Abstract
A Marine Isotope Stage (MIS) 3/early MIS 2 section from a structural high along the east coast of the North Basin of Lake Baikal was analysed for diatoms, C/N ratios, and organic carbon isotope ratios. Diatoms were present throughout MIS 3 and early MIS 2, with high concentrations of the planktonic taxa Cyclotella sp. c.f. gracilis between 54 and 51.5 kyr BP indicating relatively warm, interstadial, conditions. Following a %TOC inferred climatic cooling between 43.2 and 39.1 kyr BP, evidence of a more muted δ 13C (organic) and %TOC inferred climatic warming from c. 39.1–34.7 kyr BP coincides with a period of very high diatom concentrations, indicating high aquatic productivity, at the Buguldeika Saddle in the South Basin of Lake Baikal. No evidence exists for a ‘Kuzmin’ catchment erosional event in the North Basin during MIS 3. This, however, may reflect the location of the coring site away from major riverine inputs. Abrupt climatic cooling at the culmination of both warm phases in the North Basin are associated, on the basis of the palaeomagnetic age-model and correlations to existing sites in Lake Baikal, with the initiation of Heinrich events 5 (c. 50 kyr BP) and 4 (c. 35 kyr BP), respectively, in the North Atlantic. The amount of organic material declines across the MIS 3/MIS 2 transition while constant C/N ratios suggest organic material to be predominantly derived from phytoplankton. An increase in δ 13C (organic) at the MIS 3/MIS 2 transition may therefore indicate changes in aquatic productivity, pCO 2 or the inorganic carbon pool.
Highlights
The last glacial period in Central Asia, the Zyryanka Glacial, is separated into two cold stages, the Ermakovo and Sartan glaciation, corresponding to Marine Isotope Stages (MIS) 4 and MIS 2 respectively, and an intermediate warm period, the Karginskiy Interstadial correlating to MIS 3 (Velichko, 1984)
Carbon isotopes in addition to percentage carbon and percentage nitrogen of bulk organic matter were analysed during combustion in a Carlo Erba 1500 on-line to a VG TripleTrap and Optima dual-inlet mass spectrometer. δ13C values were converted to the VPDB scale using a within-run laboratory standard calibrated against NBS-19 and NBS-22 with C/N ratios calibrated against an Acetanilide standard
C/N mass ratios remain constant throughout MIS 3 and into MIS 2, with values between 6.3 and 8.9, indicating no significant terrestrial input of organic matter (Fig. 3)
Summary
The last glacial period in Central Asia, the Zyryanka Glacial, is separated into two cold stages, the Ermakovo and Sartan glaciation, corresponding to Marine Isotope Stages (MIS) 4 and MIS 2 respectively, and an intermediate warm period, the Karginskiy Interstadial correlating to MIS 3 (Velichko, 1984). Lasting from c.59 to c.29 calendar (cal) kyr BP (c.56 to 25 14C kyr BP) (Voelker et al 1998, van Kreveld et al 2000), MIS 3 is marked by large-scale deglaciation in Europe and Central Asia, intermixed by Heinrich and Dansgaard/Oeschger (D/O) events in the North Atlantic region and the development of large alluvial plains in south west Siberia (Nemchinov et al 1999; Arnold et al 2002). Uncertainty prevails over regional, long-term climatic trends during the interstadial with many studies focused on North Atlantic marine cores At present only 14 palaeoenvironmental and palaeoclimatic studies in Central Asia contain a sufficiently high resolution to detect Heinrich events and so provide a detailed insight into the long term climatic trends during MIS 3 (Voelker et al 2002). The majority concentrate on the Chinese Loess Plateau where clear evidence exists for climatic cooling during Heinrich events and D/O stadials throughout the last glacial (e.g. Porter and An, 1995)
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