Carbon storage and DNA absorption in allophanic soils and paleosols

Andisols and andic paleosols dominated by the nanocrystalline mineral allophane sequester large amounts of carbon (C), attributable mainly to its chemical bonding with charged hydroxyl groups on the surface of allophane together with its physical protection in nanopores within and between allophane nanoaggregates. C near-edge X-ray absorption fine structure (NEXAFS) spectra for a New Zealand Andisol (Tirau series) showed that the organic matter (OM) mainly comprises quinonic, aromatic, aliphatic, and carboxylic C. In different buried horizons from several other Andisols, C contents varied but the C species were similar, attributable to pedogenic processes operating during developmental upbuilding, downward leaching, or both. The presence of OM in natural allophanic soils weakened the adsorption of DNA on clay; an adsorption isotherm experiment involving humic acid (HA) showed that HA-free synthetic allophane adsorbed seven times more DNA than HA-rich synthetic allophane. Phosphorus X-ray absorption near-edge structure (XANES) spectra for salmonsperm DNA and DNA-clay complexes indicated that DNA was bound to the allophane clay through the phosphate group, but it is not clear if DNA was chemically bound to the surface of the allophane or to OM, or both. We plan more experiments to investigate interactions among DNA, allophane (natural and synthetic), and OM. Because DNA shows a high affinity to allophane, we are studying the potential to reconstruct late Quaternary palaeoenvironments by attempting to extract and characterise ancient DNA from allophanic paleosol

New application of density fractionation: assessing trace element/soil matrix associations within organic waste-amended agricultural soils

International audienceinc (Zn) is a trace element (TE) that occurs naturally in soils, however spreading Zn-rich organic waste (OW) on farmlands may lead to hazardous Zn levels. Common problems arerelated to phytotoxicity, introduction into the food chain and groundwater contamination. Assessing the associations between OW-borne Zn and the soil matrix is paramount to predict its short- and long-term behavior in the environment. This is usually pursued by using either single/sequential extractions (SSE) or spectroscopic methods such as XAS. Nevertheless, SSE reflects element extractability rather than the nature of its interactions with bearing phases, while XAS requires synchrotron radiation sources that are not available in certain regions of the world. We applied a third approach in this study – namely soil density fractionation – to isolate and characterize the constituents of the soil matrix (i.e. potential Zn bearing phases) and thereafter identify their associations with natural and OW-borne Zn. The target density fractionswere the following: 2.7 g cm-3, plus an extractable fraction. The soil analyzed was a clayey Hapludox soil that received controlled pig slurry applications over 11 years, causing a 2-fold increase in Zn concentration within the surface layer: from 105.8 mg kg-1 of Zn (control soil) to 206.6 mg kg-1 of Zn (amended soil). Among the six selected density fractions, two of them were the most contrasting and representative. (I) The light fraction (<1.9 g cm-3) contained high OM concentration but accounted for only ~5% of the bulk soil mass. (II) The mineral-rich fraction (2.5–2.7 g cm-3) contained mainly quartz, kaolinite, vermiculite, a small amount of hematite and accounted for ~80% of the soil mass. In the control soil (no pig slurry application), 79.7% of the Zn was found in the mineral-rich 2.5–2.7 g cm-3 fraction. In the soil amended with pig slurry, the proportion of Zn found in the 2.5–2.7 g cm-3 fraction decreased to 57.3%, as Zn was also found in the OMrich <1.9 g cm-3 fraction (13.2%) and in the extractable fraction (16.6%). Other fractions were less representative in both soils (control and amended). The extractable, <1.9 g cm-3 and 2.5– 2.7 g cm-3 fractions accounted for roughly 1/3 each of the OW-borne Zn fate in the amended soil. Finally, these results were compared with data we previously reported for the same field experiment using well-stablished SSE and XAS techniques. Density fractionation not onlyagreed but also complemented the understanding of previous observations. This work demonstrates that density fractionation may be used as either main or complementary approach for assessing the biogeochemistry of TE such as Zn in the context of OW recycling in agricultural soils

Characteristics and sources of tephra layers in the EPICA-Dome C ice record (East Antarctica): Implications for past atmospheric circulation and ice core stratigraphic correlations

International audienceThirteen discrete air-fall tephra layers were identified in the last 200,000-yr section of the EPICA-Dome C ice record drilled in the East Antarctic plateau (75°06′S, 123°21′E). Quantitative grain size, glass particle morphology, and the grain-discrete major element composition of the glass fraction of these layers were investigated. Through comparison with literature data on the rock composition of Quaternary volcanic centres located within and around Antarctica, five tephra layers were attributed to South Sandwich volcanoes in the South Atlantic Ocean, two to South Shetland volcanoes (northern Antarctic Peninsula), two to Andean volcanoes, and four to Antarctic (Marie Byrd Land and Melbourne) provinces. The abundance of layers originating in the southern part of the Atlantic confirms that westerly atmospheric circulation spiralling towards East Antarctica prevailed over the last 200 ka. Moreover, the record of events from Antarctic centres suggests that atmospheric trajectories from West to East Antarctica can also be significant. A few ash layers are geochemically distinct and appear equivalent to levels from Vostok and Dome Fuji deep ice records, located ca. 600 km and ca. 2000 km, respectively, from Dome C on the Antarctic plateau. These layers provide unambiguous markers for future correlation with other Antarctic ice cores and circumpolar marine climatic records. They also provide reliable constraints to get a common timescale by glaciological modelling, and represent a first step towards absolute ice core dating

Single column extraction of Ge and Si from natural samples allows reliable Ge analysis by ICP-MS

International audienc

Single column extraction of Ge and Si from natural samples allows reliable Ge analysis by ICP-MS

International audienc

Volcanic synchronisation between the EPICA Dome C and Vostok ice cores (Antarctica) 0–145 kyr BP

This study aims at refining the synchronisation between the EPICA Dome C (EDC) and Vostok ice cores in the time interval 0–145 kyr BP by using the volcanic signatures. 102 common volcanic events were identified by using continuous electrical conductivity (ECM), di-electrical profiling (DEP) and sulfate measurements while trying to minimize the distortion of the glaciological chronologies. This is an update and a continuation of previous works performed over the 0–45 kyr interval that provided 56 tie points to the ice core chronologies (Udisti et al., 2004). This synchronisation will serve to establish Antarctic Ice Core Chronology 2012, the next synchronised Antarctic dating. A change of slope in the EDC-depth/Vostok-depth diagram is probably related to a change of accumulation regime as well as to a change of ice thickness upstream of the Lake Vostok, but we did not invoke any significant temporal change of surface accumulation at EDC relative to Vostok. No significant phase difference is detected between the EDC and Vostok isotopic records, but depth shifts between the Vostok 3G and 5G ice cores prevent from looking at this problem accurately. Three possible candidates for the Toba volcanic super-eruption �73 kyr ago are suggested in the Vostok and EDC volcanic records. Neither the ECM, DEP nor the sulfate fingerprints for these 3 events are significantly larger than many others in the records

Role of natural nanoparticles on the speciation of Ni in andosols of la Reunion

Andosols on the island of Reunion have high nickel (Ni) concentrations due to the natural pedo-geochemical background. Enhanced knowledge of Ni speciation is necessary to predict the bioavailability and potential toxicity of this element. Ni speciation in these andosols, marked by the presence of high amounts of natural aluminosilicate nanoparticles, was investigated in two complementary systems: (i) In a soil sample-densimetric fractionation was first performed in order to separate the potential bearing phases, prior to Ni speciation characterization. (ii) In a synthetic sample-Ni reactivity with synthetic aluminosilicate nanoparticle analogs were studied. In both cases, Ni speciation was determined using X-ray absorption spectroscopy (XAS). The results revealed that Ni had the same local environment in both systems (natural and synthetic systems), and Ni was chemically linked to natural short-range ordered aluminosilicates or analogs. This complex represented about 75% of the total Ni in the studied soil