Journal: Geochimica et Cosmochimica Acta

Abbreviation

Geochim. Cosmochim. Acta

Publisher

Elsevier

Journal Volumes

ISSN

0016-7037
1872-9533

Description

Search Results

Publications1 - 10 of 955
  • Rapid changes in the redox conditions of the western Tethys Ocean during the early Aptian oceanic anoxic event
    Item type: Journal Article
    Westermann, Stéphane; Stein, Melody; Matera, Virginie; et al. (2013)
    Geochimica et Cosmochimica Acta
  • Combining a microcosm biodegradation concept with reactive transport modelling of phenol attenuation for a field case
    Item type: Conference Paper
    Watson, I. A.; Oswald, S. E.; Crouch, R. S.; et al. (2004)
    Geochimica et Cosmochimica Acta
  • The stable Si isotope composition of eastern Atlantic Ocean seawater
    Item type: Conference Paper
    De Souza, Gregory; Reynolds, Ben C.; Rickli, Jörg Dominik; et al. (2008)
    Geochimica et Cosmochimica Acta ~ Awards Ceremony Speeches and Abstracts of the 18th Annual V.M. Goldschmidt Conference Vancouver, Canada July, 2008
  • Thallium isotope composition of the upper continental crust and rivers
    Item type: Journal Article
    Nielsen, Sune G.; Rehkämper, Mark; Porcelli, Don; et al. (2005)
    Geochimica et Cosmochimica Acta
  • Speciation of Arsenic in Greek Travertines
    Item type: Journal Article
    Winkel, Lenny H.E.; Casentini, Barbara; Bardelli, Fabrizio; et al. (2013)
    Geochimica et Cosmochimica Acta
  • Effect of sulfate-availability on coupled Cu and Cd transformation during soil reduction
    Item type: Other Conference Item
    Fulda, Beate; Voegelin, Andreas; Kretzschmar, Ruben (2009)
    Geochimica et Cosmochimica Acta
  • A new method for the measurement of air/soil sorption of CFCs
    Item type: Other Conference Item
    Hofer, M.; Klump, S.; Preuschoff, P.; et al. (2004)
    Geochimica et Cosmochimica Acta
  • The role of skeletal micro-architecture in diagenesis and dating of Acropora palmata
    Item type: Journal Article
    Tomiak, Peter J.; Andersen, Morten B.; Hendy, Erica J.; et al. (2016)
    Geochimica et Cosmochimica Acta
    Past variations in global sea-level reflect continental ice volume, a crucial factor for understanding the Earth’s climate system. The Caribbean coral Acropora palmata typically forms dense stands in very shallow water and therefore fossil samples mark past sea-level. Uranium-series methods are commonly used to establish a chronology for fossil coral reefs, but are compromised by post mortem diagenetic changes to coral skeleton. Current screening approaches are unable to identify all altered samples, whilst models that attempt to correct for ‘open-system’ behaviour are not applicable across all diagenetic scenarios. In order to better understand how U-series geochemistry varies spatially with respect to diagenetic textures, we examine these aspects in relation to skeletal micro-structure and intra-crystalline amino acids, comparing an unaltered modern coral with a fossil A. palmata colony containing zones of diagenetic alteration (secondary overgrowth of aragonite, calcite cement and dissolution features). We demonstrate that the process of skeletogenesis in A. palmata causes heterogeneity in porosity, which can account for the observed spatial distribution of diagenetic features; this in turn explains the spatially-systematic trends in U-series geochemistry and consequently, U-series age. We propose a scenario that emphasises the importance of through-flow of meteoric waters, invoking both U-loss and absorption of mobilised U and Th daughter isotopes. We recommend selective sampling of low porosity A. palmata skeleton to obtain the most reliable U-series ages. We demonstrate that intra-crystalline amino acid racemisation (AAR) can be applied as a relative dating tool in Pleistocene A. palmata samples that have suffered heavy dissolution and are therefore unsuitable for U-series analyses. Based on relatively high intra-crystalline concentrations and appropriate racemisation rates, glutamic acid and valine are most suited to dating mid-late Pleistocene A. palmata. Significantly, the best-preserved material in the fossil specimen yields a U-series age of 165 ± 8 ka, recording a paleo sea-level of −35 ± 7 msl during the MIS 6.5 interstadial on Barbados.
  • Differential weathering of basaltic and granitic catchments from concentration-discharge relationships
    Item type: Journal Article
    Ibarra, Daniel E.; Rugenstein, Jeremy Kesner Caves; Moon, Seulgi; et al. (2016)
    Geochimica et Cosmochimica Acta
    A negative feedback between silicate weathering rates and climate is hypothesized to play a central role in moderating atmospheric CO2 concentrations on geologic timescales. However, uncertainty regarding the processes that regulate the operation of the negative feedback limits our ability to interpret past variations in the ocean–atmosphere carbon cycle. In particular, the mechanisms that determine the flux of weathered material for a given climatic state are still poorly understood. Here, we quantify the processes that determine catchment-scale solute fluxes for two lithologic end-members—basalt and granite—by applying a recently developed solute production model that links weathering fluxes to both discharge and the reactivity of the weathering material. We evaluate the model against long-term monitoring of concentration–discharge relationships from basaltic and granitic catchments to determine the parameters associated with solute production in each catchment. Higher weathering rates in basaltic catchments relative to granitic catchments are driven by differing responses to increases in runoff, with basaltic catchments showing less dilution with increasing runoff. In addition, results from the solute production model suggest that thermodynamic constraints on weathering reactions could explain higher concentrations in basaltic catchments at lower runoff compared to granitic catchments. To understand how the response to changing discharge controls weathering fluxes under different climatic states, we define basalt/granite weatherability as the ratio of the basalt catchment flux to the granite catchment flux. This weatherability is runoff-dependent and increases with increasing runoff. For HCO3− and SiO2(aq) fluxes, for modern global runoff, the derived mean basalt/granite weatherability is 2.2 (1.3–3.7, 2σ) and 1.7 (1.6–2.1, 2σ), respectively. Although we cannot determine the array of individual processes resulting in differences among catchments, the relative differences in certain model parameters that represent catchment-scale weathering fluxes of granitic and basaltic lithologies are robust. Our approach provides a mechanism that links runoff with the distribution of global sub-aerial silicate lithologies to understand how the basalt/granite weatherability of the Earth’s surface may have varied on geologic timescales. The relationships between basalt/granite weatherability and runoff derived in this study could be used to parameterize the silicate weathering negative feedback to model past changes in pCO2.
  • Magma genesis and Cu-Au ore formation (Apuseni Mountains, Romania) in light of Pb, Sr and Nd isotopic and chemical trends
    Item type: Other Conference Item
    Harris, Caroline R.; Pettke, Thomas; Roşu, Emilian; et al. (2005)
    Geochimica et Cosmochimica Acta
Publications1 - 10 of 955