Yoshitaka Hase

9 – Vegetation history of the southeastern and eastern coasts of Lake Baikal from bog sediments since the last interstade

Publisher Summary This chapter describes the geology and vegetation around the study sites and the regional vegetation history in the southeastern and eastern coastal areas of Lake Baikal. Various paleoecological studies of mire sediments from the coastal areas of Lake Baikal were conducted and sediment samples from the last glacial and the Holocene are taken from eight bogs and two outcrops of peat sediment on the southeastern and eastern coasts of Lake Baikal and examined for fossil pollen, plant macrofossils, and charcoal fragments. The chronology of each deposit is based on radiocarbon dating. The results of these studies reveal the vegetation history of the taiga around Lake Baikal since the last glacial period. During the last interstade (approximately 35–30000 y BP), forests on the southeastern coast consisted mainly of spruce and birch, with Gramineae and Artemisia. Herbaceous plants such as Gramineae and Artemisia and shrubs such as willow, birch, and alder characterized the vegetation of the last glacial maximum. Between 12000 and 11000 y BP, spruce expanded again in the coastal areas. The changes in spruce suggest that the Lake Baikal area is a glacial refugia of dark coniferous taiga. In the early Holocene, the spruce was replaced by fir and pine on the southeastern coast. On the eastern coast, the forests contained both spruce and fir. Diploxylon and Haploxylon pine forests shared large areas with birch since 6000 y BP. In some sites on the southeastern coast, the concentration of charcoal fragments, which indicates fires, increases sharply in the upper sediments. This increase in charcoal probably reflects forest fires caused by human activity.

Forest-desert alternation history revealed by the pollen-record in lake baikal over the past 5 million years

Publisher Summary The watershed of Lake Baikal constitutes the southern portion of the Siberian taiga and the northern part of the Mongolian steppe, and it is located at a high-latitude (51–56 N), far from the ocean. The paleoclimatic history of the Baikal region sensitively reflects past global changes, such as warm-cold and dry-moist oscillations of climate. Paleovegetational reconstruction of the region is indispensable to understanding how the Siberian taiga forest responded in timing and magnitude to past global changes. However, there are few palynological studies for paleovegetational reconstruction of the past million years in the region. This chapter presents a palynological study on the BDP96 Hole 1 core drilled by a Russian scientific drilling team in 1996. The results obtained in this study prove that the forest-desert alternations are closely related to global glacial–interglacial cycles during the Pleistocene. Considerable forest retreats are visible for relatively long periods during the late Pliocene, and a remarkable desert prevailing period during the early and middle Pliocene preceded the forest dominant period. The work in the Baikal area has also shown that these forest-desert alternations are more sensitive to global paleoclimate changes than those found in other continental region records.

Vegetation Changes in the Baikal Region during the Late Miocene Based on Pollen Analysis of the BDP-98-2 Core

A palynological study was conducted on samples taken from the bottom sediments of Lake Baikal. The pollen records from 600-m to 400-m depth of the BDP-98 core show that the vegetation consisted mainly of broad-leaved tree forests composed of Fagaceae, Ulmaceae, and Juglandaceae in the lower part of the core. In the middle and upper parts of the core, the vegetation consisted mainly of coniferous tree forests and deciduous broad-leaved tree forests. The coniferous tree forests were composed of Pinus and Picea accompanied by Tsuga and Larix, and the deciduous broad-leaved tree forests were mainly composed of Betula and Alnus. A major reduction in palynological diversity and abundance was found at 8.6 Ma. In addition, a drastic change in the Steppe/forest index (SFI; Traverse 1988) was detected, reflecting the intensification of dry conditions. After the change, Betula and Alnus became more important elements of the deciduous broad-leaved tree forests, suggesting that a cool continental climate prevailed.

Geomorphological Development of the Tunka Depression in the Baikal Rift Zone in Siberia, Russia

There is no large lake, such as Lake Baikal or Lake Hovsgol, in the Tunka depression now, but it is one of the depressions of the Baikal rift zone. The bottom of the depression is formed of Miocene to Holocene rocks set on Precambrian and Paleozoic rocks, which mainly crop out in mountains north and south of the depression. In Miocene times, lacustrine sediments were formed and basaltic lava flows erupted. However, in the Pliocene and Pleistocene, fluvial or fluvioglacial sediments were formed. Therefore, it is assumed that the development of the Tunka depression is different from that of Lake Baikal and Lake Hovsgol. The difference has to do with the outflow of water via the Irkut river during the Phocene, Pleistocene, and Holocene. In the Phocene, any large lake apparently disappeared, because the sediments are composed of coarse sand and pebbles produced by the rivers. In the Pleistocene, many gravel beds were formed by fluvial and fluvioglacial processes, and, especially in the middle Pleistocene, water probably flowed out of Lake Baikal to the Irkut river via the Kultuk vafley (Kononov and Mats 1986; Mats et al. 2000).

Paleoenvironmental record of Lake Hovsgol (Mongolia) in northeast Eurasia

Studies on paleoenvironmental changes are important to estimate future global warming induced by human activity. Information on paleoenvironmental changes in the northeast Eurasia has been collected by Baikal Drilling Project (BAIKAL DRILLING PROJECT GRouP 2000). Lake Hovsgol is located in the Lake Baikal basin at an altitude of 1667 m a.s.l. in the subarctic zone and is approximately 1200m higher than Lake Baikal (GouLDEN et al. 2006). Mean annual air temperatures of the lake area during the glacial period are assumed to have been lower than -15 oe; thus, it is possible that not only the lake surface was covered with perennial ice, but also that higher land plants almost disappeared during the glacial period. Organic components in lake sediments are chemical fossils of paleoenvironmental changes in the drainage basin and are extensively used as biomarkers to evaluate sources and sedimentary conditions of organic matter in various environments (MEYERS & ISHIWATARI 1993, MATSUMOTO et al. 2003). Here we report organic components in HDP04 sediment core from Lake Hovsgol to elucidate biological production, sources of organic matter, and paleoenvironmental changes during the last 1030 ka in the northeast Eurasia. These results are compared with Lake Baikal sediment core signals.

5.2-5.8 ka BP paleoenvironment of the southern slope of Mount Raizan, Japan

Accelerator mass spectrometry (AMS) radiocarbon dating and paleoecological analysis of slope deposits at Mt Raizan provided seven 14 C dates indicating that landslides occurred in that area at 6.0 to 6.3 cal ka BP and 6.5 cal ka BP. Plant macrofossils, pollen grains, and spores point to a mixed forest at that time, consisting of conifers and broad-leaved trees. On the other hand, insect fossil indicates slightly colder climate than that of the flora. This difference may be attributed to varied sensitivities of each proxy to climatic changes.