Chemical Geology (CHEM GEOL)

Publications in this journal

• Article: The influence of climate on 13C/12C and 18O/16O ratios in tree ring cellulose of Pinus sylvestris L. growing in the central Scandinavian Mountains

  Kristina Seftigen, Hans W. Linderholm, Neil J. Loader, Yu Liu, Giles H.F. Young
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  ABSTRACT: The stable isotope composition of tree rings is known to contain valuable information of past climatic and environmental changes, which may be used as a complement to tree ring width and maximum latewood density in climate reconstructions. In this study we examine the character and strength of the climate signal captured in the δ18O and δ13C values of Scots pine (Pinus sylvestris L.) trees growing at the tree-line in the central Scandinavian Mountains. Between 4 and 14 trees were pooled to produce annual records of carbon and oxygen isotope ratios from tree ring cellulose, spanning the period AD 1736–2006. Weather conditions of the current growing season most strongly influenced the carbon and oxygen isotope ratios in a given tree ring. Both records showed positive correlations with temperature, sunshine and air pressure, and negative associations with precipitation. The overall climate signal in δ13C appeared to be slightly stronger than that of δ18O. Spatial correlation analysis with gridded instrumental data demonstrated that the carbon series captured the summer temperature signal in a broad region of mid-west Sweden and the eastern part of Norway, greatly exceeding the spatial coverage of the signal derived from pine ring widths growing in the central Scandinavian mountains. A weak relationship between δ13C and precipitation and a much stronger temperature and sunshine dependence may imply that photosynthetic rate rather than stomatal conductance is more important in controlling the inter-annual tree ring δ13C variability in the area.Moreover, it was shown that, the climate–δ18O and δ13C relationship was temporally unstable throughout the twentieth century, which was linked to large-scale shifts in climate that may have altered the isotope-climate dependence. Our results thus demonstrate that, stable isotopes in tree rings from maritime high-altitude Scandinavia can provide high-resolution regional climate information, especially regarding parameters associated with temperature. The non-stationary nature of the isotope–precipitation relationship may provide important information on past changes in the large-scale atmospheric circulation during summer. However, these issues needs to be further investigated before pine tree ring isotopes from this region can be confidently used in palaeoclimate reconstructions.Research highlights► Annual cellulose δ18O and δ13C values of Scots pine from the Scandinavian Mountains. ► Character and strength of the climate signal in the isotopic records is examined. ► Positive relation to temperature and sunshine, and negative to precipitation. ► Overall climate signal in δ13C is slightly stronger than that of δ18O. ► Temporally unstable associations with observed climate throughout the 20th century.
  Chemical Geology 05/2013; 286:84-93.
• Article: Coupling between suboxic condition in sediments of the western Bay of Bengal and southwest monsoon intensification: A geochemical study

  J.N. Pattan a, Ishfaq Ahmad Mir a, G. Parthiban a, Supriya G. Karapurkar a, V.M. Matta b, P.D. Naidu a, S.W.A. Naqvi a
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  ABSTRACT: Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14° 02′N; Long: 82° 00′E) at a water depth of 3307 m, has been made based on redox-sensitive element geochemistry. The high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, Ce/Ce*b1 and lower Mn/Al and Fe/Al ratios, compared to upper continental crust are all indicative of prevalence of suboxic condition in the benthic environment from 15.2 ka to 4.5 ka, peaking around 9.5 ka. The suboxic condition around 9.5 ka corresponds to the previously recorded southwest (SW) monsoon intensification in response to the increase in northern hemisphere summer insulation. However, productivity proxies – organic carbon and nitrogen contents – do not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in lithogenic material supplied from land due to SW monsoon intensification, which is evident by the very high concentration of Al, Zr and Hf, the flux of fresh labile organic matter and these might have formed dense mineral matter — biogenic aggregates which sinks rapidly to the seafloor, and the degradation of labile organic matter might have led to the development of suboxic condition in the benthic environment. There exists a strong positive correlation (r=0.98) between Mo and Zr during 15.2 ka to 4.5 ka suggesting a coupling between suboxic condition and lithogenic flux supply by the intensified SW monsoon. Our results suggest that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role in benthic biogeochemistry and ecology of the Bay of Bengal. We also provide the first record of the nitrogen isotopic composition (δ15N) of sedimentary organic matter in the western Bay of Bengal, a region where the mesopelagic oxygen minimum zone (OMZ) is just short of being suboxic (denitrifying) today. The sedimentary δ15N fluctuated considerably in the past, especially during the Marine Isotope Stage 3. Oscillations in δ15N were apparently in concert with those in organic carbon and nitrogen contents and could be related to climatic changes (Heinrich and Dansgaard–Oeschger events) in the North Atlantic. The Dansgaard–Oeschger 12 event appears to have exerted the most intense effect on Bay of Bengal biogeochemistry when surface productivity, as inferred from the organic carbon and nitrogen contents, was the highest recorded in the core, and the δ15N reached up to 6.3‰. Considering the probable dilution by isotopically light terrigenous organic matter, it would appear that OMZ of the Bay of Bengal had turned denitrifying. However, the absence of suboxic conditions in the sediments at this time suggests a decoupling of the benthic processes with those in the mesopelagic water column.
  Chemical Geology 04/2013; 2013(343):55–66.
• Article: Origin of gases and water in mud volcanoes of Andaman accretionary prism: implications for fluid migration in forearcs

  Jyotiranjan S. Ray, Alok Kumar, A.K. Sudheer, R.D. Deshpande, D.K. Rao, D.J. Patil, Neeraj Awasthi, Rajneesh Bhutani, Ravi Bhushan, A.M. Dayal
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  ABSTRACT: Extensive mud volcanism on the Andaman accretionary prism occurs above a complex network of faults and is caused by the convergence of the Indian plate and the Burmese micro plate. Mud volcanoes of the Andaman forearc have received little attention in spite of the fact that they are one of the important features of this tectonic setting, located within an ocean basin that has one of the highest sedimentation rates in the world, and that the materials emitted by them present a unique opportunity to study the chemistry of the detachable parts of the subducting slab. In this study we present mineralogical, chemical and isotopic data for argillaceous matter (mud matrix), gases and water emitted by these mud volcanoes and attempt to understand the variations in terms of their sources and processes within the forearc. The mud matrix is composed of smectite-illite-kaolinite-chlorite-plagioclase-quartzcalcite assemblage derived both from sediments and altered oceanic crust and originates from a deep-burial diagenetic environment. The modes of 13C distributions for methane (> -42‰), ethane (> -27‰) and CO2 (< -3‰) indicate thermogenic origin for these gases, with TOC and N of associated mud suggesting marine organic matter as the source. The water ejected at these mud volcanoes is much fresher (Cl- = 45 to 135 mM) than seawater and its 18O (-0.2 to 2.6 ‰) and D (-24 to -14‰) isotopic compositions fall well below the global meteoric water line. From their trace element contents and stable isotopic compositions we infer that the mud water is a mixture of sediment pore water (ancient seawater) and water released from dehydration of clay minerals. The 87Sr/86Sr of mud water (~0.7071) confirms the above inference and points out that altered oceanic crust plays a significant role in controlling thechemistry of water. The formation temperatures of mud ejecta, derived from mineralogical (smectite/illite), chemical (K+/Na+) and isotopic (D18O) geothermometers, lie in the range of 50oC-120oC – which corresponds to a depth zone of 2 to 6 km within the Andaman forearc. Based on all the evidences we conclude that the sampled mud volcano ejecta originate at the plate-boundary décollement zone, from the sediments and altered oceanic crust of the subducting Indian plate.
  Chemical Geology 04/2013;
• Article: Permian peralkaline, peraluminous and metaluminous A-type granites in the Panxi district, SW China: their relationship to the Emeishan mantle plume

  Shellnutt, J.G, Zhou, M.-F
  Chemical Geology 02/2013; 243:286-316.
• Article: EFFECT OF Mn(II) INCORPORATION ON THE TRANSFORMATION OF FERRIHYDRITE TO GOETHITE

  M. Alvarez, E.E. Sileo, E.H. Rueda
  Chemical Geology 02/2013; 216:89-97.
• Article: Rheology of volatile-bearing crystal mushes: mobilization vs. viscous death

  Mattia Pistone, Luca Caricchi, Peter Ulmer, Eric Reusser, Paola Ardia
  Chemical Geology 02/2013;
• Article: Biogeochemical mercury methylation influenced by reservoir eutrophication, Salmon Falls Creek Reservoir, Idaho, USA

  John E. Gray, Mark E. Hines
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  ABSTRACT: Salmon Falls Creek Reservoir (SFCR) in southern Idaho has been under a mercury (Hg) advisory since 2001 as fish in this reservoir contain elevated concentrations of Hg. Concentrations of total Hg (HgT) and methyl-Hg (MeHg) were measured in reservoir water, bottom sediment, and porewater to examine processes of Hg methylation at the sediment/water interface in this reservoir. Rates of Hg methylation and MeHg demethylation were also measured in reservoir bottom sediment using isotopic tracer techniques to further evaluate methylation of Hg in SFCR. The highest concentrations for HgT and MeHg in sediment were generally found at the sediment/water interface, and HgT and MeHg concentrations declined with depth. Porewater extracted from bottom sediment contained highly elevated concentrations of HgT ranging from 11–230 ng/L and MeHg ranging from 0.68–8.5 ng/L. Mercury methylation was active at all sites studied. Methylation rate experiments carried out on sediment from the sediment/water interface show high rates of Hg methylation ranging from 2.3–17%/day, which is significantly higher than those reported in other Hg contaminant studies. Using porewater MeHg concentrations, we calculated an upward diffusive MeHg flux of 197 g/year for the entire reservoir. This sediment derived MeHg is delivered to the overlying SFCR water column, and eventually transferred to biota, such as fish. This study indicates that methylation of Hg is highly influenced by the hypolimnetic and eutrophic conditions in SFCR.
  Chemical Geology 01/2013; 258:157-167.
• Article: Arsenopyrite dissolution rates in O2-bearing solutions

  Maria P. Asta, Jordi Cama, Carlos Ayora, Patricia Acero, Giovanni de Giudici
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  ABSTRACT: Arsenopyrite dissolution was studied by means of long-term, stirred and non-stirred flow-through experiments in the pH range of 1 to 9 at 25, 50 and 70 °C and at different input dissolved-O2 concentrations (from 0.2 to 8.7 mg L− 1).At pH lower than 4, aqueous iron, which is mainly in the ferrous form, and arsenic are stoichiometrically released. Sulphur concentrations released were lower than stoichiometrically expected (S/As < 1). X-ray Photoelectron Spectroscopy (XPS) and MicroRaman Spectroscopy surface analyses on reacted and unreacted samples showed an enrichment of the reacted arsenopyrite surface in sulphur and arsenic under acidic conditions.In the light of these results, the steady-state dissolution rates were estimated by the release of arsenic at pH < 4 and were used to derive an empirical dissolution rate law expressed as:where aO2 and aH+ are the activities of hydrogen ions and dissolved oxygen, respectively and their exponents were estimated from multiple linear regression of the dissolution rates. Temperature increase from 25 to 70 °C yields an apparent activation energy for the arsenopyrite oxidation by dissolved oxygen of 18.5 ± 1.6 kJ mol− 1.At pH > 6, aqueous iron is mainly in the ferric form and is depleted as it precipitates as Fe-oxyhydroxide onto arsenopyrite surfaces, yielding Fe/As and Fe/S less than one; between pHs 7 and 9, iron depletion is complete, and sulphur released is more abundant than arsenic released, which is precipitated as As–O phases, as confirmed by MicroRaman spectroscopy. At pHs 6–9, iron-oxyhydroxide phases and arsenic oxide phases upon the arsenopyrite surface provide an effective layer that reduces diffusion of dissolved oxygen and arsenopyrite dissolution. As coating on the arsenopyrite surface becomes the rate-limiting step, the Shrinking Core Model (SCM) allows quantification of the surface dissolution rate, especially from data obtained where the effect of coating was still negligible. The SCM also allowed us to calculate the effective coefficient for oxygen diffusion through the coating, which can vary from 10− 17 to 1.5 · 10− 16 m2 s− 1. The formation of such a coating produced a decrease in arsenic and sulphur release over time and a final surface passivation.
  Chemical Geology 01/2013;
• Article: Natural attenuation of arsenic in the Tinto Santa Rosa acid stream (Iberian Pyritic Belt, SW Spain): The role of iron precipitates

  M. P. Asta, C. Ayora, G. Roman-Ross, J. Cama, P. Acero, A. G. Gault, J. M. Charnock, F. Bardelli
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  ABSTRACT: Acid waters and sediments of the Tinto Santa Rosa acid stream (Iberian Pyritic Belt; SW, Spain) were analysed to determine the role of sedimentary phases in the behaviour of arsenic. Aqueous arsenic and iron concentrations decreased markedly from the adit mouth to 300 m downstream indicating iron minerals precipitation as well as arsenic sorption onto these newly-formed phases. This was confirmed by the high arsenic concentrations observed in bed-stream precipitates, which play a major role in controlling arsenic mobility. To unravel the complex nature of the AMD sediments a combination of techniques including X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), total solid digestions, X-Ray Fluorescence (XRF) and X-Ray Absorption Spectroscopy (XAS) were employed. Results showed that (1) arsenic was present predominantly in its pentavalent state; (2) upstream arsenic was sorbed onto the main phase, schwertmannite, whereas downstream it was chiefly associated with goethite and jarosite; and (3) changes in arsenic speciation with depth were observed in the consolidated terrace sediments, where arsenic appeared primarily associated with schwertmannite in the upper part of the terraces, but with goethite at depth. Arsenic mobilization was controlled by sorption onto newly formed precipitates (schwertmannite, goethite and jarosite), causing natural arsenic attenuation. (C) 2009 Elsevier B.V. All rights reserved.
  Chemical Geology 01/2013; 271:1-12.
• Article: Zircon/rock partition coeficients of REEs,Y, Th,U, Nb, and Ta in granitic rocks: uses for provenance and mineral exploration purposes.

  Nardi, Formoso, Müller, Fontana, Jarvis, Lamarão
  Chemical Geology 01/2013;
• Article: Galena surface reactivity at acidic pH and 25 °C based on flow-through and in situ AFM experiments

  Jordi Cama, Patricia Acero, Carles Ayora, Agustí Lobo
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  ABSTRACT: A study of (PbS) galena dissolution at acidic conditions was carried out by means of nonstirred flow-through experiments, in situ and ex situ Atomic Force Microscopy (AFM) experiments, X-ray photoelectron spectroscopy (XPS) surface analysis, and X-ray diffraction (XRD) patterns of the reacted surfaces. The nonstirred flow-through experiments were performed at pH 3, 25 °C, and oxygen-saturated atmosphere using both raw galena and a pyritic sludge from the Aznalcóllar mine tailing (SW Spain) with 0.8 wt.% of galena. Based on the Pb release, the steady-state dissolution rate of galena, normalized to the initial specific surface area, is 1.2±0.18×10−10 mol m−2 s−1. The in situ AFM experiments were carried out at the pH range from 1 to 3 at 20±3 °C in a saturated O2 atmosphere using galena fragments of known dimensions. Also based on Pb release, the galena dissolution rates were estimated by normalizing to the geometric area. A derived empirical rate law describing the dissolution rate–pH dependency at 1<pH<3 can be expressed aswhere RPb is the galena dissolution rate in mol m−2 s−1. Moreover, using the AFM images, galena dissolution rates were estimated by carrying out a systematic section analysis of the surface microtopography variation as dissolution of the {100} cleavage surface occurred. The AFM-estimated galena dissolution rates were slower than the dissolution rates based on the Pb release probably because of lower reactivity of the area scanned by the AFM probe compared with the entire surface reactivity.The dissolution of galena appeared to be noncongruent as aqueous sulphur depletion was observed, resulting in a Pb/S ratio higher than one. We suggest that through the overall dissolution reaction, a fraction of H2S(aq) is converted into H2S(g) as S is detached from the PbS surface, causing the aqueous S deficit. The overall dissolution mechanism observed on the {100} galena surface is similar to the one reported by De Giudici and Zuddas (De Giudici, G., Zuddas, P., 2001. In situ investigation of galena dissolution in oxygen saturated solution: Evolution of surface features and kinetic rate. Geochimica et Cosmochimica Acta 65, 9, 1381–1389) in which surface protrusions form over the PbS surface and dissolve continuously. Furthermore, the ex situ Tapping mode images show the growth of larger protrusions on galena substrate at acidic pH. A potential oxidative effect of the reacting solution on the galena dissolution mechanism at acidic pH was also studied: (1) As the HNO3 solution is more oxidative than HCl solution, the protrusions formed faster over the PbS surface; (2) since the Fe(III) in solution reduces to Fe(II) to oxidize sulphur to sulphate, PbSO4 and S precipitate on the PbS surface.The XPS surface analysis and the XRD pattern of the reacted {100} PbS surfaces yield further insight into the existence of lead–sulphur phases such as anglesite (PbSO4) and elemental sulphur on the PbS surface.
  Chemical Geology 01/2013; 214(3-4):309-330.