Lacustrine evidence of Holocene environmental change from three Faroese lakes: a multiproxy XRF and stable isotope study

The vegetation history of the Faroe Islands has been investigated in numerous studies all broadly showing that the early-Holocene vegetation of the islands largely consisted of fellfield with gravely and rocky soils formed under a continental climate which shifted to an oceanic climate around 10,000 cal yr BP when grasses, sedges and finally shrubs began to dominant the islands. Here we present data from three lake sediment cores and show a much more detailed history from geochemical and isotope data. These data show that the Faroe Islands were deglaciated by the end of Younger Dryas (11,700 10,300 cal yr BP), at this time relatively high sedimentation rates with high delta C-13 imply poor soil development. delta C-13, Ti and chi data reveal a much more stable and warm mid-Holocene until 7410 cal yr BP characterised by increasing vegetation cover and build up of organic soils towards the Holocene thermal maximum around 7400 cal yr BP. The final meltdown of the Laurentide ice sheet around 7000 cal yr BP appears to have impacted both ocean and atmospheric circulation towards colder conditions on the Faroe Islands. This is inferred by enhanced weathering and increased deposition of surplus sulphur (sea spray) and erosion in the highland lakes from about 7400 cal yr BP. From 4190 cal yr BP further cooling is believed to have occurred as a consequence for increased soil erosion due to freeze/thaw sequences related to oceanic and atmospheric variability. This cooling trend appears to have advanced further from 3000 cal yr BR A short period around 1800 cal yr BP appears as a short warm and wet phase in between a general cooling characterised by significant soil erosion lasting until 725 cal yr BP. Interestingly, increased soil erosion seems to have begun at 1360 cal yr BP, thus significantly before the arrival of the first settlers on the Faroe Island around 1150 cal yr BP, although additional erosion took place around 1200 cal yr BP possibly as a consequence of human activities. Hence it appears that if humans caused a change in the Faroe landscape in terms of erosion they in fact accelerated a process that had already started. Soil erosion was a dominant landscape factor during the Little Ice Age, but climate related triggers can hardly be distinguished from human activities. (c) 2010 Elsevier Ltd. All rights reserved.

The metamorphosis of supernova SN 2008D/XRF 080109: A link between supernovae and GRBs/hypernovae

The only supernovae (SNe) to show gamma-ray bursts ( GRBs) or early x-ray emission thus far are overenergetic, broad- lined type Ic SNe ( hypernovae, HNe). Recently, SN 2008D has shown several unusual features: (i) weak x-ray flash (XRF), (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SN Ic HNe, and (iv) development of helium lines as in SNe Ib. Detailed analysis shows that SN 2008D was not a normal supernova: Its explosion energy (E approximate to 6 x 10(51) erg) and ejected mass [similar to 7 times the mass of the Sun ( M.)] are intermediate between normal SNe Ibc and HNe. We conclude that SN 2008D was originally a similar to 30 M. star. When it collapsed, a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse to black holes.

The Early Asymmetries of Supernova 2008D/XRF 080109

Spectropolarimetry of the Type Ib SN 2008D, associated with the X-ray Flash (XRF) 080109, at two separate epochs, is presented. The epochs of these observations correspond to V-band light curve maximum and 15 days after light curve maximum (or 21 and 36 days after the XRF). We find SN 2008D to be significantly polarized, although the largest contribution is due to the interstellar polarization component of Q ISP = 0% ± 0.1% and U ISP = -1.2% ± 0.1%. At the two epochs, the spectropolarimetry of SN 2008D is classified as being D1+L(He I)+L(Ca II). The intrinsic polarization of continuum wavelength regions is <0.4%, at both epochs, implying an asymmetry of the photosphere of <10%. Similar to other Type Ibc SNe, such as 2005bf, 2006aj, and 2007gr, we observed significant polarization corresponding to the spectral features of Ca II, He I, Mg I, Fe II and, possibly, O I ?7774, about a close-to-spherically symmetric photosphere. We introduce a new plot showing the chemically distinct line-forming regions in the ejecta and comment on the apparent ubiquity of highly polarized high-velocity Ca II features in Type Ibc SNe. The polarization angle of Ca II IR triplet was significantly different, at both epochs, to those of the other species, suggesting high-velocity Ca II forms in a separate part of the ejecta. The apparent structure in the outer layers of SN 2008D has implications for the interpretation of the early-time X-ray emission associated with shock breakout. We present two scenarios, within the jet-torus paradigm, which explain the lack of an apparent geometry discontinuity between the two observations: (1) a jet which punched a hole straight through the progenitor and deposited Ni outside the ejecta and (2) a jet which stalled inside the radius of the photosphere as observed at the second epoch. The lack of a peculiar polarization signature, suggesting strongly asymmetric excitation of the ejecta, and the reported properties of the shock-breakout favor the second scenario.

Rapid and nondestructive measurement of labile Mn, Cu, Zn, Pb and As in DGT by using field portable-XRF

The technique of diffusive gradients in thin films (DGT) is often employed to quantify labile metals in situ; however, it is a challenge to perform the measurements in-field. This study evaluated the capability of field-portable X-ray fluorescence (FP-XRF) to swiftly generate elemental speciation information with DGT. Biologically available metal ions in environmental samples passively preconcentrate in the thin films of DGT devices, providing an ideal and uniform matrix for XRF nondestructive detection. Strong correlation coefficients (r > 0.992 for Mn, Cu, Zn, Pb and As) were obtained for all elements during calibration. The limits of quantitation (LOQ) for the investigated elements of FP-XRF on DGT devices are 2.74 for Mn, 4.89 for Cu, 2.89 for Zn, 2.55 for Pb, and 0.48 for As (unit: µg cm(-2)). When Pb and As co-existed in the solution trials, As did not interfere with Pb detection when using Chelex-DGT. However, there was a significant enhancement of the Pb reading attributed to As when ferrihydrite binding gels were tested, consistent with Fe-oxyhydroxide surfaces absorbing large quantities of As. This study demonstrates the value of the FP-XRF technique to rapidly and nondestructively detect the metals accumulated in DGT devices, providing a new and simple diagnostic tool for on-site environmental monitoring of labile metals/metalloids

Characterization of melanoidins from a glucose-glycine model system

The properties of melanoidins prepared from glucose and glycine (GG) were investigated by a three step purification protocol consisting of dialysis, gel filtration at high ionic strength and ion metal affinity chromatography. The high molecular weight fraction obtained in the GG system is responsible for 80% of the total brown colour and its antioxidative ability was about 1/4 of that of Trolox measured by the inhibition of linoleic acid oxidation. GG melanoidins have good affinity towards Cu (II) (32% bound to the resin) while it is much lower towards Pb (II) (10%) and Fe (II) (5%). Capillary zone electrophoresis analysis suggests that GG melanoidins are positively charged, although no signal was observed analysing melanoidins by matrix-assisted laser desorption-ionisation time-of-flight mass spectrometry (MALDI-TOF/MS).

Vegetation responses to rapid climatic changes during the last deglaciation 13,500-8,000 years ago on southwest Andoya, arctic Norway

The late-glacial vegetation development in northern Norway in response to climate changes during the Allerod, Younger Dryas (YD), and the transition to the Holocene is poorly known. Here we present a high-resolution record of floral and vegetation changes at lake Lusvatnet, south-west Andoya, between 13500 and 8000 cal b.p. Plant macrofossil and pollen analyses were done on the same sediment core and the proxy records follow each other very closely. The core has also been analyzed using an ITRAX XRF scanner in order to check the sediment sequence for disturbances or hiatuses. The core has a good radiocarbon-based chronology. The Saksunarvatn tephra fits very well chronostratigraphically. During both the Allerod and the Younger Dryas time-periods arctic vegetation prevailed, dominated by Salix polaris associated with many typically arctic herbs such as Saxifraga cespitosa, Saxifraga rivularis and Oxyria digyna. Both periods were cold and dry. Between 12450 and 12250 cal b.p. during the Younger Dryas chronozone, the assemblage changed, particularly in the increased abundance of Papaver sect. Scapiflora and other high-Arctic herbs, suggesting the development of polar desert vegetation mainly as a response to increased aridity. After 11520 cal b.p. a gradually warmer and more oceanic climate initiated a succession to dwarf-shrub vegetation and the establishment of Betula woodland after 1,000 years at c. 10520 cal b.p. The overall late-glacial aridity contrasts with oceanic conditions in southern Norway and is probably related to sea-ice extent.

The effect of various treatment conditions on natural zeolites: Ion exchange, acidic, thermal and steam treatments

Two different natural zeolites having different phase compositions were obtained from different regions of Turkey and modified by ion-exchange (0.5 M NH4NO3) and acid leaching using 1 M HCl. The natural and modified samples were treated at low temperature (LT), high temperature (HT) and steam (ST) conditions and characterised by XRF, XRD, BET, FTIR, DR-UV-Vis, NH3-TPD and TGA. Ion-exchange with NH4+ of natural zeolites results in the exchange of the Na+ and Ca2+ cations and the partial exchange of the Fe3+ and Mg2+ cations. However, steam and acidic treatments cause significant dealumination and decationisation, as well as loss of crystalline, sintering of phases and the formation of amorphous material. The presence of mordenite and quartz phases in the natural zeolites increases the stability towards acid treatment, whereas the structure of clinoptilolite-rich zeolites is mostly maintained after high temperature and steam treatments. The natural and modified zeolites treated at high temperature and in steam were found to be less stable compared with synthetic zeolites, resulting in a loss of crystallinity, a decrease in the surface area and pore volume, a decrease in the surface acidity as well as dealumination, and decationisation. (C) 2012 Elsevier Inc. All rights reserved.

Selenium Characterization in the Global Rice Supply Chain

For up to 1 billion people worldwide, insufficient dietary intake of selenium (Se) is a serious health constraint Cereals are the dominant Se source for those on low protein diets, as typified by the global malnourished population. With crop Se content constrained largely by underlying geology, regional soil Se variations are often mirrored by their locally grown staples. Despite this, the Se concentrations of much of the world's rice, the mainstay of so many, is poorly characterized, for both total Se content and Se speciation. In this study, 1092 samples of market sourced polished rice were obtained. The sampled rice encompassed dominant rice producing and exporting countries. Rice from the U.S. and India were found to be the most enriched, while mean average levels were lowest in Egyptian rice: similar to 32-fold less than their North American equivalents. By weighting country averages by contribution to either global production or export, modeled baseline values for both were produced. Based on a daily rice consumption of 300 g day(-1), around 75% of the grains from the production and export pools would fail to provide 70% of daily recommended Se intakes. Furthermore, Se localization and speciation characterization using X-ray fluorescence (mu-XRF) and X-ray absorption near edge structure (mu-XANES) techniques were investigated in a Se-rich sample. The results revealed that the large majority of Se in the endosperm was present in organic forms.

Speciation and distribution of arsenic and localization of nutrients in rice grains

Arsenic (As) contamination of rice grains and the generally low concentration of micronutrients in rice have been recognized as a major concern for human health. Here, we investigated the speciation and localization of As and the distribution of (micro)nutrients in rice grains because these are key factors controlling bioavailability of nutrients and contaminants. Bulk total and speciation analyses using high-pressure liquid chromatography (HPLC)-inductively coupled plasma mass spectrometry (ICP-MS) and X-ray absorption near-edge spectroscopy (XANES) was complemented by spatially resolved microspectroscopic techniques (micro-XANES, micro-X-ray fluorescence (micro-XRF) and particle induced X-ray emission (PIXE)) to investigate both speciation and distribution of As and localization of nutrients in situ. The distribution of As and micronutrients varied between the various parts of the grains (husk, bran and endosperm) and was characterized by element-specific distribution patterns. The speciation of As in bran and endosperm was dominated by As(III)-thiol complexes. The results indicate that the translocation from the maternal to filial tissues may be a bottleneck for As accumulation in the grain. Strong similarities between the distribution of iron (Fe), manganese (Mn) and phosphorus (P) and between zinc (Zn) and sulphur (S) may be indicative of complexation mechanisms in rice grains.

Speciation and localization of arsenic in white and brown rice grains

Synchrotron-based X-ray fluorescence (S-XRF) was utilized to locate arsenic (As) in polished (white) and unpolished (brown) rice grains from the United States, China, and Bangladesh. In white rice As was generally dispersed throughout the grain, the bulk of which constitutes the endosperm. In brown rice As was found to be preferentially localized at the surface, in the region corresponding to the pericarp and aleurone layer. Copper, iron, manganese, and zinc localization followed that of arsenic in brown rice, while the location for cadmium and nickel was distinctly different, showing relatively even distribution throughout the endosperm. The localization of As in the outer grain of brown rice was confirmed by laser ablation ICP-MS. Arsenic speciation of all grains using spatially resolved X-ray absorption near edge structure (micro-XANES) and bulk extraction followed by anion exchange HPLC-ICP-MS revealed the presence of mainly inorganic As and dimethylarsinic acid (DMA). However, the two techniques indicated different proportions of inorganic:organic As species. A wider survey of whole grain speciation of white (n=39) and brown (n=45) rice samples from numerous sources (field collected, supermarket survey, and pot trials) showed that brown rice had a higher proportion of inorganic arsenic present than white rice. Furthermore, the percentage of DMA present in the grain increased along with total grain arsenic.

Field observation of sequestration of uranium in iron-rich sediments under sequential reduction-oxidation conditions at the DOE Oak Ridge IFRC

At the U.S. DOE Oak Ridge Integrated Field Research Challenge (ORIFRC) site, the iron content of shallow subsurface materials (i.e. weathered saprolite) is relatively high (up to 5-6% as w/w), and therefore, the forms of the iron species present plays a critical role in the long-term sequestration of uranium. A long term pilot-scale study of the bioreduction and reoxidation of uranium conducted at the ORIFRC area 3 site, adjacent to the former S-3 disposal ponds (source zone), has provided us with the opportunity to study the impact of iron species on the sequestration of U(VI). The aqueous U(VI) concentrations at the site were decreased to below the EPA MCL through the intermittent injection of ethanol as the electron donor. Previous field tests indicated that both oxygen and nitrate could oxidize the bioreduced U(IV) and cause a short-term rebound of aqueous phase uranium concentration after the oxidative agents were delivered directly to the bioreduced zone.

A field test has been conducted to examine the long-term effect of exposure of bioreduced sediments to nitrate in contaminated groundwater for more than 1,380 days at the Area 3 site. Contaminated groundwater was allowed to invade the previously bioreduced zone via the natural groundwater gradient after an extended period in which reducing conditions were maintained and the bioreduced zone was protected from the influx of upgradient contaminated groundwater. The geochemical response to the invasion of contaminated groundwater was dependent on whether the monitoring location is in the middle or the fringe of the previously bioreduced zone. In general, the nitrate concentrations in the previously bioreduced area, increased gradually from near zero to ~50-300 mM within 200 days and then stabilized. The pH declined from bioreduced levels of 6.2-6.7 to below 5.0. Uranium concentrations rebounded in all monitoring wells but at different rates. At most locations U concentrations rebounded, declined and then rebounded again. Methane gas disappeared while a significant level (20,000 to 44,000 ppmv) N2O was found in the groundwater of monitoring wells after three years of reoxidization.

The U(IV) in sediments was mainly reoxidized to U(VI) species. Based on XANES analysis, the predominate uranium in all samples after re-oxidation was similar to a uranyl nitrate form. But the U content in the sediment remained as high as that determined after bioreduction activates were completed, indicating that much of the U is still sequestrated in situ. SEM observations of surged fine sediments revealed that clusters of colloidal-sized (200-500nm) U-containing precipitates appeared to have formed in situ, regardless from sample of FW106 in non-bioactivity control area or of pre-bioreduced FW101-2 and FW102-3. Additionally, SEM-EDS and microprobe analysis, showed that the U-containing precipitates (~1% U) in FW106 are notably higher in Fe, compared to the precipitates (~1-2.5% U) from FW101-2 and FW102-3. However, XRF analysis indicated that the U content was remained as high as 2180 and 1810 mg/kg with U/Fe ratio at 0.077 and 0.055 vs 0.037 g/g, respectively in pre-bioreduced FW101-2 and FW102-3, suggesting more U sequestrated by Fe in pre-bioreduced sediments.

High-resolution reconstruction of atmospheric deposition of trace metals and metalloids since AD 1400 recorded by ombrotrophic peat cores in Hautes-Fagnes, Belgium

The objective of our study was to determine the trace metal accumulation rates in the Misten bog, Hautes-Fagnes, Belgium, and assess these in relation to established histories of atmospheric emissions from anthropogenic sources. To address these aims we analyzed trace metals and metalloids (Pb, Cu, Ni, As, Sb, Cr, Co, V, Cd and Zn), as well as Pb isotopes, using XRF, Q-ICP-MS and MC-ICP-MS, respectively in two 40-cm peat sections, spanning the last 600 yr. The temporal increase of metal fluxes from the inception of the Industrial Revolution to the present varies by a factor of 5–50, with peak values found between AD 1930 and 1990. A cluster analysis combined with Pb isotopic composition allows the identification of the main sources of Pb and by inference of the other metals, which indicates that coal consumption and metallurgical activities were the predominant sources of pollution during the last 600 years.

When are total concentrations not total? Factors affecting geochemical analytical techniques for measuring element concentrations in soil

Inductively coupled plasma (ICP) following aqua regia digestion and X-ray fluorescence (XRF) are both geochemical techniques used to determine ‘total’ concentrations of elements in soil. The aim of this study is to compare these techniques, identify elements for which inconsistencies occur and investigate why they arise. A study area (∼14,000 km2) with a variety of total concentration controls and a large geochemical dataset (n = 7950) was selected. Principal component analysis determined underlying variance in a dataset composed of both geogenic and anthropogenic elements. Where inconsistencies between the techniques were identified, further numerical and spatial analysis was completed. The techniques are more consistent for elements of geogenic sources and lead, whereas other elements of anthropogenic sources show less consistency within rural samples. XRF is affected by sample matrix, while the form of element affects ICP concentrations. Depending on their use in environmental studies, different outcomes would be expected from the techniques employed, suggesting the choice of analytical technique for geochemical analyses may be more critical than realised.

Hydroclimatic shifts in northeast Thailand during the last two millennia - the record of Lake Pa Kho

The Southeast Asian mainland is located in the central path of the Asian summer monsoon, a region where paleoclimatic data are still sparse. Here we present a multi-proxy (TOC, C/N, δ¹³C, biogenic silica, and XRF elemental data) study of a 1.5m sediment/peat sequence from Lake Pa Kho, northeast Thailand, which is supported by 20 AMS ¹⁴C ages. Hydroclimatic reconstructions for Pa Kho suggest a strengthened summer monsoon between BC 170-AD 370, AD 800-960, and after AD 1450; and a weakening of the summer monsoon between AD 370-800, and AD 1300-1450. Increased run-off and a higher nutrient supply after AD 1700 can be linked to agricultural intensification and land-use changes in the region. This study fills an important gap in data coverage with respect to summer monsoon variability over Southeast Asia during the past 2000 years and enables the mean position of the Intertropical Convergence Zone (ITCZ) to be inferred based on comparisons with other regional studies. Intervals of strengthened/weaker summer monsoon rainfall suggest that the mean position of the ITCZ was located as far north as 35°N between BC 170-AD 370 and AD 800-960, whereas it likely did not reach above 17°N during the drought intervals of AD 370-800 and AD 1300-1450. The spatial pattern of rainfall variation seems to have changed after AD 1450, when the inferred moisture history for Pa Kho indicates a more southerly location of the mean position of the summer ITCZ.