著者

大嶋 和雄

出版者

石油技術協会

雑誌

石油技術協会誌 (ISSN:03709868)

巻号頁・発行日

vol.56, no.4, pp.300-309, 1991 (Released:2008-03-27)

参考文献数

19

---

On the geological scale, earth history yields vital information concerning past environments and climates. This highlights the urgency for increased collaborative international response and research into solutions of problems posed by current climatic changes, whether natural or induced by the activities of man. Climatic changes occur on variety of timescales, ranging from catastrophic volcanic eruptions (minutes or days), through gradual changes in Earth's orbital parameters (104-106 years) to tectonically driven changes (106-108 years). It seems likely that the long-term fluctuations of climates (less than the time-scale of planetary evolution), which give rise to glacial epochs, are largely determined by continental plate distributions and movement, whilst the shorter-term fluctuations which produce glacial and inter-glacial periods in glacial epochs reflect variations in coming solar radiation.Attention is focussed on the possible existence of an anoxygenic, primeval atmosphere and on the history of atmospheric CO2. Five great biologic revolutions have occurred through earth history that have fundamentally shaped the modern geochemical picture. It is significant that organisms have controlled their own environment. Organic CO2 and calcium budget have played critical roles.

著者

大嶋 和雄

出版者

茨城大学教養部

雑誌

茨城大学教養部紀要 (ISSN:02884224)

巻号頁・発行日

no.27, pp.p157-165, 1994

著者

大嶋 和雄

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.100, no.6, pp.967-975, 1991-12-05 (Released:2009-11-12)

参考文献数

12

被引用文献数

36 36

著者

大嶋 和雄

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.29, no.3, pp.193-208, 1990-08-20 (Released:2009-08-21)

参考文献数

36

被引用文献数

104 142

---

The problem of the maximum depth to which the sea level dropped during the last glaciation is even more difficult and obscure than that of high sea levels. Some evaluations have been proposed, based on the estimations of the depth of the Holocene sediment base in the coastal plain or on the consideration of submerged sediments or geomorphological features now found on continental shelf. Many Japanese geologists estimate -100 to -140m for the last glacial low stand sea level, but some doubt is cast on their data and opinions. Our estimate of -80±5m was a conservative interpretation based on dates for shells and peat obtained from the shelf and coastal plains of the Japanese Islands.1. Charts show that wherever sizable inland seas are separated from the ocean by narrow straits, current erosion holes (sea caldrons) exist either in the narrow straits or directly adjacent to them. The Tsushima strait is a part of the shelf, although there is a relatively deep hole (to -160m) along the east side of Tsushima Island. The depth of this deep hole attains 50m below the surrounding relict wave-cut terrace (-110m to -115m). In this case, the depth of the relict wave-cut terrace may reflect the sea level (about -100m) at the time of the Tsushima strait formation.2. As a result of continuous seismic profiling surveys in Ishikari Bay, the buried valleys on the continental shelf are known to be deeper than 90m. The buried valleys were formed at the stage of the lowest sea level, during the last Glacial Age. However, we observed that Ishikari river may be 10m to 15m deep near its mouth. The available data indicate a relative rise of sea level since the valley was cut, amounting to about 80m.3. The breadth to depth ratio of the straits around the Japanese Islands seems to reflect each still standing sea-level stage, such as -100±10m, -80±5m and -45±5m, after the formation of these straits.4. For most of the Pleistocene, the Japanese Islands were connected with the Korean Peninsula, and the present major islands themselves were tied to each other. It is sure that large mammals such as elephants migrated into the Japanese Islands through land bridges. In the early Shimosueyoshi transgression (about 100, 000y.B.P.), when the sea level was about -100m, the Japan Sea was connected with the Pacific through narrow passages located in the Korean and Tsugaru straits. At the time of the last Glacial Age, when the sea level fell to about -80m, land bridges between Honshu and other lands were never formed. We now believe that it might have been 12, 000 years ago when the sea level rose to about -45m. This was the final stage of the land bridge in the Soya strait between Sakhalin and Hokkaido.

著者

大嶋 和雄 斎藤 文紀

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.47, no.3, pp.213-231, 1993

---

Tokyo Bay is badly polluted, but would be in much worse shape were in not for sewage treatment and regulation. Such management techniques for water quality have rid the bay of toxic mercury sludge, and have made the average water quality of the bay head up to Class C rating, which indicates no unpleasant effects on everyday life. The bay still yields fishery products; a 30,000-ton catch in 1990. However, its yield is less than only a third of the maximum of the past fisheries yield. There is a limit, however, to technology. To bring the water quality rating of the entire bay up to Class B, suitable for fishing, would require that treated sewage dumped into the bay be able to support marine life. The construction of sewage treatment plants to perform such a feat would be prohibitively expensive, and the cost of the treatment would be a continuing liability, not a one-time fix. In other words, though technology can keep death at bay, it alone cannot restore Tokyo's coastal area to health. A Tokyo-Bay restoration project must harness the area's natural ability to recover from environmental damage. That recovery is accomplished through three mechanisms; sea-water exchange, sedimentation, and biological production. The coast is the interface between land and sea, where its ecosystem has developed over thousand of years. Technology works to fight pollution, but only to a point. Coastal restoration projects must be designed to work with the powerfull cleaning system of the bay itself if they are to assist truly sustainable development.