Uranium Thorium Research Articles

Breeding of 233U in the thorium–uranium fuel cycle in VVER reactors using heavy water

A method is proposed for achieving optimal neutron kinetics and efficient isotope transmutation in the 233U–232Th oxide fuel of water-moderated reactors with variable water composition (D2O, H2O) that ensures breeding of the 233U and 235U isotopes. The method is comparatively simple to implement.

Comment on: “Uranium–thorium dating method and Palaeolithic rock art” by Sauvet et al. (2015, in press)

Abstract Sauvet et al. (in press) present a partial description of the Uranium-series or 230Th/234U dating method, which leads them to criticize this dating tool and claim that this method provides “an extremely wide range of uncertainty providing a weak base upon which to build scientific reasoning”. In this comment, we discuss three concepts introduced by these authors that could lead to a misunderstanding of the method and its application in the archaeological community and in the scientific debate about rock art chronology. The first misconception concerns the claim that “speleothems stopped during much of the Upper Palaeolithic”. A brief review of the literature demonstrates that this affirmation is not quite exact as a large number of studies document speleothem growth in Europe and circum-Mediterranean regions (as well as in other regions) during the upper Paleolithic. Secondly, Sauvet et al. claim that when age corrections are applied due to the possible presence of initial 230Th, the ages should be considered with caution or they should be rejected. However, this is not entirely correct, as this detrital fraction can be determined using several methods (and not merely assumed to be a “mean earth value”). Thirdly, with respect to their claim that “Loss of uranium or input of 230Th leads to anomalously old ages and sometimes to the impossibility to calculate an age when 230Th/234U > 1”, we present a classical figure of 230Th/234U evolution vs 234U/238U that can be drawn using the U-series equations demonstrating that 230Th/234U ratios can in fact be >1 and permit a valid age determination.

Burn up Study of an Innovative Natural Uranium-Thorium Fueled Reprocessing Free Fusion-Fission Hybrid Reactor Blanket with Closed Thorium-Uranium Fuel Cycle

In this paper, an innovative natural uranium-thorium fuel fusion-fission hybrid reactor (FFHR) design aiming at closed thorium-uranium fuel cycle, and which could operate with high energy gain, fast 233U breeding rate and tritium self-sufficiency, is presented. The reactor consists of two main modules, i.e. natural uranium module and thorium module, which are placed alternately in the blanket’s toroidal direction. Uranium module plays the role of energy generation and neutron multiplication at the initial stage. Excess neutrons are then used to drive the thorium module to breed 233U. After the 233U inventory reaches a certain level, the uranium module is then replaced by new thorium fuel module. The system is transition to the all thorium fueled operating mode. With appropriately selected thorium fuel to water volumetric ratio, the system could then be started by the limited bred 233U. The blanket could reach thorium-uranium closed fuel cycle with high energy gain and tritium self-sufficiency. The system could burn up about 90 tonnes 232Th at the end of 60 years operating.

Great Basin hydrology, paleoclimate, and connections with the North Atlantic: A speleothem stable isotope and trace element record from Lehman Caves, NV

We present a record of speleothem stable isotope (δ18O, δ13C) and trace element (Mg/Ca, Sr/Ca) variations from Lehman Caves, Nevada for an interval of time (139–128 ka) that encompasses the penultimate glacial termination, Termination II (T-II). Additional growth phases provide data from about 123 ka, a time that correlates with Marine Isotope Stage (MIS) 5e, and about 84 ka and between 82 and 81 ka (MIS 5a). Chronologies from two new stalagmites are anchored by thirty-six uranium–thorium dates. We also present new trace element data from stalagmite LC-2, which has a previously published uranium–thorium chronology and stable isotope record of T-II (Shakun et al., 2011). Our T-II δ18O record broadly replicates that of the Shakun et al. (2011) and Lachniet et al. (2014) records of this time, recording low values from 139 to 135 ka followed by an approximately 3.5‰ increase over an extended interval between 134 and 129 ka. This rise in δ18O values occurs during Heinrich Stadial 11 and the associated Weak Monsoon Interval observed in Chinese caves; our record broadly follows the marine termination, rising boreal summer insolation, and the rise in atmospheric CO2. We infer that this shift results from temperature increase due to increasing atmospheric CO2 and potentially a change in moisture source or precipitation seasonality from greater influence of the North American Monsoon accompanying summer insolation increase. It is also plausible that the melting of the ice sheet itself may have contributed to both temperature and precipitation seasonality changes. Trace element ratios and δ13C values are largely decoupled from δ18O values, showing minimal variation between 139 and 130 ka, for the duration of the Chinese Weak Monsoon Interval. However, these values increase sharply between 130 and 128 ka, which we interpret as increased prior calcite precipitation driven by a transition from wet to dry conditions. This abrupt drying event coincides within dating uncertainties with the abrupt strengthening of the East Asian summer monsoon, which marks the end of both the Weak Monsoon Interval and Heinrich Stadial 11. Our records demonstrate a link between North Atlantic climate and Great Basin moisture during this time that is consistent with the interpretation of data from the last glacial period and may result from abrupt shifts in Atlantic Meridional Overturning Circulation affecting the strength of the Aleutian Low.

Investigation of different scenarios of thorium–uranium fuel distribution in the VVER-1200 first core

Thorium fuel gives some superiority from safeguards point of view and is now being considered as an option for nuclear fuel. It is found to achieve high proliferation resistance because it has significant lower production of plutonium and minor actinides as compared with uranium fuel. The effect of the insertion of thorium, as a part of the nuclear fuel, on the neutronic parameters of the VVER-1200 first core under normal operation was studied. Two different patterns, namely mixed thorium uranium fuel and seed-blanket fuel, were compared. In addition to the amount of the inserted thorium, it was found that the position of the thorium assemblies inside the reactor core plays an important role in determining the effective multiplication factor and hence the core cycle length. It was concluded that the best location of thorium is in the periphery of the reactor core. As the preparation of thorium fuel does not involve all the requirements imposed by the uranium fuel, it is therefore expected that the economical feedback of both uranium–thorium fuels will be also positive, especially for a country with high thorium abundance.

Investigating fossil hydrothermal systems by means of fluid inclusions and stable isotopes in banded travertine: an example from Castelnuovo dell’Abate (southern Tuscany, Italy)

Southern Tuscany (Italy) hosts geothermal anomalies with associated widespread CO2 gas-rich manifestations and active travertine-deposing thermal springs. Geothermal anomalies have been active since the Late Miocene and have led to the formation of widespread Late Miocene–Pleistocene travertine deposits and meso- and epithermal mineralizations. This study investigates the travertine deposit exposed in the Castelnuovo dell’Abate area of southern Tuscany. Here, a fissure-ridge type travertine deposit and its feeding conduits, currently filled with banded calcite veins (i.e. banded travertine), represent a spectacular example of fossil hydrothermal circulation in the peripheral area of the exploited Monte Amiata geothermal field. The Castelnuovo dell’Abate travertine deposit and associated calcite veins were analysed to establish the characteristics of the parent hydrothermal fluids, and the age of this circulation. The focus of the study was on fluid inclusions, rarely considered in travertine studies, but able to provide direct information on the physico-chemical characteristics of the original fluid. Uranium–thorium geochronological data provided further constraints on the: (1) age of tectonic activity; (2) age of the hydrothermal circulation; and (3) evolution of the Monte Amiata geothermal anomaly. Results indicate that brittle deformation (NW- and SE-trending normal to oblique-slip faults) was active during at least the Middle Pleistocene and controlled a hydrothermal circulation mainly characterized by fluids of meteoric origin, and as old as 300–350 ka. This is the oldest circulation documented to date in the Monte Amiata area. The fluid chemical composition is comparable to that of fluids currently exploited in the shallow reservoir of the Monte Amiata geothermal field, therefore suggesting that fluid composition has not changed substantially over time. These fluids, however, have cooled by about 70 °C in the last 300–350 ka, corresponding to a cooling rate of the Monte Amiata geothermal area of about 20 °C 100 ka−1.

Uranium–thorium dating method and Palaeolithic rock art

Abstract Dramatic progress was seen in 14C-dating with the introduction of accelerator mass spectroscopy (AMS) which made possible the direct dating of prehistoric artworks painted or drawn with charcoal. However, in the case of engravings and red paintings, only indirect methods can be used that allow us to date deposits that have covered the works over time (TL, U/Th, oxalates, etc.). The uranium/thorium dating method gives reliable and relatively precise results in the case of massive speleothems, because the sampling is carried out at the heart of the material where the hypothesis of a closed system (that is, no exchange with the outside environment) is justified in most cases. Unfortunately, the situation is quite different in the case of thin layers of calcite that overlie Palaeolithic cave drawings. The conditions under which calcite forms depend largely on the hydrologic activity, which has greatly varied over the course of the Upper Palaeolithic and Holocene. In many cases, we can see that the growth of speleothems stopped during much of the Upper Palaeolithic. Consequently the ages obtained are minimum ages (terminus ante quem) which are frequently much younger than the real ages of the underlying artworks. Moreover, a much more serious but rarely considered source of error contradicts the assumption of a closed system. In thin layers of carbonate deposits and in damp media, the uranium incorporated into the calcite during its crystallization may be partially eliminated because of its solubility in water. Uranium leaching causes an artificial increase of the age that may reach considerable proportions (e.g. a negative hand in a cave in Borneo was dated to 27,000 years by U/Th whereas its 14C age was only 8–10,000 cal BP; Plagnes et al., 2003). Due to these two contradictory sources of error, the dates given by the U/Th method may prove to be younger or older, with deviations that are much larger than the standard deviations given by laboratories. As a result it is nearly impossible and very dangerous to base archaeological reasoning on U/Th ages of Palaeolithic artworks, so long as the dates are not confirmed by an independent method, dating the carbonates in the same samples by 14C being the best means of detecting anomalies. The application of the U/Th method for the dating of prehistoric rock art is still experimental. Technical improvements (for less damageable sampling) and fundamental research on the causes of errors are needed.

Rapid and non-destructive determination of uranium and thorium by gamma spectrometry and a comparison with ICP-AES

A rapid, simple and non-destructive method was developed for the determination of thorium, uranium by gamma ray spectrometry (high purity Ge detector) in thorium–uranium mixture. Using the calibration curves, thorium and uranium were analyzed in synthetic samples with RSD ~2 %. Inter element effect suggested that 583 and 185.7 keV gamma lines are more suitable for the determination of Th and U, respectively in a mixture of Th–U. The newly developed method was validated by routinely employed method using synthetic samples. An ICP-AES based method was developed for the determination of uranium and thorium for comparison purpose.

Evidence for global teleconnections in a late Pleistocene speleothem record of water balance and vegetation change at Sudwala Cave, South Africa

Understanding the global response to millennial-scale climatic events is essential to our comprehension of climatic teleconnections and projection of future change, however the extent and nature of their expression in areas of the Southern Hemisphere is often viewed as equivocal. Here we report uranium–thorium dating of speleothem formations sampled at Sudwala Cave in the north-eastern Lowveld region of South Africa's summer rainfall zone (SRZ). The growth intervals of multiple formations, alongside a detailed chronology and multi-proxy analysis of two periods of growth, 40–35 ka and 13.8–12.8 ka, in a stalagmite (SC1), provide information regarding key fluctuations in the palaeoclimatic and palaeoenvironmental conditions during the Late Pleistocene. High-resolution stable isotope, trace element, and micro-Raman analysis are used alongside petrographic investigation to provide a detailed assessment of the climatic conditions associated with the onset and termination of growth in SC1. The combined Raman and petrographic analysis represents a rare approach, enabling the identification of aragonite–calcite shifts both within and across growth intervals and diagenetic events, potentially significantly influencing the recorded signal and often resulting in the major loss of chemical information. Consequently, the identification of this post-depositional chemical alteration could become a crucial prerequisite in speleothem palaeoclimatology, particularly in areas prone to aragonite speleothem deposition susceptible to calcite conversion, such as cave sites hosted by dolomitic karst systems. The multiple proxies used in this study highlight the complex forcing relationships between climatically related environmental change and local cave conditions on speleothem precipitation, contesting a common paradigm by associating drier conditions at Sudwala with the initiation of speleothem growth. The growth interval identified in stalagmite SC1 during the late deglaciation (13.85–12.79 ka) coincides convincingly with both the Southern Hemispherically-Forced Antarctic Cold Reversal (14.1–12.8 ka), and the Younger Dryas (12.9–11.5 ka) of Northern Hemispheric origin, identifying Southern Africa as a vital location for the investigation of the hemispheric to global expression of the millennial-scale fluctuations of the last deglaciation.

Gamma-ray and neutron background comparison of US metropolitan areas

Gamma-ray and neutron background surveys were performed by the Naval Research Laboratory (NRL) in U.S. cities, including Washington, D.C.; Kansas City and St. Louis, Missouri; Chicago, Illinois; Richmond, Virginia; Boston, Massachusetts and Baltimore, Maryland. Measurements covered a range of industrial, residential and commercial areas. Germanium grade gamma-ray data over the energy range of 0.05–3.0MeV and neutron count rates with unmoderated He-3 sensitivity were recorded as a function of latitude, longitude and elevation in one second intervals. Typical Potassium Uranium Thorium (KUT) backgrounds were seen along with several anomalies. For example, a decrease in the thermal neutron flux in large urban canyons was seen and verified via Monte Carlo simulations. The data were collected to provide natural background models for simulation work. Germanium grade spectroscopy is required, because it provides sufficiently detailed isotopic information of the gamma-ray background. As expected a comparison of the background shows significant differences between the individual cities.

Surface Reduction of Neptunium Dioxide and Uranium Mixed Oxides with Plutonium and Thorium by Photocatalytic Reaction with Ice

The surface reductions of neptunium dioxide (NpO2) and two mixed oxides of uranium (U–Pu–O2 and U–Th–O2) with adsorbed water ice were studied by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively). The oxides were produced as thin films by reactive sputter deposition. Water was condensed as a thick ice overlayer on the surface at low temperature. Subsequent warming led to desorption of the ice. When warmed up under ultraviolet light (UV light, HeI and HeII radiation), the surface was reduced. NpO2 was reduced to surface neptunium sesquioxide (Np2O3). In the uranium–plutonium mixed oxide (U–Pu MOX), plutonium was reduced from plutonium dioxide (PuO2) to plutonium sesquioxide (Pu2O3). In uranium–thorium mixed oxide (U–Th MOX), the uranium was reduced from hyperstoichiometric uranium dioxide (UO2+x) to stoichiometric UO2 but not to lower oxides: the lowest thermodynamically stable oxides are formed. In the mixed oxides, uranium reduction seems to be activated for oxides with both tho...

Design of an MCNPX model to simulate the performance of BWRs using thorium as fuel and its validation with HELIOS code

The main target of this research was to estimate the possibility for improving the performance of Boiling Water Reactor (BWR) cores by using uranium thorium dioxide fuels instead of the commonly used oxide fuel. MCNPX (Monte Carlo N-Particle eXtend) computer code based on Mont Carlo method, is used to design two models for a BWR fuel bundle in a typical operating temperature and pressure conditions, the first is the oxide fuel bundle model and the second is the blanket–seed (BS) bundle model. A test case was compared with a previously published data calculated by HELIOS code and good agreement was found. The two models are used to determine the multiplication factor, pin-by-pin power distribution and thermal neutron flux distribution for both UO2 and (UZr/ThO2) fuels. BS bundle model improves the performance of BWR in different ways: (a) by increasing the energy extracted per fuel assembly, (b) by reducing the uranium ore, (c) reducing the plutonium accumulated in BWR through burn-up and continues to grow throughout the world, and (d) by increasing fuel burn-up and reactor lifetime. The spent fuel in the reactor can be recycled, and the plutonium and its isotopes can be extracted. The extracted plutonium can be used as a Mixed Oxide (MOX) fuel.

Landscape evolution in the periglacial zone of Eastern Europe since MIS5: Proxies from paleosols and sediments of the Cheremoshnik key site (Upper Volga, Russia)

A variety of studies of the re-examined (new exposure) Late Pleistocene key section Cheremoshnik (East European plain, middle of the Volga Basin of Yaroslavl) was conducted on a new methodological level using modern methods. For the first time, a series of paleosols (MIS5–MIS1) from the section offering significant information in regard to chronostratigraphy and landscape evolution have been studied in detail and dated. An excavation ∼7 m deep reveals a soil-sediment stratum which formed over the course of ∼115 ka in an accumulative beam-like terrace and consists of five lithological layers and six pedostratigraphical units.The base of the section was determined to be an Early Mikulino peat-dark humus paleosol which marked incipient subaerial pedogenesis on the Moscow (Riss II) moraine and was covered with a thickness of gyttja with a peat horizon (Histosol) which had formed 114–115 ka and was reliably dated using uranium–thorium dating. The following paleosols were successfully identified within the series of weak stone gullied-channel sediments within the Valdai (Wűrm) thickness (from bottom to top): (1) Bryansk paleosol (MIS3) – Gleysol – with three pedogenesis rhythms; (2) Trubchevskaya paleоsol – Gleyic Turbic Cryosol (MIS2) and (3) pedosediment formed at the end of the Bӧlling interstadial (MIS2). Terminal Pleistocene formations are marked with a gravelly stratum on the section's surface formed during the Preboreal period. Recent Regosol formed on loess-like loam deposits was identified at the top of the whole soil-sediment stratum. The 14C age of the paleosol humus varied between 27,500 and 11,400 cal. BP. The paleosols represent the northernmost occurrence of MIS5–MIS2 fossil soil in Europe, dominated by features of gleyzation, cryogenic aggregation, cracking, and humus and peat formation.Pollen analysis results allowed estimation of changes in vegetation cover, climatic conditions and the age of deposit sedimentation for the period from the Moskow Late Glacial to the Valdai Late Glacial and early Holocene times. Successive stages in the development of vegetation, high contents of alder and hazel pollen and the climax and distinct appearance of broadleaf trees relate the formation of biogenic sediments (LPAZ 2–6) in the Cheremoshnik section to the Mikulino Interglacial. Valdai (MIS4–MIS2) glacial sediment is absent within the investigated area.

Advanced x-ray spectrometric techniques for characterization of nuclear materials: An overview of recent laboratory activities

Advancements in x-ray spectrometric techniques at different stages have made this technique suitable for characterization of nuclear materials with respect to trace/major element determinations and compositional uniformity studies. The two important features of total reflection x-ray fluorescence spectrometry: 1) requirement of very small amount of sample in ng level 2) multielement analytical capability, in addition to other features, make this technique very much suitable to nuclear materials characterization as most of the nuclear materials are radioactive and the radioactive waste generated and radiation hazards to the operator are minimum when such low amount of sample is used. Similarly advanced features of energy dispersive x-ray fluorescence e.g. better geometry for high flux, reduction in background due to application of radiation filters have made the measurements of samples sealed inside thin alkathene/PVC covers possible with good sensitivity. This approach avoids putting the instrument inside a glove box for measuring radioactive samples and makes the operation/maintenance of the instrument and analysis of the samples possible in easy and fast manner. This approach has been used for major element determinations in mixed uranium–plutonium samples. Similarly μ-XRF with brilliant and micro-focused excitation sources can be used for compositional uniformity study of reactor fuel pellets. A μ-XRF study using synchrotron light source has been made to assess the compositional uniformity of mixed uranium–thorium oxide pellets produced by different processes. This approach is simple as it does not involve any sample preparation and is non-destructive. A brief summary of such activities carried out in our laboratory in past as well as ongoing and planned for the future have been discussed in the present manuscript.

Neutronic study of an innovative natural uranium–thorium based fusion–fission hybrid energy system

An innovative design for a water cooled fusion–fission hybrid reactor (FFHR), aiming at efficiently utilizing natural uranium and thorium resources, is presented. The major objective is to study the feasibility of this concept balanced with multi-purposes, including energy gain, tritium breeding and 233U breeding. In order to improve overall neutron economy of the system, the fission blanket is designed with two types of modules, i.e. the natural uranium modules (U-modules) and thorium modules (Th-modules), which are alternately arranged in the toroidal and poloidal directions of the blanket. This innovative design is based on a simple intuition of neutron distribution: with the alternate geometrical arrangement, energy multiplication by uranium fission, tritium breeding and 233U breeding are performed separately in different sub-zones in the blanket. The uranium modules which has excellent neutron economy under the combined neutron spectrum, plays the dominant role in the energy production, neutron multiplication and tritium breeding. Excess neutrons produced by the uranium modules are then used to drive the thorium modules (which have poor neutron economy) to breed 233U fuel. Therefore, it creates a new free dimension to realize the blanket’s balanced design. The COUPLE code developed by INET of Tsinghua University is used to simulate the neutronic behavior in the blanket. The simulated results show that with the volumetric ratio of thorium modules about 0.4, the balanced design for multi purposes is achievable, with energy multiplication M⩾9, tritium breeding ratio TBR⩾1.05, and at the end of the five years refueling cycle, the 233U enrichment in thorium modules exceeding 1.0%. The neutronic analysis results also show that the preliminary design of this innovative FFHR is of great potential to utilize the bred 233U effectively after the initial fuel load of the first ten-year operation.

Evolution characteristics of the Huangtupo landslide based on in situ tunneling and monitoring

Huangtupo landslide, volumetrically the largest, most complex landslide in the Three Gorges Reservoir region of China, is a dangerous mass on which the district of Badong has been inadvertently situated. Risk remediation efforts include the construction of a large observational tunnel and monitoring system that are unique in the world. This tunnel and its side branches permit detailed mapping of its 3D structure while providing samples for laboratory analysis. The new investigations validate that the Huangtupo landslide is a composite of several independent landslides and that movement occurs along the major rupture zones as well as on interlayer sliding zones in the underlying Badong Formation. Uranium–thorium disequilibrium dating establishes that the northern part of the landslide, called the Riverside Slump, underwent at least two periods of movement at about 100 and 40 ka (ka stands for a thousand years). These events were induced by the steep slope created by the downcutting of the Yangzte River. The results from in situ displacement monitoring over a 7-year period confirm that the central part of the landslide is creeping at a slow, relatively stable rate of about 15 mm/year rather than being in a stage of acceleration under the protection of anchored concrete beams and other defense structures at its toe. Available data suggest that engineering measures can control the independent landslides that together constitute the huge Huangtupo mass, which will avoid the need for costly relocation of thousands of people.

Reducing axial offset and improving stability in PWRs by using uranium–thorium fuel

The axial offset (AO) is a parameter used to monitor the core axial power distribution, and is important for safe reactor operation. Previous works have showed that a new type uranium–thorium (U–Th) based fuel assembly could be used to achieve a more homogenous radial power distribution, and thereby improve the thermal margins in the core. In this paper, it is shown that a core containing U–Th fuel assemblies also reduces the AO and improves the core stability. For an equilibrium U–Th core, the maximum AO could be reduced by 33%, and the minimum AO could be reduced by 8% compared with a standard uranium core. In the U–Th core, the maximum AO was influenced by the more negative moderator temperature coefficient of reactivity, while the minimum AO is mainly affected by the more homogenous radial power distribution. These findings conclude that the U–Th core displays a more homogenous power distribution both axially and radially, thus offering better thermal margins for power uprates and flexible power operation. Moreover, xenon oscillations in the core due to perturbations induced by the control rods are 30% more effectively damped for the U–Th core compared with the standard core, improving the stability in AO.

Testing the precision and accuracy of the U–Th chronometer for dating coral mortality events in the last 100 years

To assist with our understanding of reef dynamics prior to modern monitoring programs and recent observations of coral decline, a robust dating technique is required to place coral mortality events and historical changes in community structure in an accurate chronological framework. In this study we adopted a refined Uranium–Thorium (U–Th) isotope measurement protocol using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for rapid, precise and accurate age determination of a large branching Acropora coral death assemblage from an inshore reef of the Great Barrier Reef (GBR) where the timing of mortality is independently constrained. To achieve this, we developed a vigorous sample cleaning/treatment procedure to remove most non-carbonate detritus from the coral skeleton, and a correction scheme that accounts for initial 230Th sources in the dead coral skeletons. Using this method, the 230Th ages (with 2σ errors of 1–5 years) from 41 individual dead Acropora branches precisely bracket the timing of a documented ∼100% loss of hard coral cover, primarily Acropora, that was caused by increased sea-surface temperatures during the 1997–1998 mass bleaching event. Our results demonstrate the applicability of U–Th dating in accurately determining the timing of previous disturbance events in coral reef communities, as well as identifying potential drivers. This approach provides a powerful tool to researchers and managers in assessing the current status of reefs and identifying areas vulnerable to degradation where long-term monitoring data are absent or too recent.

Discerning the timing and cause of historical mortality events in modern Porites from the Great Barrier Reef

The life history strategies of massive Porites corals make them a valuable resource not only as key providers of reef structure, but also as recorders of past environmental change. Yet recent documented evidence of an unprecedented increase in the frequency of mortality in Porites warrants investigation into the history of mortality and associated drivers. To achieve this, both an accurate chronology and an understanding of the life history strategies of Porites are necessary. Sixty-two individual Uranium–Thorium (U–Th) dates from 50 dead massive Porites colonies from the central inshore region of the Great Barrier Reef (GBR) revealed the timing of mortality to have occurred predominantly over two main periods from 1989.2±4.1 to 2001.4±4.1, and from 2006.4±1.8 to 2008.4±2.2 A.D., with a small number of colonies dating earlier. Overall, the peak ages of mortality are significantly correlated with maximum sea-surface temperature anomalies. Despite potential sampling bias, the frequency of mortality increased dramatically post-1980. These observations are similar to the results reported for the Southern South China Sea. High resolution measurements of Sr/Ca and Mg/Ca obtained from a well preserved sample that died in 1994.6±2.3 revealed that the time of death occurred at the peak of sea surface temperatures (SST) during the austral summer. In contrast, Sr/Ca and Mg/Ca analysis in two colonies dated to 2006.9±3.0 and 2008.3±2.0, suggest that both died after the austral winter. An increase in Sr/Ca ratios and the presence of low Mg-calcite cements (as determined by SEM and elemental ratio analysis) in one of the colonies was attributed to stressful conditions that may have persisted for some time prior to mortality. For both colonies, however, the timing of mortality coincides with the 4th and 6th largest flood events reported for the Burdekin River in the past 60years, implying that factors associated with terrestrial runoff may have been responsible for mortality. Our results show that a combination of U–Th and elemental ratio geochemistry can potentially be used to precisely and accurately determine the timing and season of mortality in modern massive Porites corals. For reefs where long-term monitoring data are absent, the ability to reconstruct historical events in coral communities may prove useful to reef managers by providing some baseline knowledge on disturbance history and associated drivers.

Ancient DNA and dating of cave bear remains from Niedźwiedzia Cave suggest early appearance of Ursus ingressus in Sudetes

The migration of Ursus ingressus from Southern to Western Europe, where it replaced native forms of Ursus spelaeus, is well documented. However, its occurrence in Central and Eastern European countries is unexplored. We have characterized the cave bear population inhabiting the Sudetes Mountains during the Late Pleistocene. DNA analyses were performed on 39 cave bear specimens from the Niedźwiedzia Cave. Ten successfully yielded the 254-bp sequences of an mtDNA control region. Phylogenetic analyses allowed assignment of nine samples to the U. ingressus haplogroup and one to brown bear (Ursus arctos). The mtDNA haplotypes of U. ingressus formed a single cluster and differed from haplotypes obtained for cave bears from other excavation sites in Europe. Uranium–thorium and radiocarbon dating of selected samples has shown that U. ingressus appeared in the Sudetes region at least 80,000 years ago. This finding may suggest that the appearance of U. ingressus in this area resulted from migration that occurred earlier than the colonization of the Alps and Swabian Jura. It is possible that migration of U. ingressus proceeded along the Carpathian and Sudetes arc.