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Tracking paleoenvironmental change and past event deposits is very important to evaluate the natural hazard spatially. This paper presents how the environment changes and implies the event deposit depending on the diatom assemblage change. To investigate paleoenvironmental change and identify the difference between tsunami and typhoon deposits, we analyze diatoms from the sediments in two coastal lakes in southern Japan where flood deposits have been linked to historical typhoon and tsunami events (Lakes Kawahara and Ryuo). The sediment cores extend from B.C.E. 500 to approximately C.E. 1000 and the downcore variation in diatom assemblages indicates a series of transitions from saline to fresher conditions in both Lake Kawahara and Lake Ryuo between approximately C.E. 500 and 1700. We observe an obvious deviation in diatom assemblages in event deposits previously identified to be either of tsunami or typhoon in origin. For the most prominent event deposit preserved in Lake Ryuo by the Hoei tsunami of C.E. 1707, the deposition of marine diatoms serves as evidence of marine flooding, while the subsequent deposition of soil and freshwater diatoms indicates the mobilization of terrigenous sediment during returning seaward flows. In contrast, the most prominent event deposit in Lake Kawahara is associated with freshwater flooding by the Kamikaze typhoon of C.E. 1281 and contains very low diatom abundances and a peak of freshwater taxa, followed by a peak in diatom counts potentially due to greater biological activity induced by a resultant influx of nutrients and re‐oxygenation during the event. [ABSTRACT FROM AUTHOR]

To understand the role of the East Asian summer monsoon (EASM) and the East Asian winter monsoon (EAWM) on the hydroclimate in northern Taiwan, a multiproxy study has been conducted. This study aims to achieve its goal by using micro-XRF data of Ti and sulfur (S), carbon isotopic compositions (δ13C) along with elemental concentrations of carbon (C), nitrogen (N) and S, and diatom analyses in the sediment core extracted from the Dream Lake (DL; 25°10′01.9″ N, 121°33′36.0″ E and elevation = 588 m above sea level), northern Taiwan. The radiocarbon dates revealed that the DL core covered the time interval from 4.5 to 0.4 cal kyr BP. The current records revealed wetter phases during 4.5–3.0 cal kyr BP, 2.0–1.7 cal kyr BP, and 1.0–0.4 cal kyr BP, characterized by the dominance of C3 plants in the DL catchment, increased runoff, and higher lake levels. Drier climates observed in the current study during 3.0–2.0 cal kyr BP and 1.7–1.0 cal kyr BP, marked by a reduction in C3 plants, decreased runoff, and lower lake levels. The northern Taiwan climate during the late Holocene was observed to be regulated by the interplay of EASM and EAWM. The wet climate conditions during 4.5–3.0 were due to the La Niña-like conditions, which led to a strong EASM resulting in high precipitation conditions. The dry climate conditions during 3.0–2.0 cal kyr BP have coincided with El Niño-like conditions during 3.0–2.4 cal kyr BP and a subsequently strong EAWM during 2.4–2.0 cal kyr BP. Both situations led to a reduction in precipitation in the region. Unlike the time frame from 4.5 to 3.0 cal kyr BP, wet climate conditions during 2.0–1.7 and 1.0–0.4 cal kyr BP have coincided with weak EAWM conditions, which led to an increase in precipitation in northern Taiwan. The dry climate noticed between 1.7 and 1.0 cal kyr BP appeared to be the impact of both El Niño-like conditions and strong EAWM. [ABSTRACT FROM AUTHOR]

The 'Altai Tavan Bogd' National Park in the north-western part of the Mongolian Altai, Central Asia, is located in a forest-steppe ecosystem. It occurs under the influence of extreme continental and montane climate and is sensitive to natural and anthropogenic impacts. High-resolution (<20 years per sample) multi-proxy data of pollen, non-pollen palynomorphs (NPPs), macro-charcoal, diatoms, and XRF scanning from radiocarbon-dated lacustrine sediments reveal various environmental changes and the impact of different settlement periods for the late-Holocene. From 1350 to 820 cal. yr BP (AD 600–1130), the distribution of grass steppe indicates a climate similar to present-day conditions. Rapid improvements of climatic conditions (e.g. increased rainfall events) possibly favored a recovery of forest-steppe encouraging nomadic movements into alpine areas. In the period from 820 to 400 cal. yr BP (AD 1130–1550), the decline of forested areas suggests an increasingly drier and possibly colder climate. Some political shifts during the Mongol Empire (744–582 cal. yr BP; AD 1206–1368) favored variations in nomadic grazing habits. After 400 cal. yr BP (AD 1550), moisture and temperature increased slightly, and from ca. 40 cal. yr BP (AD 1910) to present, annual temperature continued to increase more markedly favoring an additional water availability due to permafrost degradation. Diatom data suggest several intervals of increased water availability in all periods which might have caused erosion due to heavier rainfall events or increased snow melt. Immediately after most of these high-water intervals, NPP data reveal periods of increased grazing activities in the area. [ABSTRACT FROM AUTHOR]

Four palynological and three diatom zones of Mid-to Late Holocene are identified along a 370-cm-long radiocarbon dated sediment core collected in Lake Hamra at Wadi El Natrun (Western Nile Delta, Egypt). The Mid- Late Holocene between the Predynastic to Old Kingdom was terrestrial wetland habitat with high seasonal rainfall and/or Nile flood as revealed by the dominance of Cyperaceae pollen. Therefore, people gathered in and around the Nile Valley and the agricultural activities increased. During the early stage of Late Holocene coincident with the Old Kingdom to Middle Kingdom, the paleoclimate became more arid with low seasonal precipitation and/or Nile flood as reflected by the increasing abundance of Poaceae pollen and the absence of diatoms in addition to low values of TOC, TN, TS, C/S and high values of C/N. These drought conditions possibly played a role in the Old Kingdom collapsing. The late stage of the Late Holocene showed terrestrial wetland habitat with brackish conditions coupled with aquatic contribution under oxic conditions as inferred by the dominance of Typha sp. and Amaranthaceae pollens as well as the diatom assemblages. The relatively high values of TOC, C/N, C/S coupled with low values of TS and TN reveal terrestrial origin of organic matter. The Late Holocene-recent has turned into a terrestrial wetland habitat with more brackish conditions and increasing in the seasonal rainfall as supported by the marked increasing of Cyperaceae pollen. The overall increase of the Diatom Inferred Salinity (DIS) as well as the marked increasing of C/S, TN and decreasing of TOC, C/N and TS values towards the recent point to higher saline brackish wetland paleoenvironment and a terrestrial origin of the organic matter with more aquatic contribution under oxic conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Holocene hydrological changes of fen peatland in northern Mongolia were reconstructed using diatom fossils with an aid of Sphagnum leaf fossils. Analyses were conducted on three cores taken across the basin and reconstructed water environments were compared to find basin-wide hydrological changes and climate anomalies. The peatland has been covered by sedges during most of its 10 thousand years history, but all cores showed common peatland hydrosere processes from fluvial environment in the early Holocene period, shallow marsh to present acidic fen peatland. The establishment of fen peatland at 6.8–6.4 cal ka BP was marked synchronously by the shift of diatom and Sphagnum taxa assemblages and this period was inferred as the onset of the mid-Holocene dry climate which is widely observed around Mongolia. The dry environment lasted until around 2.8 cal ka BP with a temporal wetter condition at 4.4–3.5 cal ka BP. Short term diatom trend shifts indicated temporal wetter environments at 8.7–8.4, 8.0–7.6, 2.4–2.1, 1.2–0.5 cal ka BP and a dry environment at 0.4–0.2 cal ka BP. These periods of hydrology changes were correlative with other studies in Mongolia and East Siberia, so they would represent climate-induced hydrological changes, and those regions might share the same response to long term insolation changes or global climate anomalies. However, disagreements of climate data even within northern Mongolian region suggest large influence of regional geography and the balance of evapotranspiration on climate behaviors as shown by recent dendrological paleoenvironment researches. Coherent differences of main taxa compositions between three cores were attributed to core site-specific local hydrology mainly in terms of relative wetness from wettest core site accompanied by abundant planktonic diatom taxa to driest site with acidic peat indicator taxa. Timings and manners of temporal diatom trend shifts were also largely different between cores suggesting significant difference in each core site sensitivity to basin-wide hydrology changes, confirming the necessity of using multiple cores and proxies in peatland sediments to detect climate-induced environmental changes. [ABSTRACT FROM AUTHOR]

Abstract: The Holocene paleoenvironment in Nur sphagnum bog, northern Mongolia, was reconstructed by diatom, pollen analysis and measurement of chemical properties on a 3.7m long peat boring sample. Development processes of peatland are well reflected in these multiproxy records, showing that peat accumulation started as early as 9kacalBP, and the present acidic peat bog was established no later than 6kacalBP. Synchronous trends in diatom and pollen assemblages revealed wetter climate in the early Holocene and extensive drought in the mid-late Holocene centered at 5900–2800calBP as a result of temperature increase and low precipitation. Periods of shifts in proxy data were potentially correlated with other studies in not only Mongolia and Siberia, but also the North Atlantic Ocean, and the climatic periods at 8.4 and 2.8kacalBP were highly significant. However, responses to climate changes seem regionally varied in time and strength, demonstrating that local differences in vegetation and orography greatly influence the balance of precipitation and evapotranspiration. Climate changes that coincided in time with the Medieval Climate Anomaly and Little Ice Age were observed as wetter (1200–980calBP) and drier (370–240calBP) conditions, probably caused by meridional shifts of westerlies. [Copyright &y& Elsevier]

Climatic changes during the Late Quaternary have been studied using three sediment cores from closed and semi-arid lacustrine basins in central Anatolia, Turkey, based on diatom assemblages of sediments. The first step in using diatoms as salinity indicators is to obtain quantitative data concerning their ecological characteristics along salinity gradients. Using 51 samples of living diatoms from 38 lakes and rivers in Turkey, an abundance-weighted mean salinity was calculated for each taxon. On the basis of a strong relationship between diatom composition and salinity, the diatom-based transfer functions were defined for the salinity reconstruction, and then applied to three drill cores from Late Quaternary lacustrine sediments from Konya Basin. The oscillations of the diatom-inferred salinity of the cores generally indicate “glacial-pluvial” correlations. High salinity levels were associated with inter-glacial stages, and low sanity levels indicate glacial stages. The curves also included the phases of shorter oscillations ranging from 10,000 to 20,000 years, presumably caused by global climate changes and local environmental changes. [Copyright &y& Elsevier]

Our study demonstrates the importance of detailed lithostratigraphic and biostratigraphic analyses of deposits of lake-side terraces and alluvial fans in attempts to identify fluctuations of climate characteristics such as precipitation and evaporation rates, and of local conditions for water balance changes in the central part of Turkey during the last 20,000 years.Lake Tuz basin, central part of the Anatolian Plateau, Turkey, had two high lake-level stages dated as about 20,000–17,000 years ago and about 13,000 years ago. At the high lake stages, water level rose more than 15 m higher than the present lake level, and the lake area spread widely to near the southern edge of the basin, as inferred by lithologic and chronological investigation of drilling cores. In the Holocene, lake level fell and the southeast part of the basin became extensive lake terraces.Alluvial fans have formed along the edge of the upland area on the terraces in the Holocene. Stratigraphy and dating of the fan deposits show the fluctuations in the depositional rates of the fans. Major formative stages of the fans are dated about 7000–5500 and 2500–2000 years BP, and several times of minor stages (probably 4300 and 3000 years BP) occurred between the two major stages. Our archaeological research shows that there are strong relationships between the distributions of archaeological sites of this area and the above geo-environmental histories. [Copyright &y& Elsevier]

This study examines the 1500-year history of massive floods as recorded in the slackwater deposits of the Kherlen River basin in Mongolia. The study area is located along the Kherlen River in Baganuur district, Ulaanbaatar. Site HL1 has a flood frequency of 89 years and an accumulation rate of 1.2 mm/y over approximately 1500 years. Site HL2 has a flood frequency of 72.2 years and an accumulation rate of 1.46 mm/y during about 700 years. The range of calculated value for flood frequency and annual accumulation rate during the period of the 10th century to the early 20th century at site HL1 is entirely different from that in other periods. It is considered that the palaeohydrological environment of the study site during that time might have been influenced by climatic change as well as geomorphological and hydrological change. Based on the results of identification of discrete flooding and age dating ( 137 Cs and 14 C), the sedimentary layers of HL1 and HL2 were divided into 4 periods (period 1: 1960–2012, period 2: 970–1960, period 3: 533–970, period 4: 427–533) and 2 periods (period 1: 1960–2012, period 2: 1290–1960), respectively. The authors suggest that the past climate of the region was greatly influenced by the East Asia summer monsoon. It is suggested that the occurrence of the large-scale floods in eastern Mongolia was influenced by the strengthening and weakening of the summer monsoon due to climate change. [ABSTRACT FROM AUTHOR]

Paleo-relative sea level (paleo-RSL) records in the far-field are essential for constraining models for global sea level change. We compared the early Holocene RSL history on the central east coast of the Yellow Sea with those of Bohai Bay, the northernmost point, and Gunsan Bay, south of the study area. A multi-proxy approach, including lithostratigraphy, biostratigraphy, combined with radiocarbon and OSL dating, facilitated the generation of 28 sea level index points (SLIPs) using 11 borehole samples. Excavation of basal peat of the 10.3 ka in the study area established that the observed RSL of the transgression in the early Holocene was −14.88 m, which was much shallower than −27.9 m in Gunsan Bay at 9.8 ka and was similar to −17.3 m in Bohai Bay at 9.7 ka. The observed RSL and the prediction curves of the study area were compared with those of other areas. In Gunsan Bay, the early Holocene GIA prediction curves are consistent with those observed, which seems to be the result of a "low setting" of the crust thickness and mantle viscosity. Therefore, it is presumed that the significant difference in the elevations observed between the study area and Gunsan Bay is caused by the levering effect owing to the difference in the tectonic characteristics. Conversely, other observed groups during 7.6–6 ka have a similar slope to the prediction curve of the Early Holocene in the study site, and it is thought that the sediments of the early Holocene were eroded and re-deposited along the channel. These results are of great importance as data of sea level variability in the far field due to glacial collapse and as data for the GIA modeling process. • The RSL in the early Holocene is 13 m shallower than Gunsan on the west coast. • During the 8.2 ka event, the RSL difference between the two sites is 5 m. • GIA models suggest the different costal levering effects between two sites. • Different GIA responses of Gyeonggi Massif and Ockcheon Belt to IESL. [ABSTRACT FROM AUTHOR]

Late Holocene environmental changes in Lake Hamana, a coastal lagoon in central Japan, were reconstructed by a diatom fossil analysis and tephra and radiocarbon dating of a lakebed sediment core (HMN08-7) with high temporal resolution. On the basis of major species composition changes in diatom assemblages, we divided the core into six zones (I to VI), and subdivided zones V and VI into 3 subzones. The environment of Lake Hamana developed in six stages that corresponded to the diatom zones: stage I (4700–4600 cal BP) was characterized by vigorous seawater inflow in an inner bay environment; during stage II (4600–4500 cal BP), a closed inner bay environment with laminated sediments formed as a result of the formation of sand barriers; stage III (4500–2650 cal BP) was characterized by a well-mixed brackish water environment caused by active mixing with riverine fresh water and, after 3500 cal BP, an enhanced inflow of seawater; during stage IV (2650–2250 cal BP), the salinity of the lake water gradually decreased owing to reduced seawater inflow; during stage V (2250 cal BP to 480 cal BP), the lake water changed from brackish to fresh, although salinity increased temporarily during the middle of the period, and the depth of the lake increased; and during Stage VI (480 cal BP to the present), an inner bay environment developed again following the AD 1498 Meio earthquake, although salinity increased temporarily from AD 1600–1750. We also identified two event deposits, E A and E B , on the basis of spikes in the abundance of minor diatom species. In E A layer (4600–4500 cal BP), Glyphodesmis williamsonii , a marine or brackish water species, was temporarily dominant, and lamination disappeared; therefore, this layer was interpreted to represent a brief episode of sediment supply from seaward, such as by a tsunami or storm surge. The E B layer (ca. 4200 cal BP), in contrast, was characterized by an increase in fresh and fresh to brackish water species, suggesting a temporary supply of allotopic riverine or lake shore sediments during a large flood event. [ABSTRACT FROM AUTHOR]

Diatom, pollen, geomagnetic and geochemical analyses were carried out on a 3.6 m 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 3.6–3.1 cal ky BP, and multi-proxy records showed generally drier climate in these sections especially at 3.6–3.1 cal ky BP. 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 6.5 cal ky 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 3.1 cal ky BP to the present and this might reflect increased importance of Austral hemisphere atmospheric convection and subsequent southerly position of ITCZ in Austral summer time. [ABSTRACT FROM AUTHOR]

Abstract: Holocene environmental changes were reconstructed by analyzing diatom assemblages from sediment cores YM, KZN, NK, and MC from the Nobi Plain, central Japan. Five diatom assemblage zones were identified: (1) at the beginning of the Holocene, freshwater species were dominant; (2) then, marine and brackish-marine species increased, indicating transgression; (3) in the middle Holocene, proportions of marine and brackish-marine species became almost constant, with marine species dominant; (4) marine species began to be replaced by freshwater species, indicating marine regression as a result of delta progradation; and (5) freshwater species again became dominant. These diatom assemblages correlate with previously defined lithological units: zones 1 and 2 with unit B (fluvial to coastal plain), zone 3 with unit C (inner bay or prodelta), zone 4 mainly with unit D1 (delta front slope), and zone 5 with units D2 (delta front platform) and E (delta plain and flood plain). Although the shoreline migrated landward (transgression) faster than it migrated seaward (regression), transgressive diatom assemblage changes (decrease in marine-brackish water species) took up to 1000 years, whereas regressive changes required only a few hundred years. Diatom analysis is useful for reconstructing not only Holocene sea-level changes and sedimentary environments but also local geographic effects. [ABSTRACT FROM AUTHOR]

Shores of eastern Hokkaido rose by perhaps 1 m a few centuries ago. The uplifted area extended at least 50 km along the southern Kuril Trench. It included the estuaries Akkeshi-ko and Hichirippu, on the Pacific coast, and Furen-ko and Onneto, which open to the Okhotsk Sea. At each estuary, intertidal and subtidal flats rose with respect to tide level; wetland plants colonized the emerging land; and peaty wetland deposits thereby covered mud and sand of the former flats. Previous work at Akkeshi-ko and Onneto showed that such emergence occurred at least three times in the past 3000 years. Volcanic-ash layers date the youngest emergence to the seventeenth century AD. New evidence from Akkeshi-ko, Hichirippu and Furen-ko clarifies the age and amount of this youngest emergence. Much of it probably dates from the century's middle decades. Some of the newly emerged land remained above high tides into the middle of the eighteenth century or later. The emergence in the last half of the seventeenth century probably exceeded 0.5 m (inferred from stratigraphy and diatom palaeoecology) without far exceeding 1 m (estimated by comparing seventeenth- and eighteenth-century descriptions of Akkeshi-ko). The stratigraphy and palaeoecology of the emergence are better explained by tectonic uplift than by bay-mouth blockage, tidal-flat accretion or sea-level fall. Eastern Hokkaido needs occasional uplift, moreover, to help reconcile its raised marine terraces with its chronic twentieth-century subsidence. Because it took place above forearc mantle, eastern Hokkaido's seventeenth-century uplift probably lacks analogy with coseismic uplift that occurs above typical plate-boundary ruptures at subduction zones. [ABSTRACT FROM AUTHOR]