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601.
Decoding the complex internal chemical structure of garnet porphyroblasts from the Zermatt area,Western Alps 总被引:1,自引:0,他引:1
Kurt Bucher Tobias Bjrn Weisenberger Oliver Klemm Sebastian Weber 《Journal of Metamorphic Geology》2019,37(9):1151-1169
Garnet is a prototypical mineral in metamorphic rocks because it commonly preserves chemical and textural features that can be used for untangling its metamorphic development. Large garnet porphyroblasts may show extremely complex internal structures as a result of a polycyclic growth history, deformation, and modification of growth structures by intra‐ and intercrystalline diffusion. The complex internal structure of garnet porphyroblasts from garnet–phengite schists (GPS) of the Zermatt area (Western Alps) has been successfully decoded. The centimetre‐sized garnet porphyroblasts are composed of granulite facies garnet fragments overgrown by a younger generation of grossular‐rich eclogite facies garnet. The early granulite facies garnet (G‐Grt) formed from low‐P, high‐T metamorphism during a pre‐Alpine orogenic event. The late garnet (E‐Grt) is typical of high‐pressure, low‐temperature (HPLT) metamorphism and can be related to Alpine subduction of the schists. Thus, the garnet of the GPS are polycyclic (polymetamorphic). G‐Grt formation occurred at ~670 MPa and 780°C, E‐Grt formed at ~1.7 GPa and 530°C. The G‐Grt is relatively rich in Prp and poor in Grs, while E‐Grt is rich in Grs and poor in Prp. The Alm content (mol.%) of G‐Grt is 68 of E‐Grt 55. After formation of E‐Grt between and around fragmented G‐Grt at 530°C, the GPS have been further subducted and reached a maximum temperature of 580°C before exhumation started. Garnet composition profiles indicate that the initially very sharp contacts between the granulite facies fragments of G‐Grt and fracture seals of HPLT garnet (E‐Grt) have been modified by cation diffusion. The profiles suggest that Ca did not exchange at the scale of 1 µm, whereas Fe and Mg did efficiently diffuse at the derived maximum temperature of 580°C for the GPS at the scale of 7–8 µm. The Grt–Grt diffusion profiles resulted from spending c. 10 Ma at 530–580°C along the P–T–t path. The measured Grt composition profiles are consistent with diffusivities of log DMgFe = ?25.8 m2/s from modelled diffusion profiles. Mg loss by diffusion from G‐Grt is compensated by Fe gain by diffusion from E‐Grt to maintain charge balance. This leads to a distinctive Fe concentration profile typical of uphill diffusion. 相似文献
602.
The impact of upland land management on flooding: results from an improved pasture hillslope 总被引:1,自引:0,他引:1
Miles R. Marshall Oliver J. Francis Zoe L. Frogbrook Bethanna M. Jackson Neil McIntyre Brian Reynolds Imogen Solloway Howard S. Wheater Joanne Chell 《水文研究》2009,23(3):464-475
In response to growing concern about impacts of upland agricultural land management on flood risk, an intensely instrumented experimental catchment has been established at Pontbren, a sheep‐farmed headwater catchment of the River Severn, UK. Primary aims are to develop understanding of the processes governing flood generation and the associated impacts of land management practices, and to bridge the gap between process understanding and ability to predict effects on downstream flooding. To achieve this, the experiment is designed to operate at plot (~100 m2), hillslope (~0·1 km2) and small catchment scale (~10 km2). Hillslope‐scale data, from an under‐drained, agriculturally ‘improved’ pasture, show that drain flow is a dominant runoff process. However, depending on antecedent moisture conditions, overland flow may exceed drain flow rates and can be an important contributor to peak flow runoff at the hillslope‐scale. Flow, soil tension data and tracer tests confirm the importance of macropores and presence of perched water tables under ‘normal’ wet conditions. Comparisons of pasture runoff with that from within a 10 year‐old tree shelterbelt show significantly reduced overland flow due to the presence of trees and/or absence of sheep. Comparisons of soil hydraulic properties show significant increases in hydraulic conductivity and saturated moisture content of soil under trees compared to adjacent improved pasture. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
603.
The global economy is currently experiencing one of its biggest contractions on record. A sharp decline in global imports and exports since 2008 has affected global merchant vessel traffic, the principal mode of bulk commodity transport around the world. During the first quarter of 2009, 10% and 25% of global container and refrigerated vessels, respectively, were reported to be unemployed. A large proportion of these vessels are lying idle at anchor in the coastal waters of South East Asia, sometimes for periods of greater than 3 months. Whilst at anchor, the hulls of such vessels will develop diverse and extensive assemblages of marine biofouling species. Once back in service, these vessels are at risk of transporting higher-than-normal quantities of marine organisms between their respective global trading ports. We discuss the potential ramifications of the global economic crisis on the spread of marine non-indigenous species via global commercial shipping. 相似文献
604.
The resolution achievable for chironomid identifications has increased in recent years because of significant improvements
in taxonomic literature. However, high taxonomic resolution requires more training for analysts. Furthermore, with greater
taxonomic resolution, misidentifications and the number of rare, poorly represented taxa in chironomid calibration datasets
may increase. We assessed the effects of various levels of taxonomic resolution on the performance of chironomid-based temperature
inference models (transfer functions) and temperature reconstruction. A calibration dataset consisting of chironomid assemblage
and temperature data from 100 lakes was examined at four levels of taxonomic detail. The coarsest taxonomic resolution primarily
represented identifications to genus or suprageneric level. At the highest level of taxonomic resolution, identification to
genus level was possible for 37% of taxa, and identification below genus was possible for 60% of taxa. Transfer functions
were obtained using Weighted Averaging (WA) and Weighted Averaging-Partial Least Squares (WA-PLS) regression. Cross-validated
performance statistics, such as the root mean square error of prediction (RMSEP) and the coefficient of determination (r
2) between inferred and observed values improved considerably from the lowest taxonomic resolution level (WA: RMSEP 1.91°C,
r
2 0.78; WA-PLS: RMSEP 1.59°C, r
2 0.86) to the highest taxonomic resolution level (WA: RMSEP 1.66°C, r
2 0.84; WA-PLS: RMSEP 1.41°C, r
2 0.89). Reconstructed July air temperatures during the Lateglacial period based on fossil chironomid assemblages from Hijkermeer
(The Netherlands) were similar for all levels of taxonomic resolution, except the coarsest level. At the coarsest taxonomic
level, reconstruction failed to infer one of the known Lateglacial cold episodes in the record. Also, the difference in reconstructed
values based on lowest and highest taxonomic resolutions exceeded sample-specific estimated standard errors of prediction
in several instances. Our results suggest that chironomid-based transfer functions at the highest taxonomic resolution outperform
models based on lower-resolution calibration data. However, transfer functions of intermediate taxonomic resolution produced
results very similar to models based on high-resolution taxonomic data. In studies that include analysts with different levels
of expertise, inference models based on intermediate taxonomic resolution, therefore, might provide an alternative to transfer
functions of maximum taxonomic detail in order to ensure taxonomic consistency between calibration datasets and down-core
records produced by different analysts. 相似文献
605.
Maarten van Hardenbroek Oliver Heiri Jonathan Grey Paul L. E. Bodelier Frederike Verbruggen André F. Lotter 《Journal of Paleolimnology》2010,43(2):235-245
We used a series of experiments to determine whether stable carbon isotope analysis of modern and fossil larval head capsules
of chironomids allowed identification of their dietary carbon source. Our main focus was to assess whether carbon from naturally
13C-depleted methane-oxidizing bacteria (MOB) can be traced in chironomid cuticles using stable carbon isotope analysis. We
first showed that a minimum sample weight of ~20 μg was required for our equipment to determine head capsule δ13C with a standard deviation of 0.5‰. Such a small minimum sample weight allows taxon-specific δ13C analyses at a precision sufficient to differentiate whether head capsules consist mainly of carbon derived from MOB or from
other food sources commonly encountered in lake ecosystems. We then tested the effect of different chemical pre-treatments
that are commonly used for sediment processing on δ13C measurements on head capsules. Processing with 10% KOH (2 h), 10% HCl (2 h), or 40% HF (18 h) showed no detectable effect
on δ13C, whereas a combination of boiling, accelerated solvent extraction and heavy chemical oxidation resulted in a small (0.2‰)
but statistically significant decrease in δ13C values. Using culturing experiments with MOB grown on 13C-labelled methane, we demonstrated that methanogenic carbon is transferred not only into the larval tissue, but also into
chironomid head capsules. Taxon-specific δ13C of fossil chironomid head capsules from different lake sediments was analyzed. δ13C of head capsules generally ranged from −28 to −25.8‰, but in some instances we observed δ13C values as low as −36.9 to −31.5‰, suggesting that carbon from MOB is traceable in fossil and subfossil chironomid remains.
We demonstrate that stable carbon isotope analyses of fossil chironomid head capsules can give insights into dietary links
and carbon cycling in benthic food webs in the past and that the method has the potential to reconstruct the importance of
MOB in the palaeo-diet of chironomid larvae and, indirectly, to infer past changes in methane flux at the sediment water interface
in lakes. 相似文献
606.
Boris P. Ilyashuk Elena A. Ilyashuk Eugeny A. Makarchenko Oliver Heiri 《Journal of Paleolimnology》2010,44(2):667-676
Larvae of the genus Pseudodiamesa Goetghebuer, which includes 12 described valid species and is divided by Makarchenko and Makarchenko (1999) into two species groups, Pseudodiamesa branickii group and Pseudodiamesa
nivosa group, are widespread in lakes and running waters of cold, high-latitude and high-altitude areas of the Northern Hemisphere.
Larval remains of the genus are often found in subfossil assemblages from these cold regions, but intra-genus morphotypes
usually are not distinguished by palaeoecologists. Current knowledge of the ecology of the species indicates that the Pseudodiamesa nivosa group is more cold-adapted than the Pseudodiamesa branickii group and, therefore, these two intra-genus morphotypes cannot be amalgamated into a larger taxonomic unit without losing
substantial information. Here we present the morphological characters of head capsules of Pseudodiamesa larvae attributed to the different species-group morphotypes, which are clearly visible in subfossil specimens. The information
summarized in this paper will help provide more reliable chironomid-based palaeoclimatic inferences from lake sediment records
covering colder phases through the late Quaternary in the Northern Hemisphere. 相似文献
607.
S. Serjeant A. Efstathiou S. Oliver C. Surace P. Héraudeau M. J. D. Linden-Vørnle C. Gruppioni F. La Franca D. Rigopoulou T. Morel H. Crockett T. Sumner M. Rowan-Robinson M. Graham 《Monthly notices of the Royal Astronomical Society》2001,322(2):262-268
We present the luminosity function of 90-μm-selected galaxies from the European Large Area ISO Survey (ELAIS), extending to z =0.3. Their luminosities are in the range 109 65 −2 L /L⊙ <1012 , i.e. non-ultraluminous. From our sample of 37 reliably detected galaxies in the ELAIS S1 region from the Efstathiou et al. S 90 100 mJy data base, we have found optical, 15-μm or 1.4-GHz identifications for 24 (65 per cent). We have obtained 2dF and UK Schmidt FLAIR spectroscopy of 89 per cent of identifications to rigid multivariate flux limits. We construct a luminosity function assuming that (i) our spectroscopic subset is an unbiased sparse sample, and (ii) there are no galaxies that would not be represented in our spectroscopic sample at any redshift. We argue that we can be confident of both assumptions. We find that the luminosity function is well described by the local 100-μm luminosity function of Rowan-Robinson, Helou & Walker. Assuming this local normalization, we derive luminosity evolution of (1+ z )2.45±0.85 (95 per cent confidence). We argue that star formation dominates the bolometric luminosities of these galaxies, and we derive comoving star formation rates in broad agreement with the Flores et al. and Rowan-Robinson et al. mid-infrared-based estimates. 相似文献
608.
Distribution of landslides in southwest New Zealand 总被引:3,自引:0,他引:3
Oliver Korup 《Landslides》2005,2(1):43-51
This study examines the size distribution of a regional medium-scale inventory of 778 landslides in the mountainous southwest of New Zealand. The spatial density of mapped landslides per unit area can be expressed as a negative power–law function of Landslide area AL spanning three orders of magnitude (10–2–101 km2). Although observed in other studies on landslide inventories, this relationship is surprising, given the lack of absolute ages, and thus uncertainty about the temporal observation window encompassed by the data. Large slope failures (arbitrarily defined here as having a total affected area AL>1 km2) constitute 83% of the total affected landslide area ALT. This dominance by area affects slope morphology, where large-scale landsliding reduces slope angles below the regional modal value of hillslopes, mod39°. More numerous smaller and shallower failures tend to be superimposed on the pre-existing relief. Empirical scaling relationships show that large landslides involve >106 m3 of material. The volumes VL of individual preserved and presumably prehistoric (i.e. pre-1840) landslide deposits equate to 100–102 years of total sediment production from shallow landsliding in the respective catchments, and up to 103 years of contemporary regional sediment yield from the mountain ranges. Their presence in an erosional landscape indicates the geomorphic importance of landslides as temporary local sediment storage. 相似文献
609.
Orpin AR Ridd PV Thomas S Anthony KR Marshall P Oliver J 《Marine pollution bulletin》2004,49(7-8):602-612
Coastal development activities can cause local increases in turbidity and sedimentation. This study characterises the spatial and temporal variability of turbidity near an inshore fringing coral reef in the central Great Barrier Reef, under a wide range of natural conditions. Based on the observed natural variability, we outline a risk management scheme to minimise the impact of construction-related turbidity increases. Comparison of control and impact sites proved unusable for real-time management of turbidity risks. Instead, we suggest using one standard deviation from ambient conditions as a possible conservative upper limit of an acceptable projected increase in turbidity. In addition, the use of regional weather forecast as a proxy for natural turbidity is assessed. This approach is simple and cheap but also has limitations in very rough conditions, when an anthropogenic turbidity increase could prove fatal to corals that are already stressed under natural conditions. 相似文献
610.