoformed origins of smectites during glacial confined environments, i.e., periods with extensive permafrost.…”

“…For example, the initiation of chemical weathering in the northern Baikal watershed is recorded in the sediment clay fraction only after 125 kyr BP (within CZ4). This period corresponds to the initiation of chernozem development in Siberian soils (dated at 125 ±5 kyr BP) because of progressive climatic warming (Chlachula et al, 2004). In Southern Siberia, the last interglacial is characterized by a succession of loess-palaeosols: the landscape stabilization is indicated by the formation of distinct soil horizons formed during warm and humid intervals separated by thin loess units accumulated during dry, cold stages.…”

“…Indeed, the study of landscape development indicated a major distortion of last interglacial palaeosol documented over Siberia during the following major cooling at ca. 111 kyr BP (Chlachula et al, 2004). In the Lake Baikal area, soil stratigraphy consists in a cryoturbated unit corresponding to the interglacial maximum.…”

“…In Siberia, climate reconstructions for the last inter-glacial (Eemian s.s. or Kazantsevo according to European or Siberian stratigraphy, respectively) were mainly derived from pollen analyses (e.g., Velichko, 1984;Arkhipov and Volkova, 1994;Volkova and Bakhareva, 1995), loess deposition and soil complexes (Vorobyova, 1990;Chlachula, 2003;Chlachula et al, 2004). Based on palaeofloristic reconstructions of 25 localities, the last interglacial climate over Siberia was wetter and warmer than present (Velichko, 1984).…”