Last glacial to post glacial climate changes in continental Asia inferred from multi-proxy records (geochemistry, clay mineralogy, and paleontology) from Lake Hovsgol, northwest Mongolia

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• 作者：Takahiro Watanabe^a ; ^b ; ^{twatanabe@geo.kankyo.tohoku.ac.jp} ; Koji Minoura^c ; Fumiko Watanabe Nara^b ; Koji Shichi^d ; Kazuho Horiuchi^e ; Takeshi Kakegawa^b ; Takayoshi Kawai^f
• 关键词：stable carbon and oxygen isotope ratios ; lake sediment ; Mongolia ; East Asian monsoon
• 刊名：Global and Planetary Change
• 出版年：2012
• 期刊代码：35_09218181
• 类别：env
• 出版时间：May, 2012
• 卷：88-89
• 期：Complete
• 页码：53-63
• 文件大小：2130 K

摘要

Multi-proxy records (geochemistry, clay mineralogy and paleontology) from three sediment cores from Lake Hovsgol, northwest Mongolia, provide paleoenvironmental changes in continental Asia from the last glacial to the present (during the last 29 cal ka BP). This paper presents the first continuous 未¹³C and 未¹⁸O dataset for ostracod shells (Cytherissa lacustris) from Lake Hovsgol sediments. A positive shift in ostracod 未¹³C values (from + 0.5鈥?to + 3.2鈥? began at ca. 21 cal ka BP, and was associated with a decrease in 未¹³C values of total organic carbon (from 鈭?#xA0;24.7鈥?to 鈭?#xA0;27.3鈥? and an increase in the mass accumulation rate of total organic carbon (MAR-TOC). These results suggest that increased lake productivity led to the ¹³C-enrichment of dissolved inorganic carbon in Lake Hovsgol. In addition, decreases in clay content and the illite crystallinity index (full width at half maximum of the 10 脜 peak) began at ca. 21 cal ka BP, indicating an increase in surface runoff and a change in sources of clastic materials in the watershed. The highest 未¹⁸O_ostracod values (up to 鈭?#xA0;4.8鈥? at 16-15 cal ka BP indicate the increases in precipitation from the East Asian monsoon. The total pollen amount increased, and Betula, Alnus, and Salix were dominant (up to 53%, 30%, and 6%, respectively) after 16-15 cal ka BP. These findings indicate that broad-leaved trees expanded around Lake Hovsgol. In addition, fossil diatom valves appeared after 16-15 cal ka BP, suggesting climate amelioration, and increased input of soil-derived nutrients and dissolved silica. Between 10 and 5 cal ka BP (Holocene climate optimum), productivity was high in and around the lake (MAR-TOC, up to 47.3 mg/cm² kyr; MAR-diatoms, up to 14.4 脳 10⁸ valves/cm² kyr; total pollen concentration, up to 9.0 脳 10⁵ grains/cm³). Environmental changes during the last 29 kyr in and around Lake Hovsgol are clearly associated with fluctuations in summer insolation and East Asian monsoon intensity.