Insolation regime in Siberia as a major factor controlling diatom production in Lake Baikal during the past 800,000 years

Abstract

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.