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Volume 49 (2010)
- Issue 6 Pages 337-
- Issue 5 Pages 241-
- Issue 4 Pages 191-
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Volume 49, Issue 6
Displaying 1-4 of 4 articles from this issue
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The Paper for the 2008 Japan Association for Quaternary Research Academic Award
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Yusuke Yokoyama2010 Volume 49 Issue 6 Pages 337-356
Published: December 01, 2010
Released on J-STAGE: March 27, 2012
JOURNAL FREE ACCESSThe Glacial-Interglacial cycle is the most prominent feature of the Quaternary environment. The cycles are induced from changes in Earth’s orbital parameters though detailed mechanisms such as temporal and spatial asynchronous climate responses which at given times are still uncertain. High-resolution palaeoclimate archives including polar ice cores have been available for the last several decades, and they have revealed the strong coupling between carbon cycle and global climate changes. In this paper, I discuss recent developments in our understanding of surface environmental changes during the last two glacial-interglacial transitions. Providing that glacial to interglacial is the biggest environmental change of Earth’s recent history, palaeoclimate reconstructions based on various proxies can be useful constraints on AOGCMs (Atmosphere Ocean General Circulation Models). To do so, I focus discussions on-sea-level history since it is a unique proxy to identify the average status of the surface environment of Earth. Quantities of ocean water, namely global ice volume, can be deduced from sea-level observations if glacio-hydro-isostatic effect is properly treated. Relations among various components of Earth’s climate, such as Earth’s orbital parameters, carbon cycles, and global ice volumes, are particularly discussed.View full abstractDownload PDF (2335K)
Articles
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Toru Tamura, Yoshinori Kodama, Yu Saitoh, Kazuaki Watanabe, Naofumi Ya ...2010 Volume 49 Issue 6 Pages 357-367
Published: December 01, 2010
Released on J-STAGE: March 27, 2012
JOURNAL FREE ACCESSThe stratigraphy of the Holocene dunes along the coast of the Japanese Islands has been established based on organic sand layers. These organic layers were formed during inactive periods of dunes, possibly synchronously over many places, implying the influence of climate changes and human activities in the past. However, Japanese coastal dunes have not been investigated well since the 1980s due to methodological restrictions. The Tottori dunes are located in a coastal dune field facing the Japan Sea, in western Japan. The dune field shows three shore-oblique transverse dune ridges, whose crests are more than 50 m high relative to the present sea level. We undertook a ground-penetrating radar (GPR) survey along crest-normal transects of the Tottori dunes. This survey visualized internal structures of the transverse dune ridges with maximum penetration 25 m deep. The GPR profile reveals sedimentary structures, including foreset stratification, reactivation surface, and truncation surface, showing landward migration of dune sand driven by the NW to NNW winter monsoon. Depositional units, defined by truncation surfaces and other boundaries, have information on stratigraphy that is laterally variable, thus providing criteria for sampling dating material to establish a high-resolution chronology of dune deposits. Loam layers and volcanic tuffs, intercalated between the Pleistocene and Holocene dunes, were detected as a strong reflector to outline the shape of the buried Pleistocene dune. The GPR survey, combined with appropriate dating methods, potentially unravels the detailed story of the coastal dune evolution along the Japanese Islands, which may have reflected past climate and human activities.View full abstractDownload PDF (1471K) -
Takuma Ito, Shinji Tanizawa, Fujio Kumon, Koichi Iijima, Tatsuhiko Sak ...2010 Volume 49 Issue 6 Pages 369-382
Published: December 01, 2010
Released on J-STAGE: March 27, 2012
JOURNAL FREE ACCESSA 54-m-long lacustrine sediment core was taken from the Late Pleistocene Takano Formation, Nagano City, Japan, in 2004. The cored sediment consists mainly of homogenous clayey silt associated with many tephra beds, and its major part is the object of this study, covering from 140 to 40 ka in age. The variability of diatom productivity was reconstructed by chemical compositions. The SiO2/Al2O3 ratio shows a correlation with biogenic silica content measured in a part of the same cored sediment. This fact indicates that the SiO2/Al2O3 ratio can be regarded as a proxy for past diatom productivity. The profile of the SiO2/Al2O3 ratio shows a greater similarity to that of pollen-based temperature than to that of pollen-based humidity. This fact implies that the diatom productivity has been mainly controlled by temperature change in this region. When the lake water overturns, stored nutrients in hypolimnion are transported to the photic zone, and support high diatom productivity in general. Thus, the air temperature might control surface water temperature, and subsequently afect the strength and duration of thermal stratification in the lake. This phenomenon must be controlled by a precession cycle, because spectral analysis of the temporal change in the SiO2/Al2O3 ratio revealed a dominant frequency of 20.3 kyr. The period of high diatom productivity often delays a temperature rise ; however, this fact may reflect the accumulation time of nutrients from soil produced by temperature rise. Nutrient supply must depend not only on temperature but also on rainfall, because rivers transport nutrients from the soil. In the case of the Takano basin with its small catchment, diatom productivity appears to be influenced by temperature as a more critical factor than rainfall.View full abstractDownload PDF (1835K)
Note
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Yoshihiko Kariya2010 Volume 49 Issue 6 Pages 383-387
Published: December 01, 2010
Released on J-STAGE: March 27, 2012
JOURNAL FREE ACCESSDownload PDF (720K)
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