1,721,273 research outputs found
Rose in Australia [music] /
No full text420-2 (Publisher number). For voice and piano.; Cover title.; Pl. no.: 420-2.; Also available online http://nla.gov.au/nla.mus-vn3118715
Determination of lead isotope ratios in seawater by quadrupole inductively coupled plasma mass spectrometry after Mg(OH)2 co-precipitation
No full textA low blank Mg(OH)2 pre-concentration method was evaluated for the determination of lead isotope ratios (208Pb/206Pb, 207Pb/206Pb) in seawater using a quadrupole ICP-MS VG Plasma Quad II+. Possible matrix effects derived from the Mg(OH)2 co-precipitate were assessed by spiking lead-free seawater (PbFS) and 1% (v/v) HNO3 with the certified common lead standard NBS 981 to give solutions with concentrations in the lower picogram per millilitre range. The standard curves for all three masses were linear in both matrices with minor signal loss (18%) in the Mg matrix. Mass fractionation showed similar mass biases (<2% frac./amu) for 208Pb/206Pb and 207Pb/206Pb in both seawater and 1% (v/v) HNO3, indicating that there is no significant matrix influence on the isotope ratio determination. Using the Mg(OH)2 precipitation method, real seawater samples were pre-concentrated approximately 28-fold, and 1 ml of 5% (v/v) HNO3 end volume was used for the subsequent measurement. The data acquisition parameters dwell time, replicates per analysis, and acquisition time were first varied to optimize analytical precision and accuracy of the ICP-MS measurements. On the basis of these results, approximately 0.5 ml of pre-concentrated solution was finally used employing a low-flow, CETAC microconcentric nebulizer to minimize sample consumption and extend acquisition time. Analyzing 18 seawater samples from the North Atlantic, the average 1? external precision of triplicate measurements was approximately 0.3% for both ratios, 208Pb/206Pb and 207Pb/206Pb, at the level of approximately 20 pg ml?1 Pb. Blanks accounted for less than 3% of total lead analyzed for each sample. Six samples were also measured with TIMS and agreed in average within 0.26% for 207Pb/206Pb and 0.37% for 208Pb/206Pb. Three surface water samples from the Sargasso Sea, collected in 1989, showed ratios in line with previous published ratios from the western North Atlantic.<br/
Cool tropical temperatures shift the global δ18O-T relationship: An explanation for the ice core δ18O- borehole thermometry conflict?
Full text linkThe discrepancy between central Greenland borehole temperatures and the isotopic composition of Last Glacial Maximum ice can be explained by a shift in the δ[superscript 18]O-T relationship for the hydrological cycle linked to cooler tropical temperatures. This concept is illustrated using a simple Rayleigh distillation model. An estimate for α=Δδ[superscript 18] O/ΔT (LGM-Holocene) of −0.37 ‰/°C is determined with a simple graphical technique.National Science Foundation (U.S.) (Grant OCE9402198)United States. National Oceanic and Atmospheric Administration (Grant NA46GP0282
A century long sedimentary record of anthropogenic lead (Pb), Pb isotopes and other trace metals in Singapore
No full textReconstructing the history of metal deposition in Singapore lake sediments contributes to understanding the anthropogenic and natural metal deposition in the data-sparse Southeast Asia. To this end, we present a sedimentary record of Pb, Pb isotopes and eleven other metals (Ag, As, Ba, Cd, Co, Cr, Cu, Ni, Tl, U and Zn) from a well-dated sediment core collected near the depocenter of MacRitchie Reservoir in central Singapore. Before the 1900s, the sedimentary Pb concentration was less than 2 mg/kg for both soil and sediment, with a corresponding ²⁰⁶Pb/²⁰⁷Pb of ∼1.20. The Pb concentration increased to 55 mg/kg in the 1990s, and correspondingly the ²⁰⁶Pb/²⁰⁷Pb decreased to less than 1.14. The ²⁰⁶Pb/²⁰⁷Pb in the core top sediment is concordant with the ²⁰⁶Pb/²⁰⁷Pb signal of aerosols in Singapore and other Southeast Asian cities, suggesting that Pb in the reservoir sediment was mainly from atmospheric deposition. Using the Pb concentration in the topmost layer of sediment, the estimated atmospheric Pb flux in Singapore today is ∼1.6 × 10⁻² g/m² yr. The concentrations of eleven other metals preserved in the sediment were also determined. A principal component analysis showed that most of the metals exhibit an increasing trend towards 1990s with a local concentration peak in the mid-20th century. Keywords: Pb; Pb isotopes; Heavy metals; Southeast Asia; Singapore; Sedimen
Nitrogen pollution knows no bounds
No full textIn recent decades, the flow of fixed—that is, biologically usable—nitrogen from human activities into the environment has grown substantially. The sources include excess production and use of nitrogen fertilizers; ammonia emitted from animal husbandry and sewage; and nitrogen oxides emitted by automobiles, airplanes, and fossil fuel power plants. The resulting nitrogen flux into the ocean may approach the magnitude of natural sources (1–3). However, it is difficult to specify the integrated increase over natural sources precisely because there is very little data for when nitrogen sources were mostly natural. On page 749 of this issue, Ren et al. use the nitrogen isotope composition of a 50-year coral core from the South China Sea to show that the natural upwelling flux of fixed nitrogen has risen by 20% during the past two decades (4)
Impact of anthropogenic Pb and ocean circulation on the recent distribution of Pb isotopes in the Indian Ocean
No full textb and Pb isotope ratios in the modern ocean have been altered significantly by anthropogenic Pb inputs over the past century. Most studies of anthropogenic Pb in the ocean have focused on the North Atlantic and North Pacific Oceans, and the impact of anthropogenic Pb inputs to the Indian Ocean and processes controlling the distribution of Pb in the Indian Ocean are poorly known. This study presents the Pb and Pb isotopic composition (²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁷Pb) of 11 deep stations from the Indian Ocean Japanese GEOTRACES cruise (KH-09-5), from the Bay of Bengal and Arabian Sea to the Southern Ocean (62°S). The Pb isotope ratios of the Indian Ocean range 1.140–1.190 for ²⁰⁶Pb/²⁰⁷Pb and 2.417–2.468 for ²⁰⁸Pb/²⁰⁷Pb, with lower ratios appearing in the shallow waters of the northern Indian Ocean and higher ratios appearing in the deep layers of the Southern Ocean. This result agrees with a previous study on Pb concentrations (Echegoyen et al., 2014) showing that the Indian Ocean, particularly its northern part, is largely perturbed by anthropogenic Pb inputs. ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb of the Indian sector Southern Ocean are still lower than natural Pb, showing this region was also affected by anthropogenic Pb. Anomalously low or high ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb were observed in the thermocline and shallow waters of the southern Indian Ocean and the Arabian Sea, which are ascribed to water mass distribution (e.g., Subantarctic Mode Water) and evolving Pb isotope ratios of this region as dominant anthropogenic Pb sources change. ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb in the Bay of Bengal are higher than those in the Arabian Sea, which might be the result of the anthropogenic Pb inputs from different provenance or seawater exchanging Pb isotopes with natural particles derived from rivers and/or sediments at the basin boundaries
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Helium and thorium isotope constraints on African dust transport to the Bahamas over recent millennia
No full textDespite its potential linkages with North Atlantic climate, the variability in Saharan dust transport to the western North Atlantic over the past two millennia has not been well-characterized. A factor of 4 increase in dust production in sub-Saharan Africa has been attributed to the onset of Sahelian agriculture 200 yr ago. The regional extent of this anthropogenic dust increase, however, remains uncertain. Additionally, while millennial-scale cold periods of the last deglaciation have been associated with strong increases in North African dust emissions, few adequate records exist to observe dustiness during the Little Ice Age, a century-scale cooling of the North Atlantic (AD 1400–1800). In this study, we develop a new technique for the paired use of ²³⁰Th-normalized ²³²Th fluxes and ³He-normalized ⁴He fluxes in Bahamian tidal flat sediments. After justifying the fact that ²³⁰Th and ³He have had relatively constant sources to tidal flat and banktop waters, and accounting for the smoothing effect of bioturbation, a factor of 4 change in far-field dust transport to the western North Atlantic between the pre-industrial and modern era is not supported by our dust proxies over the past 2000 yr. Furthermore, we speculate why the response of western North Atlantic dust deposition associated with the Little Ice Age climate anomalies may have been modest compared to prior climatic events of the early Holocene or the last deglaciation. Keywords: aerosols; mineral dust; thorium isotopes; Anthropocene; Little Ice Ag
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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