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Distribution of glycerol dialkyl glycerol tetraethers in Lake Biwa basin and the reconstruction of lake water pH during the last 300,000 years

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Please use this identifier to cite or link to this item:https://doi.org/10.14943/doctoral.r6934
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Title: Distribution of glycerol dialkyl glycerol tetraethers in Lake Biwa basin and the reconstruction of lake water pH during the last 300,000 years
Other Titles: 琵琶湖集水域系におけるGDGTの分布と過去30万年間の湖水pHの復元
Authors: 味岡, 拓1 Browse this author
Authors(alt): Ajioka, Taku1
Issue Date: 25-Sep-2014
Publisher: Hokkaido University
Abstract: We investigated glycerol dialkyl glycerol tetraether (GDGT) distributions in soilsand river/lake sediments in the Lake Biwa basin of central Japan, in order to understandtheir source and fate in a terrestrial environment. GDGTs analyzed in 16 soil profilesexhibited significant depth variation at each site. Branched GDGTs were generally mostabundant in the surface litter layer (O layer) and decreased with depth, while themaximum concentration of crenarcheol appeared in the upper soil layer (A layer), abovethe maximum concentration of the other isoprenoid GDGTs. This finding is consistentwith different microbial communities contribution to these GDGT pools the subsurfacesoil sequences. The relationship between methylation index of branchedtetraethers/cyclization ratio of branched tetraethers (MBT /CBT) and pH/MAAT in LakeBiwa basin soils was consistent with those of a previous report for global soils. TheGDGT distributions in surface sediments from the lake differed from those of soils andriver sediments in the watershed, suggesting that the GDGTs were produced in the lakewater rather than supplied from the land. The CBT for lake sediments from differentwater depths corresponded to water pH values. We thus infer that the CBT for lakesediments may serve as proxy for lake water pH and can be applied topaleoenvironmental reconstruction.Based on these results, we generated a 280,000-year record of water pH andtemperature in Lake Biwa, central Japan, by analysing the methylation index (MBT )and cyclisation ratio (CBT) of branched tetraethers in sediments from piston andborehole cores to understand the responses of precipitation and air temperature incentral Japan to the East Asian monsoon variability on the orbital timescale. Because water pH in Lake Biwa is determined by phosphorus and alkali cation inputs driven byprecipitation and temperature, the record of water pH should indicate changes inprecipitation and temperature in central Japan. Comparison with pollen assemblage in aLake Biwa core suggests that lake water pH was determined by summer temperature inlow eccentricity period before 55 ka, while it was determined by summer precipitationin high eccentricity period after 55 ka. From 130 to 55 ka, variation in lake pH (summerprecipitation) was lagged behind that in summer temperature by several thousand years.This perspective is consistent with the conclusions of previous studies (Igarashi andOba, 2006; Yamamoto, 2009) that the temperature variation preceded the precipitationvariation in central Japan
Conffering University: 北海道大学
Degree Report Number: 乙第6934号
Degree Level: 博士
Degree Discipline: 環境科学
Examination Committee Members: (主査) 准教授 山本 正伸, 教授 吉川 久幸, 教授 河村 公隆, 准教授 豊田 和弘, 教授 鈴木 德行 (大学院理学研究院)
Degree Affiliation: 環境科学院
Type: theses (doctoral)
URI: http://hdl.handle.net/2115/57145
Appears in Collections:学位論文 (Theses) > 博士 (環境科学)
論文博士 (Doctorate by way of Dissertation) > 環境科学院(Graduate School of Environmental Science)

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