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381.
A Holocene pollen and diatom record from Vanderlin Island, Gulf of Carpentaria, lowland tropical Australia 总被引:1,自引:0,他引:1
Sedimentary, palynological and diatom data from a dunefield lake deposit in the interior of Vanderlin Island in the Gulf of Carpentaria are presented. Prior to the formation of present perennial lake conditions, the intensified Australian monsoon associated with the early Holocene marine transgression allowed Cyperaceae sedges to colonise the alluvial margins of an expansive salt flat surrounded by an open Eucalyptus woodland. As sea level stabilised between 7500 and 4500 cal yr B.P. coastal dunes ceased to develop allowing dense Melaleuca forest to establish in a Restionaceae swamp. Dune-sand input into the swamp was diminished further as the increasingly dense vegetation prevented fluvial and aeolian transported sand arriving from coastal sources. This same process impounded the drainage basin allowing a perennial lake to form between 5500 and 4000 cal yr B.P. Myriophyllum and other aquatic taxa colonised the lake periphery under the most extensive woodland recorded for the Holocene. The palynological data support an effective precipitation model proposed for northern Australia that suggests more variable conditions in the late Holocene. A more precise measure of effective precipitation change is provided by diatom-based inferences that indicate few changes in lake hydrology. Such interpretations are explained in terms of palynological sensitivity to adjustments in local fire regimes where regional precipitation change may only be recorded indirectly through fire promoting mechanisms, including intensified ENSO periodicity and human impact. 相似文献
382.
Metal Complexation with Different types of Soluble and Adsorbed Freshwater Ligands Followed by DPASV
Cidália Maria Sousa Botelho Rui Alfredo Rocha Boaventura Maria de Lurdes Sadler Simões Gonçalves 《Aquatic Geochemistry》2007,13(2):173-186
In order to understand metal speciation in a polluted river (Este River, Northern Portugal) filtrate, freeze dried particles
and organics desorbed from surfaces were titrated with Cd(II) and Zn(II), followed by differential pulse anodic stripping
voltammetry (DPASV). The obtained results are compared with those previously published for Pb(II) and Cu(II). Due to the heterogeneity
of the system, a continuous and a discrete ligand model were used to interpret the titration data. Two types of ligands could
be detected and quantified by the discrete ligand model: small molecules with high affinities for cations such as Cd(II),
Cu(I), and Zn(II) and macromolecules with higher affinities for Pb(II) and Cu(II). Small ligands were strongly adsorbed onto
the particles, as inferred from the desorption of Zn(II) during titration with Pb(II) and Cd(II). The total concentrations
of the different ligands and the complex formation constants with the different metals are reported. 相似文献
383.
This paper discusses application of a structural-morphologic method for interpreting covered territories; in the present case, covered by lava flows. The study resulted in recognizing a network of recent faults and in determining their strike-slip kinematics. The relation of volcanoes and thermal springs to these faults is discussed. 相似文献
384.
Microbial methane turnover at mud volcanoes of the Gulf of Cadiz 总被引:2,自引:0,他引:2
H. Niemann J. Duarte E. Omoregie V.H. Magalhães M. Elvert A. Kopf 《Geochimica et cosmochimica acta》2006,70(21):5336-5355
The Gulf of Cadiz is a tectonically active area of the European continental margin and characterised by a high abundance of mud volcanoes, diapirs, pockmarks and carbonate chimneys. During the R/V SONNE expedition “GAP-Gibraltar Arc Processes (SO-175)” in December 2003, several mud volcanoes were surveyed for gas seepage and associated microbial methane turnover. Pore water analyses and methane oxidation measurements on sediment cores recovered from the centres of the mud volcanoes Captain Arutyunov, Bonjardim, Ginsburg, Gemini and a newly discovered, mud volcano-like structure called “No Name” show that thermogenic methane and associated higher hydrocarbons rising from deeper sediment strata are completely consumed within the seabed. The presence of a distinct sulphate-methane transition zone (SMT) overlapping with high sulphide concentrations suggests that methane oxidation is mediated under anaerobic conditions with sulphate as the electron acceptor. Anaerobic oxidation of methane (AOM) and sulphate reduction (SR) rates show maxima at the SMT, which was found between 20 and 200 cm below seafloor at the different mud volcanoes. In comparison to other methane seeps, AOM activity (<383 mmol m−2 year−1) and diffusive methane fluxes (<321 mmol m−2 year−1) in mud volcano sediments of the Gulf of Cadiz are low to mid range. Corresponding lipid biomarker and 16S rDNA clone library analysis give evidence that AOM is mediated by a mixed community of anaerobic methanotrophic archaea and associated sulphate reducing bacteria (SRB) in the studied mud volcanoes. Little is known about the variability of methane fluxes in this environment. Carbonate crusts littering the seafloor of mud volcanoes in the northern part of the Gulf of Cadiz had strongly 13C-depleted lipid signatures indicative of higher seepage activities in the past. However, actual seafloor video observations showed only scarce traces of methane seepage and associated biological processes at the seafloor. No active fluid or free gas escape to the hydrosphere was observed visually at any of the surveyed mud volcanoes, and biogeochemical measurements indicate a complete methane consumption in the seafloor. Our observations suggest that the emission of methane to the hydrosphere from the mud volcano structures studied here may be insignificant at present. 相似文献
385.
Christian Béghin Orélien Randriamboarison Michel Hamelin Erich Karkoschka Christophe Sotin Robert C. Whitten Jean-Jacques Berthelier Réjean Grard Fernando Simões 《Icarus》2012,218(2):1028-1042
This study presents an approximate model for the atypical Schumann resonance in Titan’s atmosphere that accounts for the observations of electromagnetic waves and the measurements of atmospheric conductivity performed with the Huygens Atmospheric Structure and Permittivity, Wave and Altimetry (HASI–PWA) instrumentation during the descent of the Huygens Probe through Titan’s atmosphere in January 2005. After many years of thorough analyses of the collected data, several arguments enable us to claim that the Extremely Low Frequency (ELF) wave observed at around 36 Hz displays all the characteristics of the second harmonic of a Schumann resonance. On Earth, this phenomenon is well known to be triggered by lightning activity. Given the lack of evidence of any thunderstorm activity on Titan, we proposed in early works a model based on an alternative powering mechanism involving the electric current sheets induced in Titan’s ionosphere by the Saturn’s magnetospheric plasma flow. The present study is a further step in improving the initial model and corroborating our preliminary assessments. We first develop an analytic theory of the guided modes that appear to be the most suitable for sustaining Schumann resonances in Titan’s atmosphere. We then introduce the characteristics of the Huygens electric field measurements in the equations, in order to constrain the physical parameters of the resonating cavity. The latter is assumed to be made of different structures distributed between an upper boundary, presumably made of a succession of thin ionized layers of stratospheric aerosols spread up to 150 km and a lower quasi-perfect conductive surface hidden beneath the non-conductive ground. The inner reflecting boundary is proposed to be a buried water–ammonia ocean lying at a likely depth of 55–80 km below a dielectric icy crust. Such estimate is found to comply with models suggesting that the internal heat could be transferred upwards by thermal conduction of the crust, while convective processes cannot be ruled out. 相似文献
386.
Carlos L. Liesa Antonio M. Casas-Sainz Marcos Aurell José L. Simón Ana R. Soria 《Basin Research》2023,35(1):295-335
Many works in the last decades underline the role of evaporites, not just as a conditioning factor but as the engine for subsidence and eventually basin inversion. The western Mediterranean alpine ranges are being investigated in this regard because of the presence of discontinuous units of Permian to Triassic evaporites, deposited in the western Tethys basins. This work presents a thorough analysis of two particular structures (Cañada Vellida and Miravete anticlines) in the intraplate Maestrazgo basin (eastern Iberian Chain, Spain) in which evidence to support their reinterpretation as salt-driven structures have been recently reported. Our analysis includes (i) a comprehensive stratigraphic and structural study of the folds along their entire trace, (ii) the compilation of thickness and distribution of evaporite–bearing and supraevaporite units, paying special attention to changes in the thickness of units in relation to anticlines, and (iii) the study of fault patterns, sometimes in relation to the mechanical stratigraphy. All three aspects are also documented and discussed on a regional scale. The new data and interpretations reported here reinforce the extensional origin of the Late Jurassic–Early Cretaceous basins, and the role of regional extensional tectonics as the responsible for the development of first-order syn-sedimentary normal fault zones driving the formation and evolution of sub-basins. These basins were subsequently inverted and deformed, including the formation of complex, box-geometry anticlines that, in their turn, controlled deposition in Cenozoic basins. The review of the arguments that support the alternative of salt tectonics for the origin of such anticlines has allowed us to delve into the sedimentary and tectonic evolution of the inverted extensional basins and to propose a specific model for the development of these faulted anticlines. The role of salt levels and other interlayered detachments in the structuring of sedimentary basins and their inversion is also pondered. The observations in the eastern Iberian Chain reported here have implications to assess ongoing reinterpretations in terms of salt tectonics in other alpine basins and ranges of the western Mediterranean. 相似文献
387.
Rosmeri Porfírio da Rocha Michelle Simões Reboita Lívia Márcia Mosso Dutra Marta Pereira Llopart Erika Coppola 《Climatic change》2014,125(1):95-109
Interannual variability over South America (SA) is mainly controlled by the El Niño-Southern Oscillation (ENSO) phenomenon. This study investigates the ENSO precipitation signal during austral spring (September–October–November-SON) over SA. Three global circulation models-GCMs-(MPI, GFDL and HadGEM2) are used for RegCM4 (Regional Climate Model version 4) downscaling of the present (1975–2005) near-future (2020–2050) and far-future (2070–2098) climates using two greenhouse gas stabilization scenarios (RCP4.5 and RCP8.5). For the present climate, only HadGEM2 simulates a frequency of El Niño (EN) and La Niña (LN) years similar to the observations. In terms of ENSO frequency changes, only in the far-future RCP8.5 climate there is greater agreement among GCMs, indicating an increase (decrease) of EN (LN) years. In the present climate, validation indicates that only the RegCM4 ensemble mean provides acceptable precipitation biases (smaller than ±20 %) in the two investigated regions. In this period, the GCMs and RegCM4 agree on the relationship between ENSO and precipitation in SA, i.e., both are able to capture the observed regions of positive/negative rainfall anomalies during EN years, with RegCM4 improving on the GCMs’ signal over southeastern SA. For the near and far future climates, in general, the projections indicate an increase (decrease) of precipitation over southeastern SA (northern-northeastern SA). However, the relationship between ENSO and rainfall in most of RegCM4 and GCM members is weaker in the near and far future climates than in the present day climate. This is likely connected with the GCMs’ projection of the more intense ENSO signal displaced to the central basin of Pacific Ocean in the far future compared to present climate. 相似文献
388.
389.
The scheme of recent fault tectonics and neotectonic stresses of the area adjacent to the Strel’tsovka Caldera in the southeastern
Transbaikal region has been compiled for the first time on the basis of structural and geomorphic study. The faults were ranked
by criteria of slip direction stability along separate segments and their expression in topography. Neotectonic stresses of
corresponding ranks were ascertained as well. The heterogeneity of neotectonic stress field is related to the mosaic development
of compression, extension, and the three-axial stress state. Comparison of morphogenetic features of recent and older faults
shows the different character of the deformation mechanism and orientation of tectonic displacements. It has been established
that the Strel’tsovka Caldera and its northwestern segment, in particular, developed as an echeloned system of pull-apart
grabens, but the caldera itself is situated in a recent rise, whereas the northwestern segment is located in a neotectonic
depression corresponding to the Dry Urulyungui Basin filled with volcanic and sedimentary rocks. Such a structure markedly
expands the outlook for discovery of hidden uranium mineralization in the studied area. The elaborated scheme of neotectonic
faults and stresses reflects the postore geodynamic setting and completes the reconstruction of geodynamic conditions pertaining
to the periods of preore preparation and ore-forming tectonomagmatic reactivation. 相似文献
390.
Presence of fluoroquinolones and sulfonamides in urban sewage sludge and their degradation as a result of composting 总被引:4,自引:4,他引:0
M. Lillenberg M.Sc. S. Yurchenko Ph.D. K. Kipper M.Sc. K. Herodes Ph.D. V. Pihl Ph.D. R. Lõhmus Ph.D. M. Ivask A. Kuu Ph.D. S. Kutti M.Sc. S. V. Litvin B.Sc. L. Nei 《International Journal of Environmental Science and Technology》2010,7(2):307-312
The concentrations of some widely used pharmaceuticals, namely fluoroquinolones (ciprofloxacin C17 H18FN3O3, norfloxacin C17 H18FN3O3 and ofloxacin C18 H20FN3O4 and sulfonamides (sulfadimethoxine C12 H14N4O4s and sulfamethoxazole C10 H11N3O3S were determined in urban sewage sludge utilized for making compost. The levels of degradation of these pharmaceuticals resulting from sludge treatment were assessed. The concentrations of the studied pharmaceuticals sufficiently varied both in sewage sludge and in compost and due to this phenomenon the possible danger resulting from the presence of pharmaceuticals in sewage sludge, used for composting, can not be ignored. The concentrations of the studied pharmaceuticals were lower in compost, if compared to the relevant concentrations in sewage sludge. The highest pharmaceutical concentration in sewage sludge — 426 μg/kg — was detected in the case of ciprofloxacin. The highest concentrations present in compost were 22 μg/kg of norfloxacin and 20 μg/kg of ciprofloxacin. Results show that before using the sewage sludge for making compost or before using the compost a fertilizer for food plants, they should be carefully tested against the content of commonly used pharmaceuticals. 相似文献