In order to reconstruct paleoclimatic changes quantitatively during the last 400,000 years in and around Lake Biwa, four short cores were recovered from lake bottom surface and correlation between proxies of sediment and equipment data were examined. Proxies of sediment were obtained by determination of sedimentary age using lead-210 method and several kinds of analytical data at each depth. Meteorological data were based on those of Hikone meteorological observatory. Good correlation existed between density of sediments, content of biogenic silica and mean annual temperature or mean temperature of May or September. These facts reflect that primary production in the lake is chiefly controlled by mean temperature during the bloom season of diatoms. Based on the transfer function established by correlation of mean temperature and density of sediment or content of biogenic silica of sediment, quantitative climatic change history of in and around Lake Biwa are discussed. Results of these studies were published as 15 refereed papers and presented as 64 oral presentations

In this project, long-term monitoring of water quality including nutrients was conducted at the tip of Sada Peninsula by using the autonomous monitoring system. The long-term environmental variations of nearby areas were analysed by using the historical data and the sediment samples. Moreover, the structure of the ecosystem at present were surveyed.The major results relating to the nutrient environments of the Seto Inland Sea are as follow. (1) More than 60% of the nitrogen and phosphorous in the Seto Inland Sea are originated from the Pacific ocean. In case of Bungo Channel, supply of the nutrients from the Pacific Ocean is mainly carried out by the intrusion of cold, nutrient-rich water mass from the bottom layer of the shelf slope region south of the channel. (2)The intrusion of the nutrients into Bungo Channel varied at the decadal time scale. It generally decreased from 1980 to 2000, resulting in the decreases of the nutrient concentration and the spieces diversity of phytoplankton in Iyo-Nada.These are very important results showing the high possibility that the nutrient conditions and the ecosystems in the Seto Inland Sea can vary due to the variations of global ocean circul

地質学と地質学界の将来についての検討を行い学会の大規模な改革の方向が必要なことが明らかとなった。1)地質学の歴史とその日本の中でのこれまでの発展を総括し、地質学のもつ理念についてまとめた。それを地質学会ニュースにて配布し、議論を展開した。2)地質学を発展させる方策として大学など高等教育におけるありかたを検討した。その結果、地球惑星や地球環境として再編された学部および大学院教育の中で、学会として均質なカリキュラムを提供して、地質学の基礎的教育を展開する方向が打ち出された。また、最新の技術や情報処理に関する均質な再教育システムの必要性が明らかとなり、学会として方策をとることを確認した。3)平成14年度からの初等中等教育の再編成に伴い、学校教育とは独立した自然科学教育の普及と発展を学会として建設する必要性が確認された。博物館や各種のボランティア活動に学会としても旺盛に参加する方向が打ち出された。4)地質学の

To assess abnormal warming of temperature in southwest Japan's coastal seas during the twentieth century, we developed a 200 yr interannually resolved record of planktonic and benthic foraminiferal Mg/Ca-based temperature using neritic coastal sediment cores. The winter to late spring bottom temperature (50 m) record, based on benthic foraminiferal (Nonion japonicum) Mg/Ca ratios in the Bungo Channel (BC), showed consistent variation with observed temperatures on a five-year average basis. The BC bottom temperature record showed a significant increasing trend of 1.5 degrees C/100 yr during the twentieth century, which was never apparent in nineteenth century, That result suggests that our Mg/Ca-based thermometry approach using coastal benthic foraminifera can detect abnormally rising temperatures in neritic coastal seas in southwest Japan. The abnormal warming of winter to late spring bottom temperature in the BC contrasts with the lack of an increasing trend in the Globigerinoides ruber-based summer to autumn temperature for the upper 20 m in the slope region of southwest Japan and the lack of an increasing trend in the steric sea level in the region. These results indicate a warming trend of the neritic coastal ocean in southwest Japan, especially in winter to late spring. The timing of the onset of the prolonged abnormal high-temperature stage, which started in the early twentieth century, suggests a link of the neritic coastal ocean in Japan with human-induced global warming.

To assess abnormal warming of temperature in southwest Japan's coastal seas during the twentieth century, we developed a 200 yr interannually resolved record of planktonic and benthic foraminiferal Mg/Ca-based temperature using neritic coastal sediment cores. The winter to late spring bottom temperature (50 m) record, based on benthic foraminiferal (Nonion japonicum) Mg/Ca ratios in the Bungo Channel (BC), showed consistent variation with observed temperatures on a five-year average basis. The BC bottom temperature record showed a significant increasing trend of 1.5 degrees C/100 yr during the twentieth century, which was never apparent in nineteenth century, That result suggests that our Mg/Ca-based thermometry approach using coastal benthic foraminifera can detect abnormally rising temperatures in neritic coastal seas in southwest Japan. The abnormal warming of winter to late spring bottom temperature in the BC contrasts with the lack of an increasing trend in the Globigerinoides ruber-based summer to autumn temperature for the upper 20 m in the slope region of southwest Japan and the lack of an increasing trend in the steric sea level in the region. These results indicate a warming trend of the neritic coastal ocean in southwest Japan, especially in winter to late spring. The timing of the onset of the prolonged abnormal high-temperature stage, which started in the early twentieth century, suggests a link of the neritic coastal ocean in Japan with human-induced global warming.

The total carbon content analysis for Takashima-oki core extracted from Lake Biwa with time resolutions of approximately 150 years was used to reconstruct millennial-scale climate change in the East Asian monsoon region over the past 300 ka. The total carbon content of the Takashima-oki core is an indirect proxy for the East Asian summer monsoon, because the total carbon content reflects primary productivity within the lake, which is controlled by precipitation in the catchment area. Using these data, we clarify temporal variations in the East Asian summer monsoon prior to MIS 5, which were previously unresolved. The observed variations show a ∼1,500-year cycle that is also recorded by paleoclimate indices in the North Atlantic region. We propose that the East Asian summer monsoon underwent abrupt millennium-scale changes during interglacial stages such as MIS 5 and 7. © 2006 Springer-Verlag.

The total carbon content analysis for Takashima-oki core extracted from Lake Biwa with time resolutions of approximately 150 years was used to reconstruct millennial-scale climate change in the East Asian monsoon region over the past 300 ka. The total carbon content of the Takashima-oki core is an indirect proxy for the East Asian summer monsoon, because the total carbon content reflects primary productivity within the lake, which is controlled by precipitation in the catchment area. Using these data, we clarify temporal variations in the East Asian summer monsoon prior to MIS 5, which were previously unresolved. The observed variations show a -1,500-year cycle that is also recorded by paleoclimate indices in the North Atlantic region. We propose that the East Asian summer monsoon underwent abrupt millennium-scale changes during interglacial stages such as MIS 5 and 7.

The total carbon content analysis for Takashima-oki core extracted from Lake Biwa with time resolutions of approximately 150 years was used to reconstruct millennial-scale climate change in the East Asian monsoon region over the past 300 ka. The total carbon content of the Takashima-oki core is an indirect proxy for the East Asian summer monsoon, because the total carbon content reflects primary productivity within the lake, which is controlled by precipitation in the catchment area. Using these data, we clarify temporal variations in the East Asian summer monsoon prior to MIS 5, which were previously unresolved. The observed variations show a -1,500-year cycle that is also recorded by paleoclimate indices in the North Atlantic region. We propose that the East Asian summer monsoon underwent abrupt millennium-scale changes during interglacial stages such as MIS 5 and 7.

This paper reports the first reconstruction of a pollution history in tropical Asia from sediment cores. Four sediment core samples were collected from an offshore transect in the upper Gulf of Thailand and were analyzed for organic micropollutants. The cores were dated by measurement of 137 Cs and geochronometric molecular markers (linear alkylbenzenes, LABs; and tetrapropylene-type alkylbenzenes, TABs). Polychlorinated biphenyl (PCB) concentrations showed a subsurface maximum in layers corresponding to the 1970s, indicating the effectiveness of regulation of PCBs in Thailand. LAB concentrations increased over time, indicating the increase in input of sewage into the Gulf during the last 30 years. Hopanes, biomarkers of petroleum pollution, also increased over time, indicating that the inputs of automobile-derived hydrocarbons to the coastal zone has been increasing owing to the increased number of cars in Thailand since the 1950s. Polycyclic aromatic hydrocarbons (PAHs) increased in the layers corresponding to the 1950s and 1960s, probably because of the increased inputs of automobile-de rived PAHs. PAH concentrations in the upper layers corresponding to the 1970s and later remained constant or increased. The absence of a subsurface maximum of PAHs contrasts with results observed in industrialized countries. This can be explained by the facts that the Thai economy did not depend on coal as an energy source in the 1960s and that economic growth has continued since the 1970s to the present. The deposition flux of PAHs and hopanes showed a dramatic offshore decrease, whereas that of LABs was uniform. (C) 2007 Elsevier Ltd. All rights reserved.

This paper reports the first reconstruction of a pollution history in tropical Asia from sediment cores. Four sediment core samples were collected from an offshore transect in the upper Gulf of Thailand and were analyzed for organic micropollutants. The cores were dated by measurement of 137 Cs and geochronometric molecular markers (linear alkylbenzenes, LABs; and tetrapropylene-type alkylbenzenes, TABs). Polychlorinated biphenyl (PCB) concentrations showed a subsurface maximum in layers corresponding to the 1970s, indicating the effectiveness of regulation of PCBs in Thailand. LAB concentrations increased over time, indicating the increase in input of sewage into the Gulf during the last 30 years. Hopanes, biomarkers of petroleum pollution, also increased over time, indicating that the inputs of automobile-derived hydrocarbons to the coastal zone has been increasing owing to the increased number of cars in Thailand since the 1950s. Polycyclic aromatic hydrocarbons (PAHs) increased in the layers corresponding to the 1950s and 1960s, probably because of the increased inputs of automobile-de rived PAHs. PAH concentrations in the upper layers corresponding to the 1970s and later remained constant or increased. The absence of a subsurface maximum of PAHs contrasts with results observed in industrialized countries. This can be explained by the facts that the Thai economy did not depend on coal as an energy source in the 1960s and that economic growth has continued since the 1970s to the present. The deposition flux of PAHs and hopanes showed a dramatic offshore decrease, whereas that of LABs was uniform. (C) 2007 Elsevier Ltd. All rights reserved.

This paper reports the first reconstruction of a pollution history in tropical Asia from sediment cores. Four sediment core samples were collected from an offshore transect in the upper Gulf of Thailand and were analyzed for organic micropollutants. The cores were dated by measurement of 137 Cs and geochronometric molecular markers (linear alkylbenzenes, LABs; and tetrapropylene-type alkylbenzenes, TABs). Polychlorinated biphenyl (PCB) concentrations showed a subsurface maximum in layers corresponding to the 1970s, indicating the effectiveness of regulation of PCBs in Thailand. LAB concentrations increased over time, indicating the increase in input of sewage into the Gulf during the last 30 years. Hopanes, biomarkers of petroleum pollution, also increased over time, indicating that the inputs of automobile-derived hydrocarbons to the coastal zone has been increasing owing to the increased number of cars in Thailand since the 1950s. Polycyclic aromatic hydrocarbons (PAHs) increased in the layers corresponding to the 1950s and 1960s, probably because of the increased inputs of automobile-de rived PAHs. PAH concentrations in the upper layers corresponding to the 1970s and later remained constant or increased. The absence of a subsurface maximum of PAHs contrasts with results observed in industrialized countries. This can be explained by the facts that the Thai economy did not depend on coal as an energy source in the 1960s and that economic growth has continued since the 1970s to the present. The deposition flux of PAHs and hopanes showed a dramatic offshore decrease, whereas that of LABs was uniform. (C) 2007 Elsevier Ltd. All rights reserved.

This paper reports the first reconstruction of a pollution history in tropical Asia from sediment cores. Four sediment core samples were collected from an offshore transect in the upper Gulf of Thailand and were analyzed for organic micropollutants. The cores were dated by measurement of 137 Cs and geochronometric molecular markers (linear alkylbenzenes, LABs; and tetrapropylene-type alkylbenzenes, TABs). Polychlorinated biphenyl (PCB) concentrations showed a subsurface maximum in layers corresponding to the 1970s, indicating the effectiveness of regulation of PCBs in Thailand. LAB concentrations increased over time, indicating the increase in input of sewage into the Gulf during the last 30 years. Hopanes, biomarkers of petroleum pollution, also increased over time, indicating that the inputs of automobile-derived hydrocarbons to the coastal zone has been increasing owing to the increased number of cars in Thailand since the 1950s. Polycyclic aromatic hydrocarbons (PAHs) increased in the layers corresponding to the 1950s and 1960s, probably because of the increased inputs of automobile-de rived PAHs. PAH concentrations in the upper layers corresponding to the 1970s and later remained constant or increased. The absence of a subsurface maximum of PAHs contrasts with results observed in industrialized countries. This can be explained by the facts that the Thai economy did not depend on coal as an energy source in the 1960s and that economic growth has continued since the 1970s to the present. The deposition flux of PAHs and hopanes showed a dramatic offshore decrease, whereas that of LABs was uniform. (C) 2007 Elsevier Ltd. All rights reserved.

The Seto Inland Sea formed during a rise in sea level following the Last Glacial Maximum. There are various studies of geological and geographical aspects of the formation of the Seto Inland Sea. This paper deals with temporal variations in sea conditions deduced from acoustic profiles around Nakajima Island, in the eastern part of the Houyo Islands, to the western side of Takanawa Peninsula within the western Seto Inland Sea. Our results indicate that seawater invaded this area approximately 11,000 years ago, when there were small bays to the north and southeast of Nakajima Island. Subsequent to this, the Imoko and Sekido Straits formed with caldrons. Following the formation of Takahama Strait, the shallow Ozu Bank began to form at the eastern part of the Tsurushima Strait.

The Seto Inland Sea formed during a rise in sea level following the Last Glacial Maximum. There are various studies of geological and geographical aspects of the formation of the Seto Inland Sea. This paper deals with temporal variations in sea conditions deduced from acoustic profiles around Nakajima Island, in the eastern part of the Houyo Islands, to the western side of Takanawa Peninsula within the western Seto Inland Sea. Our results indicate that seawater invaded this area approximately 11,000 years ago, when there were small bays to the north and southeast of Nakajima Island. Subsequent to this, the Imoko and Sekido Straits formed with caldrons. Following the formation of Takahama Strait, the shallow Ozu Bank began to form at the eastern part of the Tsurushima Strait.

This study reconstructed environmental changes to the seafloor associated with reclamation in Mishou Bay, Bungo Channel, Japan, based on measurements of sediment grain size, organic matter and sulfur contents of surface sediments and data from sediment cores. Grain size within sediment cores from the middle of Mishou Bay decreased from the beginning of the 1800s to the 1900s. In contrast, a grain size profile from the river mouth shows a gradual increase in grain size up through the sediment core. These changes in grain size indicate a decrease in tidal current velocity within the middle of the bay and that the delta system is gradually prograding from the river mouth. Records of organic matter composition and sulfur contents indicate that the effect of the river on seafloor sedimentation became stronger during the nineteenth century. These changes are related to reclamation during the late 1700s and 1800s. The decrease in sea area resulting from reclamation probably led to a decrease in tidal prism and current velocity. It is likely that the increasing effect of river water on sedimentation is associated with reclamation-related progradation of the river delta system.

This study reconstructed environmental changes to the seafloor associated with reclamation in Mishou Bay, Bungo Channel, Japan, based on measurements of sediment grain size, organic matter and sulfur contents of surface sediments and data from sediment cores. Grain size within sediment cores from the middle of Mishou Bay decreased from the beginning of the 1800s to the 1900s. In contrast, a grain size profile from the river mouth shows a gradual increase in grain size up through the sediment core. These changes in grain size indicate a decrease in tidal current velocity within the middle of the bay and that the delta system is gradually prograding from the river mouth. Records of organic matter composition and sulfur contents indicate that the effect of the river on seafloor sedimentation became stronger during the nineteenth century. These changes are related to reclamation during the late 1700s and 1800s. The decrease in sea area resulting from reclamation probably led to a decrease in tidal prism and current velocity. It is likely that the increasing effect of river water on sedimentation is associated with reclamation-related progradation of the river delta system.

Two sediment cores recovered in the central part of Daihai Lake in north-central China were analysed at 2- to 4- cm intervals for total inorganic and organic carbon ( TIC and TOC) concentrations. The TIC concentration is inferred to reflect temperatures over the lake region and an increase in the TIC concentration implies an increase in the temperature. TOC concentration is considered to reflect the precipitation in the lake basin and higher TOC concentrations denote more precipitations. Thus AMS C-14 time series of the TIC and TOC records of Daihai Lake sediments uncovers a detailed history of changes in temperature and precipitation in north- central China during the last c. 12 000 yr. The Holocene, an epoch of postglacial warmth, started c. 11 500 cal. yr BP, and can be subdivided into three stages: the early ( c. 11 500 - 8100 cal. yr BP), middle ( c. 8100 - 3300 cal. yr BP) and the late Holocene ( c. 3300 - 0 cal. yr BP). The climate was warm and dry during the early Holocene, warm and wet during the middle Holocene, and in the late Holocene became cooler and drier but displayed a relatively warmer and wetter interval between c. 1700 and 1300 cal. yr BP. The Holocene Climatic Optimum, defined as a postglacial episode of both megathermal and megahumid climate, might have occurred in north- central China between c. 8100 and 3300 cal. yr BP, and the climate during this period was variable and punctuated by cool and/ or dry events. We infer that changes in the temperature were directly controlled by changes in summer solar radiation in the Northern Hemisphere resulting from progressive changes in the Earth's orbital parameters. Whereas an increase in the monsoonal precipitation could be closely related to an increase in the sea surface temperature of the low- latitude Pacific Ocean, an increase in the temperature and size of the Western Pacific Warm Pool and a westward shifted and strengthened Kuroshio Current in the western Pacific.

Two sediment cores recovered in the central part of Daihai Lake in north-central China were analysed at 2- to 4- cm intervals for total inorganic and organic carbon ( TIC and TOC) concentrations. The TIC concentration is inferred to reflect temperatures over the lake region and an increase in the TIC concentration implies an increase in the temperature. TOC concentration is considered to reflect the precipitation in the lake basin and higher TOC concentrations denote more precipitations. Thus AMS C-14 time series of the TIC and TOC records of Daihai Lake sediments uncovers a detailed history of changes in temperature and precipitation in north- central China during the last c. 12 000 yr. The Holocene, an epoch of postglacial warmth, started c. 11 500 cal. yr BP, and can be subdivided into three stages: the early ( c. 11 500 - 8100 cal. yr BP), middle ( c. 8100 - 3300 cal. yr BP) and the late Holocene ( c. 3300 - 0 cal. yr BP). The climate was warm and dry during the early Holocene, warm and wet during the middle Holocene, and in the late Holocene became cooler and drier but displayed a relatively warmer and wetter interval between c. 1700 and 1300 cal. yr BP. The Holocene Climatic Optimum, defined as a postglacial episode of both megathermal and megahumid climate, might have occurred in north- central China between c. 8100 and 3300 cal. yr BP, and the climate during this period was variable and punctuated by cool and/ or dry events. We infer that changes in the temperature were directly controlled by changes in summer solar radiation in the Northern Hemisphere resulting from progressive changes in the Earth's orbital parameters. Whereas an increase in the monsoonal precipitation could be closely related to an increase in the sea surface temperature of the low- latitude Pacific Ocean, an increase in the temperature and size of the Western Pacific Warm Pool and a westward shifted and strengthened Kuroshio Current in the western Pacific.

Two sediment cores recovered in the central part of Daihai Lake in north-central China were analysed at 2- to 4-cm intervals for grain-size distribution. Grain-size distributions of the lake sediments are inferred to be a proxy for past changes in East Asian monsoon precipitation, such that greater silt-size percentage and higher median grain size reflect increased monsoonal precipitation rates. The grain-size record of Daihai Lake sediments spanning the last ca 10,000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages: the Early, Middle and Late Holocene. During the Early Holocene before ca 7900 cal yr BP, the median grain size (Md) and the silt-fraction content were relatively low and constant, suggesting relatively low precipitation over the lake region. The Middle Holocene between ca 7900 and 3100 cal yr BP was marked by intensified and highly variable monsoonal precipitation, as indicated by high and variable Md values and silt contents of the lake sediments. During this period, average precipitation rate gradually increased from ca 7900 to 6900 cal yr BP, displayed intense oscillations between ca 6900 and 4400 cal yr BP, and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr BP. Although generally high during the Middle Holocene, both the Md and the silt content assumed distinctly low values at the short intervals of ca 6500-6400, 6000-5900, 5700-5600, 4400-4200 cal yr BP, implying that monsoonal precipitation might have been significantly reduced during these intervals. During the Late Holocene since ca 3100 cal yr BP, grain-size values suggest that precipitation decreased. However, during the Late Holocene, relatively higher Md values and silt contents occurring between ca 1700 to 1000 cal yr BP may denote an intensification of hydrological cycles in the lake area. Changes in the East Asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the Earth's orbital parameters, but also may have been closely related to variations in the temperature and size of the Western Pacific Warm Pool, in the intensity of the El Nino-Southern Oscillation, and in the path and strength of the North Equatorial Current in the western Pacific. (C) 2005 Elsevier B.V. All rights reserved.

Two sediment cores recovered in the central part of Daihai Lake in north-central China were analysed at 2- to 4-cm intervals for grain-size distribution. Grain-size distributions of the lake sediments are inferred to be a proxy for past changes in East Asian monsoon precipitation, such that greater silt-size percentage and higher median grain size reflect increased monsoonal precipitation rates. The grain-size record of Daihai Lake sediments spanning the last ca 10,000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages: the Early, Middle and Late Holocene. During the Early Holocene before ca 7900 cal yr BP, the median grain size (Md) and the silt-fraction content were relatively low and constant, suggesting relatively low precipitation over the lake region. The Middle Holocene between ca 7900 and 3100 cal yr BP was marked by intensified and highly variable monsoonal precipitation, as indicated by high and variable Md values and silt contents of the lake sediments. During this period, average precipitation rate gradually increased from ca 7900 to 6900 cal yr BP, displayed intense oscillations between ca 6900 and 4400 cal yr BP, and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr BP. Although generally high during the Middle Holocene, both the Md and the silt content assumed distinctly low values at the short intervals of ca 6500-6400, 6000-5900, 5700-5600, 4400-4200 cal yr BP, implying that monsoonal precipitation might have been significantly reduced during these intervals. During the Late Holocene since ca 3100 cal yr BP, grain-size values suggest that precipitation decreased. However, during the Late Holocene, relatively higher Md values and silt contents occurring between ca 1700 to 1000 cal yr BP may denote an intensification of hydrological cycles in the lake area. Changes in the East Asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the Earth's orbital parameters, but also may have been closely related to variations in the temperature and size of the Western Pacific Warm Pool, in the intensity of the El Nino-Southern Oscillation, and in the path and strength of the North Equatorial Current in the western Pacific. (C) 2005 Elsevier B.V. All rights reserved.

長期的な海岸地形保全には, 海岸流砂系全体の土砂動態の解明と理解が必要である.本研究では, 皆生海岸において, 沖合の美保湾で表層堆積物と柱状試料を採取し, 粒度分析と鉛-210法堆積速度測定を組み合わせ, 日野川・皆生海岸から美保湾内への土砂移動量を推定した. 底質調査結果から, 堆積物は美保湾内にほとんどトラップされ域外への移動はないと判断される. 海岸を形成している細粒砂以上の土砂の美保湾内への単位面積当り移動量は泥堆積域で約200ton/km2/年, 湾中央部で約1, 800ton/km2/年となる.これを海域全体に適用すると, 皆生海岸漂砂系外の水深9m以深に移動する細粒砂以上の年間土砂量は95, 000ton/年となる.

Seismic survey using "Bubble Pulser" was carried out in Miho Bay off eastern Shinji lowland, Southwest Japan. Based on the seismic profiles, geologic history since the Late Pleistocene was reconstructed. Three distinctive reflectors, formed before the Jomon transgression were recognized in seismic profiles. The lowest reflector was formed before the last interglacial stage. The distinctive reflector in Sakaiminato area was recognized along old scour hole. The uppermost reflector was formed during the last glacial maximum. The geologic history since the late Pleistocene in the eastern Shinji lowland can be divided into following five stages. Stage 1 (MIS 6) was the regression period before the last interglacial. At stage 2 (MIS 5), the sea level was the same as of now, and also the old Yumigahama Peninsula was formed at the position where it is at the present. The erosional scour hole at the northern end of Yumigahama Peninsula was formed at this stage by the tidal current erosion. Topographical features similar to the present basin was formed. At stage 3 (MIS 4-3), scour hole was buried by clastic materials at the northern end of Yumigahama Peninsula. At stage 4 (MIS 2), valley system was formed during the late Pleistocene at eastern Shinji Lowland. At stage 5 (Holocene), present geographical features are formed after the Jomon transgression.

The particle density of BDP 98 core sediments (total length 674m) drilled in Lake Baikal in 1998 is controlled by their diatom valve contents. Deposition of abundant diatom valves occurs during warm periods, and clay particles with few diatom valves deposit during cold periods. Paleoclimates around Lake Baikal are reconstructed based on these facts.<br>Climatic history recorded in the BDP 98 core during the last 6.5Ma can be roughly classified into three phases based on the variation of particle density: Phase 3 (6.5-3.2Ma) of constant lower density, Phase 2 (3.2-1.8Ma) of abrupt shift to higher density, and Phase 1 (1.8Ma-to present) of high amplitude density changes with overall higher density. Climatic changes shown in the particle density profile of Phases 3 to 1 show a rough similarity with the δ¹⁸O record of benthic foraminifers of marine sediment cores.<br>Particle density of the BDP 98 core of Quaternary, Phase 1, also has good similarity with the δ¹⁸O record in a scale of tens of thousands years. Therefore, sediment ages and sedimentation rates of this period can be estimated by comparing the particle density profile of the BDP 98 core with the oxygen isotope ratio curve. Further, the biogenic silica content in sediments can also be estimated by particle density of the BDP 98 core postulating some other factors. Diatom production (biogenic silica flux), calculated from both biogenic silica content in sediments and sedimentation rate, fluctuates periodically in concordance with the δ¹⁸O record. These results also reveal some local characteristics of the Lake Baikal region such as cold periods of 1.77-1.45Ma and 0.9-0.8Ma, distinct cold events in interglacial periods since MIS 9, and the presence of a clear 100-kyr-frequency since 1.5Ma.

Lake-level changes inferred from seismic surveying and core sampling of the floor of Lake Baikal near the Selenga River delta can be used to constrain regional climatic history and appear to be correlated to global climate changes represented by marine oxygen isotope stages (MIS). The reflection pattern and correlation to the isotope stages indicate that the topset and progradational foreset sediments of the deltas formed during periods of stable lake levels and warm climatic conditions. During warm stages, the lake level was high, and during cold stages it was low. The drop in the lake level due to cooling from MIS 5 through MIS 4 is estimated to be 33-38 m; from MIS 3 through MIS 2, it fell an additional 11-15 m. Because the lake level is chiefly controlled by evaporation and river input, we infer that more water was supplied to Lake Baikal during warm stages. (C) 2004 University of Washington. All rights reserved.

Lake-level changes inferred from seismic surveying and core sampling of the floor of Lake Baikal near the Selenga River delta can be used to constrain regional climatic history and appear to be correlated to global climate changes represented by marine oxygen isotope stages (MIS). The reflection pattern and correlation to the isotope stages indicate that the topset and progradational foreset sediments of the deltas formed during periods of stable lake levels and warm climatic conditions. During warm stages, the lake level was high, and during cold stages it was low. The drop in the lake level due to cooling from MIS 5 through MIS 4 is estimated to be 33-38 m; from MIS 3 through MIS 2, it fell an additional 11-15 m. Because the lake level is chiefly controlled by evaporation and river input, we infer that more water was supplied to Lake Baikal during warm stages. (C) 2004 University of Washington. All rights reserved.

DH99a sediment core recovered at the center of Daihai Lake in north-central China was analyzed at 4-cm intervals for pollen assemblage and concentration. The pollen record spanning the last ca 10,000 yr revealed a detailed history of vegetation and climate changes over the Daihai Lake region during the Holocene. From ca 10,250 to 7900 cal yr BP, and herbs and shrubs dominated the lake basin in company with patches of mixed pine and broadleaved forests, indicating a mild and dry climatic condition. Over this period, the woody plants displayed an increasing trend, which may suggest a gradual increase in warmth and humidity. The period between ca 7900 and 4450 cal yr BP exhibits large-scale covers of mixed coniferous and broadleaved forests, marking a warm and humid climate. Changes in the composition of the forests indicate that both temperature and precipitation displayed obvious fluctuations during this period, i.e., cool and humid ca 7900-7250 cal yr BP, warm and slightly humid ca 7250-6050 cal yr BP, warm and humid between ca 6050 and 5100 cal yr BP, mild and slightly humid ca 5100-4800 cal yr BP, and mild and humid ca 4800-4450 cal yr BP. The period can be viewed as the Holocene optimum (characterized by a warm and moist climate) of north-central China, with the maximum (dominated both by warmest temperatures and by richest precipitations) occurring from ca 6050 to 5100 cal yr BP. During the period of ca 4450-2900 cal yr BP, the woody plants declined, and the climate generally became cooler and drier than the preceding period. This period is characterized by a cold, dry episode from ca 4450 to 3950 cal yr BP, a warm, slightly humid interval between ca 3950 and 3500 cal yr BP and a mild, slightly dry episode from ca 3500 to 2900 cal yr BP, and appears to be a transition from warm and humid to cold and dry climatic conditions. Since ca 2900 cal yr ago, the forests disappeared and the vegetation density decreased, reflecting a cool and dry climate. However, a relative recovery of the woody plants occurring between ca 1700 and 1350 cal yr BP may denote an increase both in temperature and in precipitation. Fluctuations in the climatic condition of the Daihai Lake region were not only related to changes in the seasonal distribution of solar insolation and in the axis and intensity of the ocean current in the western North Pacific but were also closely linked to variations in the position and strength of polar high-pressure systems and in the pattern and intensity of the Westerly winds. (C) 2004 Elsevier Ltd. All rights reserved.

DH99a sediment core recovered at the center of Daihai Lake in north-central China was analyzed at 4-cm intervals for pollen assemblage and concentration. The pollen record spanning the last ca 10,000 yr revealed a detailed history of vegetation and climate changes over the Daihai Lake region during the Holocene. From ca 10,250 to 7900 cal yr BP, and herbs and shrubs dominated the lake basin in company with patches of mixed pine and broadleaved forests, indicating a mild and dry climatic condition. Over this period, the woody plants displayed an increasing trend, which may suggest a gradual increase in warmth and humidity. The period between ca 7900 and 4450 cal yr BP exhibits large-scale covers of mixed coniferous and broadleaved forests, marking a warm and humid climate. Changes in the composition of the forests indicate that both temperature and precipitation displayed obvious fluctuations during this period, i.e., cool and humid ca 7900-7250 cal yr BP, warm and slightly humid ca 7250-6050 cal yr BP, warm and humid between ca 6050 and 5100 cal yr BP, mild and slightly humid ca 5100-4800 cal yr BP, and mild and humid ca 4800-4450 cal yr BP. The period can be viewed as the Holocene optimum (characterized by a warm and moist climate) of north-central China, with the maximum (dominated both by warmest temperatures and by richest precipitations) occurring from ca 6050 to 5100 cal yr BP. During the period of ca 4450-2900 cal yr BP, the woody plants declined, and the climate generally became cooler and drier than the preceding period. This period is characterized by a cold, dry episode from ca 4450 to 3950 cal yr BP, a warm, slightly humid interval between ca 3950 and 3500 cal yr BP and a mild, slightly dry episode from ca 3500 to 2900 cal yr BP, and appears to be a transition from warm and humid to cold and dry climatic conditions. Since ca 2900 cal yr ago, the forests disappeared and the vegetation density decreased, reflecting a cool and dry climate. However, a relative recovery of the woody plants occurring between ca 1700 and 1350 cal yr BP may denote an increase both in temperature and in precipitation. Fluctuations in the climatic condition of the Daihai Lake region were not only related to changes in the seasonal distribution of solar insolation and in the axis and intensity of the ocean current in the western North Pacific but were also closely linked to variations in the position and strength of polar high-pressure systems and in the pattern and intensity of the Westerly winds. (C) 2004 Elsevier Ltd. All rights reserved.

The fluvial quartz flux (FQF, g cm(-2) ka(-1)) to Lake Biwa of central Japan is developed as a proxy of variations in palaeoprecipitation over the lake catchment. Lake Biwa sediments spanning the last c. 145 ka are characterized by 4 main intervals when the FQF values were significantly greater than 2 g cm(-2) ka(-1), and 5 main periods during which FQF values were lower. Three of the intervals with high FQF values occur from c. 128 to 78 ka BP, with peak values at c. 122, 101 and 82 ka BP; the fourth of two narrow peaks exists between c. 48 and 35 ka BP. Three main periods with lower FQF values intervene between intervals of high FQF values, and two others lie before c. 128 ka BP and after c. 35 ka BP. The data imply that palaeoprecipitation over the lake catchment increased during the intervals of high FQF values, and decreased during the periods of lower FQF values. High FQF values between c. 48 and 35 ka BP are interpreted to reflect an effective runoff of meltwater from the surrounding mountains during the interstade of the last glaciation. Relatively low FQF values during the early Holocene are interpreted to reveal a sluggish northward retreat of the polar front in the North Pacific Ocean that suppressed the northward advance of the summer monsoonal front and regional precipitation. During the last interglaciation, the increasing trend of FQF values is interpreted to indicate a progressive expansion of the Sea of Japan related to the rise in global sea level, which increased moisture advection to, and precipitation within, the Lake Biwa region.

The fluvial quartz flux (FQF, g cm(-2) ka(-1)) to Lake Biwa of central Japan is developed as a proxy of variations in palaeoprecipitation over the lake catchment. Lake Biwa sediments spanning the last c. 145 ka are characterized by 4 main intervals when the FQF values were significantly greater than 2 g cm(-2) ka(-1), and 5 main periods during which FQF values were lower. Three of the intervals with high FQF values occur from c. 128 to 78 ka BP, with peak values at c. 122, 101 and 82 ka BP; the fourth of two narrow peaks exists between c. 48 and 35 ka BP. Three main periods with lower FQF values intervene between intervals of high FQF values, and two others lie before c. 128 ka BP and after c. 35 ka BP. The data imply that palaeoprecipitation over the lake catchment increased during the intervals of high FQF values, and decreased during the periods of lower FQF values. High FQF values between c. 48 and 35 ka BP are interpreted to reflect an effective runoff of meltwater from the surrounding mountains during the interstade of the last glaciation. Relatively low FQF values during the early Holocene are interpreted to reveal a sluggish northward retreat of the polar front in the North Pacific Ocean that suppressed the northward advance of the summer monsoonal front and regional precipitation. During the last interglaciation, the increasing trend of FQF values is interpreted to indicate a progressive expansion of the Sea of Japan related to the rise in global sea level, which increased moisture advection to, and precipitation within, the Lake Biwa region.

The fluvial quartz flux (FQF, g cm(-2) ka(-1)) to Lake Biwa of central Japan is developed as a proxy of variations in palaeoprecipitation over the lake catchment. Lake Biwa sediments spanning the last c. 145 ka are characterized by 4 main intervals when the FQF values were significantly greater than 2 g cm(-2) ka(-1), and 5 main periods during which FQF values were lower. Three of the intervals with high FQF values occur from c. 128 to 78 ka BP, with peak values at c. 122, 101 and 82 ka BP; the fourth of two narrow peaks exists between c. 48 and 35 ka BP. Three main periods with lower FQF values intervene between intervals of high FQF values, and two others lie before c. 128 ka BP and after c. 35 ka BP. The data imply that palaeoprecipitation over the lake catchment increased during the intervals of high FQF values, and decreased during the periods of lower FQF values. High FQF values between c. 48 and 35 ka BP are interpreted to reflect an effective runoff of meltwater from the surrounding mountains during the interstade of the last glaciation. Relatively low FQF values during the early Holocene are interpreted to reveal a sluggish northward retreat of the polar front in the North Pacific Ocean that suppressed the northward advance of the summer monsoonal front and regional precipitation. During the last interglaciation, the increasing trend of FQF values is interpreted to indicate a progressive expansion of the Sea of Japan related to the rise in global sea level, which increased moisture advection to, and precipitation within, the Lake Biwa region.

The fluvial quartz flux (FQF, g cm(-2) ka(-1)) to Lake Biwa of central Japan is developed as a proxy of variations in palaeoprecipitation over the lake catchment. Lake Biwa sediments spanning the last c. 145 ka are characterized by 4 main intervals when the FQF values were significantly greater than 2 g cm(-2) ka(-1), and 5 main periods during which FQF values were lower. Three of the intervals with high FQF values occur from c. 128 to 78 ka BP, with peak values at c. 122, 101 and 82 ka BP; the fourth of two narrow peaks exists between c. 48 and 35 ka BP. Three main periods with lower FQF values intervene between intervals of high FQF values, and two others lie before c. 128 ka BP and after c. 35 ka BP. The data imply that palaeoprecipitation over the lake catchment increased during the intervals of high FQF values, and decreased during the periods of lower FQF values. High FQF values between c. 48 and 35 ka BP are interpreted to reflect an effective runoff of meltwater from the surrounding mountains during the interstade of the last glaciation. Relatively low FQF values during the early Holocene are interpreted to reveal a sluggish northward retreat of the polar front in the North Pacific Ocean that suppressed the northward advance of the summer monsoonal front and regional precipitation. During the last interglaciation, the increasing trend of FQF values is interpreted to indicate a progressive expansion of the Sea of Japan related to the rise in global sea level, which increased moisture advection to, and precipitation within, the Lake Biwa region.

During the last 40 years, a huge amount of sandy sediments were dredged from the seafloor of the Seto Inland Sea and hence sea bottom environments have been suffering various kinds of damages. For example, bottom topography and sediments of Mihara-seto Sea have been greatly changed. In order to clarify the possibility and the speed of restoration of bottom topography and sediments, precise depth measuring survey using SeaBat in regular time intervals were carried out. Comparison of depth between the data of old navigation chart and our survey shows the disappearance of large sand dunes. At the central part of the surveyed area, where the water depth was less than 20 meters, water depth exceeds 50 meters at present. Sediment composition also changed in the dredged areas from sandy to gravelly bottom.
Sand waves stretching in north-south direction are distributed at the northern part of the surveyed area. Result of recent depth comparison indicates shifting of sand waves from the channels to the area far away. Their shifting velocity is estimated to be a maximum 40m per year. Their height, width and shifting velocity decreased toward the central part. However, other kinds of topographical changes were not observed in the surveyed area. In addition, based on bottom topography data obtained by SeaBat, it was found that the total volume of sediments in the area has not changed.
Based on the data obtained during the last two years, it was also clear that the undulations made by sand dredging buried into flat bottom by the shifting of sandy sediments.
Restoration of bottom topography in the area is less probable because of the little amount of sediments supplied by both channels but restoration of bottom sediments may be very much probable at areas of sand wave distribution.

During the last 40 years, a huge amount of sandy sediments were dredged from the seafloor of the Seto Inland Sea and hence sea bottom environments have been suffering various kinds of damages. For example, bottom topography and sediments of Mihara-seto Sea have been greatly changed. In order to clarify the possibility and the speed of restoration of bottom topography and sediments, precise depth measuring survey using SeaBat in regular time intervals were carried out. Comparison of depth between the data of old navigation chart and our survey shows the disappearance of large sand dunes. At the central part of the surveyed area, where the water depth was less than 20 meters, water depth exceeds 50 meters at present. Sediment composition also changed in the dredged areas from sandy to gravelly bottom.
Sand waves stretching in north-south direction are distributed at the northern part of the surveyed area. Result of recent depth comparison indicates shifting of sand waves from the channels to the area far away. Their shifting velocity is estimated to be a maximum 40m per year. Their height, width and shifting velocity decreased toward the central part. However, other kinds of topographical changes were not observed in the surveyed area. In addition, based on bottom topography data obtained by SeaBat, it was found that the total volume of sediments in the area has not changed.
Based on the data obtained during the last two years, it was also clear that the undulations made by sand dredging buried into flat bottom by the shifting of sandy sediments.
Restoration of bottom topography in the area is less probable because of the little amount of sediments supplied by both channels but restoration of bottom sediments may be very much probable at areas of sand wave distribution.

皆生海岸での長期的な海岸地形の変形過程を, 地層解析の視点から明らかにする調査をおこなった.同海岸での侵食・堆積域の代表各1測線で計9地点の地層をジオスライサーで連続的に採取した.採取試料の堆積物解析から地層を9ユニットに区分し, 各々の堆積環境を推定した.年代測定により, かんな流し開始以前, 同期問中, 同終了以降に, 地層を区別した.侵食域では, かんな流し期間中の堆積物が削剥されながら海岸線が後退し, 堆積域では, 堆積物の付加により堆積場の浅海化と堆積物の粗粒化を伴いながら海岸線が前進することを, 堆積物から認定した.

鳥取県皆生海岸では, 離岸堤群が完成するまで海岸線の後退が続いた.長期的に海岸を保全するには, 海岸の土砂動態と長期的な変遷過程を解明する必要がある.そのために, 日野川流域および皆生海岸で表層堆積物を採取し, また現在の侵食域と堆積域それぞれの沿岸海域でジオスライサーを用いて柱状試料を採取し, 粒度分析・鉱物組成分析・花粉分析と放射年代測定 (炭素-14と鉛-210) を組み合わせ, 日野川・皆生海岸流砂系の過去約400年間の環境変遷を推定した.侵食域では17世紀から「かんな流し」による急激な海岸線の前進があり, 20世紀初めのかんな流し終了に伴ない海岸侵食が始まった.堆積域では砂州の前進に起因する堆積速度の増大が認められた.

To investigate the Recent lacustrine sedimentary environments, 16 bottom samples and 2 cores from Lake Amida and 7 bottom samples and a single core from Lake Kamegaike, both in Ehime Prefecture, Japan, were analyzed in terms of sedimentation rates and grain size distribution.<br>In Lake Amida, the average sedimentation rate calculated from a core taken at a shallower water depth site was 1.35cm/y, which is faster than the average rate of 0.92cm/y calculated from another core taken at a deeper site in the same lake. In the core from Lake Kamegaike, an increase of the sedimentation rate from 0.54cm/y to 1.36cm/y was detected at the core depth of 60cm. The surface of this increase is dated to be ca. 1954, which roughly corresponds the time when a water gate was constructed. This increase would be explained as an effect of the gate that should have prevented the suspended matter in the lake to flow out into the sea.<br>The sedimentation rates obtained in this study were generally larger than those in other Japanese lakes. This may be due to a probable higher rate of soil erosion and transportation, because the area around the lakes of this study has been exploited largely for agriculture such as orange fields. In addition, the variation of depth profiles of Pb-214 and K of the three cores is well correlated to artifact events such as shore protection and road works, which suggests that such events should have affected even on the distribution of nuclides.<br>These results have given some important clues to study sedimentation models and environmental changes of lakes.

Bottoun environmental changes during the past 100 years in Kitanada Bay, Southwest Japan were reconstructed, based on the data on grain size, total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS) concentrations, ratio of total organic carbon to total nitrogen (C/N) and to total sulfur (C/S) in surface sediments and sediments cores. The grain size distribution pattern in surface sediment at the present study site showed predominance of coarser sediments around the bay mouth and more finer towards the bay interior, suggesting that tidal current is more swift around the bay mouth and its velocity decreases toward bay interior. The present results indicate a stagnant hydrodynamic condition in inner Kitanada Bay. High levels of TOC, TN and TS concentrations around fish farming cages in the north suggest the use of large quantities of organic substances for fish farming. Benthic environment has become highly reductive due to the supply of organic substances in combination with stagnant hydrodynamic environment. TOC and TN concentrations in sediment cores (33-79cm) showed an increase from 1970's when fish farming started. This result suggests that Kitanada Bay has become eutrophic due to fish farming. At the same time, grain size profiles show a decrease in grain size toward the top, while it is reverse in the southern and bay mouth area. This result suggests a transformation in the hydrodynamic environment by the resistance perpetrated on tidal current by fish cages. In the northern area of Kitanada Bay, hydrodynamic environment has become stagnant. In the southern and bay mouth area where no fish cages are observed, tidal current has become more agile. As the result, sea water exchange has become more active, and bottom environment has become less reductive.

During the last 40 years, a huge amount of sandy sediments were dredged from the seafloor of the Seto Inland Sea and hence sea bottom environments have been suffering various kinds of damages. For example, bottom topography and sediments of Mihara-seto Sea have been greatly changed. In order to clarify the possibility and the speed of restoration of bottom topography and sediments, precise depth measuring survey using SeaBat in regular time intervals were carried out. Comparison of depth between the data of old navigation chart and our survey shows the disappearance of large sand dunes. At the central part of the surveyed area, where the water depth was less than 20 meters, water depth exceeds 50 meters at present. Sediment composition also changed in the dredged areas from sandy to gravelly bottom.
Sand waves stretching in north-south direction are distributed at the northern part of the surveyed area. Result of recent depth comparison indicates shifting of sand waves from the channels to the area far away. Their shifting velocity is estimated to be a maximum 40m per year. Their height, width and shifting velocity decreased toward the central part. However, other kinds of topographical changes were not observed in the surveyed area. In addition, based on bottom topography data obtained by SeaBat, it was found that the total volume of sediments in the area has not changed.
Based on the data obtained during the last two years, it was also clear that the undulations made by sand dredging buried into flat bottom by the shifting of sandy sediments.
Restoration of bottom topography in the area is less probable because of the little amount of sediments supplied by both channels but restoration of bottom sediments may be very much probable at areas of sand wave distribution.

For high-resolution reconstruction of climate change in Lake Biwa catchment area, we have analyzed concentration of diatom valve (DVC; valves g^-1) and diatom valve flux (DVF; valves cm^-2 yr^-1) for the past 140ka using the upper part of a 140-m core from Takashima-oki. Time resolution of sampling intervals is 150 to 500 years.<br>The DVF records show higher values during the Holocene (0-7ka) and the last interglacial age (68-135ka) than the present value. By contrast, during the last glacial age (7-68ka) the DVF is relatively low. In addition, the DVF record shows millennial-scale fluctuations over the last 140ka.<br>We have checked the relationship among the DVF, sedimentation rate, and climatic parameters such as temperature, snow depth, and precipitation. We concluded that the DVF reflects diatom productivity, which is strongly controlled by the precipitation level of the preceding summer period.<br>If the DVF can be a proxy for precipitation, the characteristics of the precipitation around Lake Biwa are summarized as follow: the low-level duration during 56-68ka, corresponding to the oxygen-isotope stage 4, is longer than that during the LGM (oxygen-isotope stage 2); after 8ka, the levels gradually rise toward 5.5ka, and increased levels occur at 3 and 5.5ka.<br>The pattern and the episodic events in the record of the DVF in the Lake Biwa sediment can be very closely correlated to the Dansgaard-Oeschger episodes in the North Atlantic climatic record which is revealed from the Greenland ice core. This concordance indicates a possible teleconnection between the precipitation over Japan and temperature over the North Atlantic. The possible mechanism of the teleconnection might be related to changes in westerlies which are driven by temperature changes over the North Atlantic.

Total organic carbon (TOC), total nitrogen (TN), and fossil pollen compositions have been measured at 1- to 2-cm intervals for the upper part of an all-core sample recovered from Lake Nojiri in 1988. TOC and TN contents rapidly increase from the depth zone of 610 to 540cm, with one reversal. The fossil pollen of cool-temperate deciduous trees also becomes abundant around this horizon. Subarctic conifers decrease from 730 to 540cm depth, with some fluctuations.<br>Judging from these results and sediment ages estimated with ¹⁴C dates and some marker tephras, the Last Glacial Maximum is reconstructed to have been around 20, 000yrsBP. A warming suggested by increasing fossil pollen of cool-temperate deciduous trees started around 15, 000yrsBP and lasted until about 11, 000yrsBP (about 12, 000calBP), being intercalated with some cooler phases. The warming was especially accelerated around 12, 000yrs BP (14, 000calBP). The cool phases recognized in the Late Last Glacial Age can be compared with the three Dryas periods in Northern Europe by pattern matching, but their ages are older by about 2, 000 to 3, 000 years. This discordance may be a key to understand the mechanism which controls short-term climate changes.<br>A slight cooling phase is also recognized around 9, 000yrsBP. This phase is characterized by decreases in TOC and TN contents, but is not so clearly seen in pollen compositions. This phase may be correlated to the Boreal period in Northern Europe.<br>This study presents the first detailed illustration of climate changes though the termination of the Last Glacial Age in central Japan. The studied core offers a useful standard of climate history, because it can be precisely correlated using the numerous marker tephras.

In order to study sedimentation environments and sedimentation rates of Lake Nakaumi, Shimane and Tottori Prefectures, the Pb-210 and Cs-137 radioactivities were measured in 14 cores taken on the September in 1996. The sedimentation rate varied in the range of 0.1-1.9 cm/y. Those of the western and southern areas are larger, because some rivers run into the lake at there. Detrital materials are transported through the Ohhashi river, the Iu (Ou) river and the Iinashi river and deposit near the estuaries. Such a high sedimentation rate is supported by the chemical components such as U and K (Pb-214 and K-40) in the sediments, because they suggest the provenance. The fluxes and inventories of radionuclides that indicate the rate and the amount of accumulation correlated with the sedimentation rates. The inventories of excess Pb-210 and Cs-137 are in good correlation with each other (R=0.87). However the ratios of excess Pb-210 inventory to Cs-137 inventory for the cores of Lake Nakaumi are about 11, between those for the Sea of Japan (about 38) and Lake Shinji (about 5). The sources of radionuclides are supposed to be terrestrial fallout, suspended particles carried from rivers and seawater. Although the terrestrial fallout may be the major source, it is considered that the others are more important in contrast to the case of Lake Shinji.

Detailed diatom records from a 140-m sediment core with a time resolution of approximately 1000-1500 yr were obtained from Lake Biwa to examine possible correlations between diatom concentrations and paleoclimatic changes during the last approximately 400 ka. In the sediments, the diatom assemblages are generally dominated by planktonic diatoms. The diatom stratigraphy is characterized by four zones with distinctly higher concentration values and 12 horizons with low concentration values. Diatom records from the 140-m core and another core indicate that these changes were not local phenomena, but occurred throughout the lake basin. Comparison of diatom concentration records with pollen records from Lake Biwa sediments indicates that higher diatom concentrations represent warmer and wetter climatic conditions, and that lower concentrations represent colder and drier climatic conditions. Comparison of diatom records from Lake Biwa with marine oxygen isotopic records shows that the number of peaks and their relative amplitudes are similar in both profiles
therefore, peaks and drops in diatom concentration profile might correlate with most oxygen isotopic events. This finding indicates that during approximately the last 400 ka, the changes in diatom concentration, represented as diatom productivity in Lake Biwa, correlate closely with global paleoclimatic changes at the scale of the Milankovitch cycle (precession cycles of 23 and 19 ka), and that diatom concentration was higher during warm events and lower during cold or cooling events. © 2002 Elsevier Science B.V. All rights reserved.

Detailed diatom records from a 140-m sediment core with a time resolution of approximately 1000-1500 yr were obtained from Lake Biwa to examine possible correlations between diatom concentrations and paleoclimatic changes during the last approximately 400 ka. In the sediments, the diatom assemblages are generally dominated by planktonic diatoms. The diatom stratigraphy is characterized by four zones with distinctly higher concentration values and 12 horizons with low concentration values. Diatom records from the 140-m core and another core indicate that these changes were not local phenomena, but occurred throughout the lake basin. Comparison of diatom concentration records with pollen records from Lake Biwa sediments indicates that higher diatom concentrations represent warmer and wetter climatic conditions. and that lower concentrations represent colder and drier climatic conditions. Comparison of diatom records from Lake Biwa with marine oxygen isotopic records shows that the number of peaks and their relative amplitudes are similar in both profiles; therefore, peaks and drops in diatom concentration profile might correlate with most oxygen isotopic events. This finding indicates that during approximately the last 400 ka, the changes in diatom concentration, represented as diatom productivity in Lake Biwa, correlate closely with global paleoclimatic changes at the scale of the Milankovitch cycle (precession cycles of 23 and 19 ka), and that diatom concentration was higher during warm events and lower during cold or cooling events. (C) 2002 Elsevier Science B.V. All rights reserved.

In this study, Lake Biwa sediment covering the last 130ka is examined by analysis of the abundance of microscopic charcoal. Based on the abundance variation, the last 130ka is divided into four periods: 130ka to 10ka, 10ka to 1.5ka, 1.5ka to A. D. 1920, and since 1920. Charcoal abundance was low between about 130ka and 10ka, which indicates that climatic variation has not greatly influenced the frequency of forest fires. Charcoal abundance increased markedly from 10ka, and the highest abundance of charcoal between about 10ka and 1.5ka was associated with the ancient human activities after the Jomon period. The reduction of charcoal abundance since about 1.5ka was probably derived from changes in ancient human activities: the shift to agricultural activities and so on. Charcoal abundance has increased since 1920 due to combustion of organic substances for fuel. Consequently, charcoal abundance evidence suggests that variation of fire frequency around Lake Biwa was affected more by human activities than by climatic variation.

Seismo-turbidite layers are deposited at the foot of the steep slope of the half graben in which Lake Biwa has accumulated. Sedimentary studies, especially of grain-size distribution of selected turbidites provide excellent information for clarifying the distinctive features of general seismo-turbidites. Development of the two constituent sublayers (lower sandy sublayer and upper silt sublayer), lack or limited appearances of traction-indicating structures and characteristic grain-size distribution in the two constituent sublayers are most remarkable and significant. The characteristic grain-size distribution features are coarse tail grading in a relatively thick sandy sublayer, exceptionally rapid distribution grading through the thin boundary interval between the two sublayers, height increase and fluctuation of the silt mode, and high clay content. Brief discussion was made on the causes of these sedimentary features. The need and importance of further comparative studies of various turbidites known triggering forces are emphasized. (C) 2000 Elsevier Science B.V. All rights reserved.

Seismo-turbidite layers are deposited at the foot of the steep slope of the half graben in which Lake Biwa has accumulated. Sedimentary studies, especially of grain-size distribution of selected turbidites provide excellent information for clarifying the distinctive features of general seismo-turbidites. Development of the two constituent sublayers (lower sandy sublayer and upper silt sublayer), lack or limited appearances of traction-indicating structures and characteristic grain-size distribution in the two constituent sublayers are most remarkable and significant. The characteristic grain-size distribution features are coarse tail grading in a relatively thick sandy sublayer, exceptionally rapid distribution grading through the thin boundary interval between the two sublayers, height increase and fluctuation of the silt mode, and high clay content. Brief discussion was made on the causes of these sedimentary features. The need and importance of further comparative studies of various turbidites known triggering forces are emphasized. (C) 2000 Elsevier Science B.V. All rights reserved.

High-resolution, three-dimensional submarine topographic mapping of Kaihara, a shallow marine sandridge, off Nogutsuna Island in the Seto Inland Sea, Japan was carried out using a narrow multibeam echo sounder SEABAT 8101. Through the mapping, two kinds of topographic features suggesting directions of sediment transport, such as subaqueous dunes and obstacle marks, were recognized. The dunes are seen on the southern part of Kaihara and show asymmetrical forms with steeper west-northwestern and northwestern slopes suggesting that the directions of sediment transport are west-northwestward and northwestward. In the northeastern part, three obstacle marks having E-W and WSW-ENE trends are seen to the west and west-southwest of artificial fish-gathering constructions. The directions of sediment transportation in this area are thus westward and west-southwestward. As a large submarine caldron is situated on the east of Kaihara and surface sediments become finer from the caldron to Kaihara, the sediments comprising the Kaihara sandridge are interpreted to have transported from the caldron by tidal currents, which are known as most likely agents of sediment transportation in the Seto Inland Sea, and accumulated where the currents dispersed and lost their energy.

The loess-paleosol sequence on the Loess Plateau of central China constitutes an excellent proxy record of variations in Asian monsoon climate over the past 2.5 Ma. Magnetic susceptibility of loess and paleosols has been used as a proxy indicator for summer monsoon intensity, while the median diameter of quartz isolated from the loess and paleosols has been regarded as a proxy index of the strength of winter monsoon winds that were responsible for most of the dust transport. The eolian quartz flux to Lake Biwa of central Japan during the last 130,000 yr provides direct information on variations of the East Asian winter monsoon; whereas the fluvial quartz flux reflects significant changes in paleoprecipitation over the lake area. The intervals of high eolian quartz flux values during marine oxygen isotope substages 5d and 5b, and stages 4 and 2 correspond to the periods of large quartz median diameter values of the Chinese loess and paleosols, indicating strengthened winter monsoon winds; whereas the intervals of high fluvial quartz flux values during isotope substages 5e, 5c, and 5a, and stages 3 and 1 correlate to the periods of high magnetic susceptibility values of the Chinese loess and paleosols, suggesting increased summer monsoon intensity. Variations in winter monsoon strength indicated by the eolian quartz flux and quartz median diameter proxies bear a general inverse relation to those in summer monsoon intensity inferred from the fluvial quartz flux and magnetic susceptibility proxies. (C) 1998 Elsevier Science Ltd. All rights reserved.

The loess-paleosol sequence on the Loess Plateau of central China constitutes an excellent proxy record of variations in Asian monsoon climate over the past 2.5 Ma. Magnetic susceptibility of loess and paleosols has been used as a proxy indicator for summer monsoon intensity, while the median diameter of quartz isolated from the loess and paleosols has been regarded as a proxy index of the strength of winter monsoon winds that were responsible for most of the dust transport. The eolian quartz flux to Lake Biwa of central Japan during the last 130,000 yr provides direct information on variations of the East Asian winter monsoon; whereas the fluvial quartz flux reflects significant changes in paleoprecipitation over the lake area. The intervals of high eolian quartz flux values during marine oxygen isotope substages 5d and 5b, and stages 4 and 2 correspond to the periods of large quartz median diameter values of the Chinese loess and paleosols, indicating strengthened winter monsoon winds; whereas the intervals of high fluvial quartz flux values during isotope substages 5e, 5c, and 5a, and stages 3 and 1 correlate to the periods of high magnetic susceptibility values of the Chinese loess and paleosols, suggesting increased summer monsoon intensity. Variations in winter monsoon strength indicated by the eolian quartz flux and quartz median diameter proxies bear a general inverse relation to those in summer monsoon intensity inferred from the fluvial quartz flux and magnetic susceptibility proxies. (C) 1998 Elsevier Science Ltd. All rights reserved.

Radionuclides distribution and chemical components in the two cored sediments in the two Chinese lakes were studied, and the rates of sedimentation were determined. The average sedimentation rate of Lake Daihai (DH-1), the inland lake, was about 0.3cm/y, which is in the range of those reported in some Japanese lakes. It is suggested that the chemical composition varied a little as the source of sediments changed. On the other hand, the average sedimentation rate of Lake Blackspring (KS-2), the closed lake, was calculated to be about 0.1cm/y, which is 1/3 of DH-1. The samples around 16-18cm depth of KS-2 core where water contents and chemical components varied largely, were estimated to have deposited 160-180y ago, and thereafter the different sediment might deposit. The inventories of Cs-137 in the Chinese lakes were larger than those expected from its relationships with excess Pb-210 in the Japanese lakes. This fact indicates the larger amount of Cs-137 fallout in China than in Japan, and a little loss of Cs-137 in the Chinese lakes.

Eolian quartz flux (EQF, g cm(-2) (10(3) yr)(-1)) to Lake Biwa, central Japan, provides direct information on variations of the East Asian winter monsoon, Lake Biwa sediments spanning the past ca, 145,000 yr are characterized by two main periods when EQF values were significantly greater than 5.50 g cm(-2) (10(3) yr)(-1), and two main intervals during which EQF values were lower, Two periods with EQF values &gt;5.50 g cm(-2) (103 yr)(-1) occurred from ca. 145,000 to 125,000 and 73,000 to 13,000 yr B.P., while times of lower EQF values occurred from ca. 125,000 to 73,000 yr B.P. and around ca. 5500 yr B.P. Between ca. 125,000 and 73,000 yr B,P., three minimum EQF values and two intervening peaks of slightly higher EQF values are recorded. EQF increased markedly from ca. 73,000 to 13,000 yr B.P., whereas between ca. 53,000 and 20,000 yr B.P. the values recorded were relatively lower than those recorded during either the preceding or the subsequent episodes, The data imply that the East Asian winter monsoon strengthened during the periods when EQF values were high, and weakened during the intervals with low EQF values. The EQF record of Lake Biwa can be correlated with the grain-size record of the quartz fraction in Chinese loess and with the SPECMAP marine delta(18)O record, However, the EQF record apparently lags ca, 5000 yr behind the loess and delta(18)O records during stage 6/5 and 2/1 transitions and ca, 10,000 yr during stage 5/4 transition, These apparent lags could be due to problems with the chronology; alternatively, they may imply that the eolian quartz flux depended more on the extent of dust source regions than on wind intensity during these transitions. (C) 1997 University of Washington.

Eolian quartz flux (EQF, g cm(-2) (10(3) yr)(-1)) to Lake Biwa, central Japan, provides direct information on variations of the East Asian winter monsoon, Lake Biwa sediments spanning the past ca, 145,000 yr are characterized by two main periods when EQF values were significantly greater than 5.50 g cm(-2) (10(3) yr)(-1), and two main intervals during which EQF values were lower, Two periods with EQF values &gt;5.50 g cm(-2) (103 yr)(-1) occurred from ca. 145,000 to 125,000 and 73,000 to 13,000 yr B.P., while times of lower EQF values occurred from ca. 125,000 to 73,000 yr B.P. and around ca. 5500 yr B.P. Between ca. 125,000 and 73,000 yr B,P., three minimum EQF values and two intervening peaks of slightly higher EQF values are recorded. EQF increased markedly from ca. 73,000 to 13,000 yr B.P., whereas between ca. 53,000 and 20,000 yr B.P. the values recorded were relatively lower than those recorded during either the preceding or the subsequent episodes, The data imply that the East Asian winter monsoon strengthened during the periods when EQF values were high, and weakened during the intervals with low EQF values. The EQF record of Lake Biwa can be correlated with the grain-size record of the quartz fraction in Chinese loess and with the SPECMAP marine delta(18)O record, However, the EQF record apparently lags ca, 5000 yr behind the loess and delta(18)O records during stage 6/5 and 2/1 transitions and ca, 10,000 yr during stage 5/4 transition, These apparent lags could be due to problems with the chronology; alternatively, they may imply that the eolian quartz flux depended more on the extent of dust source regions than on wind intensity during these transitions. (C) 1997 University of Washington.

The record of the biogenic silica flux (BSF, g cm(-2) (10(3) yr)(-1)) in Lake Biwa reflects changes in diatom productivity in the lake and provides information regarding changes in paleoclimatic conditions, The BSF record of Lake Biwa demonstrates five periods over the past ca, 145,000 yr when the BSF values were significantly greater than 7.5 g cm(-2) (10(3) yr)(-1), and five intervals when they were lower, The data imply that paleoclimatic conditions were warmer and wetter from ca. 123,000 to 115,000, 103,000 to 95,000, 88,000 to 72,000, 57,000 to 32,000 yr B.P., and around ca. 6000 yr B.P, when the BSF values were greater, and relatively dry and cold from ca. 141,000 to 123,000 yr B.P. and during intervals between two of the five warm and wet episodes when the BSF values were lower. Time series of the BSF record can be correlated with the record of biogenic silica content in Lake Baikal and the marine oxygen isotope stages 1 through 6. Furthermore, the BSF values varied with much higher amplitude during the last interglaciation than during the last glaciation, probably implying that the diatom productivity in Lake Biwa was likewise more variable and had a larger range under interglacial conditions than under glacial conditions. (C) 1997 University of Washington.

The record of the biogenic silica flux (BSF, g cm(-2) (10(3) yr)(-1)) in Lake Biwa reflects changes in diatom productivity in the lake and provides information regarding changes in paleoclimatic conditions, The BSF record of Lake Biwa demonstrates five periods over the past ca, 145,000 yr when the BSF values were significantly greater than 7.5 g cm(-2) (10(3) yr)(-1), and five intervals when they were lower, The data imply that paleoclimatic conditions were warmer and wetter from ca. 123,000 to 115,000, 103,000 to 95,000, 88,000 to 72,000, 57,000 to 32,000 yr B.P., and around ca. 6000 yr B.P, when the BSF values were greater, and relatively dry and cold from ca. 141,000 to 123,000 yr B.P. and during intervals between two of the five warm and wet episodes when the BSF values were lower. Time series of the BSF record can be correlated with the record of biogenic silica content in Lake Baikal and the marine oxygen isotope stages 1 through 6. Furthermore, the BSF values varied with much higher amplitude during the last interglaciation than during the last glaciation, probably implying that the diatom productivity in Lake Biwa was likewise more variable and had a larger range under interglacial conditions than under glacial conditions. (C) 1997 University of Washington.

Studies on sedimentary fluxes of quartz grains carried into Lake Biwa, central Japan by the streams and rivers from the surrounding catchments of the lake show that fluvial quartz flux (FQF, g/cm²·10³yr) offers direct information on variations of paleoprecipitation in the lake area. Lake Biwa sediments spanning the last ca. 145, 000 years are characterized generally by four main intervals when the FQF values were significantly greater than 2.00 g/cm²·10³yr, and five main periods during which FQF values were lower. Three of the peaks with FQF values >2.00g/cm²·10³yr occur from ca. 128, 000 to 78, 000yrs BP, and culminated at ca. 122, 000, 101, 000, and 82, 000yrs BP. Another one comprising three narrow peaks concentrated between ca. 48, 000 and 26, 000yrs BP. This interval of triple peaks displays much higher FQF values than during either the preceding or subsequent episodes. The data imply that paleoprecipitation in the lake area was greater during the intervals with high FQF values, which coincide with marine oxygen isotope substages 5e, 5c, and 5a, and stage 3, and was relatively less during isotope stages 6, 4, and 2.

In 1986, Takashima-oki core boring was carried out in the central part of Lake Biwa. The sediment samples are composed mainly of silty clay sediments extending over the past ca. 400, 000 years. The sediments are intercalated with many volcanic ash layers, and thus are rich in time control. We analyzed for diatom with high-resolution on the sediments, and have obtained the following results, <br>1. The variations of the total number of diatom valves in 1g dry sample, which is interpreted as the fluctuations of diatom productivity, have occurred widely off the main basin of Lake Biwa.<br>2. The profile of the total number of diatom valves during the past 400, 000 years shows good correlation with the marine oxygen isotope profile. The fluctuation of the total number of diatom valves in Lake Biwa reflects global climate changes sensitively. That is to say, the total number of diatom valves increases under warm and wet paleoclimatic conditions, and decreases under cold and dry conditions.<br>Stages 1 through 9 of the marine oxygen isotope stratigraphy can be recognized. Moreover, for the short-time fluctuations of the total number of diatom valves, correlation can be made with the detailed marine oxygen isotope stratigraphy. The Biwako diatom horizons (BDH) with rare diatom valves are well correlated with the coldclimate events of the marine oxygen isotope stratigraphy. The BDHs at 8.5m, 19.0m, 28.0m, 35.3m, 43.3m, 53.6m, 63.5m, 80.2m, 86.9 and 93.5m in depth correspond to stages 2.2, 4, 5.2 (5b), 5.4 (5d), 6.2, 6.4, 6.6, 7.4, 8.2 and 8.4, respectively.

Studies on sedimentary fluxes of quartz grains carried into Lake Biwa, central Japan by the streams and rivers from the surrounding catchments of the lake show that fluvial quartz flux (FQF, g/cm²·10³yr) offers direct information on variations of paleoprecipitation in the lake area. Lake Biwa sediments spanning the last ca. 145, 000 years are characterized generally by four main intervals when the FQF values were significantly greater than 2.00 g/cm²·10³yr, and five main periods during which FQF values were lower. Three of the peaks with FQF values >2.00g/cm²·10³yr occur from ca. 128, 000 to 78, 000yrs BP, and culminated at ca. 122, 000, 101, 000, and 82, 000yrs BP. Another one comprising three narrow peaks concentrated between ca. 48, 000 and 26, 000yrs BP. This interval of triple peaks displays much higher FQF values than during either the preceding or subsequent episodes. The data imply that paleoprecipitation in the lake area was greater during the intervals with high FQF values, which coincide with marine oxygen isotope substages 5e, 5c, and 5a, and stage 3, and was relatively less during isotope stages 6, 4, and 2.

Some 20 turbidites were collected in the uppermost 3 m of surface sediments in Lake Biwa, southwest Japan. These turbidites coil-elate in age to historical earthquakes that caused severe loss of lives and property near Lake Biwa. The age of each turbidite was estimated precisely, based on sedimentation rate (by weight) and the age of tephra markers below the turbidites. The magnitudes and epicentas of major historical earthquakes during the last 1300 years are available from historical documents. Empirical equations relating intensity, distance to the epicentre and magnitude enable us to calculate the ground shaking at Lake Biwa from these historical earthquakes. Earthquakes having intensity stronger than grade IVL on the Japan Meteorological Agency (JMA) earthquake scale, that is 44 gal acceleration at Lake Biwa, all coincide with the turbidite ages. This intensity is apparently the lower threshold for turbidity-current initiation in Lake Biwa.

Some 20 turbidites were collected in the uppermost 3 m of surface sediments in Lake Biwa, southwest Japan. These turbidites correlate in age to historical earthquakes that caused severe loss of lives and property near Lake Biwa. The age of each turbidite was estimated precisely, based on sedimentation rate (by weight) and the age of tephra markers below the turbidites. The magnitudes and epicentres of major historical earthquakes during the last 1300 years are available from historical documents. Empirical equations relating intensity, distance to the epicentre and magnitude enable us to calculate the ground shaking at Lake Biwa from these historical earthquakes. Earthquakes having intensity stronger than grade IVL on the Japan Meteorological Agency (JMA) earthquake scale, that is 44 gal acceleration at Lake Biwa, all coincide with the turbidite ages. This intensity is apparently the lower threshold for turbidity-current initiation in Lake Biwa.

The sequence stratigraphic analysis on the latest Pleistocene-Holocene incised-valley fill of Nita Bay of the Tsushima Islands, Western Japan has been done, using the TN core taken from the dalta front of the Nita River delta. The sequence of the incised-valley fill is divided into three parts, 1) the lowest part: gravelly fluvial sediment, 2) the lower part: fining-upward deltaic sediment consisting of gravelly intertidal sediment and overlying sandy to muddy delta front sediment containing abundant plant fragments, and 3) the upper part: coarsening-upward deltaic sediment consisting of muddy prodelta sediment and sandy delta front sediment. These facies and stacking patterns have been controlled by the latest Pleistocene to Holocene sea-level changes. The maximum flooding surface situated between the lower and upper parts coincides with the end of Holocene sea-level rise, which is 6 ka in age from an age-known tephra of K-Ah tephra. The transgressive succession is characterized by thick, subtidal sediments containing abundant plant fragments and coarse grains. Regressive successionis characterized by upward-coarsening, thick delta front and prodelta sediments and formed a clear contrast between delta front and prodelta facies.

The 1888 eruption of Bandai volcano, Fukushima Pref. Northeast Japan is famous for its large debris avalanche that killed 461 people. After the eruption, the avalanche deposit dammed up the old river and made many lakes such as Lake Hibara, Lake Akimoto etc. To investigate the area of the avalanche deposit and structure of the deposit, side scan sonar survey was carryed out at Lake Hibara. Bathymetry and side scan sonar clearly showed the lake bottom fabric. The avalanche deposit with many hummocky mounds reached 11 km from the volcanic edifice, which collapsed in 1888, and covered former existed river which shows smooth bottom surface. The avalanche deposit was, also, divided into two parts from the density and the size of the mounds.

In order to re-examine an earlier theory on the subdivision of the soft sediment which is sometimes called "Alluvium" in enclosed coastal seas, an acoustic survey was carried out in Osaka Bay. Although the tools which were used for the surveys differ, the depths of acoustic reflectors in the old and the new records correspond well. The results of the new acoustic survey and drilling show good correlation between the depths of the reflectors and those of tephra seams and facies boundaries, for example, between those of mud and sand or those of sand and gravel.<br>The earlier stratigraphic subdivision was based chiefly on differences in reflection patterns; the importance of reflectors as time markers was neglected. Consequently, the boundary between Alluvium A and Alluvium B in the earlier stratigraphy apparently crosses some reflectors. The distribution boundary between Alluvium A and Alluvium B on the sea floor was regarded as corresponding to that between sand and mud in the same area. This is, however, not correct. The combined thickness of Alluvium A and Alluvium B, which was supposed to equal that of total "Alluvium", only corresponds to that of the upper and middle muddy parts, excluding the channel areas.<br>On the basis of these facts, stratigraphy in enclosed coastal seas can be better understood, as follows. Unconsolidated muddy sediment, which forms the upper and middle parts of "Alluvium" in Japanese enclosed coastal seas, cannot be stratigraphically subdivided. The sandy part near the channel area and the muddy parts in the central bay and the area far away from the channels (both on the bottom surface) are in the relation of a contemporaneous heterotopic facies. The most obvious reflector in the acoustic record, which had been regarded as the boundary between "Alluvium" and the underlying strata, is better understood as the boundary between the upper and middle muddy "Alluvium" and the underlying "lower Alluvium". The previous stratigraphy for the subdivision of unconsolidated sediment in other enclosed coastal seas around the Japanese Islands should be corrected in a similar way.

A method to estimate mass sedimentation rate is proposed in the following procedure; 1. drafting of isopach map of sediment based on the depth of specific reflector in acoustic (UNIBOOM) record, 2. making vertical prone of standard water content in sediments at selected point(s) in the area, 3. conversion of the data of water content into those of dry weight and cumulative dry weight of sediments, 4. age determination of the critical reflector, (in general, some of reflectors are age-known tephras.) 5. making a standard curve of " thickness versus sedimentation rate" through dividing cumulative dry weight in each depth by sedimentary age of the reflector, 6. conversion of thickness of sediments into sedimentation rate by using that curve. In Lake Biwa, depths of reflectors beneath the bottom coincide with those of the top of corresponding sediment layers which contain more than 1% of sand. Consequently, thickness of sediment can be caluculated easily based on the acoustic record. Vertical profile of water content is obtainde using drilled samples in the area. It is converted into that of dry weight and cumulative dry weight profiles, assuming that specific gravity of sediment grains to be 2.65 and that all pores in sediments are filled with water. In Lake Biwa, the top of Kikai-Akahoya tephra (K-Ah; aged ca. 6300 Y. B. P.) makes a good reflector. Mean sedimetation rate in the whole area of Lake Biwa, obtained by this method, is 38.2 mg/cm_2/year. Comparison between the results and the rates by 210Pb, 137Cs and specified tephra methods shows good correlation, with a few exceptions. The result of isotope method show a little smaller values than those of acoustic method. There are several factors to make an error in this methd. They are; 1. difference between sediment thickness obtaind through acoustic record and the real thickness, caused by vertical change of acoustic velocity (This is, however, negligible in Lake Biwa.), 2. areal difference of water content, 3. difference in degrees of compaction with time and depth, 4. age determination error (As for 14C dating, they are within a few percent.), 5. sporadic sedimentation, such as turbidite, 6. change of sedimentation rate in recent years caused by the anthropogenic deformation of surrounding land area. As there are many active and non active volcanoes in Japan, many volcanic ash seams can be found in the lake and shallow sea sediments. Consequently, this method will be applied in various lakes and shallow sea areas with muddy sediments.