Defining an absolute reference frame for ‘clumped’ isotope studies of CO₂     

Kate J. Dennis  Hagit P. Affek  Daniel P. Schrag 《Geochimica et cosmochimica acta》2011,75(22):7117-7131

We present a revised approach for standardizing and reporting analyses of multiply substituted isotopologues of CO₂ (i.e., ‘clumped’ isotopic species, especially the mass-47 isotopologues). Our approach standardizes such data to an absolute reference frame based on theoretical predictions of the abundances of multiply-substituted isotopologues in gaseous CO₂ at thermodynamic equilibrium. This reference frame is preferred over an inter-laboratory calibration of carbonates because it enables all laboratories measuring mass 47 CO₂ to use a common scale that is tied directly to theoretical predictions of clumping in CO₂, regardless of the laboratory’s primary research field (carbonate thermometry or CO₂ biogeochemistry); it explicitly accounts for mass spectrometric artifacts rather than convolving (and potentially confusing) them with chemical fractionations associated with sample preparation; and it is based on a thermodynamic equilibrium that can be experimentally established in any suitably equipped laboratory using commonly available materials.By analyzing CO₂ gases that have been subjected to established laboratory procedures known to promote isotopic equilibrium (i.e., heated gases and water-equilibrated CO₂), and by reference to thermodynamic predictions of equilibrium isotopic distributions, it is possible to construct an empirical transfer function that is applicable to data with unknown clumped isotope signatures. This transfer function empirically accounts for the fragmentation and recombination reactions that occur in electron impact ionization sources and other mass spectrometric artifacts. We describe the protocol necessary to construct such a reference frame, the method for converting gases with unknown clumped isotope compositions to this reference frame, and suggest a protocol for ensuring that all reported isotopic compositions (e.g., Δ₄₇ values; [Eiler and Schauble, 2004] and [Eiler, 2007]) can be compared among different laboratories and instruments, independent of laboratory-specific analytical or methodological differences. We then discuss the use of intra-laboratory secondary reference frames (e.g., based on carbonate standards) that can be more easily used to track the evolution of each laboratory’s empirical transfer function. Finally, we show inter-laboratory reproducibility on the order of ±0.010 (1σ) for four carbonate standards, and present revised paleotemperature scales that should be used to convert carbonate clumped isotope signatures to temperature when using the absolute reference frame described here. Even when using the reference frame, small discrepancies remain between two previously published synthetic carbonate calibrations. We discuss possible reasons for these discrepancies, and highlight the need for additional low temperature (<15 °C) synthetic carbonate experiments.  相似文献   

Mercury in the Southern Ocean     

Daniel Cossa  Lars-Eric Heimbürger  Stephen R. Rintoul  Edward C.V. Butler  Andrew R. Bowie  Roslyn J. Watson 《Geochimica et cosmochimica acta》2011,75(14):4037-4052

We present here the first mercury speciation study in the water column of the Southern Ocean, using a high-resolution south-to-north section (27 stations from 65.50°S to 44.00°S) with up to 15 depths (0-4440 m) between Antarctica and Tasmania (Australia) along the 140°E meridian. In addition, in order to explore the role of sea ice in Hg cycling, a study of mercury speciation in the “snow-sea ice-seawater” continuum was conducted at a coastal site, near the Australian Casey station (66.40°S; 101.14°E). In the open ocean waters, total Hg (Hg_T) concentrations varied from 0.63 to 2.76 pmol L⁻¹ with “transient-type” vertical profiles and a latitudinal distribution suggesting an atmospheric mercury source south of the Southern Polar Front (SPF) and a surface removal north of the Subantartic Front (SAF). Slightly higher mean Hg_T concentrations (1.35 ± 0.39 pmol L⁻¹) were measured in Antarctic Bottom Water (AABW) compared to Antarctic Intermediate water (AAIW) (1.15 ± 0.22 pmol L⁻¹). Labile Hg (Hg_R) concentrations varied from 0.01 to 2.28 pmol L⁻¹, with a distribution showing that the Hg_T enrichment south of the SPF consisted mainly of Hg_R (67 ± 23%), whereas, in contrast, the percentage was half that in surface waters north of PFZ (33 ± 23%). Methylated mercury species (MeHg_T) concentrations ranged from 0.02 to 0.86 pmol L⁻¹. All vertical MeHg_T profiles exhibited roughly the same pattern, with low concentrations observed in the surface layer and increasing concentrations with depth up to an intermediate depth maximum. As for Hg_T, low mean MeHg_T concentrations were associated with AAIW, and higher ones with AABW. The maximum of MeHg_T concentration at each station was systematically observed within the oxygen minimum zone, with a statistically significant MeHg_Tvs Apparent Oxygen Utilization (AOU) relationship (p < 0.001). The proportion of Hg_T as methylated species was lower than 5% in the surface waters, around 50% in deep waters below 1000 m, reaching a maximum of 78% south of the SPF. At Casey coastal station Hg_T and Hg_R concentrations found in the “snow-sea ice-seawater” continuum were one order of magnitude higher than those measured in open ocean waters. The distribution of Hg_T there suggests an atmospheric Hg deposition with snow and a fractionation process during sea ice formation, which excludes Hg from the ice with a parallel Hg enrichment of brine, probably concurring with the Hg enrichment of AABW observed in the open ocean waters. Contrastingly, MeHg_T concentrations in the sea ice environment were in the same range as in the open ocean waters, remaining below 0.45 pmol L⁻¹. The MeHg_T vertical profile through the continuum suggests different sources, including atmosphere, seawater and methylation in basal ice. Whereas Hg_T concentrations in the water samples collected between the Antarctic continent and Tasmania are comparable to recent measurements made in the other parts of the World Ocean (e.g., Soerensen et al., 2010), the Hg species distribution suggests distinct features in the Southern Ocean Hg cycle: (i) a net atmospheric Hg deposition on surface water near the ice edge, (ii) the Hg enrichment in brine during sea ice formation, and (iii) a net methylation of Hg south of the SPF.  相似文献   

Palaeoenvironmental analysis of Cenomanian-Turonian dinocyst assemblages from the Castilian Platform (Northern-Central Spain)     

Daniel Peyrot  Fernando Barroso-Barcenilla  Eduardo BarrónMaría José Comas-Rengifo 《Cretaceous Research》2011,32(4):504-526

The palynological assemblages from three Cenomanian-Turonian sections from the Castilian Platform are described. The 49 levels analysed yielded a well-diversified palynological content including dinoflagellate cysts, acritarchs, prasinophytes and miospores. The comparison of the terrestrial and marine assemblages from these three sections reveals significant differences that are mainly related to their relative palaeogeographical locations. The quantitative study performed on dinocyst assemblages suggests an association interpreted as inner neritic including Xenascus ceratioides, Cribroperidinium exilicristatum, Canningia reticulata and Kallosphaeridium? ringnesiorum. On the contrary, the group inferred to show outer neritic preferences is integrated by Palaeohystrichophora infusorioides, Spiniferites spp., Odontochitina spp., Trichodinium castanea and Impletosphaeridium polytrichum. In the Castilian Platform, the Cenomanian-Turonian Boundary Event (CTBE) may be manifested by a higher proportion of Cyclonephelium spp. in the distal dinocyst assemblages.  相似文献   

Speleothems and pine trees as sensitive indicators of environmental pollution – A case study of the effect of uranium-ore mining in Hungary     

Zoltan Siklosy  Zoltan Kern  Attila Demeny  Sebastian Pilet  Szabolcs Leel-Ossy  Ke Lin  Chuan-Chou Shen  Eva Szeles  Daniel Breitner 《Applied Geochemistry》2011,26(5):666-678

Four decades of U ore production in Hungary provides an opportunity to study the possible environmental effects of mining. The study reveals significant changes in chemical composition of a stalagmite (cave deposit). The good fit between U content changes in the studied deposit and the U ore production rate support the assumption of the relationship with mining activity. An independent chemoenviromental archive, living pine (Pinus sylvestis) trees were also investigated. Data on pine tree cores collected from the same region show different levels of pollution (Cu, Zn, Mn, U) after the 1950s and 1960s, linked to the opening of mines and subsequent dust fallout around the site. Elevated concentrations of detritally derived elements (Si, Al, Th) coupled with a rise in U concentration and change in δ²³⁴U values of the stalagmite suggest increasing amounts of mine-derived dust from 1 to 3 km distance that settled and washed into the karst system. The combined usage of different proxies not only provides historic records for the anthropogenic impact in the environment, but also allows the timing of U concentration increases within the stalagmite and the identification of elemental behavior from the pollution. This study shows that complementary geochemical archives such as stalagmites and tree rings used together can enhance understanding of past environmental contamination.  相似文献   

Ultramafic-derived arsenic in a fractured bedrock aquifer     

Peter C. Ryan  Jonathan KimAndrew J. Wall  Jonathan C. MoenLilly G. Corenthal  Daniel R. ChowColleen M. Sullivan  Kevin S. Bright 《Applied Geochemistry》2011,26(4):444-457

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Patterns of Mangrove Wood and Litter Production Within a Beach Ridge-Fringing Reef Embayment,Northern Great Barrier Reef Coast   总被引：1，自引：0，他引：1  

Daniel M. Alongi 《Estuaries and Coasts》2011,34(1):32-44

Mortality, litter fall, and patterns of stem growth were examined in Rhizophora- and Ceriops-dominated forests located upstream and downstream in four tidally dominated creeks within a beach reef embayment on the northern Great Barrier Reef coast. Although patterns of stem densities, basal area, and diameter-at-breast height (DBH) between upstream–downstream sites and creeks were inconsistent, aboveground biomass, wood production, litter fall, and aboveground net primary productivity (ANPP) were greater in the Rhizophora-dominated forests. Incremental growth of stems (SI, cm year⁻¹) was slow compared to other mangroves, declining among species as follows: Rhizophora stylosa (mean = 0.080) > Bruguiera exaristata (0.066) = Xylocarpus australasicus (0.064) = Ceriops australis (0.056); SI was greater upstream than downstream, possibly due to nutrient inputs from upland sugarcane cultivation. The DBH of dead trees were less than the DBH of live trees, suggesting natural mortality, which was greatest for X. australasicus (annual rate = 3.27%), followed by B. exaristata (0.84%), C. australis (0.48%), and R. stylosa (0.33%). Rates of litter fall were seasonal and equivalent to those measured in other mangroves, but rates of ANPP were, on average, low in most plots. Salinity was likely the main factor limiting growth as correlations of salinity with tree growth and production were negative. Nutrients may have also played a key regulatory role, with positive correlations between mangrove production and N and P content of soils and leaves and the comparatively low nutrient content of these sandy soils. The low ratio of wood to litter production suggests that these forests are in a mature stage of development.  相似文献   

Determination of Reference Values for NIST SRM 610–617 Glasses Following ISO Guidelines     

Klaus Peter Jochum  Ulrike Weis  Brigitte Stoll  Dmitry Kuzmin  Qichao Yang  Ingrid Raczek  Dorrit E. Jacob  Andreas Stracke  Karin Birbaum  Daniel A. Frick  Detlef Günther  Jacinta Enzweiler 《Geostandards and Geoanalytical Research》2011,35(4):397-429

We present new reference values for the NIST SRM 610–617 glasses following ISO guidelines and the International Association of Geoanalysts’ protocol. Uncertainties at the 95% confidence level (CL) have been determined for bulk‐ and micro‐analytical purposes. In contrast to former compilation procedures, this approach delivers data that consider present‐day requirements of data quality. New analytical data and the nearly complete data set of the GeoReM database were used for this study. Data quality was checked by the application of the Horwitz function and by a careful investigation of analytical procedures. We have determined quantitatively possible element inhomogeneities using different test portion masses of 1, 0.1 and 0.02 μg. Although avoiding the rim region of the glass wafers, we found moderate inhomogeneities of several chalcophile/siderophile elements and gross inhomogeneities of Ni, Se, Pd and Pt at small test portion masses. The extent of inhomogeneity was included in the determination of uncertainties. While the new reference values agree with the NIST certified values with the one exception of Mn in SRM 610, they typically differ by as much as 10% from the Pearce et al. (1997) values in current use. In a few cases (P, S, Cl, Ta, Re) the discrepancies are even higher.  相似文献   

Neoproterozoic to Lower Palaeozoic successions of the Tandilia System in Argentina: implication for the palaeotectonic framework of southwest Gondwana     

Udo Zimmermann  Daniel G. Poir��  Luc��a G��mez Peral 《International Journal of Earth Sciences》2011,100(2-3):489-510

The Cryogenian to Uppermost Ediacaran successions of the Tandilia System (Sierras Bayas Group and Cerro Negro Formation) in central-eastern Argentina is exceptional because of its unmetamorphosed and nearly undeformed character, its sediment provenance trend and the absence of any identified glacial deposit and the deposition of warm water carbonates. We decipher a dramatic change in the basin evolution from small-scale depositional areas during the Neoproterozoic to a larger basin related to an active continental margin throughout the Uppermost Ediacaran. The base of the succession is represented by immature detritus of alkaline composition (Villa Mónica Formation), but towards the top of this formation, the material is sorted and reworked, nonetheless still reflecting in its detritus the local rocks. The clastic deposition is interrupted by diagenetic overprinted dolomites. The unconformable overlying quartz-arenitic Ediacaran Cerro Largo Formation reworked the Cryogenian Villa Mónica Formation and contains mainly felsic granitic and metamorphic basement material of slightly wider variety, while the dominant alkaline geochemical signature in rocks of the Villa Mónica Formation disappears. Based on diagenetic, petrographic and sedimentological data, we can interpret the unconformity representing a longer time of erosion. The Cerro Largo Formation shows a transition to mudstones and the heterolithic facies of the Olavarría Formation. The top of the Sierras Bayas Group is represented by limestones (Loma Negra Formation), which are discordantly overlain by the Uppermost Ediacaran Cerro Negro Formation. The latter displays detrital material derived from a continental arc, mafic and felsic sources. Several arc-related geochemical proxies (Th/Sc?<?0.8; Zr/Sc?<?10; La/Sc?<?2; Ti/Zr?>?20) are recorded in the sediment detritus, as are syn-depositional pyroclastites. The absence of volcanic material in the underlying rocks allows proposing that the Cerro Negro Formation is related to an active continental margin fringing Gondwana (??Terra Australis Orogen??) as a retro-arc or retro-arc foreland basin.  相似文献   

The Rio de la Plata craton and the adjoining Pan-African/brasiliano terranes: Their origins and incorporation into south-west Gondwana     

Carlos W. Rapela  C. Mark Fanning  Cesar Casquet  Robert J. Pankhurst  Luis Spalletti  Daniel Poiré  Edgardo G. BaldoAuthor vitae 《Gondwana Research》2011,20(4):673-690

The Neoproterozoic to Early Cambrian amalgamation of SW Gondwana through the Brasiliano/Pan-African orogeny is reviewed with emphasis on the role of the Río de la Plata craton of South America in the light of new evidence from a borehole at the eastern end of the Tandilia belt (38°S). U–Pb, Hf and O isotope data on zircon indicate that this un-reworked Palaeoproterozoic craton abuts against a distinct continental terrane to the east (Mar del Plata terrane). The craton is bounded everywhere by transcurrent faults and there is no evidence to relate it to the Neoproterozoic mobile belts now seen on either side. The Punta Mogotes Formation at the bottom of the borehole contains 740–840 Ma detrital zircons that are assigned to a widespread Neoproterozoic rifting event. The data suggest that the Mar del Plata terrane rifted away from the southwestern corner of the Angola block at c. 780 Ma. Negative εHf_t values and δ¹⁸O > 6.5‰ suggest derivation by melting of old crust during a protracted extensional episode. Other continental terranes may have formed in a similar way in Uruguay (Nico Pérez) and southeastern Brazil, where the Schist Belt of the Dom Feliciano orogenic belt is probably a correlative of the Punta Mogotes sequence, implying that the Dom Feliciano belt must extend at least as far as 38°S. A new geodynamic scenario for West Gondwana assembly includes at least two major oblique collisional orogenies: Kaoko–Dom Feliciano (580–680 Ma) and Gariep–Saldania (480–580 Ma), the latter resulting from oblique impingement of the Rio de la Plata craton against the Kalahari craton. Assembly of this part of South-West Gondwana was accomplished before the Ordovician (to Silurian?) siliciclastic platform sediments of the Balcarce Formation in the Tandilia Belt covered the southern sector of Río de la Plata craton.  相似文献   

Impact of pulsed Atlantic water inflow into the Alboran Basin at the time of the Zanclean flooding     

Ferran Estrada  Gemma Ercilla  Christian Gorini  Bel��n Alonso  Juan Tom��s V��zquez  Daniel Garc��a-Castellanos  Carmen Juan  Andr��s Maldonado  Abdellah Ammar  Mohammed Elabbassi 《Geo-Marine Letters》2011,31(5-6):361-376

The study of more than 500 single- and multichannel seismic records enabled the generation of a detailed palaeo-bathymetric map of the Messinian surface over most of the Alboran Basin, Western Mediterranean. This regional surface is characterized by several erosional features (channels, terraces and canyons) and topographic highs (structural, volcanic and diapiric in origin). The most prominent feature is the incised Zanclean Channel crossing the entire basin, its entrenchment having been associated with the opening of the Strait of Gibraltar and subsequent inflow of Atlantic waters. The incision depth of the channel is variable, suggesting local variations in the erosive capacity of the Atlantic inflow, conditioned mainly by the regional basin topography and the local presence of topographic highs. Adjacent to this channel along the Spanish and Moroccan margins, and near the Strait of Gibraltar, several submarine terraces developed at different depths suggest a pulsed flooding of the Alboran Basin. There could have been two major inflow phases of Atlantic water, one shortly before and another during the Zanclean flooding, the latter accompanied by periods of relative sea-level stillstands that enabled terrace development. Alternatively, these features were all generated during the main flooding evident and subsequent pulsed infilling of the basin.  相似文献