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A synthesis of paleoclimate responses from Lake Baikal during the MIS 11 interglacial is presented based on proxy records from two drill sites 245 km apart. BDP-99 is located in vicinity of the delta of the major Baikal tributary, whereas the BDP-96 site represents hemipelagic setting distant from riverine influence. The comparison of thicknesses of interglacial intervals in these contrasting depositional settings confirms the extended ca. 33-kyr duration of the MIS 11 interglacial. The new BDP-99 diatom biostratigraphic record matches that of the BDP-96-2 holostratotype and thus allows establishing establishes robust correlation between the records on the same orbitally-tuned timescale. The first detailed MIS 11 palynological record from the BDP-99 drill core indicates the dominance of boreal conifer (taiga) forest vegetation in the Baikal region throughout the MIS 11 interglacial, since at least 424 ka till ca. 396 ka. The interval ca. 420–405 ka stands out as a "conifer optimum" with abundant Abies sibirica, indicative of climate significantly warmer and less continental than today. The closest Baikal analog to this type of vegetation in the history of the current Holocene interglacial is at ca. 9–7 ka. The warm conifer phase lasted for ca. 15 kyr during MIS 11 interrupted by two millennial-scale cooling episodes at ca. 411–410 and 405–404 ka. Reconstructed annual precipitation of 450–550 mm/yr during the MIS 11 interglacial is by ca. 100 mm higher than during the Holocene; regional climate was less continental with warmer mean temperatures both in summer and in winter. At both drill sites, the two-peak structure of the MIS 11 diatom abundance profiles reflects the orbital signature of precession in the interglacial paleoclimate record of continental Eurasia. MIS 11 interglacial was characterized by the sustained high level of primary production and accumulation of autochthonous organic matter at both study sites. The responses of paleoclimate-sensitive indices in the mineralogy of the MIS 11 sediments in BDP-96-2 are consistent with those during the Holocene. Illitization of secondary clay minerals in the Baikal watershed was an important process, but it appears to have been subdued during the first half of the MIS 11, apparently due to elevated humidity and muted seasonality of regional climate.

The Early Holocene paleoclimate in Bosten Lake on the northern margin of the Tarim Basin, southern Xinjiang, is reconstructed through an analysis of a 953 cm long core (BSTC2000) taken from Bosten Lake. Multiple proxies of this core, including the mineral components of carbonate, carbonate content, stable isotopic compositions of carbonate, Ca/Sr, TOC and C/N and C/S of organic matter, are used to reconstruct the climatic change since 8500 a B.P. The chronology model is made by nine AMS 14C ages of leaves, seeds and organic matter contained in two parallel cores. The climate was cold and wet during 8500 to 8100 a B.P. Temperature increased from 8100 to 6400 a B.P., the climate was warm and humid, and the lake expanded. The lake level was highest during this stage. Then from 6400 to 5100 a B.P., the climate became cold and the lake level decreased slightly. During the late mid-Holocene, the climate was hot and dry from 5100 to 3100 a B.P., but there was a short cold period during 4400 to 3800 a B.P. At this temporal interval, a mass of ice and snow melting water supplied the lake at the early time and made the lake level rise. The second highest lake level stage occurred during 5200 to 3800 a B.P. The climate was cool and wet during 3100 to 2200 a B.P., when the lake expanded with decreasing evaporation. The lake had the last short-term high level during 3100 to 2800 a B.P. After this short high lake level period, the lake shrank because of the long-term lower temperature and reduced water supply. From 2200 to 1200 a B.P., the climate was hot and dry, and the lake shrank greatly. Although the temperature decreased somewhat from 1200 a B.P. to the present, the climate was warm and dry. The lake level began to rise a little again, but it did not reach the river bed altitude of the Konqi River, an outflow river of the Bosten Lake.

A study of 15 gravity cores reveals consistent patterns of lithologic change throughout the Lake Hovsgol basin. Sediments of the last glacial are composed of calcareous clayey silt with an admixture of coarse material from sand to gravel. During the last deglaciation, a basin-wide deposition of finely laminated carbonate mud took place and was ultimately succeeded by the deposition of diatomaceous clayey ooze during the entire Holocene interval. Diatom productivity in Lake Hovsgol during the early Holocene was higher than today, but declined by ca. 6.6 cal ka BP. Sedimentation rate estimates for post-glacial section range from 1.5 to over 6.7 cm/ka for different parts of Lake Hovsgol. Rates appear to have decreased in the late Holocene. The last glacial maximum (LGM) corresponded to a dramatic low stand of Lake Hovsgol on the order of 100 m below today's level, as reflected by littoral facies retrieved in cores from intermediate depths. Age dating of plant fragments in these sediments suggests that lake level started rising no later than 15.4 cal ka BP. By the beginning of the Holocene, Lake Hovsgol evolved from a low-level closed basin lake to an overflowing freshwater lake. The observed dramatic lithologic change and evidence for lake-level change suggest that Lake Hovsgol may in fact serve as a sensitive ‘water gauge’ in continental interior Asia and that the Hovsgol sedimentary record preserves reliable proxies for past changes in effective moisture balance in the Lake Baikal catchment area.

Sedimentary sections from Lake Baikal in Siberia and Lake Hovsgol in Mongolia show that during the Last Glacial Maximum (LGM), planktonic/benthic diatoms, chrysophyte cysts, sponge spicules and zooplankton remains did not accumulate in the lake sediments. The combined data suggest a drastic lowering of photosynthetic production and perhaps the collapse of the ecosystems of both lakes due to significant environmental changes during the LGM. Both lakes were almost uninhabited during the LGM. Starting from ∼12,000 to 13,000 14C years ago, the planktonic communities redeveloped and primary production increased in both lakes. As a result, Holocene sediments contain abundant and well-preserved planktonic/benthic diatoms, stomatocysts, sponge spicules and zooplankton remains. The ecosystem stress in Lake Baikal during glacial time appears to be due to a decrease in nutrient loading from the watershed, lowering of surface water temperature, and very low transparency of water and ice. We believe that endemic species in Baikal survived during glacial ecological catastrophes in refugia that could have been a source of species that invaded and repopulated Baikal after intense and long glacial winters. The ecosystem stress in Lake Hovsgol during glacial time appears to be due primarily to drastic lake level falls, and changes in water chemistry. At the beginning of the Holocene, Lake Hovsgol was reoccupied again by cosmopolitan species probably from surrounding small lakes and rivers. In addition to the LGM results, we also show that Lake Baikal planktonic diatom species diversity during the last 350 ka is closely related to solar insolation fluctuations caused by the 23 and 41 ka cycles of the Earth's precession and obliquity. Our results also indicate that Baikal's planktonic diatom species diversity, as measured by the Shannon–Weiner index, correlates with the oxygen isotope record that represents changes in global ice volume.

The large difference in carbon and oxygen isotope data from the marine record between marine oxygen isotope stage 12 (MIS 12) and MIS 11, spanning the interval between about 480 and 380 kyr ago, has been interpreted as a transition between an extremely cold glacial period and an unusually warm interglacial period, with consequences for global ice volume, sea level and the global carbon cycle1,2,3,4. The extent of the change is intriguing, because orbital forcing is predicted to have been relatively weak at that time5. Here we analyse a continuous sediment record from Lake Baikal, Siberia, which reveals a virtually continuous interglacial diatom assemblage, a stable littoral benthic diatom assemblage and lithogenic sediments with ‘interglacial’ characteristics for the period from MIS 15a to MIS 11 (from about 580 to 380 kyr ago). From these data, we infer significantly weaker climate contrasts between MIS 12 and 11 than during more recent glacial–interglacial transitions in the late Pleistocene epoch (about 130 to 10 kyr ago). For the period from MIS 15a to MIS 11, we also infer an apparent lack of extensive mountain glaciation.

Paleoproductivity records from Lake Baikal indicate that the last interglaciation in southeastern Siberia lasted ca. 12,000 yr from 127,000 to 115,000 yr B.P., was punctuated by a climatic oscillation about 120,000 yr ago, and ended abruptly with a rapid onset of regional glaciation during marine isotope substage (MIS) 5d. The Siberian equivalent of the MIS 5e–5d transition appears to lead the post-Eemian cold pulses in Europe and in the central North Atlantic by 5000 to 8000 yr. The Baikal record also registers a pronounced cold event during early MIS 5c, which correlates with the Montaigu event in pollen records from France. In Siberia, the climatic deterioration during the MIS 5d was a full-scale glacial pulse unlike the short, moderate cooling during the Montaigu event.

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.

Detailed siliceous microfossil records (diatoms and chrysophyte cysts) from the BDP-93-2 borehole with resolution of ca 30–120 years were obtained from Lake Baikal sediments to test the sensitivity of the Lake Baikal system to minor climate changes during the Holocene. Our new results demonstrate that the Subboreal period is characterized by the highest accumulations of diatom frustules and chrysophyte cysts in Lake Baikal sediments. The siliceous microfossil record suggests that the Holocene climatic optimum in this interior part of Asia corresponds to the Subboreal period 2.5–4.5 ka and not to the Atlantic period 4.6–6 ka. Although quite different from Holocene reconstructions for the European part of Eurasia, the Holocene sedimentary record from Lake Baikal shows good correlation with palynological and soil climatic records from southeast Siberia and Mongolia where similar responses of the terrestrial biosphere are also documented. A distinctive monospecific lamina of Synedra acus diatom species, coincident with the maximum of chrysophyte cyst accumulation during the Subboreal period, argues for the possible short-term changes of the trophic state of Lake Baikal from oligotrophic, with a cold-water diatom assemblage, to eutrophic with a thermophilic monospecific diatom flora. Comparison of diatom and cyst responses provides a key to distinguishing the humidity from temperature response in future studies of high-resolution records of Lake Baikal.

The δ 13 C record of total organic carbon in the Lake Baikal core BDP-93-2 over the last glacial/interglacial transition shows remarkable correlation with atmospheric CO 2 fluctuations and the negative isotopic shift of 3.5–4‰ in response to the global increase in paleo- p CO 2 level. With rapid evolution of the Lake Baikal carbon cycle from full glacial to full interglacial modes, however, the p CO 2 signal in the Baikal δ 13 C sedimentary organic matter is inundated by the basin-wide productivity signal, in the Holocene. The Baikal diatom abundance record, as a paleotemperature proxy, lags behind the GISP2 ice core δ 18 O temperature proxy record by ca. 1 ka, possibly reflecting the response time of the Baikal ecosystem to major climatic transitions. There is no lag associated with the pronounced Younger Dryas cooling, however, suggesting a different forcing mechanism, with a short response time, for this abrupt climatic event in continental interior Asia. The phase difference observed between the diatom abundance and δ 13 C proxies in Lake Baikal core BDP-93-2 suggests their independent responses to different forcing mechanisms, further justifying their importance for paleoclimate reconstructions from Lake Baikal records.

This chapter presents a conceptual framework for understanding the impact of glacial/interglacial climate changes on the carbon cycle of Lake Baikal. To do so, we bring together evidence from mass-balance estimates, from the carbon and nitrogen compositions of plankton, particulate organic matter and the surface layer of bottom sediments, and watershed soils and riverine sediments, as well as from Lake Baikal organic sedimentary records of the last glacial/interglacial transition and of the last climatic cycle to 130 Ka BP. The goal of this synthesis is to offer new ways of examining organic carbon paleoproductivity records.

Five boreholes, drilled in different geological structures of Lake Baikal by the International Baikal Drilling Project, allowed us to obtain unique paleoclimatic records, which can be regarded as being representative of continental Asia. One of the most sensitive paleoclimate proxies in the sedimentary core is the number of diatoms, and correspondingly the amount of biogenic silica. The major and trace elements, the magnetic susceptibility, the clay mineral composition, and a number of other parameters also reflect changes in the environment and the climate.

The sedimentary record of Lake Baikal reveals details about the climatic response of continental Asia during the interval 423-362 Ka BP, corresponding to marine oxygen isotope stage MIS 11. The MIS 11 record in Lake Baikal is marked by two plateaus of high biogenic silica content corresponding to MIS 11.3 and 11.2. The middle part of MIS 11 (substage 11.2) exhibits the highest biogenic silica accumulation, reflecting the warmest regional climate, of the last 450 Ka. These interglacial conditions in continental Asia were uninterrupted for about 32 Ka, making MIS 11 the longest interglacial in Siberia, greatly exceeding the duration of interglacial conditions during MIS 5e, 7e and 9e. This extremely long and warm interglacial period of MIS 11.3-11.2 in Siberia ended abruptly with dramatic cooling at 394-390 Ka BP. This cooling resulted in brief mountain glaciation in Siberia due to the amplified response of continental Asia to insolation forcing. The cooling during MIS 11 produced irreversible change in the climate of continental Asia as suggested by diatom succession and by biogenic silica accumulation. Diatom species composition further reveals more complex structure of MIS 11 and makes a strong case for insolation control of diatom production in Lake Baikal.

Publisher Summary This chapter describes the paleoclimatic record over the period of 5 million years based on variations in diatom abundance in the sediments of a 200 m core obtained from Lake Baikal. The data represent a long, continuous continental record of climate changes in Central Asia during the Late Cenozoic. The record shows the climatic cooling trend that started in Pleistocene and is superimposed on the short-term cyclic climatic variations controlled by the Earth's orbital parameters. The record also reveals the presence of the two cold episodes (each about 300 Ka long) at the time intervals 2.82–2.48 Ma and 1.75–1.45 Ma characterized by glaciations at their maximum phases. These cooling periods in Lake Baikal record are also registered as global cooling in other paleoclimate records of the Northern Hemisphere. The continental record of Lake Baikal contains the majority of climatic events found in marine records and demonstrates that continental regions of Asia responded to all major changes in the Earth's climate recorded in the long oxygen isotopic records.

The new BDP-98 drill core of the Baikal Drilling Project is a key palaeoclimate record in continental Asia because globally sensitive sedimentary records of such length and continuity are very rare1,2,3. Kashiwaya et al.4 have attempted signal processing of the BDP-98 average grain-size record, but in constructing their age model they excised a 100-metre interval from the 600-metre section, stating that it is “erroneous”4. On the basis of our lithological studies, we consider that this excision is unjustified.