CONTINENTAL PALEOCLIMATE PROXY RESPONSES DURING THE MIS 11 INTERGLACIAL IN CONTINUOUS SEDIMENTARY RECORD OF LAKE BAIKAL, SE SIBERIA

Here we review climatic proxy responses in the mid-Pleistocene portion of the continuous sedimentary record from Lake Baikal, Siberia. The MIS 11 interval in Baikal record is characterized by two plateaus of high biogenic silica (BioSi) content corresponding to MIS 11.3 and 11.2 and reflecting warm regional interglacial climate conditions, which lasted for about 32 Ka. MIS 11 is thus the longest interglacial in Siberia, greatly exceeding the duration of MIS 5e, 7e and 9e interglacials. At the peak interglacial conditions, ca. 9-10 Ka into the MIS 11, two distinct cooling episodes in Siberia are recorded in Baikal sediments, marked by short drops in diatom abundance and BioSi accumulation. Also evident are distinct changes in the seasonal lake productivity pattern: during these cooling episodes the dominant summer diatom assemblage was suppressed, whereas autumn assemblage expanded. These short-term climatic deteriorations in Siberia, spaced at ca.3 Ka, correlate with millennial-scale climate shifts in European pollen records. These important observations suggest the existence of a poorly understood natural mechanism to perturb the stability of climatic conditions during a ‘full’ interglacial. Our detailed clay mineral studies indicate that during the last interglacial and during MIS 11 the vertical profiles of smectite index in Baikal sediments are highly correlative with BioSi, organic carbon and other lacustrine paleoproductivity indices. Using the smectite layer index to compare the present and the last interglacials with MIS 11, we found no evidence in the non-biogenic fraction of Baikal sediments to support the proposition that MIS 11 was an anomalously warm interval in Siberia. The Baikal sedimentary record allows putting the MIS 11 interval into a larger context of mid-Pleistocene climate change. We found that glacial/interglacial climatic contrasts in southeast Siberia during mid-Pleistocene were muted. Instead of the extreme changes surmised from some marine climate proxy responses, the period of almost 200,000 years from MIS 15a to MIS 11 (ca. 580-380 Ka BP) apparently lacked extensive mountain glaciation, and was characterized by virtually continuous existence of a monodominant interglacial diatom assemblage in Lake Baikal, by stable littoral benthic diatom assemblage, and by lithogenic sediments with “interglacial” properties.