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11.
Sachiko Takahashi 《Journal of Paleolimnology》1988,1(4):279-292
The 1400 m deep drilling of Lake Biwa has revealed that the lake probably originated ca. 5 · 106 yr ago. After a geographic shift to its present position, and by more than 3.105 yr ago, it had become a large and deep lake. The considerable longevity, large size and high diversity of habitats of this lake are considered to have contributed to its high abundance of endemic taxa. These taxa fall into two categories: (1) relict species of the Asiatic continent, higher latitude or marine origin; (2) species differentiated in the lake from littoral-lacustrine species, and having adapted to habitats peculiar to Lake Biwa. I discuss some of these endemic organisms, briefly review recent in vestigations on fossil organisms of the lake, and more fully discuss the origin of a representative endemic species, the pelagic gobiid fish Chaenogobius isaza Tanaka. This species is regarded as having differentiated from some littoral Chaenogobius species, creating a novel niche in the open water area after Lake Biwa was established as a deep lake.This is the seventh of a series of papers to be published by this journal that was presented in the paleolimnology sessions organized by R. B. Davis and H. Löffler for the XIIth Congress of the International Union for Quaternary Research (INQUA), which took place in Ottawa, Canada in August 1987. Drs. Davis and Löffler are serving as guest editors of this series. 相似文献
12.
A high-resolution pollen record covering the last 40,000 yr (BIW95-4) from Lake Biwa, western Japan, shows regional vegetation responses to millennial-scale climate changes. From 40 to 30 ka, Cryptomeria japonica was dominant around the lake among pinaceous conifers and deciduous broad-leaved trees. During this period, fluctuations of C.japonica are correlated with Dansgaard-Oeschger (D-O) cycles recognized from the anhysteretic remanent magnetization (ARM) record. Increases in the abundance of this taxon may have been caused by wetter summer conditions influenced by the East Asian monsoon or increased snowfall on the Sea of Japan side of the Japanese archipelago. Between 29 and 14 ka, pinaceous conifer forests mainly composed of Pinus subgenus Haploxylon, Tsuga, and Picea trees developed. At approximately 23 ka, Picea trees increased in abundance as ARM values decreased. This expansion of Picea trees has been correlated with Heinrich event (HE) 2 in the North Atlantic. At about 14 ka, the distribution of broad-leaved forest (mainly composed of deciduous oaks) began to expand after D-O 1. Evidence of significant vegetation change related to the abrupt Younger Dryas cooling event has not been found. 相似文献
13.
Shusaku Goto Hideki Hamamoto Makoto Yamano 《Physics of the Earth and Planetary Interiors》2005,152(4):314-325
In order to infer past climatic change in central Japan, we measured temperatures in a borehole at the Karasuma site, on the southeastern coast of Lake Biwa, and reconstructed sediment surface temperature history during the last 3000 years. The reconstructed temperature history shows apparent Medieval Warm Period, Little Ice Age, and contemporary temperature warming. However, the large amplitude of the temperature changes up to 4-5 K cannot be explained by past climatic change only, suggesting that there was some other cause of the larger amplitude temperature changes. The onsets of temperature decrease in the late 12th century a.d. and temperature increase in the mid 17th century a.d. appear to coincide with occurrences of two destructive earthquakes (1185 and 1662 a.d.) that caused water level changes of Lake Biwa. It suggests that the reconstructed sediment surface temperature history reflects the environmental change due to tectonically induced water level changes of the lake. If the annual mean of the ground surface temperature was higher than that of the bottom water temperature in a shallow part of the lake, which is consistent with the present-day data, the large amplitude of the sediment surface temperature change may be attributed to a combined effect of past climatic and environmental changes. Thus, we suggest that the borehole temperature at the Karasuma site preserves information not only on past climate changes but also on environmental changes due to tectonically induced water level changes. 相似文献
14.
High-resolution magnetostratigraphic analysis of three sediment cores from the base of the volcanic seamount Vesteris Banken in the Greenland Basin and one core from the Jan Mayen Fracture Zone revealed records of three pronounced geomagnetic events within the last 200 ka. Dating by stable carbon and oxygen isotope analysis, AMS14 C measurements and biostratigraphic data (foraminifera abundances) yielded ages of 28–27 ka for the Mono Lake excursion, 37–33 ka for the Laschamp event, and 189–179 ka for the Biwa I event. In at least one of the cores the Laschamp event exhibits a full reversal of the local geomagnetic field vector. The same is true of the Biwa I event, documented in one of the cores. 相似文献
15.
日本琵琶湖的水动力三维数值模拟 总被引：2，自引：0，他引：2
在笛卡尔坐标下，运用流体水动力学的方法，并在前人观测资料的基础上建立了一个三维水动力数值模式，并对日本琵琶湖风生流进行了数值模拟。结果表明，在５ｍ／ｓ的东南风、西南风、东北风作用下，湖的北端均有气旋式环流出现，在５ｍ／ｓ西北风作用下，湖的北端有反气旋式环流出现。在各种方向风速驱动下，中、低层场或形成与表层一致的环流型，或呈现明显的垂直切变。 相似文献
16.
17.
太湖、琵琶湖中水平扩散系数的探讨 总被引：1，自引：0，他引：1
根据１９９２年和１９９３年在太湖和日本琵琶湖观测到的长序列湖流资料,依据Ｔａｙｌｏｒ扩散理论计算了太湖和琵琶湖中的水平扩散系数,计算结果与通过浓度扩散方程计算基本一致。 相似文献
18.
日本琵琶湖流域大气边界层的三维数值模拟 总被引：1，自引：0，他引：1
本文在地形坐标下引入一种水平导数差分近似方法,建立一个适合日本琵琶湖复杂地形、满足静力平衡条件的三维非定常大气边界层数值模式。在弱的背景风场下,模式加入了琵琶湖流域的实际地形,计算结果表明:模式运行十分稳定,且占机内存小,节省计算时间,同时模式还做了流域地形、湖泊本身存在与否等因子对边界层风场影响的数值试验。在强的背景风场下,模式加入了经过适当平滑的琵琶湖流域地形,得出了一些有益的看法。 相似文献
19.
从居民生活视角谈太湖环境保护与治理——太湖与琵琶湖的比较分析 总被引：4，自引：1，他引：3
在环境问题日益受到社会关注的今天,环境研究者有必要从社会学和人文学科的角度来关注太湖的环境问题。本文用“生活环境主义”的观点对近年来在太湖和日本琵琶湖畔实施的调查结果进行分析和比较。得出的基本结论是：两国虽然现代化的时间和经历不同,但居民的生活行为和地域环境变化都有密切的相互影响。在人口稠密地区,只有充分重视生活经验－生活意识－生活行为－地域环境的演进和循环,从技术、经济、居民生活方式等多方面入手才能从根本上解决区域的环境问题。 相似文献
20.
To clarify long-term variations in the resting egg production of Daphnia galeata in Lake Biwa during the 20th century, we examined an abundance of plankton remains and ephippia in a 26-cm sediment core
with a time resolution of approximately 2–6 years. Historical changes shown by these plankton remains indicated that the Daphnia population has not produced resting eggs since the 1980s, but it has remained the most abundant zooplankton species in the
lake. Plankton monitoring data collected from 1966 to 2000 revealed that the overwintering individuals (January–March) of
D. galeata plankters showed a significant increasing trend in recent years, such increase being negatively correlated with ephippial
abundance in the sediment samples. Further analyses showed that the dominant phytoplankton in winter has changed from large
inedible diatoms to edible flagellated algae, probably due to changes in vertical mixing regimes resulting from winter warming.
These changes that occurred in the last several decades suggest that global warming has improved winter food conditions and
thus enabled the Daphnia plankton to maintain its population without producing resting eggs in Lake Biwa. 相似文献