Constant Rate Of Supply Research Articles

Influence of self-absorption corrections in the quantification of 210Pb and 241Am for sediment dating

The nuclides 210Pb and 241Am are used in geochronological studies. In this work, we examine the influence of the sediment chemical composition on the self-attenuation corrections needed for the accurate determination of specific activities for 210Pb and 241Am used for sediment dating. A theoretical exercise was carried out evaluating the relative bias obtained by four different analytical laboratories in the quantification of the 210Pb and 241Am activity concentration by gamma-ray spectrometry. The laboratories considered the same density for the sediment sample, but each one used a different chemical composition in the Monte Carlo calculations, and six different HPGe detectors (including n and p-types). An estimate of the impact that would have the relative biases found in the estimation of the 210Pb sediment ages, applying the Constant Rate of Supply (CRS) dating model, is also given. In addition, the performance scores that the laboratories would have obtained in a hypothetical IAEA proficiency test are also presented.

Recent sedimentation rates in the Caravelas estuary (Bahia, Brazil) using unsupported 210Pb and 137Cs modeling

Abstract The Caravelas estuary is located in a zone of the Brazilian coast (Southern Bahia State) which has been submitted to different kinds of land uses during the last 50 years. This zone has an important ecological role, due to its mangroves and its location next to Abrolhos coral reef, the most important in the Southern Atlantic Ocean. 210Pb and 137Cs dating methods, accompanied by a sedimentological study, were applied to sediment cores in order to establish sedimentation rates and identify historical trends of land use and erosive processes. Sedimentation rates were established according to the “Constant Rate of Supply” (CRS) 210Pb dating model, which was preferred rather than the “Constant Initial Concentration” (CIC) model. Corrected sedimentation rates obtained from 210Pb dating were corroborated through a second independent radionuclide tracer such as 137Cs. The sedimentation rates obtained according to the CRS model for the cores were 1.07 ± 0.13 cm yr –1 for T#2 (inner sector), 0.65 ± 0.06 cm yr –1 for T#5 and 0.85 ± 0.09 cm yr –1 for T#8 (outer sector). The difference in sedimentation rates among the sampling sites could be due to hydrodynamic processes and could be related to the tendency of increase of erosive processes, conditioned by the changes in the landscape and land use to, which this region has been submitted.

Arsenic, lead, and uranium concentrations on sediments deposited in reservoirs in the Rio Grande Basin, USA–Mexico border

The El Granero reservoir is the last reservoir of the Rio Conchos before it joins the Rio Grande at the Mexico–USA border. This reservoir, together with the San Marcos reservoir, is located in the arid region of Chihuahua, Mexico. High, naturally occurring radioactivity levels, as well as high arsenic (As) concentrations, have been found in both reservoirs. The main goal of this research was to establish the spatial and temporal distribution of trace and radioactive elements in surface sediments and cores collected from these reservoirs. Sediment cores were dated using 210Pb and 137Cs measurements and applying the constant rate of supply (CRS) model. Major, trace, and radioactive elements were determined in surface samples and three sediment cores. Radioactive elements were determined by both alpha and gamma spectrometry. Major and trace elements were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using the EPA 3051a method. Enrichment factors (EF), contamination factors (CF), and pollution load indexes (PLI) were calculated in order to identify the human impact in both reservoirs, whereas the chemical index weathering (CIW) was used to assess differences in the degree of weathering. High uranium (U) enrichment (EFs = 24.9–54.7) was observed in core layers at the San Marcos reservoir, while in surface sediments, this enrichment was lower. The high variability of lead (Pb) and As in sediment cores from the Granero reservoir was attributed to human influence. Arsenic and Pb enrichment differences between entry and exit sediment cores were explained by the filtering capabilities of the elongated shape, the topography, and the presence of plants on the reservoir’s bed. The highest PLI was found at the entrance core of the Granero reservoir. The natural element concentration levels of As, Pb, and U were established at the Granero reservoir. High EFs for As and Pb suggest an anthropogenic origin of these pollutants at specific time intervals. High U concentrations in the San Marcos area are explained as naturally occurring. The concentrations of As in most of the studied sediments could pose a risk to human health by As ingestion, since they are above the probable effect level (PEL).

Multiple sediment cores from reservoirs are needed to reconstruct recent watershed changes from stable isotopes (δ13C and δ15N) and C/N ratios: case studies from the mid-western United States

Watershed land-use changes, including urbanization, have caused accelerated soil erosion, which in turn has increased sediment accumulation rates in most aging reservoirs in the mid-western United States (USA), thereby posing a threat to their longevity and productivity. We analyzed three sediment cores from each of two reservoirs in the mid-western USA, the Webber Dam impoundment in Michigan and Goshen Pond in Indiana. Core chronologies were established using 137Cs and 210Pb. Concentrations of organic carbon and nitrogen and their stable isotope compositions (δ13C and δ15N) were measured to investigate past land-use changes. We used three excess 210Pb-based (210Pbxs) sedimentation rate models (constant 210Pb flux and sedimentation, constant rate of supply of 210Pb and constant initial 210Pb concentration) to develop core chronologies and compared them to the chronology obtained from the 137Cs peak. Validation of the excess 210Pb-based chronology with137Cs-based chronology requires more than one 210Pbxs-based-model. That is, even in one watershed, output from more than one 210Pbxs-based model may have to be compared with an independent time marker. We compared C/N ratios, δ13C and δ15N among three time horizons in each of the three cores from the reservoirs (corresponding to dates of 1950, 1970 and 2010). Within a reservoir, there can be large differences between cores for a given time horizon, indicating there could be spatial differences in sources of C and N and the processes that influence carbon and nitrogen isotopes. We conclude that multiple sediment cores from reservoirs should be analyzed if carbon and nitrogen isotopes in sediments are to be used for paleoenvironmental inference.

Radionuclides in ornithogenic sediments as evidence for recent warming in the Ross Sea region, Antarctica

Radionuclides including 210Pb, 226Ra and 137Cs were analyzed in eight ornithogenic sediment profiles from McMurdo Sound, Ross Sea region, East Antarctica. Equilibration between 210Pb and 226Ra were reached in all eight profiles, enabling the determination of chronology within the past two centuries through the Constant Rate of Supply (CRS) model. Calculated fluxes of both 210Pb and 137Cs varied drastically among four of the profiles (MB4, MB6, CC and CL2), probably due to differences in their sedimentary environments. In addition, we found the flux data exhibiting a clear decreasing gradient in accordance with their average deposition rate, which was in turn related to the specific location of the profiles. We believe this phenomenon may correspond to global warming of the last century, since warming-induced surface runoff would bring more inflow water and detritus to the coring sites, thus enhancing the difference among the profiles. To verify this hypothesis, the deposition rate against age of the sediments was calculated based on their determined chronology, which showed ascending trends in all four profiles. The significant increase in deposition rates over the last century is probably attributable to recent warming, implying a potential utilization of radionuclides as environmental indicators in this region.

Beryllium-7 and lead-210 chronometry of modern soil processes: The Linked Radionuclide aCcumulation model, LRC

Soil systems are known to be repositories for atmospheric carbon and metal contaminants, but the complex processes that regulate the introduction, migration and fate of atmospheric elements in soils are poorly understood. This gap in knowledge is attributable, in part, to the lack of an established chronometer that is required for quantifying rates of relevant processes. Here we develop and test a framework for adapting atmospheric lead-210 chronometry (210Pb; half-life 22years) to soil systems. We propose a new empirical model, the Linked Radionuclide aCcumulation model (LRC, aka “lark”), that incorporates measurements of beryllium-7 (7Be; half-life 54days) to account for 210Pb penetration of the soil surface during initial deposition, a process which is endemic to soils but omitted from conventional 210Pb models (e.g., the Constant Rate of Supply, CRS model) and their application to sedimentary systems. We validate the LRC model using the 1963–1964 peak in bomb-fallout americium-241 (241Am; half-life of 432years) as an independent, corroborating time marker. In three different soils we locate a sharp 241Am weapons horizon at disparate depths ranging from 2.5 to 6cm, but with concordant ages averaging 1967±4 via the LRC model. Similarly, at one site contaminated with mercury (HgT) we find that the LRC model is consistent with the recorded history of Hg emission. The close agreement of Pb, Am and Hg behavior demonstrated here suggests that organo-metallic colloid formation and migration incorporates many trace metals in universal soil processes and that these processes may be described quantitatively using atmospheric 210Pb chronometry. The 210Pb models evaluated here show that migration rates of soil colloids on the order of 1mmyr−1 are typical, but also that these rates vary systematically with depth and are attributable to horizon-specific processes of leaf-litter decay, eluviation and illuviation. We thus interpret 210Pb models to quantify (i) exposure of the soil system to atmospheric aerosol deposition in the context of (ii) organic carbon assimilation, colloid production, and advection through the soil profile. The behavior of some other elements, such as Cs, diverges from the conservative colloid behavior exemplified by Pb and Am, and in these cases the value of empirical 210Pb chronometry models like LRC and CRS is as a comparator rather than as an absolute chronometer. We conclude that 210Pb chronometry is valuable for tracing colloidally-mediated transport of Pb and similarly-refractory metals, as well as the mobile pool of carbon in soils.

Calibrating 210Pb dating results with varve chronology and independent chronostratigraphic markers: Problems and implications

Varved lake sediments provide a unique opportunity to validate results of isotope dating methods. This allows testing of different numerical models and constraining procedures to produce reliable and precise chronologies. Here we present results of the model testing and validation by multiple dating approaches for the varved sediment record from Lake Żabińskie (northeastern Poland). Our goal was to assess possible deviations of 210Pb-derived ages from true sediment ages provided by varve chronology and to check how different numerical procedures can improve the consistency of the chronologies. Different methods for age estimation were applied including varve counting, 210Pb, 137Cs, 14C and tephra identification. Microscopic analysis of the varve microfacies revealed that laminations found in Lake Żabińskie were biogenic (calcite) varves. Three independent counts indicated a good preservation quality of laminae in the sediment profile which contained 178+4/−8 varve years. The calendar-year time scale was verified with two maxima of 137Cs activity concentrations in the sediments (AD 1963 and 1986) and a terrestrial leaf dated to AD 1957–1958 by the 14C method. Additionally, geochemical analysis of the glass shards found in the sediments indicated a clear correlation with the Askja AD 1875 eruption of Iceland which provided an unambiguous verification of the varve chronology. For testing 210Pb dating we used two routinely applied models: Constant Flux Constant Sedimentation (CFCS) and Constant Rate of Supply (CRS). None of the models in their standard forms produced a chronology consistent with varve counts and independent chronostratigraphic markers. Both models yielded ages much younger than the calendar age with a difference of ca. 50 years at the bottom part of the profile. However, a significant improvement was introduced after using the composite CFCS model with sediment accumulation rates calculated for different zones of the sediment profile. This provided highly consistent values along the time scale with deviations <5 yrs compared with calendar ages. Also constraining the CRS model with 137Cs peaks as well as testing the correction values for incomplete 210Pb inventory provided results that finally deviated from the calendar age only by ≈ 10 yrs for the 120 years old sediments.

Modeling the downward transport of 210Pb in Peatlands: Initial Penetration‐Constant Rate of Supply (IP-CRS) model

The vertical distribution of 210Pb is commonly used to date peat deposits accumulated over the last 100–150years. However, several studies have questioned this method because of an apparent post-depositional mobility of 210Pb within some peat profiles. In this study, we introduce the Initial Penetration–Constant Rate of Supply (IP-CRS) model for calculating ages derived from 210Pb profiles that are altered by an initial migration of the radionuclide. This new, two-phased, model describes the distribution of atmospheric-derived 210Pb (210Pbxs) in peat taking into account both incorporation of 210Pb into the accumulating peat matrix as well as an initial flushing of 210Pb through the uppermost peat layers. The validity of the IP-CRS model is tested in four anomalous 210Pb peat records that showed some deviations from the typical exponential decay profile not explained by variations in peat accumulation rates. Unlike the most commonly used 210Pb-dating model (Constant Rate of Supply (CRS)), the IP-CRS model estimates peat accumulation rates consistent with typical growth rates for peatlands from the same areas. Confidence in the IP-CRS chronology is also provided by the good agreement with independent chronological markers (i.e. 241Am and 137Cs). Our results showed that the IP-CRS can provide chronologies from peat records where 210Pb mobility is evident, being a valuable tool for studies reconstructing past environmental changes using peat archives during the Anthropocene.

The rare earth element geochemistry on surface sediments, shallow cores and lithological units of Lake Acıgöl basin, Denizli, Turkey

The sediments in Lake Acıgöl, located in SW Anatolia, Turkey, were formed under tectono-sedimentary events. REE geochemical investigations of the Lake Acıgöl sediments, from surface and shallow core sediments at different depths (0–10cm, 10–20cm and 20–30cm) are presented to clarify the characteristics of REE and the nature of source rocks in the lake sediments’ and to deduce their paleoenvironmental proxies. The chondrite-normalized REE patterns of these sediments are shown as light enrichment in LREE and flat HREE with a negative Eu anomaly that is close to the continental collision basin (CCB) in its profile; this is not comparable with PAAS and UCC. Inorganic detrital materials control the REE characteristics of the Lake Acıgöl sediments and these sediments were accumulated in oxic and dysoxic depositional conditions and/or at passive margins derived from oceanic island arc rocks. They were affected by low chemical weathering, either at the original source or during transport, before deposition under arid or subtropical humid climatic conditions. In addition, we used GIS techniques (such as Inverse Distance Weighted (IDW) and Geographically Weighted Regression (GWR)) to investigate the spatial interpolation and spatial correlation of the REEs from the lake surface sediments in Lake Acıgöl and its surrounding lithological units. GIS techniques showed that the lithological units (e.g., Hayrettin Formation) north of Lake Acıgöl have high REE contents; however, Eu/Eu∗ values were higher in some lake surface sediments than in lithological units, and that refers to a negative Eu-anomaly. Therefore, Lake Acıgöl sediments are derived from the weathered products, mainly from local, highly basic bedrock around the lake from the Archean crust. The chronology of Lake Acıgöl sediment was conducted using the Constant Rate of Supply (CRS) model. Using the CRS methods for the calculation of sedimentation rate, we obtained a 0.012g/cm2/year value which is an average value for the first 20cm depth of this lake. The core activity profiles of 210Pb and 137Cs were measured to estimate the age of the sediments; we observed activities of 8.08±5.5Bq/kg for 210Pb and 0.86±0.6Bq/kg for 137Cs.

Examining 239+240Pu, 210Pb and historical events to determine carbon, nitrogen and phosphorus burial in mangrove sediments of Moreton Bay, Australia

Two sediment cores were collected in a mangrove forest to construct geochronologies for the previous century using natural and anthropogenic radionuclide tracers. Both sediment cores were dated using 239+240Pu global fallout signatures as well as 210Pb, applying both the Constant Initial Concentration (CIC) and the Constant Rate of Supply (CRS) models. The 239+240Pu and CIC model are interpreted as having comparable sediment accretion rates (SAR) below an apparent mixed region in the upper ∼5 to 10 cm. In contrast, the CRS dating method shows high sediment accretion rates in the uppermost intervals, which is substantially reduced over the lower intervals of the 100-year record. A local anthropogenic nutrient signal is reflected in the high total phosphorus (TP) concentration in younger sediments. The carbon/nitrogen molar ratios and δ15N values further support a local anthropogenic nutrient enrichment signal. The origin of these signals is likely the treated sewage discharge to Moreton Bay which began in the early 1970s. While the 239+240Pu and CIC models can only produce rates averaged over the intervals of interest within the profile, the 210Pb CRS model identifies elevated rates of sediment accretion, organic carbon (OC), nitrogen (N), and TP burial from 2000 to 2013. From 1920 to 2000, the three dating methods provide similar OC, N and TP burial rates, ∼150, 10 and 2 g m−2 year−1, respectively, which are comparable to global averages.

Dating Sediment in a Fast Sedimentation Reservoir using Cesium‐137 and Lead‐210

More than 10,000 reservoirs have been constructed in agricultural watersheds in the United States since the 1940s to control floods and sediments. Reservoir sedimentation records provide a unique opportunity to retrospectively study the effects of land use changes and climate variations on sediment production if the sediment chronology could be properly determined. The objectives of this study were to: (i) evaluate the applicability of four unsupported 210Pb (210Pbex) models for dating deposited sediments in fast‐sedimentation environments; (ii) estimate the sedimentation rates; and (iii) relate the sedimentation rates to changes in soil conservation measures, land use, and climate. Three sediment profiles were sampled at 5‐cm intervals in a flood control reservoir in the Fort Cobb Reservoir Experimental Watershed in southwestern Oklahoma. Radioactivity was measured with a γ spectrometer for radioisotopes 137Cs and 210Pb. Four 210Pbex dating models were tested. Three models (constant flux–constant sedimentation [CFCS], constant initial concentration [CIC], and constant rate of supply [CRS]), which are widely used in the lacustrine and marine environments under slow‐sedimentation conditions, were not applicable to fast‐sedimentation conditions because of considerable 210Pbex input with the sediment, which is assumed negligible in the models. A modified CRS model that uses 137Cs age markers as references improved determination of the sediment chronology. The average sedimentation rates were three to five times higher during the 1957 to 1963 time period than during the 1964 to 2011 period. The significant sediment reductions coincided with the implementation of numerous conservation measures in the watershed, including check dams, terraces, changing cropping patterns, and progressive adoption of no‐till and conservation tillage systems.

210Pb and compositional data of sediments from Rondonian lakes, Madeira River basin, Brazil

Gold exploration has been intensive in Brazilian Amazon over the last 40 years, where the use of mercury as an amalgam has caused abnormal Hg concentrations in water bodies. Special attention has been directed to Madeira River due to fact it is a major tributary of Amazon River and that since 1986, gold exploration has been officially permitted along a 350km sector of the river. The 210Pb method has been used to date sediments taken from nine lakes situated in Madeira River basin, Rondônia State, and to verify where anthropogenic Hg might exist due to gold exploitation in Madeira River. Activity profiles of excess 210Pb determined in the sediment cores provided a means to evaluate the sedimentation rates using a Constant Flux: Constant Sedimentation (CF:CS) and Constant Rate of Supply (CRS) of unsupported/excess 210Pb models. A significant relationship was found between the CF:CS sedimentation rates and the mean values of the CRS sedimentation rates (Pearson correlation coefficient r=0.59). Chemical data were also determined in the sediments for identifying possible relationships with Hg occurring in the area. Significant values were found in statistical correlation tests realized among the Hg, major oxides and Total Organic Carbon (TOC) content in the sediments. The TOC increased in the sediment cores accompanied by a loss on ignition (LOI) increment, whereas silica decreased following a specific surface area raising associated to the TOC increase. The CRS model always provided ages within the permitted range of the 210Pb-method in the studied lakes, whereas the CF:CS model predicted two values above 140 years.

Evidence that excess 210Pb flux varies with sediment accumulation rate and implications for dating recent sediments

Most 210Pb dating models assume that atmospheric flux of excess 210Pb (210Pbexc) to the sediment–water interface remains constant over time. We revisited this assumption using statistical analysis of a database of laminated sediments and evaluated the implications for radiometric dating of recent deposits. A bibliographic survey enabled us to create a database with 10 annually laminated sediment cores from a variety of aquatic systems. The database has records of 210Pbexc flux, initial 210Pbexc activity, and sediment accumulation rate (SAR). 210Pbexc flux to sediments varied with time, and 1/3 of the data had relative deviations from the mean value >25 %. There was no statistically significant correlation between activities at the core top and SAR, whereas a statistically significant (p < 0.01) linear regression between 210Pbexc flux and SAR was found for nine of the ten cores. Thus, in most of the studied aquatic systems, 210Pbexc flux to the sediment was governed primarily by flux of matter, rather than by direct atmospheric 210Pbexc deposition. Errors in chronology and SAR, attributable to varying 210Pbexc flux and estimated by the constant rate of supply (CRS) model, were evaluated from its analytical solutions, and tested against SAR values from this database that were derived independently from varves. We identified several constraints for general application of the CRS model, which must be taken into account to avoid its misuse.

A comparative evaluation of the CF:CS and CRS models in 210Pb chronological studies applied to hydrographic basins in Brazil

The Constant Flux: Constant Sedimentation (CF:CS) and Constant Rate of Supply (CRS) of unsupported⧸excess 210Pb models have been applied to a 210Pb data set providing of eighteen sediments profiles sampled at four riverine systems occurring in Brazil, South America: Corumbataí River basin (S1=Site 1, São Paulo State), Atibaia River basin (S2=Site 2, São Paulo State), Ribeirão dos Bagres basin (S3=Site 3, São Paulo State) and Amazon River mouth (S4=Site 4, Amapá State). These sites were chosen for a comparative evaluation of the performance of the CF:CS and CRS models due to their pronounced differences on the geographical location, geological context, soil composition, biodiversity, climate, rainfall, and water flow regime, among other variable aspects. However, all sediments cores exhibited a common denominator consisting on a database built from the use of the same techniques for acquiring the sediments major chemical composition (SiO2, Al2O3, Na2O, K2O, CaO, MgO, Fe2O3, MnO, P2O5, TiO2 and LOI-Loss on Ignition) and unsupported⧸excess 210Pb activity data. In terms of sedimentation rates, the performance of the CRS model was better than that of the CF:CS model as it yielded values more compatible with those expected from field evidences. Under the chronological point of view, the CRS model always provided ages within the permitted range of the 210Pb-method in the studied sites, whereas the CF:CS model predicted some values above 150 years. The SiO2 content decreased in accordance with the LOI increase in all cores analyzed and such inverse relationship was also tracked in the SiO2–LOI curves of historical trends. The SiO2–LOI concentration fluctuations in sites S1 and S3 also coincided with some Cu and Cr inputs in the drainage systems.

Radiometric dating of sediment records in Kuwait’s marine area

Six sediment cores collected from the Northwestern Arabian/Persian Gulf have been radiometrically dated by 210Pb. Three cores were collected from stations within the Kuwait Bay, and three others were collected from stations outside the bay. Two models have been used for 210Pb dating of sediment cores, i.e. Constant Flux: Constant Sedimentation (CF:CS) Model and the Constant Rate of Supply (CRS) Model. The average rates were found to vary significantly between 0.16 and 1.00 cm y−1 for stations outside and within the bay respectively. The variability of the sedimentation rate was essentially physiographic characteristics and variable hydrodynamic condition. In this study, 137Cs fallout radiotracer was also used to construct a realistic chronology. It was observed that the 137Cs in the entire vertical profile has been continuously contributed by fluvial and atmospheric deposition.

Sedimentation rates in the Lake Qattinah using 210Pb and 137Cs as geochronometer

Abstract The constant rate of supply (CRS) of excess 210Pb model was successfully applied to assess 210Pb data of two sediment cores from the lake Qattinah, Syria. Gamma spectrometry was used to determine 137Cs and 210Pb activity concentrations. The bottom of the cores was 210Pb-dated to years 1907 and 1893. The accumulation rates were determined using 210Pb method and found to vary similarly in both cores from 0.10 ± 0.01 to 3.78 ± 0.57 kg m−2 y−1 during the past century. 137Cs was used as an in-dependent chronometer. The two distinct peaks observed on the 137Cs record of both cores, corresponding to 1965 and 1986, have allowed a successful validation of the CRS model.

Reconstruction of the historical deposition environment from 210Pb and 137Cs records at two tidal flats in China

To examine the historical depositional environment with the evolution of vegetation at tidal flats, sediment samples were collected and grain-size distribution, 137Cs and 210Pb characteristics, heavy metals content, stratigraphy and the vegetation information were measured at Linhong and Chongming Dongtan tidal flat in China. Sediment grain size parameters exhibited transitional lines of the unvegetated flat to the vegetated flat. The vertical profiles of the 137Cs and 210Pbex reflected different depositional environment at the tidal flats. The linear/slumps profiles of 210Pbex indicated complex hydrodynamics or rapid changes in sediment supply. The maximum peaks of 137Cs activity were observed in some cores. The sedimentation rates from the 137Cs maximum deposition peaks in 1963–1964 were comparable with the results from the 210Pbex-CRS (Constant Rate of Supply) method. Positive relationships between the average activities of 137Cs, 210Pbex, inventory of 210Pbex and the mean clay composition, suggested that grain size control effect was an important factor to influence the characteristics of 137Cs and 210Pb distribution at the tidal flats. For heavy metals, only Hg, Cd and Cr were moderately polluted at the Linhong tidal flat and the Chongming Dongtan, respectively. Integrating the results above and the stratigraphy, the vegetation introduction historical information, the clearer sedimentation evolution processes of the tidal flats were reconstructed, which is necessary for the coastal zone management and the pollution evaluation.

Eruption history, conduit migration, and steady discharge of magma for the past 50,000 yr at Esan volcanic complex, northern Japan

We have undertaken a detailed field, petrological, geochronological, and modeling study of Esan volcanic complex, northern Japan, in order to establish its eruptive history over the past 50,000 yr. The Esan volcanic complex includes seven lava domes, which are endogenous domes developed without basal edifices. Each dome was produced by intermediate to silicic magmas with 57–67 wt% SiO 2 that were erupted in magnitude 4–5 eruptions. Five explosively erupted pyroclastic units cover the aprons of these lava domes. The spatial and temporal relationships of the domes and the pyroclastic units have been determined in order to constrain the eruptive sequence of the Esan volcanic complex. A simple elastic model, assuming a hydraulic connection state, was utilized to study variations in long-term magma discharge at the Esan volcanic complex, which have been attributed to changes in magma storage conditions. The stepwise change in magma discharge with time, which is 4.2–5.3 × 10 4 m 3 /yr, is interpreted to reflect a change between magma chamber radius ( R c ) and magma depth ( H c ) caused by an upward migration of magma. Assuming a continuous input of magma from a deep source at a constant supply rate, the magma storage system that existed during the early stage of the Esan volcanic complex has been renewed, which will result in a shorter recurrence interval between eruptions rather than a long period of dormancy (22,400 yr). Given this finding, and the fact that the most recent eruption occurred 9000 yr ago, there is currently a risk of a large eruption at the Esan volcanic complex.

Sedimentation rates in Bera Lake (Peninsular Malaysia) using 210Pb and 137Cs radioisotopes

The evolutionary environmental history of Bera Lake was studied using the fallout radioisotopes137Cs and 210Pb. 317Cs horizons in the all ten studied cores showed a constant rate of 210Pb supply along all distinctive layers in each core. The lithology of layers significantly affected the variation of 210Pb value with depth. The chronology of Bera Lake sediment was conducted using the Constant Rate of Supply (CRS) model. The 1963 fallout maximum 137Cs from atmospheric testing of nuclear weapons found in all selected master cores at the depth of 40 cm. The mean pre-1950 sediment accumulation rate was ranged between 0.06 ± 0.02 and 0.16 ± 0.2 g cm−2 y−1. Environmental impacts of five deforestation projects performed from 1972 to 1995 at the catchment area, contributed significantly toward increasing the sedimentation rate within Bera Lake. Besides the 137Cs horizons, the charcoal horizon at the lower contact of white sandy mud revealed the datum of maximum deforestation in the study area. 210Pb dates using the CRS model correlated historical sediment fluxes to anthropogenic changes in Bera Lake catchment area. Organicrich sediments deposited mostly at the top of the Bera Lake sediment columns with a mean rate of 0.2 ± 0.1 g cm−2 y−1 since 1994. High biomass productivity of mature oil palm plantations, which were developed in the catchment area, dictated organic-rich deposit distribution. This study highlighted capability of radioisotopes to reconstruct long-term (100–150 years) history of a natural lake at a tropical area where surrounding catchment has extensively deforested over the recent decades.

Effect of Surface Cooling on Fatigue Life Improvement

In this study, we investigate the influence of surface cooling on the life of specimens undergoing low-to-intermediate-cycle fatigue. The experiments involve rotating-bending tests with Stainless Steel 304L and Steel 4145 specimens. External cooling air is provided via a vortex tube at a constant supply rate. Results are compared with the case of fatigue at room temperature. The results of experiments reveal significant improvement in fatigue life when the surface of the specimen is cooled. A possible explanation for the observed phenomenon is the notion of self-organization within the context of irreversible thermodynamics.