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941.
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
942.
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 (HgT) 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 HgT 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 (HgR) concentrations varied from 0.01 to 2.28 pmol L−1, with a distribution showing that the HgT enrichment south of the SPF consisted mainly of HgR (67 ± 23%), whereas, in contrast, the percentage was half that in surface waters north of PFZ (33 ± 23%). Methylated mercury species (MeHgT) concentrations ranged from 0.02 to 0.86 pmol L−1. All vertical MeHgT 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 HgT, low mean MeHgT concentrations were associated with AAIW, and higher ones with AABW. The maximum of MeHgT concentration at each station was systematically observed within the oxygen minimum zone, with a statistically significant MeHgTvs Apparent Oxygen Utilization (AOU) relationship (p < 0.001). The proportion of HgT 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 HgT and HgR 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 HgT 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, MeHgT 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 MeHgT vertical profile through the continuum suggests different sources, including atmosphere, seawater and methylation in basal ice. Whereas HgT 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
943.
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
944.
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
945.
946.
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
947.
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
948.
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
949.
Laura L. Brothers Joseph T. Kelley Daniel F. Belknap Walter A. Barnhardt Brian D. Andrews Melissa Landon Maynard 《Geo-Marine Letters》2011,31(4):237-248
Mechanisms and timescales responsible for pockmark formation and maintenance remain uncertain, especially in areas lacking
extensive thermogenic fluid deposits (e.g., previously glaciated estuaries). This study characterizes seafloor activity in
the Belfast Bay, Maine nearshore pockmark field using (1) three swath bathymetry datasets collected between 1999 and 2008,
complemented by analyses of shallow box-core samples for radionuclide activity and undrained shear strength, and (2) historical
bathymetric data (report and smooth sheets from 1872, 1947, 1948). In addition, because repeat swath bathymetry surveys are
an emerging data source, we present a selected literature review of recent studies using such datasets for seafloor change
analysis. This study is the first to apply the method to a pockmark field, and characterizes macro-scale (>5 m) evolution
of tens of square kilometers of highly irregular seafloor. Presence/absence analysis yielded no change in pockmark frequency
or distribution over a 9-year period (1999–2008). In that time pockmarks did not detectably enlarge, truncate, elongate, or
combine. Historical data indicate that pockmark chains already existed in the 19th century. Despite the lack of macroscopic
changes in the field, near-bed undrained shear-strength values of less than 7 kPa and scattered downcore 137Cs signatures indicate a highly disturbed setting. Integrating these findings with independent geophysical and geochemical
observations made in the pockmark field, it can be concluded that (1) large-scale sediment resuspension and dispersion related
to pockmark formation and failure do not occur frequently within this field, and (2) pockmarks can persevere in a dynamic
estuarine setting that exhibits minimal modern fluid venting. Although pockmarks are conventionally thought to be long-lived
features maintained by a combination of fluid venting and minimal sediment accumulation, this suggests that other mechanisms
may be equally active in maintaining such irregular seafloor morphology. One such mechanism could be upwelling within pockmarks
induced by near-bed currents. 相似文献
950.
Sin Chan Chou Andr de Arruda Lyra Jorge Lus Gomes Daniel Andrs Rodriguez Minella Alves Martins Nicole Costa Resende Priscila da Silva Tavares Claudine Pereira Dereczynski Isabel Lopes Pilotto Alessandro Marques Martins Lus Felipe Alves de Carvalho Jos Luiz Lima Onofre Idalcio Major Manuel Penhor Adrito Santana 《Climate Dynamics》2020,54(9):4021-4042
Sao Tome and Principe is a small insular African country extremely vulnerable to rising sea levels and impacts such as inundation, shore line change, and salt water intrusion into underground aquifers. Projections of climate change have considered coarse model resolutions. The objective of this work is to dynamically downscale the global model projections to 4-km resolution and to assess the climate change in the Sao Tome and Principe islands. The global climate projections are provided by the Canadian Earth System Model under two Representative Concentration Pathways greenhouse gas scenarios, RCP4.5 and RCP8.5. The downscaling is produced by the Eta regional climate model. The baseline period is taken between 1971 and 2000, and the future climate period is taken between 2041 and 2070. The 2-m temperature simulations show good agreement with station data. The model simulates temperature more accurately than precipitation. The precipitation simulations systematically show underestimation and delay of the rainy and the dry seasons by about 1 month, a feature inherited from the global climate model. In the middle of the 21st century, projections show the strongest warming in the elevated parts of the Sao Tome Island, especially in February under RCP8.5. Warmer nights and warmer days become more frequent in the islands when compared with those in the present. While under RCP4.5, precipitation increases in the islands; under RCP8.5, it decreases everywhere in both islands. Heavy precipitation rates should increase, especially in the south-southwestern parts of the Sao Tome islands. Detailed spatial variability of the temperature and precipitation changes in the islands can only be revealed at very high spatial model resolution. Implications for the potential energy production from two major river basins are assessed in this work. 相似文献