The summer climate of northern Japan since the last glacial period has likely been determined by atmospheric and oceanic dynamics, such as changes in the North Pacific High, the position of the westerlies, the Kuroshio Current, the Tsushima Warm Current (TWC), and the East Asian summer monsoon. However, it is unclear which factor has been most important. In this study, we analyzed leaf wax δ13C and δD and glycerol dialkyl glycerol tetraethers (GDGTs) in sediments from Lake Kushu, Rebun Island, northern Japan, and discuss changes in climate over the past 17,000 years. The GDGT-based temperature, the averaged chain length, δ13C and δD of long-chain n-fatty acids indicated that the climate was cold during the Oldest Dryas period ∼16 ka and warm in the early Middle Holocene from ∼9 to 6 ka. This climate change is consistent with the sea surface temperature in the Kuroshio–Oyashio transition, but inconsistent with changes in the TWC in the Sea of Japan. The results imply that the summer climate of northern Japan was controlled mainly by changes in the development of the North Pacific High via changes in the position of the westerly jet and East Asian summer monsoon rainfall, whereas the influence of the TWC was limited over a millennial timescale.

An increase in nutrient levels due to eutrophication has considerable effects on lake ecosystems. Cladocerans are intermediate consumers in lake ecosystems; thus, they are influenced by both the bottom-up and top-down effects that occur as eutrophication progresses. The long-term community succession of cladocerans and the effects cladocerans experience through the various eutrophication stages have rarely been investigated from the perspective of the early-stage cladoceran community assemblage during lake formation. In our research, long-term cladoceran community succession was examined via paleolimnological analysis in the currently eutrophic Lake Fukami-ike, Japan. We measured the concentration of total phosphorus and phytoplankton pigments and counted cladoceran and other invertebrate subfossils in all layers of collected sediment cores, and then assessed changes in the factors controlling the cladoceran community over a 354-year period from lake formation to the present. The cladoceran community consisted only of benthic taxa at the time of lake formation. When rapid eutrophication occurred and phytoplankton increased, the benthic community was replaced by a pelagic community. After further eutrophication, large Daphnia and high-order consumers became established. The statistical analysis suggested that bottom-up effects mainly controlled the cladoceran community in the lake's early stages, and the importance of top-down effects increased after eutrophication occurred. Total phosphorus and phytoplankton pigments had positive effects on pelagic Bosmina, leading to the replacement of the benthic cladoceran community by the pelagic one. In contrast, the taxa established posteutrophication were affected more by predators than by nutrient levels. A decrease in planktivorous fish possibly allowed large Daphnia to establish, and the subsequent increase in planktivorous fish reduced the body size of the cladoceran community.

Magnitude 8 megathrust earthquakes that have generated large tsunamis with wave heights of >5 m in coastal areas of southwestern Japan have occurred every 100–150 years along the Nankai–Suruga Trough, which marks the convergent boundary between the Eurasian and Philippine Sea plates. Using sedimentological, geochemical, and paleontological analyses, as well as 14C dating, we examined tsunami deposits in 12 sediment cores collected from the Hamatome lowland, Yaizu Plain, Shizuoka, which faces the Suruga Trough. Four sandy tsunami deposits (Sands 1–4) are identified in sediments deposited during the last 5000 years. Sand 1 was deposited between 805 and 405 BC, suggesting that only one tsunami left a sedimentological imprint in the Hamatome lowland lagoon during the period of ∼4000 years between 3090 and 2913 BC and the AD 1096 Eicho-Tokai earthquake. This very low frequency of tsunami inundation may suggest that this tsunami was larger than those typically associated with megathrust earthquakes. Sands 2–4 are correlated with tsunamis associated with the Eicho-Tokai, AD 1361 Shohei-Koan, and AD 1498 Meio-Tokai earthquakes, respectively. Our data indicate that a sand spit, which had previously protected the lagoon from oceanic waves, was abruptly destroyed following the AD 1096 Eicho-Tokai earthquake and did not re-form at the same location. This disappearance of the sand spit is inferred to have involved an earthquake-induced submarine landslide. The data presented in this paper, together with information obtained from historical documents, indicates that M8 megathrust earthquakes in AD 1096 and AD 1498 caused submarine landslides in the study area, resulting in coastal subsidence and damage to coastal areas additional to that caused by the tsunamis.

Megathrust earthquakes of magnitude ~ 8 and ensuing large tsunamis occur along the Nankai and Suruga troughs, central Japan, with a recurrence interval of 90–270 years since an AD 684 Hakuho earthquake. Historical records show that the AD 1854 Ansei-Tokai earthquake caused coseismic uplift of ~ 1 m in coastal areas west of Suruga Bay, including the Shimizu Plain, east Shizuoka Prefecture. The 1361 Shohei Tokai earthquake was accompanied by coseismic uplift, but no evidence has been found to indicate uplift before the earthquake. This study examined sediment cores recovered from the coastal beach ridge in the Shimizu Plain using sedimentological and paleontological analyses and radiocarbon dating. We infer from the results that a relative sea-level fall of 1.6 m took place at AD 398–428. This coincides with archeological evidence suggesting the occurrence of a large earthquake in west Shizuoka Prefecture in AD 400. This combination of evidence indicates that the drop in sea level was caused by coseismic uplift associated with a megathrust rupture along the Suruga Trough, with a recurrence interval of ~ 500–1000 years. The results also indicate that a megathrust rupture occurred in the region from the Eastern Nankai Trough to the Suruga Trough at ca. AD 400. [Figure not available: see fulltext.].

Reconstruction of natural hazards from tidal flat sediments is essential for assessment of coastal hazards, and is based on knowledge of recent sediments. This study therefore examined recent sediments deposited on a narrow, muddy tidal flat on Miura Peninsula, metropolitan Tokyo, Japan, by means of sedimentological analysis, C, N, and S elemental analysis, carbonate content, 137Cs dating, and analysis of benthic foraminifera (species composition and degree of preservation). 137Cs profiles of four sediment cores of ∼20 cm in length showed that the sediments were deposited after the release of 137Cs by the accident at the Fukushima No. 1 Nuclear Power caused by the Tohoku-oki tsunami at March 2011. Results of C/S ratios of mud fractions indicated that the intertidal deposits in the central bay are characterized by low C/S ratios (4.9–11.4) and the bayhead deposits of the upper intertidal and supratidal zones by higher ratios (13.9–24.9). A fluid–mud layer identified in the central bay had the same C/S ratios and carbonate contents as marine sediments, indicating that the fluid-mud deposits probably resulted from resuspension of mud caused by storm-wave action after March 2011. Faunal analysis of benthic foraminifera showed that very low density of foraminifera can be regarded as one of the defining characteristics of fluid-mud deposits.

Paleoenvironment and paleoclimate changes during the Little Ice Age (LIA)were investigated using sediments from Lake Hamana. This lagoon in central Japan is under a complicated climate system influenced by the East Asian summer monsoon (EASM), East Asian winter monsoon (EAWM), and strong typhoon events. Diatom assemblages and chemical components of a 1.3 m sediment core suggest historical events of rapid salination and cyclical ecosystem shifts accompanied by monsoon condition changes. Most research has indicated that Lake Hamana changed from a freshwater lake to a brackish lagoon because of the Meio earthquake in 1498 CE. However, based on results from the diatom assemblage and chemical components, this salination occurred because of changes in the Hamana paleoriver flow, and this change happened before the earthquake, around the mid-15th century. Furthermore, it is clear that Lake Hamana was an oligohaline lagoon before salination. The lithology of the lake sediments and the diatom assemblage changed during the LIA; sand, water, and total diatom contents decreased. However, the relative abundance of marine diatom taxa increased during the LIA. These changes were introduced by a weakening EASM coupled with low precipitation under low solar activity during the LIA. Several flood events represented by freshwater diatom taxa and magnetic susceptibility peaks co-occurred with strong El Niño events during the LIA. It is inferred that this strong El Niño during the LIA induced frequent typhoons causing floods in central Japan.

One of the most profound environmental changes in the Mesozoic occurred during the Pliensbachian-Toarcian (Pl/To) time interval, including massive black shale deposition across Pl/To boundary and early Toarcian Oceanic Anoxic Event (T-OAE). These events are associated with negative carbon isotope excursions (CIEs), but their temporal link with 12C-rich carbon injection, possibly related with Karoo-Ferrar volcanisms and carbon cycle feedbacks, such as terrestrial methanogenesis and methane hydrate dissociation, is still debated. Here we present a new chemostratigraphy of the carbon isotopic ratio of organic matter (δ13Corg) from Pl/To deep-sea successions, in conjunction with bio-astrochronology. The deep-sea successions are located at the Katsuyama and Sakahogi outcrops in the Inuyama area, Japan, and contain two black bedded chert intervals named T-BBCs 1 and 2, which have astrochronologic ages of 183.25–183.01 ± 0.2 Ma and 183.55–182.80 ± 0.2 Ma. Negative CIEs of ~2‰ and ~5‰ are recognized across the base of T-BBCs 1 and 2, respectively, which are correlated with Pl/To boundary and classical T-OAE in shallow marine sections based on biostratigraphy. Astrochronologic ages of the onset of T-BBCs 1 and 2 are within the errors of the oldest high-precision U-Pb ages of Karoo and Ferrar LIPs, respectively. These temporal relations suggest a link between the 12C-rich carbon injection associated with Karoo and Ferrar volcanism, and CIEs associated with widespread black shale deposition across the Pl/To and T-OAE, respectively. Obliquity cycles in classic T-OAE CIE could have linked with terrestrial methanogenesis and methane hydrate dissociation in high-latitudes areas, whereas 405-kyr pacing of termination of T-CIE and T-BBCs deposition would be related with decreased chemical weathering and nutrient supply under weaker monsoon intensity, and possibly suppressed methane cycle across the termination of Pl/To and T-OAE periods.

Alkenones are C35–C42 polyunsaturated ketone lipids that are commonly employed to reconstruct changes in sea surface temperature. However, their use in coastal seas and saline lakes can be hindered by species-mixing effects. We recently hypothesized that freshwater lakes are immune to species-mixing effects because they appear to exclusively host Group I haptophyte algae, which produce a distinct distribution of alkenones with a relatively consistent response of alkenone unsaturation to temperature. To evaluate this hypothesis and explore the geographic extent of Group I haptophytes, we analyzed alkenones in sediment and suspended particulate matter samples from lakes distributed throughout the mid- and high latitudes of the Northern Hemisphere (n=30). Our results indicate that Group I-type alkenone distributions are widespread in freshwater lakes from a range of different climates (mean annual air temperature range: −17.3–10.9 °C; mean annual precipitation range: 125–1657 mm yr−1; latitude range: 40–81°N), and are commonly found in neutral to basic lakes (pH > 7.0), including volcanic lakes and lakes with mafic bedrock. We show that these freshwater lakes do not feature alkenone distributions characteristic of Group II lacustrine haptophytes, providing support for the hypothesis that freshwater lakes are immune to species-mixing effects. In lakes that underwent temporal shifts in salinity, we observed mixed Group I/II alkenone distributions and the alkenone contributions from each group could be quantified with the RIK37 index. Additionally, we observed significant correlations of alkenone unsaturation (U37K) with seasonal and mean annual air temperature with this expanded freshwater lakes dataset, with the strongest correlation occurring during the spring transitional season (U37K=0.029⁎T−0.49; r2=0.60; p<0.0001). We present new sediment trap data from two lakes in northern Alaska (Toolik Lake, 68.632°N, 149.602°W; Lake E5, 68.643°N, 149.458°W) that demonstrate the highest sedimentary fluxes of alkenones in the spring transitional season, concurrent with the period of lake ice melt and isothermal mixing. Together, these data provide a framework for evaluating lacustrine alkenone distributions and utilizing alkenone unsaturation as a lake temperature proxy.

【災害のためプログラム中止】 平成30年北海道胆振東部地震により学術大会のプログラムが大幅に中止となりました．中止となったプログラムの講演要旨については，著者のプライオリティ保護の見地からJ-STAGEに公開し，引用可能とします．ただし，学術大会においては専門家による議論には供されていませんので「災害のためプログラム中止」との文言を付記します．（日本地質学会行事委員会）

【台風のためプログラム中止】台風18号により学術大会の一部プログラムが中止となりました．中止となったプログラムの講演要旨については，著者のプライオリティ保護の見地から今回に限りJ-STAGEに公開し，引用可能とします．ただし，学術大会においては専門家による議論には供されていませんので「台風のためプログラム中止」との文言を付記します．（日本地質学会行事委員会）

Varves (annually laminated sediments) are one of the most important terrestrial archives of past environments with an annual- to century-scale resolution (Brauer 2004). Sediments from small and deep maar lakes have great potential in this respect due to their specific conditions for the formation and preservation of the laminated sediments (Zolitschka and Negendank 1996; Zolitschka et al. 2000; Mingram et al. 2004).

In the densely populated region of East Asia, it is important to know the mechanism, scale, and frequency of heavy precipitation brought about during the monsoons and typhoons. However, observational data, which cover only several decades, are insufficient to examine the long-term trend of extreme precipitation and its background mechanism. In humid areas, the transport flux of a suspended detrital material through a river system is known to have an empirical power relationship with precipitation. Thus, the sedimentation flux of a fine detrital material could potentially be used as a proxy for reconstructing past heavy precipitation events. To test the idea that the sedimentation flux of detrital materials records past heavy precipitation events (e.g., typhoons), we focused on the detrital flux estimated from the annually laminated sediment of Lake Suigetsu, central Japan, which is capable of accurately correlating the age of detrital flux with the precipitation record. We first established a precise age model (error within ±1 year in average) beginning in 1920 A.D. on the basis of varve counting fine-tuned by correlation between event layers with historical floods. The flux of the detrital material (g/cm2/year) was estimated on the basis of Al2O3 content (wt%), dry bulk density (g/cm3), and sedimentation rate (cm/year) calculated from the age model. The detrital flux of background sedimentation showed a weak positive correlation with annual and monthly (June and September) precipitation excluding heavy precipitation that exceeded 100 mm/day. Furthermore, the thickness of instantaneous event layers, which corresponds to several maxima of detrital flux and is correlated with floods that occurred mainly during typhoons, showed a positive relationship with the total amount of precipitation that caused a flood event. This result suggests that the detrital flux maxima (deposition of event layers) record past extreme precipitation events that were likely associated with typhoons that hit the middle part of Honshu Island. Based on this result, the record of typhoon-caused flood events can go back to older period (e.g., last glacial period) on the basis of the occurrence, and thickness, or mass flux of event layers using long sediment cores from Lake Suigetsu.

Akita-sugi (Cryptomeria japonica, Japanese cedar that is grown in Akita) forests are among the most important for commercially valuable timber in Japan. Historically, these forests have been severely exploited, although now some parts of them are conserved. It is important to know the detailed history of the forests in order to utilize them sustainably in the future. This study analyzes the pollen in an annually laminated lake sediment core from Ichi-no-Megata on the Oga peninsula, Akita, Japan, to understand the history of Akita-sugi cedar forests. An age-depth model was developed based on the results of an accelerator mass spectrometer dating of 13 plant macrofossils from the surface to 422 cm in depth, the Towada-a tephra and other well-known event layers. The dominant pollen taxa were Cryptomeria and Fagus crenata by ad 1000. The first increase of Cryptomeria was detected around 1700 bc. By the 1st century ad, Cryptomeria forest was established. At that time, Cryptomeria was mixed with deciduous trees, mainly F. crenata. The pollen analysis found evidence that the main loss of woodland occurred during the 11th century ad, when forest lands were cleared for agriculture. Substantial natural forests nevertheless remained until the 16th century, after which forest resources were exhausted. Conservation and plantation activities took place later, but human activity in response to severe famines prevented the recovery of the forests. After the famine periods, the remaining forests recovered to their previous condition, but after World War II, the natural forests shrank further and plantation forests without deciduous trees were established over large areas.

Asian dust has a significant impact on the natural environment. Its variability on multiple timescales modulates the ocean biogeochemistry and climate. We demonstrate that temporal changes in the deposition flux of Aeolian dust recorded in sediments from Lake Suigetsu, central Japan, during the last century exhibit a continuous decreasing trend and a decadal-scale decrease in 1952-1974. The former decreasing trend can be explained by a decrease in the dust storm frequency at source regions due to the warming of Mongolia in the twentieth century, suggesting future decrease of Asian dust transport with further warming in Mongolia. Decadal-scale decrease of Aeolian dust is explained by weaker westerlies in lower latitudes in central Japan, reflecting a weaker Aleutian Low during the corresponding period. Decadal-scale westerly change probably causes north-south shifts of the dominant dust transport path, which affects subarctic northern Pacific Ocean biogeochemistry by changing the micronutrient iron supply.

To examine limnological conditions in Lake Ogawara on the Pacific coast of northwestern Japan, we investigated the magnetic properties of dredged bottom sediment originally collected from the lake in the summer of 2011. We used non-destructive methods to measure the low-field magnetic susceptibility shortly after sampling, and anhysteretic remanent magnetization (ARM) was assessed in 2012 and 2015. The ARM acquisition and demagnetization curves from littoral sites showed several patterns that reflect the provenance of the sediments. At water depths below 10 m, the magnetic susceptibility and ARM of greenish black mud with high organic content decreased considerably with the increase in water depth, but ARM increased slightly at water depths greater than 16 m. We also found that the magnetic concentrations of mud samples were reduced markedly during a period of storage for about 3 years. We attributed these reductions to diagenetic loss of magnetic minerals, which had been enhanced at deeper sites. It is possible that the ARM carriers in deeper areas were derived from authigenic formation of iron sulfide or from deposition of suspended matter in the hypolimnion water. We propose that the magnetic properties of surficial sediments are controlled by limnological stratification of the brackish lake water, thus possibly providing an analog for down-core variations of magnetic parameters associated with the modification of magnetic minerals during reductive diagenesis.

To examine limnological conditions in Lake Ogawara on the Pacific coast of northwestern Japan, we investigated the magnetic properties of dredged bottom sediment originally collected from the lake in the summer of 2011. We used non-destructive methods to measure the low-field magnetic susceptibility shortly after sampling, and anhysteretic remanent magnetization (ARM) was assessed in 2012 and 2015. The ARM acquisition and demagnetization curves from littoral sites showed several patterns that reflect the provenance of the sediments. At water depths below 10 m, the magnetic susceptibility and ARM of greenish black mud with high organic content decreased considerably with the increase in water depth, but ARM increased slightly at water depths greater than 16 m. We also found that the magnetic concentrations of mud samples were reduced markedly during a period of storage for about 3 years. We attributed these reductions to diagenetic loss of magnetic minerals, which had been enhanced at deeper sites. It is possible that the ARM carriers in deeper areas were derived from authigenic formation of iron sulfide or from deposition of suspended matter in the hypolimnion water. We propose that the magnetic properties of surficial sediments are controlled by limnological stratification of the brackish lake water, thus possibly providing an analog for down-core variations of magnetic parameters associated with the modification of magnetic minerals during reductive diagenesis.

Diatom, pollen, geomagnetic and geochemical analyses were carried out on a 3.6m long sediment core taken from Lake Buyan, a highland caldera lake in central Bali Island, to reconstruct the Holocene climate changes in equatorial southern Indonesia. The core represents ~8 thousand years sedimentation of organic-diatomaceous lake mud. Constant inclusion of benthic diatom fossils as main components indicated that suspension and inflow of littoral materials were the main sedimentary process. The core contained laminated sediments in two distinct intervals at 6.5-5.0 and 3.6-3.1calkyBP, and multi-proxy records showed generally drier climate in these sections especially at 3.6-3.1calkyBP. Lake bottom waters were more reducing condition in these laminated periods probably due to increased lake productivity by prolonged dry season and wind mixing. Laminae structures were made up of a layer composed of benthic diatoms and amorphous organic materials, and a layer made by only planktonic diatom fossils, each of which may represent rainy and dry period deposits. Although southern Indonesia shows clear Australian monsoon rainfall seasonality at present, counting of layer numbers showed interannual cycles of laminae formation. Prolonged dry seasons could obscured the rainfall seasonality in these periods, but precise depositional patterns were elusive. Unlaminated sections showed homogeneous sediment mixture of benthic, planktonic diatoms and more volume of terrigenous materials indicating wetter climate and seasonality similar to the present time. This was supported by the higher share of marsh environment pollens reflecting more stable lake level trends. The dry climate from 6.5calky BP was in line with the general perception of stronger ENSO dynamics from the mid Holocene due to weaker than before boreal summer insolation, but the sporadic appearances of dry periods imply the influence of regional climate forcings such as temporal migrations of inter tropical convergence zone (ITCZ). It was, however, possible that temporal shifts of large climate mode occurred in equatorial Pacific and Indian Oceans. Wettest climate was inferred from 3.1calkyBP to the present and this might reflect increased importance of Austral hemisphere atmospheric convection and subsequent southerly position of ITCZ in Austral summer time.

The Kiso-hinoki (Kiso-Japanese cypress, Chamaecyparis obtusa) woodland underwent severe deforestation in the early 17th century, then regenerated through conservation during the Edo period. Now, a suitable management strategy is sought in order to maintain its ecological function in the forest. To understand the vegetation changes and human impact, sediment cores were recovered from Lake Tadachi in the Kiso-hinoki cypress woodland in the central uphill region of Honshu island. In addition, stratigraphic pollen analysis on two cores (Nos. 6 and 10) and phytolith analysis on three strata of one core (No. 6) was conducted. The age-depth models were constructed based on 14C dating, greyscale analysis on the sediments, and the increasing level of Cryptomeria pollen (about a.d. 1960) from the pollen profiles. In all periods, the dominant pollen taxa were Cupressaceae and Quercus subgen. Lepidobalanus type. Our analysis indicates that after the commencement of Shikinen-sengu, which is the rebuilding of the Ise Grand Shrine every 20 years, Cupressaceae pollen decreased and the woodland was gradually replaced by Quercus subgen. Lepidobalanus. The percentages of Cupressaceae pollen decreased dramatically and the expansion of secondary woodlands was accompanied by an increase of Quercus subgen. Lepidobalanus in the early 17th century cal. a.d. However, depletion of the woodland was determined from a decrease in concentration of Quercus pollen. The conservation activity during the Edo period and after the Meiji Restoration brought about woodland recovery. However, based on our pollen and phytolith analysis, significant changes to the woodland habitats can be detected. These were probably due to human impacts, most notably in the years after World War II. Four major turning points as the result of human influence were identified: the 10th century, the late 16th century, the Meiji restoration (a.d. 1863), and the end of World War II. The original cypress woodland mixed with deciduous broad-leaved elements has been greatly reduced, preventing future cypress woodland regeneration after World War II.

Total organic carbon (TOC) and total nitrogen (TN) analyses have been performed for three core samples obtained recently from Lake Biwa, which include BIW07-5, BIW07-6, and BIW08-B cores. The TOC and TN data from these cores show similar stratigraphic changes and can be regarded as reliable records of biological productivity occurring in the lake during the past 52 ka. Pollen analysis data are also used to determine climate change during the past 40 ka by reconstructing meteorological parameters such as annual temperature and precipitation. Temporal changes in TOC concentration show detailed climate changes in tens-year intervals. Climate change of orbital scale are well recognized, demonstrating the change from MIS 3 to 1 associated with severe cold periods known as Heinrich events 1 to 5 and warm periods known as Greenland interstadials (GIS 1-13). These climate events in millennial time scale are also well supported by pollen characteristics and by modern analogue analysis. The good concordance of climate change between North Atlantic region and Japan is explained by a hypothesis that the intensity of the Arctic air mass controls the climate in both the North Atlantic and East Asia regions through the migration of the Arctic polar front. Although the average annual mean temperature in MIS 3 was 8.2 ± 0.8 (2. σ) °C, it varied largely and frequently among its substages. For example, 9.4 ± 2.0 °C was detected in a warm interstadial (GIS 8), and 6.3 ± 1.5 °C indicated in a cold stadial (Heinrich event 4). The average annual temperature was 4.5 ± 0.3 °C in MIS 2, when the average temperature of the coldest month was -7.3 ± 0.2 °C and that of the warmest month was 16.8 ± 0.2 °C. Through Termination 1, the annual mean temperature suddenly increased more than 5 °C, and the annual mean temperature became 11.2 ± 0.8 °C in early MIS 1, which is much lower than that of the present temperature. This low temperature estimation is attributed to the delay in expansion of evergreen broadleaf trees. The annual mean temperature in the late MIS 1 was as same as that of present meteorological observation. © 2014 Elsevier Ltd and INQUA.

New evidence from Lake Buyan, a 65-m-deep caldera lake in central Bali, presents an 8,000-year record of vegetation and climate change through palynological and physio-geochemical analyses. The distinct sediment phases associated with relative vegetation fluctuations and change of physio-geochemical index suggest that Bali might have experienced cycles of wet and dry climate change over 8,000 years. Vegetation composed of marshland/gap-colonizers, being coeval with the intensive process of erosion as indicated by an increased input of minerogenic material from the catchment, characterizes the periods when homogeneous lake mud sediments are formed, indicating relatively higher rainfall at period of 8.0–6.6 ka BP, 5.1–3.6 ka BP and 2.8 ka BP to present. At the time when laminated lake sediments commence, e.g., 6.6–5.1 ka BP and 3.6–2.8 ka BP, vegetation of a rather dry and fire-resistant character dominates, in concomitant with lower input of minerogenic material and suggests drier episodes. Regional comparison indicates that human-induced vegetation destruction is insignificant in Bali, except that cultivation activities might have been manifested in the recent 3,000 years, and the climatic variability observed from this core was probably El Niño Southern Oscillation (ENSO)-related.

© Springer Japan 2013. Reconstruction of the paleoclimate based on analyses of annually laminated sediments in Japan and moat sediments from Angkor Thom in Cambodia indicates that there had been a period of drastic cooling during AD 1430–1500 accompanied by a weakening of monsoon activity. The annual mean temperatures show that—compared to the peak of medieval warm epoch around AD 1150—the mean temperature dropped by nearly 5°C in AD 1430. The climatic cooling brought about the weakening of the summer monsoon, which in turn would have resulted in the delayed arrival of the wet season. This might have had a catastrophic impact on rice cultivation in Cambodia leading to the decline of the Khmer Civilization.

Lake Qarun lies in the Egyptian Faiyum Depression and is the modern remnant of a much larger Holocene lake. Variations in water level occurred during the Holocene as a result of palaeoclimate changes and, since ca. 4000 bp, there have been hydrological interventions. Past lake levels have been inferred from the locations of archaeological sites, former beaches and exposed lake sediments, but there is no continuous Holocene palaeolimnogical record for the lake. To explore the potential of this record, three sediment cores (10.4-21.4m long) were collected from terrestrial locations on the southern margin of the lake in 2008. The basal sections of all three cores consisted of thinly laminated diatom marl sediments overlying coarse sand. The nature of these laminations was investigated in thin sections from two cores (QARU9 and 10). Quantitative very high-resolution diatom analysis revealed seasonal succession patterns of Aulacoseira and Stephanodiscus species within diatom-rich laminae. Elemental microprobe analysis of one thin section (QARU10) confirmed the presence of alternating Ca- and Si-rich laminae. The results indicate annually deposited sediment sequences with seasonality signals provided by microlayers of diatoms, calcite and clastic material. According to diatom counting, mean varve thicknesses equated to 6.0 (QARU9) and 9.4 (QARU10) annual diatom laminae accumulated cm?1. Radiocarbon dates from a third core (adjacent to QARU9) indicated that the QARU9 thin section material was bracketed between 8693 and 9935 cal bp. Diatom microstratigraphy was used to infer seasonality in varve forming processes. Gross sediment stratigraphy indicated that varve forming conditions had persisted for >1500 years. The presence of early Holocene varved sediments in palaeo-Lake Qarun provides an exceptional palaeoenvironmental archive for northeast Africa. © 2012 The International Society for Diatom Research.

This study explored the feasibility of rapid, nondestructive near-infrared (NIR) reflection spectroscopy for the prediction of conventional physical properties, carbon-nitrogen-sulfur (CNS) analysis, and concentration of inorganic components in sediment cores from a brackish lake. A long core sample, which consisted of well-preserved annually formed lamina from Lake Ogawara along the Pacific coast in Aomori Prefecture, northeastern Japan, was used to investigate the past environmental record. The core was previously analyzed for physical properties, CNS, and inorganic components. Calibration models were developed from NIR reflection spectra of 149 core samples. Partial least squares (PLS) analysis provided good regression models between measured and predicted values for water content, total nitrogen (TN), total organic carbon (TOC), total sulfur (TS), Al 2O 3, S/Al 2O 3, Fe 2O 3/Al 2O 3, Sc/Al 2O 3, Cu/Al 2O 3, and Zn/Al 2O 3 with coefficients of determination (r 2) for cross-validation of 0.73, 0.89, 0.88, 0.73, 0.92, 0.81, 0.82, 0.75, 0.82, and 0.82, respectively. The variation of predicted component values as a function of depth showed the same trend as that of conventionally measured values. This study also showed the possibility of NIR spectroscopy as an on-site, rapid analytical tool for the identification of tephra (fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism), which is important for dating. © 2012 Society for Applied Spectroscopy.

Lake Ichi-no-Megata is a maar in the Oga Peninsula, which is connected with the western side of Honshu Island, NE Japan. A 37-m long sediment core (IMG06) obtained from the center of the lake contains five fine ash layers. Stratigraphic positions in the core provide ages of five ashes to be 30, 21, 17, 7.3, and 1.0 cal ka BP, respectively. These layers are correlated with Aira-Tn (AT), Daisen-Kusatanihara (D-KsP), Asama-Kusatsu (As-K), Kikai-Akahoya (K-Ah) and Baitoushan-Tomakomai (B-Tm) tephras in ascending order, based on stratigraphy and petrographic characteristics such as grain assemblages, refractive indices, and major element compositions of glass shards. Although the AT, K-Ah and B-Tm tephras have been well known as widespread tephras, this study finds that the D-KsP, As-K and K-Ah tephras have more extensive distributions than the previous studies estimated. The D-KsP and As-K tephras have the potential to become useful time-markers in and around the Sea of Japan between the AT and K-Ah tephras. © 2011 Elsevier Ltd and INQUA.

Micro-sedimentological, geochemical data from Lakes Ni-no-Megata and San-no-Megata in northeastern Japan are used to reconstruct environmental and climate changes over the last 2000 years. Comparing these records in two neighboring maar lakes allows reconstruction of centennial scale climate change concerned the East Asian monsoon activities without the influence of human activities. S content and coarse mineral grains records show that long-term climate changes, with one warm/humid interval from AD 1200 to 750, and two cold/dry intervals from AD 1 to 750, AD 1200 to the present. These climate changes have similar trends to Asian monsoon records in China, and could correspond to the Dark Age Cold Period (DACP), the Medieval Warm Period (MWP) and the Little Ice Age (LIA) climate changes in Europe. Moreover, short-term climatic deterioration events occurred in the 6th, 10th and 18th centuries. Particularly the event around the 10th century is well correlated with other paleoclimate proxies in China, Europe and Mesoamerica, suggesting tele-connection by atmospheric circulation through the Northern Hemisphere. However, the record is asynchronous with solar activity. This might suggest the solar forcing has indirectly influenced lake sedimentation associated with Asian monsoon activities in Japan. © 2009 Elsevier Ltd and INQUA.

Lake Nakaumi, southwest Japan, is an enclosed lagoon characterized by polyhaline and halocline conditions. Since the last century, its ecological state has been altered by eutrophication. We used a paleolimnological approach and studied multiple proxies, including chemical compounds, diatoms, foraminifera and molluscs, to infer the eutrophication history of the ecosystem. Eutrophication in Lake Nakaumi was associated with several factors, including increased nutrient loading, input of herbicides, and dike building since the 1920s. The ecological condition of this lake was divided into several stages that reflect the eutrophication process after the 1940s. A catastrophic "regime shift" from a clear state with aquatic vegetation to a turbid one with phytoplankton occurred in the early 1950s. Environmental degradation in the Honjo area, a part of Lake Nakaumi, was attributed primarily to physical changes caused by the construction of an enclosing dike. Eutrophication occurred almost simultaneously with the physical changes to the Honjo area in the 1970s. Until recently, no regime shift was observed in this area, though the core-top sediments show possible symptoms of incipient change. © 2008 Springer Science+Business Media B.V.

Fossil benthic foraminifera from a sediment core taken from central Lake Shinji, western Japan, were investigated as an indicator of paleoenvironmental change in the Shinjiko-Nakaumi lake system during the 20th century. A transition from dominance of Haplophragmoides canariensis to that of Ammonia beccarii forma 1 occurred in the middle 20th century. This faunal association and its transition are similar to those observed in previous studies of Lake Shinji and the Ohashi River. This faunal transition might be affected by not only environmental change in Lake Shinji but also that in the Ohashi River.

Crystal- and magnetic-structure analyses for a single crystal of Nd2 CuO4 (NCO) have been carried out to visualize the spin density distribution on 3d-electron orbital for Cu2 + ion. NCO is an antiferromagnet with 3 d9 electronic configuration in Cu2 + ion, where S = 1 / 2 spin localizes on dx2 - y2 orbital. Spin density distribution ρ (r) of Cu2 + spin in NCO, which is directly obtained by three-dimensional Fourier synthesis of magnetic form factor f (Q), quite well agree with the calculated value of ρ (r) for 3d-electron on dx2 - y2 orbital. The present results demonstrated that our method is of great use for imaging the electron orbital, and is applicable to various system where the orbital degree of freedom contributes to their physical properties. © 2006 Elsevier B.V. All rights reserved.

日本海南部沿岸域における完新世初～中期の暖水系生物相と対馬海流の挙動との関係を理解するために, 出雲平野北西部と鳥取沖でそれぞれ採取された柱状試料HS02とGH87-2-308について, 浮遊性有孔虫化石を検討した. GH87-2-308における暖水系種Globigerinoides ruber の産出傾向は, 約8,300～8,000年前と約7,300～6,800年前の2つの時期に, 対馬海流の影響が強かったことを示す. 本種はHS02でも, 暖水系底生生物相が産出する約7,800年前の層準で見出される. 日本海のより沖合 (たとえば隠岐堆) の研究事例では, 暖水系微化石の産出は約7,300年前に普遍的なものの, 同様な普遍的産出は約8,300～7,800年前では不明瞭である. よって, 約8,300～7,800年前の対馬海流の影響は, 沿岸域で顕著に現れ, それが当時の山陰地方沿岸域における暖水系生物相の産出傾向を左右したと考えられる.

本論では，これまでの東アジアのレス・湖沼堆積物の研究を概観し，約120編の文献を取り上げて紹介した．東アジアのレス・湖沼堆積物には，陸上域での第四紀古環境変動が記録されている．この研究史は新しく，現在までの約20年間で東アジアモンスーンの成立やその変動について多くの証拠が蓄積されてきた．その結果，レスの堆積開始時期は2.6 Maであり，それ以降ミランコビッチフォーシングによる氷期－間氷期サイクルに伴ってモンスーン変動が生じたこと，および，最終氷期以降のモンスーンには，D-Oサイクルと同調する短時間周期の変動が生じていたことが明らかにされた．さらに，レス古土壌の直下に堆積する紅粘土の研究から，モンスーンの成立時期が7～8 Maまで遡るかもしれないという新知見が明らかにされてきた．<br>

Lake Jinzai is a small brackish water lake located in the southwestern part of the Izumo Plain, Shimane Prefecture, western Japan. The JZ-01 sediment core was taken at the center of the lake(35°19′N, 132°41′E; water depth 1.55 m)using a thin-wall type piston core sampler. The core length is 24.3 m. This study clarified the stratigraphy and sedimentation rates in the JZ-01 core on the basis of an initial core description and eleven AMS radiocarbon dates of organic material and shell fragments. This study also reconstructs high resolution Holocene environmental change from the mineralogy and chemical composition of the core sediments. The variability in Lake Jinzai water conditions is apparent in the content of authigenic iron minerals(pyrite, marcasite and siderite)and the sulfur content of the sediment. These results demonstrate that lake water conditions changed drastically throughout the Holocene, with brackish water intervals from 9,500 to 7,300, 4,100 to 1,900 and from 400 cal. yr B.P. to the present. Also the influence of human activity on the lake environment began around 2,000 cal. yr B.P. - a time which may be related to a significant increase in the number and size of archaeological sites of the Ancient Izumo Kingdom.

Recent studies on ice cores and deep sea sediments have revealed that abrupt and rapid climate and sea-level changes occurred frequently durmg the Late Quaternary. The brackish lake sediments which represent non-glacial varve layers record the detailed environmental changes, however, it has been difficult to detect such rapid changes from lake sediment cores. One of the reason of the difficulty is the lack of the method for collecting intact sediments for systematic ana1ysis. Here we present our systematic research procedure with improved efficiency，which includes an improved coring device for obtaining intact brackish lake sediments，initial description, sampling, and several analytical methods. This enables us to detect environmental variations on annual to decadal time scale.人類が急速に進化した時代である第四紀には，数～十万年スケールの氷期一間氷期サイクルにともなう，自然環境の変動が生じていたと考えられてきた（成瀬，1982）。しかし，近年グリーンランドの氷床堆積物や北大西洋や日本海の海底堆積物および中国内部の陸上堆積物の研究から，約1000～3000年周期で気侯や海水準が突然かつ急激に変動することが知られるようになってきた（Dansgaard et al.,1993；Bond et al.,1997；Chen et al.,1997；多田，1997）。このような急激な環境変動は，過去の人類活動に大きな影響を与えてきたと思われる。海陸境界に位置する汽水湖沼は，さまざまな環境変動を堆積物に記録している。たとえば，福澤（1995）は，水月湖湖底堆積物の明暗ラミナの互層が１年ごとに形成された「年縞」であり，さらに湖底堆積物は天然の寒暖計，検潮儀，雨量計，地震計などの環境変動検出計でもあることを明らかにしている。また，湖沼堆積物の堆積速度は海洋堆積物と比較すると大きいことからも，汽水湖底堆積物を分析することによって，さまざまな環境変動を高時間分解能で復元できると考えられる。しかしながら，湖沼堆積物コアの従来の研究からは，短い時問スケールの急激な環境変動を捉えることができなかった。その原因として，堆積物の記載を含む採取・分析方法に問題があったと考えられる。堆積物の採取や試料の分割・分析には多くの時間と労力が費やされる。琵琶湖深層掘削研究の例が典型的である。世界に先駆けて行われた琵琶湖の湖底掘削では，有機・無機地球化学，微化石，火山灰などの総合的な研究がなされ，気侯変動や古地磁気変化などに関する多くの情報が明らかにされた（Horie，1984）。しかし，堆積物の欠層や分析試料の時間分解能の低さ，分析機器の測定誤差などのために，この研究成果がまとめられるまでには多くの時間と労力が費やされたばかりでなく、数千年単位の自然環境変動を検出することはできなかった。これらのことから，短い時間スケールの急激な環境変動を湖沼堆積物から検出するためには，より効率的な精度のよい堆積物の採取・記載・分析が必要となる。近年，地球環境の将来予測が重要視されてきている。その将来を知るためには過去を知らなければならず，そのためにもわれわれは，地球環境の変化してきた過程を総合的に明らかにしなければならない。すなわち，汽水湖底堆積物をこれまでよりも効率的に精度よく採取・分析することは，われわれ人類が将来歩む道を考えるうえで非常に重要であるといえる。われわれの研究グループは，季節単位あるいは１年単位で過去の環境変動を記録している堆積物を欠層なく連続的に採取して，年単位の気候・海水準変動を明らかにしてきた。この論文では，われわれの研究グループで行っている堆積物の採取・分析方法を，堆積物から得られる情報について，その意味する堆積機構や環境の変遷に言及しながら紹介する。

Recent atmospheric circulations over the Asian Continent have been influenced by the Himalayan Range and the Tibetan Plateau as a wind barrier. Based on recent meteorological data, the existence of the Himalaya-Tibet within the troposphere has caused meandering of the Westerlies, intense activity of the Asian Monsoon and appearance of the Easterlies. Meandering of the Westerlies has led to increase precipitation in the East Asia region including northeastern China and Japan, and has formed the soils with poorly crystalized illite minerals in the Chinese Loess Plateau and the Japanese Islands. In nothern India and Nepal including the frontal basin of the Himalayan Range such as the Kathmandu Basin, intense activity of the Asian Monsoon has led abruptly to increase precipitation named &ldquo;onset of monsoon&rdquo;. Also, appearance of the Easterlies from the Himalaya-Tibet to northern Africa within the upper part of the troposphere has led to dry and spread the arid area in the northern Africa.<BR>There are many sedimentary records indicating Late Quaternary climatic changes around the Himalayan-Tibetan Plateau. We expected to determine the formation age of recent atmospheric circulation. This age indicates when the Himalayan-Tibetan Plateau was abruptly uplifted and elevated. In other words, formation ages of more humid climate in northeastern China, the Japanese Islands and the Kathmandu Basin, and the driest climate in the northern Africa are useful to determine age of uplift and elevation of the Himalayan-Tibetan Plateau.<BR>On the base of above-mentioned evidences and hypothesis, we attempted to investigate magnetic susceptibility of the loess-paleosol sequence in the Luochuan area of th e northeastern China, and illite crystallinity of loess-paleosol sequence in the Kathmandu Basi n and deep-sea sediments of the Japan Sea and the Mediterrannean Sea. Because characteristic changes of magnetic susceptibility and illite crystallinity indicate dry -wet oscillations as useful detectors.<BR>As results, we clarified three evidences as follows:<BR>1) Large amplitudes of magnetic susceptibility oscillations by large pricipitation in interglacial periods appeared in the Luochuan loess -paleosol sequence during last 600ka.<BR>2) Large amplitudes of illite crystallinity oscillations by large precipitations caused decomposition of illite minerals appeared in the deep-sea sediments of the Sea of Japan during the last 800ka and in the loess-paleosol sequence of the Kathmandu Basi n during the last 1.1Ma. 3) Amplitudes of illite crystallinity oscillation during the last 800k a were smaller than those amplitudes since 800ka ago.<BR>Investigation mentioned above indicates that critical uplift and elevations of the Himalayan-Tibetan Plateau achieved to induce activity of westerlies, easterlies and the Asian Monsoon, and suggests that determined ages of critical elevation caused atmospheric circulation changes range from 0.6 million years to 1.1 million years ago.

We attempted to clarify changes of magnetic susceptibility and clay mineralogy of the deep-sea sediments in ODP site 974B during the last 4.5 Ma. These sediments are composed mainly of calcareous nannoplankton ooze with organic matters and eolian dusts. Sequential changes of illite crystallinity, expressing as full width of half maximun of 10 A peaks by X-ray diffraction patterns, indicate changes of dry-wet climatic conditions in a supply area.<BR>Due to the atmospheric circulation pattern influenced by the Himalayan -Tibetan Plateau, the tropical easterly jets have lead northern Africa to dry conditions. So, it is possible to settle the uplift age of the Himalayan-Tibetan Plateau from the beginning age of dry climatic condition in northern Africa.<BR>As a results, we could clarify two evidences as follows:<BR>1) Illite concentrations and magnetic susceptibility indicate concentrations of eolia n dust carrying from northern Africa have increased from 3.5 Ma ago. In other words, the recent atmospheric circulation, that is carrying eolian dust into the Mediterranean Sea, has been confirmed from 3.5 Ma ago.<BR>2) Based on oscillations of illite crystallinity during the 4.5 Ma, the northern Africa region became dry condition 0.8 Ma ago. We thought that this event of 0.8 Ma was caused by the uplift of the Himalayan-Tibetan Plateau.

The Baikal Drilling Project (BDP) is a multinational effort to investigate the paleoclimatic history and tectonic evolution of the Baikal sedimentary basin during the Late Neogene. In March 1993 the Baikal drilling system was successfuly deployed from a barge frozen into position over a topographic high, termed the Buguldeika saddle, in the southern basin of Lake Baikal. The BDP-93 scientific team, made up of Russian, American and Japanese scientists, successfully recovered the first long (>100 m) hydraulic piston cores from two holes in 354 m of water. High quality cores of 98 m (Hole 1) and 102 m (Hole 2), representing sedimentation over the last 500,000 years, were collected in 78 mm diameter plastic liners with an average recovery of 72% and 90%, respectively. Magnetic susceptibility logging reveals an excellent hole-to-hole correlation. In this report the scientific team describes the preliminary analytical results from BDP-93 hole 1 cores. Radiocarbon dating by accelerator mass spectrometry provides an accurate chronology for the upper portion of Hole 1. Detailed lithologic characteristics, rock magnetic properties and inorganic element distributions show a significant change to the depositional environment occuring at 50 m subbottom depth, approximately 250,000 BP. This change may be due to uplift and rotation of the horst block in the Buguldeika saddle. The sedimentary section above 50 m is pelitic with varve-like laminae, whereas the section below 50 m contains a high proportion of sand and gravel horizons often organized into turbidite sequences. Accordingly, high resolution seismic records reveal a change in sonic velocity at this depth. It is inferred that sedimentation prior to 250 ka BP was from the west via the Buguldeika river system. After 250 ka BP the Buguldeika saddle reflects an increase in hemipelagic sediments admixed with fine-grained material from the Selenga River drainage basin, east of Lake Baikal. Variations in the spore-pollen assemblage, diatoms, biogenic silica content, rock magnetic properties, clay mineralogy and organic carbon in the upper 50 m of BDP-93-1 reveal a detailed record of climate change over approximately the last 250,000 years. These variables alternate in a pattern characteristic of glacial/interglacial climatic fluctuations. The present age model suggests that the climate signal recorded in Lake Baikal sediments is similar to Late Quaternary signals recorded in Chinese loess sections and in marine sediments. Copyright © 1996 INQUA/ Elsevier Science Ltd.

遠距離輸送されるバイオマス燃焼起源物質の定量を目指して，堆積物中の極細粒元素状炭素（EC）量評価のために，Thermal optical transmittance法の応用を検討した．スクロース，フミン酸，フルボ酸，フラーレンのEC・有機炭素（OC）分析を行った結果，O2雰囲気，550℃-700℃に耐えるOCも存在することが分かったので，700℃-850℃で検出されるフラクションのみをECとして定義した．この方法で，礼文島・久種湖の湖底堆積物コアから選んだ試料を，2μmを境に粗粒および細粒に分画し，それぞれの粒度画分についてEC・OC分析を行った．その結果，粗粒・細粒画分中のEC・OC変動が異なる事が分かり、粗粒ECはローカルな，細粒ECはローカル，遠方両方のバイオマス燃焼起源である可能性が示唆された．ECの細粒/粗粒比変動は大陸規模でのバイオマス燃焼変動を反映する可能性がある．

発表では、一の目潟ボーリングコアを用いて、新しい編年モデルを構築し、高時間分解能地球化学分析に基づき、26,000年前以降の東北日本の陸上古環境変動を復元した結果を報告する。秋田県男鹿半島に位置する一の目潟では、2006年秋、湖中央部においてシンウォールコアリングによる平行コアリング法（Nakagawa et al., 2012）によって、湖底下から約37mまで完全な連続堆積物（IMG06コア）を採取している。IMG06コアのコンポジット深度－年代モデルを構築する際、イベントフリー編年モデルを作成した。つまり、堆積物中で、層厚1cm以上褐色層（上方細粒化の構造あり）をイベント層として、これら一過性の堆積物を除外したイベントフリー・コンポジット深度に対して、合計74個の放射性炭素年代値から求めた暦年代値をプロットして、編年モデルを作成した。なお、イベント層は、全層にほぼ均一に挟在し全体の約4割を占めることが明らかになった。その結果、過去28,000年間において、堆積速度の異なる３つのステージが存在して、0.5～16 ka、16～24 ka、24～28 kaで、それぞれ0.325、0.463、0.786 mm/yearと求められた。また、コアの表層部（コンポジット深度で0～80 cm）は、年縞計数により、435年分の堆積物であることも示された。次に、気候プロキシーによる環境変動を明らかにするために、深度26.1mより上位の年縞堆積物の部分（タービダイト層は含まない）の試料（n=887）についてCNS元素分析及びICP-AESによって総数17の主要及び微量化学成分量を求めた。分析の試料間隔は平均15 mmであり、分析用試料は層厚2～10 mmで分取し、その時間分解能は最大で30年と見積もられた。これらの高時間分解能試料を用いた無機分析結果に基づき、気候プロキシーを用いて推定された過去26,000年間の男鹿半島周辺の気候変動は、大局的に15 kaまでは寒冷乾燥期、15-9 kaは、寒冷乾燥期から温暖湿潤期移行期、9 ka以降は、温暖湿潤期となっている。また、変動の振幅の激しさは、15-9kaで最も大きくになる一方、9ka以降では中間程度、26-15 kaでは極端に小さくなっている。とくに、晩氷期の気候変動に着目すると、今回の一目潟堆積物の記録は、15 kaより緩やかな気候温暖湿潤化が生じており、その中で、14 ka付近と、12.5-11.3 kaに、一時的な気候寒冷乾燥化傾向が認められる。このような傾向は、琵琶湖堆積物の記録と同調する一方、中国の石筍やグリーンランドの氷床コアの記録とは類似しない。この原因として、男鹿半島周辺の気候変動が、アジアモンスーンのような大気循環の変化よりも、海水面の急激な上昇による対馬暖流の流入による気候変動の影響を大きく受けた可能性があげられる。15 kaからのゆるやかな温暖化傾向は、14.6 ka頃の海水準変動の急激な上昇（MWP1a：Yokoyama and Esat, 2011）にともない、それが対馬暖流の日本海への本格的流入を促し、それが、男鹿半島で徐々に気候温暖化を生じさせたと解釈される。一方、ヤンガードリアス期は、男鹿半島では12.5-11.3 kaあたりに存在しているものの、そのシグナルは弱い。これは、男鹿半島のような日本列島の日本海沿岸地域では、顕著にあらわれなかった可能性がある。

本発表では、一の目潟および水月湖の湖沼年縞堆積物から、過去の地震や津波イベントの推定がどの程度まで可能なのか明らかにして、災害検出計としての湖沼年縞堆積物の有効性について検討をおこなった。

地震学者の今村明恒は，1943年の「遠州東南地塊の傾動に就いて」で，御前崎において平均海面上0.5mと1.6mの位置から二枚貝が岩石に穿った孔の列を見つけ，前者は安政地震直前の汀線を，後者は宝永地震直前の汀線を示すとした．だが，位置図などがないためか，穿孔列は未確認だった．北村は御前崎で穿孔性二枚貝Penitella gabbii(オニカモメガイ)の体化石を波食台(標高1.05～1.35m)から発見し，10個体の14C年代値と御前崎の海成段丘の形成年代(Fujiwara et al., 2010)から，二枚貝化石の示す隆起は1361年の正平(康安)東海地震によるとした．また，P. gabbiiの生息深度(大潮時の低潮線より下)から隆起量を2.55m以上と推定した．この値は1854年安政東海地震(レベル1地震)の隆起量(1m)の2.5倍以上なので，1361年の地震はレベル1.5地震になる．本発見は，石橋・佐竹(1998)が古文書から推測した正平(康安)東海地震―1361年の正平(康安)南海地震の2日前に発生―の可能性を裏付け，南海・駿河トラフの海溝型地震が，東側で起きる東海地震の発生後，数時間から数年の期間をおいて，西側で起きる東南海地震あるいは南海地震が発生した事例を１つ追加した．本成果はKitamura et al. (2018a)で公表した．
本年度は，石垣島の津波堆積物の貝類群集に関する研究成果を2編の国際誌に公表した(Kitamura et al., 2018b, c)．１つは津波堆積物中の貝類群集の種組成・重量の特徴に関するもので，これにより高潮堆積物との識別が可能となる．もう１つは，殻が閉じており，内側が空で，殻表面が摩滅していない二枚貝の貝殻の酸素同位体比変動から津波の発生季節を特定する手法の提示である．これらの内容はレベル1.5津波の実態解明に役立つ．
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2018年度は，研究目的に沿った４つのサブテーマのうち３つを行い，それらを総合的に考察した．
サブテーマ１．湖水濁度調査：セジメントトラップが行方不明のため，春季から夏季までの短い期間のデータしか取れていない．来年度はサイドスキャンソナーを用いて地形調査を行うとともにセジメントトラップの回収に務め，最終まで観測を続ける．湖沼および流域の珪藻群集調査：藻琴川の中流から下流までの複数の地点で，採水を行い，懸濁態有機炭素量と珪藻の群集解析を行なった．想定した大量発生は起っていないが，藻琴川の珪藻が藻琴湖に堆積していることが明らかとなった．ラミナのパターンの地域的変化，洪水イベントによるラミナ形成過程：藻琴湖と網走湖のコアを，ラミナ解析などを行なった．その結果，2015,2016年に藻琴湖で見られた特徴的な洪水性高密度層は網走湖では見られなかった．流域の状態によって高密度層の特徴が異なることが明らかとなった．
サブテーマ２．前年度末に藻琴湖において得られた18Mk-8Cコアおよび20m級のボーリングの分割処理，記載および分析を行なった．その結果，年縞と思われるラミナのある年代は少なくとも中期完新世まで連続的に見られることが明らかとなった．コアの解析についてはコアトップ付近において超高解像度分析を行なった．その結果，近年に堆積環境が著しく変化し，河川から供給される堆積物が増加していることが示唆された．これは継続的な現世調査の結果からも支持されている．また，ある種の珪藻について太陽活動に見られる11年周期で変化するものが見られることが明らかとなっている．
サブテーマ３．昨年度に引き続き網走湖のコア解析を行なった．
これらで得られた成果は，日本地質学会やJpGUなどの個別講演，AGU，EEIWの国際学会，汽水域研究会のスペシャルセッションで発表を行なうとともに，一部が国際詩に掲載された．

本研究は、国内の年縞堆積物を対象として環境DNA分析を実施して、化学成分や微化石から復元できない動植物相や人間活動履歴情報を網羅的に把握することができるのか、その検証を世界ではじめて試みた。そのために、気候変動や文化人類学的に景観の異なる北海道藻琴湖および、静岡県浜名湖に堆積する完新世の湖底堆積物を対象として、環境DNA分析の解析手法を援用して、景観を構成する生物相や人間活動履歴を時系列変化として復元した。
その結果、藻琴湖においては、かつて生息していたイトウの在不在を議論できる可能性が見いだされた。しかしながら、堆積環境や堆積年代の違いによって、DNAの損傷程度に違いがあることが示唆された。

一の目潟ボーリングコアを用いて、新しい編年モデルを構築し、高時間分解能地球化学分析に基づき、26,000年前以降の東北日本のアジアモンスーン変動を復元した。過去26,000年間の男鹿半島周辺のモンスーン変動が導く気候環境は、大局的に15 kaまでは寒冷乾燥期、15-9 kaは、寒冷乾燥期から温暖湿潤期移行期、9 ka以降は、温暖湿潤期となっている。また、変動の振幅の激しさは、15-9kaで最も大きくになる一方、9ka以降では中間程度、26-15 kaでは極端に小さくなっていることが明らかになった。このような傾向は、琵琶湖堆積物の記録と同調することが示唆された。

フィリピン諸島には，日本と同様にプレートの沈み込みに伴う火山が多く分布している．この研究では，同国の火山地震研究所（PHIVOLCS）との共同研究により，ルソン島のPinatuno, Taal, Irosinの各火山，さらに南方のミンダナオ島にあるParkerとMatutumの両火山の噴火史，およびそこから噴出された広域テフラの年代学的フレームワークの構築を試みた．特にPinatubo火山については，約60 km 北東にあるPaitan湖でボーリング・コア試料を採取して，噴火年代の高精度化とこれまで未検出であった噴火を発見することができた．

本研究では，環境変動と環太平洋の古代の諸文明との関わりを明らかにすることを目的とした。そのために，高精度な年代と多様な環境指標が得られる湖沼堆積物を，グアテマラ，ペルー南部，カンボジア，日本において収集し，過去の気候，地震・津波等の自然災害，遺跡周辺の植生，立地環境，人類による環境破壊等を復元した。また，考古遺物の年代測定や植物学的分析を実施した。その結果，世界最高水準の放射性炭素年代の較正曲線が得られた（福井県水月湖）。中米，ペルー南部，カンボジア，南西諸島の古代文明が経験した環境変動が明らかとなった。

年縞の解析による高精度の気候変動の復元によって、モンスーンアジアの稲作漁撈文明の興亡が、気候変動からいかなる影響を受けたかを解明した。とりわけメコン文明の一つであるカンボジアのクメール文明の興亡については、プンスナイ遺跡の発掘調査を実施し、水の祭壇をはじめ、数々の新事実の発見を行った。稲作漁撈文明は水の文明でありアンコールワットの文明崩壊にも、気候変動が大きな役割を果たしていたことを明らかにした。

本研究は,山陰地方の汽水湖沼堆積物を用いて,完新世における自然環境変動の検出と人間活動史との関連を解明することを目的とするものである.平成19年度は,これまでに出雲平野および宍道湖,神西湖,中海で掘削されたボーリングコア解析を通じて,完新世における汽水域の形成と平野の地形発達の関連を堆積学的および地球化学分析によって詳細に明らかにすることができた.とくに,完新世以降の出雲平野の地形発達史を,高精度に復元できたことは本研究によってはじめて成し得たことである.これの成果を論文としてまとめることができた.また,近過去の環境復元研究では,中海および宍道湖を対象として,複数のショートコアを採取して,過去100年間の環境変動の検出を試みた.この研究成果の特筆できる点として,富栄養化が少なくとも1950年には生じていていること,本庄工区の近年の底質環境は改善されつつあることの新知見を得ることができた.さらに,今年度から着手した秋田県一の目潟コアの研究では,世界的にも類を見ない過去三万年間の連続した年縞堆積物を発見した.この年縞堆積物の解析により,東アジアの環境変動を高精度に復元できる手がかりをつかんだ.本年度中は,イニシャルレポートとして研究成果の基礎的な段階を報告した.今後,一の目潟コア研究は,重点的に進めていくことになり,これら研究成果は,国内外の学会等で講演していくとともに,また現在国際誌に投稿中である.