A unique diatom biostratigraphy of the Brunhes chron in Lake Baikal revealed by detailed studies of pelagic diatom paleo-assemblages, indicates that dramatic changes in insolation during the past 800 ka BP produced surprisingly rapid diatom speciation and extinctions. The orbitally-tuned age model allows the diatom assemblages to be compared with individual marine isotopic stages and substages during the Brunhes. Most of the interglacial periods are characterized by explosive speciation and appearances of new pelagic planktonic diatom species. In contrast, most of the glacial periods are characterized by spectacular extinctions. Three broad periods characterized by different degrees of stability in the pelagic diatom assemblages are distinguished during the Brunhes chron in the Lake Baikal sedimentary record: MIS 19-15e, MIS 15a-11 and MIS 9-5, these periods are apparently associated with the long-term changes in the amplitude of precessional insolation variations. Examination of individual interglacial periods further reveals the sensitivity of the Baikal ecosystem to the regional energy balance: virtually every precessional insolation peak during the early Brunhes is characterized by a unique and peculiar paleo-assemblage. For the first time the siliceous microfossil record has demonstrated such a high degree of sensitivity to insolation forcing of regional climate. Despite the dramatic changes in the pelagic plankton driven by extreme climatic changes, diatoms never went fully extinct during any glacial period. Although greatly or completely renewed during each subsequent interglacial, the pelagic diatom assemblage still managed to return dominated by the new Baikal endemic species. The diatom assemblage observed in modern Lake Baikal, despite being mostly endemic, has formed during the past 50-100 ka and is therefore rather young. These results demonstrate the remarkable capacity of this large freshwater system to sustain the dynamic stability on the large time scales.
Bibliographical noteFunding Information:
This work was implemented as a part of Baikal Drilling Project supported by NSF grants EAR-93-1720401 and EAR-9614770, by the Siberian Branch of Russian Academy of Sciences, by the Russian Ministry of Geology, and by the Science and Technology Agency (STA) of Japan. We thank the scientific drilling team of Nedra Enterprise, the crew of R/V Ulan-Ude and the scientists of the Institute of Geochemistry, Limnological Institute and Institute of the Earth Crust (Irkutsk) who participated in primary description and sampling of the BDP drill cores.
Copyright 2007 Elsevier B.V., All rights reserved.
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