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231.
The wreck of the Rainbow Warrior, a 40-m ship sunk on 12 December 1987 in Matauri Bay (34° 59′ S, 173° 56′ E), Cavalli Islands, northeastern New Zealand, offers an opportunity to investigate the impact of artificial substrate on temperate carbonate sedimentation. Surface sediment samples showed no significant textural or compositional difference between sediments near the wreck and those far from it. The large and diverse carbonate-producing community resident on the wreck (dominated by bryozoans, corals and sponges) has not had a measurable influence on adjacent bottom sediments (dominated by bivalves and barnacles), even after 21 years. It is likely that carbonate production on the Rainbow Warrior is insufficient to leave any sedimentary record over the potential lifetime of the wreck on the seafloor, which informs our understanding of the long-term impacts of shipwrecks (and other artificial substrata) on the local benthic environment in shallow temperate ecosystems. 相似文献
232.
Praca E Laran S Lepoint G Thomé JP Quetglas A Belcari P Sartor P Dhermain F Ody D Tapie N Budzinski H Das K 《Marine pollution bulletin》2011,62(5):1058-1065
Risso’s dolphins, pilot whales and sperm whales rarely strand in the northwestern Mediterranean. Thus, their feeding ecology, through the analysis of stomach contents, is poorly known. The aim of this study was to gain further insight into the segregation/superposition of the diet and habitat of Risso’s dolphins, pilot whales and sperm whales using chemical tracers, namely, stable isotopes (δ13C, δ15N) and organochlorines. Significantly different δ15N values were obtained in Risso’s dolphins (11.7 ± 0.7‰), sperm whales (10.8 ± 0.3‰) and pilot whales (9.8 ± 0.3‰), revealing different trophic levels. These differences are presumably due to various proportions of Histioteuthidae cephalopods in each toothed whale’s diet. Similar δ13C contents between species indicated long-term habitat superposition or corroborated important seasonal migrations. Lower congener 180 concentrations (8.20 vs. 21.73 μg.g−1 lw) and higher tDDT/tPCB ratios (0.93 vs. 0.42) were observed in sperm whales compared with Risso’s dolphins and may indicate wider migrations for the former. Therefore, competition between these species seems to depend on different trophic levels and migration patterns. 相似文献
233.
Contribution to characterisation of biochar to estimate the labile fraction of carbon 总被引:6,自引:0,他引:6
R. Calvelo Pereira J. KaalM. Camps Arbestain R. Pardo LorenzoW. Aitkenhead M. HedleyF. Macías J. HindmarshJ.A. Maciá-Agulló 《Organic Geochemistry》2011,42(11):1331-1342
Different analytical techniques were used to find the most reliable and economic method for determining the labile fraction of C in biochar. Biochar was produced from pine, poplar and willow (PI, PO and WI, respectively) at two temperatures (400 and 550 °C) and characterised using spectroscopic techniques [solid state 13C nuclear magnetic resonance spectroscopy (NMR)], molecular markers [pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS)], thermogravimetry (TG), elemental composition and wet oxidation (potassium permanganate and potassium dichromate). Short term incubation (110 h) of an A horizon from an Umbrisol amended with the biochar samples at two doses (7.5 and 15 t ha−1) was also carried out to provide supplementary information on the influence of biochar-soil interaction on CO2 evolution. Spectroscopic analysis demonstrated that the degree of biochar carbonisation was influenced by the type of feedstock and heating conditions and followed the order WI-400 < PI-400 ∼ WI-550 ∼ PO-400 < PO-550 < PI-550. The thermo-labile fraction of the biochar samples, estimated from TG, ranged between 21% and 49%. The fraction of total C oxidised with potassium permanganate (Cper/Ctotal) was <50 g kg−1 in all cases, whereas potassium dichromate (Cdichro/Ctotal) oxidation efficiency ranged between 180 and 545 g kg−1. For each type of feedstock, the highest values of either chemically or thermally degradable C corresponded to the biochar produced at low temperature. Results indicate that low cost methodologies, such as dichromate oxidation and TG, reflected the degree of biochar carbonisation, and could therefore be used to estimate the labile fraction of C in biochar. 相似文献
234.
I. A. Pérez M. L. Sánchez M. A. García N. Pardo 《International Journal of Environmental Science and Technology》2017,14(3):653-662
Calculating air mass trajectories is common in atmospheric analyses. However, if explainable results are to be achieved, several procedures are needed to process the vast amount of information handled. Clustering methods are statistical tools usually considered for such a purpose. Although they are based on rigorous algorithms, certain questions still remain when these methods are applied. The current review is organised in sections according to the sequence followed by such procedures. First, the types of clustering methods are described, with their core being the distance used. One key point is the stopping rule, which determines the final number of clusters. A simple classification based on this number is then suggested. Finally, the graphical presentation of the results is examined and the main drawbacks are commented on. A range of applications and results are considered to illustrate each section, and certain caveats and recommendations are also presented. 相似文献
235.
Sophie Oldfield 《Geoforum》2004,35(2):189-201
The paper addresses the question of racial integration in Delft South, a desegregated low-income neighbourhood in Cape Town developed through the provision of state funded housing to families previously classified coloured and African. Through a qualitative analysis, the research examines the effect relocation has had on the racial character of economic and social networks around which resident families construct their everyday activities. In light of the importance of race in shaping these networks, the paper then examines the relationship between access to housing and practices of social and spatial integration, in particular organisation of and participation in street- and neighbourhood-level organisations. I demonstrate that in Delft South legacies of segregation persist in residents’ reliance on economic and social networks built on long, durable histories and geographies of racial segregation. Although physical relocation has not led to a lessening of the importance of racial identities, other identities built around issues such as neighbourhood norms, housing politics, and issues of criminality and legality manifest according to circumstances and residents’ interests. Context and situation therefore are significant for whether and to what degree race and place matter in the post-apartheid context. 相似文献
236.
Martine Mullet Sophie BoursiquotMustapha Abdelmoula Jean-Marie GéninJean-Jacques Ehrhardt 《Geochimica et cosmochimica acta》2002,66(5):829-836
Tetragonal FeS1−x mackinawite, has been synthesized by reacting metallic iron with a sodium sulfide solution and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), transmission Mössbauer spectroscopy (TMS) and X-ray photoelectron spectroscopy (XPS). Based on XRD and TEM analyses, synthetic mackinawite exhibits crystallization and is identical to the natural mineral. Unit cell parameters derived from XRD data are a = b = 0.3670 nm and c = 0.5049 nm. The bulk Fe:S ratio derived from the quantitative dispersive energy analysis is practically 1. XPS analyses, however, showed that mackinawite surface is composed of both Fe(II) and Fe(III) species bound to monosulfide. Accordingly, monosulfide is the dominant S species observed at the surface with lesser amount of polysulfides and elemental sulfur. TMS analysis revealed the presence of both Fe(II) and Fe(III) in the mackinawite structure, thus supporting the XPS analysis. We propose that the iron monosulfide phase synthesized by reacting metallic iron and dissolved sulfide is composed of Fe(II) and S(-II) atoms with the presence of a weathered thin layer covering the bulk material that consists of both Fe(II) and Fe(III) bound to S(-II) atoms and in a less extent of polysulfide and elemental sulfur. 相似文献
237.
Sophie Decrée Étienne Deloule Gilles Ruffet Stijn Dewaele Florias Mees Christian Marignac Johan Yans Thierry De Putter 《Mineralium Deposita》2010,45(7):621-629
The Katanga province, Democratic Republic of Congo, hosts world-class cobalt deposits accounting for ~50% of the world reserves.
They originated from sediment-hosted stratiform copper and cobalt sulfide deposits within Neoproterozoic metasedimentary rocks.
Heterogenite, the main oxidized cobalt mineral, is concentrated as “cobalt caps” along the top of silicified dolomite inselbergs.
The supergene cobalt enrichment process is part of a regional process of residual ore formation that also forms world-class
“manganese cap” deposits in western Katanga, i.e., the “black earths” that are exploited by both industrial and artisanal
mining. Here, we provide constraints on the genesis and the timing of these deposits. Ar–Ar analyses of oxidized Mn ore and
in situ U–Pb SIMS measurements of heterogenite yield Mio–Pliocene ages. The Ar–Ar ages suggest a multi-phase process, starting
in the Late Miocene (10–5 Ma), when the metal-rich substratum was exposed to the action of meteoric fluids, due to major regional
uplift. Further oxidation took place in the Pliocene (3.7–2.3 Ma) and formed most of the observed deposits under humid conditions:
Co- and Mn-caps on metal-rich substrata, and coeval Fe laterites on barren areas. These deposits formed prior to the regional
shift toward more arid conditions in Central Africa. Arid conditions still prevailed during the Quaternary and resulted in
erosion and valley incision, which dismantled the metal-bearing caps and led to ore accumulation in valleys and along foot
slopes. 相似文献
238.
The sedimentary coastal basin of Togo: example of a multilayered aquifer still influenced by a palaeo-seawater intrusion 总被引:3,自引:0,他引:3
Ari Akouvi Martial Dray Sophie Violette Ghislain de Marsily Gian Maria Zuppi 《Hydrogeology Journal》2008,16(3):419-436
In Togo, the hydrogeology of the sedimentary coastal aquifers along the Gulf of Guinea has been studied for the last three decades to define the recharge processes and the origin and evolution of the salinity. Isotope hydrology and fluid geochemistry suggest that the current recharge of all aquifers, both confined and unconfined, occurs through the crystalline basement and the Plio-Quaternary deposits. Two main groundwater mineralization processes are observed: the first one, in recharge areas, is due to farming, village and city life and concerns unconfined aquifers (crystalline basement, Continental Terminal and Quaternary sediments); the second one is a mixing process between recent freshwater and fossil saline water still present in the deep confined aquifers inland, several kilometers away from the coast. Brackish water was trapped in low-permeability lenses of confined aquifers (Eo-Palaeocene and Maastrichtian) during the Quaternary, in periods of low recharge, notably during the last glacial maximum (LGM), and has not yet been flushed out. Hydrodynamic simulations indicate that, at that time, the aquifers experienced a maximum seawater intrusion as far as 20–22 km inland, depending on the palaeo-recharge value at the outcrops. 相似文献
239.
Natalia Pardo Shane J. Cronin Alan S. Palmer Karoly Németh 《Bulletin of Volcanology》2012,74(3):617-640
We analysed the tephra record of Mt. Ruapehu for the period 27,097 ± 957 to ~10,000 cal. years BP to determine the largest-scale
explosive eruptions expected from the most active New Zealand andesitic volcano. From the lithostratigraphic analysis, a systematic
change in the explosive behaviour is identified from older deposits suggesting dry magmatic eruptions and steady eruptive
columns, characterised by frothy to expanded pumice fabrics, to younger deposits that are products of unsteady conditions
and collapsing columns, characterised by microvesicular, fibrous, and colour-banded pumice fabrics. The end-members were separated
by eruptions with steady columns linked to water–magma interaction and highly unstable conduit walls. Dry magmatic eruptions
producing steady plinian columns were most common between 27,097 ± 957 and shortly after 13,635 + 165 cal. years BP. Following
this time, activity continued with eruptions that produced dominantly oscillating unsteady columns, which engendered pyroclastic
density currents, until ~10 ka when there was an abrupt transition at Mt. Ruapehu since which eruptions have been an order
of magnitude lower in intensity and volume. These data demonstrate long-period transitions in eruption behaviour at an andesitic
stratovolcano, which is critical to understand if realistic time-variable hazard forecasts are to be developed. 相似文献