Diel variation of dissolved organic carbon during large flow events in a lowland river     

Douglas P. Westhorpe  Simon M. Mitrovic  K. Benjamin Woodward 《Limnologica》2012,42(3):220-226

Diel variation in dissolved organic carbon (DOC) within lotic systems has been reported on numerous occasions. However, to our knowledge there has been no published work on diel DOC variation within lowland rivers during high flow events. We sampled DOC at 4 h intervals from two sites across two distinct flow regimes in the regulated lower Namoi River, Australia. This included a large flood (mean flow 224 m³ s⁻¹ and a peak flow of 376 m³ s⁻¹) sampled every 4 h for 10 consecutive days. DOC concentrations were significantly greater at night than during the day (P < 0.05) and the mean DOC concentration was 23.4 mg L⁻¹ at night compared to 18.9 mg L⁻¹ during daylight hours. The magnitude and duration of flow within this lowland river system and the mobilisation of large quantities of allochthonous carbon appeared to play a role in increasing DOC concentration and the diel difference.  相似文献   

Seismic coda due to non-linear elasticity     

Klaus Bataille  Ignacia Calisto 《Geophysical Journal International》2008,172(2):572-580

Non-linear elastic response of rocks has been widely observed in laboratory, but very few seismic studies are reported in the literature, even though it is the most natural environment where this feature could be observed. Analytic solutions to the non-linear wave propagation phenomena are not readily available, and there is a need to use approximated techniques. It is clear that when a seismic wave propagates through a homogeneous non-linear elastic media, it will be perturbed by the non-linearity. This perturbation can be treated as a source of scattering, spreading the energy of the primary wave in space and time, contributing to the seismic coda. This is in some sense similar to the effect of heterogeneities. The properties of the coda due to the non-linearity depend on the amount of non-linearity and the seismic moment. Using a perturbation approach we calculate the amplitude of the scattered waves, and show that it can describe reasonably well the main features of real seismic codas.  相似文献   

Small valley glaciers and the effectiveness of the glacial buzzsaw in the northern Basin and Range, USA   总被引：2，自引：0，他引：2  

David Foster  Simon H. Brocklehurst  Rob L. Gawthorpe 《Geomorphology》2008,102(3-4):624-639

The glacial buzzsaw hypothesis suggests that efficient erosion limits topographic elevations in extensively glaciated orogens. Studies to date have largely focussed on regions where large glaciers (tens of kilometres long) have been active. In light of recent studies emphasising the importance of lateral glacial erosion in lowering peaks and ridgelines, we examine the effectiveness of small glaciers in limiting topography under both relatively slow and rapid rock uplift conditions. Four ranges in the northern Basin and Range, Idaho, Montana, and Wyoming, USA, were chosen for this analysis. Estimates of maximum Pleistocene slip rates along normal faults bounding the Beaverhead–Bitterroot Mountains (~ 0.14 mm y^− 1), Lemhi Range (~ 0.3 mm y^− 1) and Lost River Range (~ 0.3 mm y^− 1) are an order of magnitude lower than those on the Teton Fault (~ 2 mm y^− 1). We compare the distribution of glacial erosion (estimated from cirque floor elevations and last glacial maximum (LGM) equilibrium line altitude (ELA) reconstructions) and fault slip rate with three metrics of topography in each range: the along-strike maximum elevation swath profile, hypsometry, and slope-elevation profiles. In the slowly uplifting Beaverhead–Bitterroot Mountains, and Lemhi and Lost River Ranges, trends in maximum elevation parallel ELAs, independent of variations in fault slip rate. Maximum elevations are offset ~ 500 m from LGM ELAs in the Lost River Range, Lemhi Range, and northern Beaverhead–Bitterroot Mountains, and by ~ 350 m in the southern Beaverhead–Bitterroot Mountains, where glacial extents were less. The offset between maximum topography and mean Quaternary ELAs, inferred from cirque floor elevations, is ~ 350 m in the Lost River and Lemhi Ranges, and 200–250 m in the Beaverhead–Bitterroot Mountains. Additionally, slope-elevation profiles are flattened and hypsometry profiles show a peak in surface areas close to the ELA in the Lemhi Range and Beaverhead–Bitterroot Mountains, suggesting that small glaciers efficiently limit topography. The situation in the Lost River Range is less clear as a glacial signature is not apparent in either slope-elevation profiles or the hypsometry. In the rapidly uplifting Teton Range, the distribution of ELAs appears superficially to correspond to maximum topography, hypsometry, and slope-elevations profiles, with regression lines on maximum elevations offset by ~ 700 and ~ 350 m from the LGM and mean Quaternary ELA respectively. However, Grand Teton and Mt. Moran represent high-elevation “Teflon Peaks” that appear impervious to glacial erosion, formed in the hard crystalline bedrock at the core of the range. Glacier size and drainage density, rock uplift rate, and bedrock lithology are all important considerations when assessing the ability of glaciers to limit mountain range topography. In the northern Basin and Range, it is only under exceptional circumstances in the Teton Range that small glaciers appear to be incapable of imposing a fully efficient glacial buzzsaw, emphasising that high peaks represent an important caveat to the glacial buzzsaw hypothesis.  相似文献   

The fine-grained phase-space structure of cold dark matter haloes     

Mark Vogelsberger  Simon D. M. White  Amina Helmi  Volker Springel 《Monthly notices of the Royal Astronomical Society》2008,385(1):236-254

We present a new and completely general technique for calculating the fine-grained phase-space structure of dark matter (DM) throughout the Galactic halo. Our goal is to understand this structure on the scales relevant for direct and indirect detection experiments. Our method is based on evaluating the geodesic deviation equation along the trajectories of individual DM particles. It requires no assumptions about the symmetry or stationarity of the halo formation process. In this paper we study general static potentials which exhibit more complex behaviour than the separable potentials studied previously. For ellipsoidal logarithmic potentials with a core, phase mixing is sensitive to the resonance structure, as indicated by the number of independent orbital frequencies. Regions of chaotic mixing can be identified by the very rapid decrease in the real-space density of the associated DM streams. We also study the evolution of stream-density in ellipsoidal NFW haloes with radially varying isopotential shape, showing that if such a model is applied to the Galactic halo, at least 10⁵ streams are expected near the Sun. The most novel aspect of our approach is that general non-static systems can be studied through implementation in a cosmological N -body code. Such an implementation allows a robust and accurate evaluation of the enhancements in annihilation radiation due to fine-scale structure such as caustics. We embed the scheme in the current state-of-the-art code gadget -3 and present tests which demonstrate that N -body discreteness effects can be kept under control in realistic configurations.  相似文献   

Northwest Africa 2526: A partial melt residue of enstatite chondrite parentage     

Klaus KEIL  Addi BISCHOFF 《Meteoritics & planetary science》2008,43(7):1233-1240

Abstract— NWA 2526 is a coarse‐grained, achondritic rock dominated by equigranular grains of polysynthetically twinned enstatite (?85 vol%) with frequent 120° triple junctions and ?10–15 vol% of kamacite + terrestrial weathering products. All other phases including troilite, daubreelite, schreibersite, and silica‐normative melt areas make up 相似文献   

Sink rate of baited hooks during deployment of a pelagic longline from a New Zealand fishing vessel     

Simon Anderson  Brian Mcardle 《新西兰海洋与淡水研究杂志》2013,47(1):185-195

The sink rate of baited hooks during the deployment of a pelagic longline was determined using time depth recorders. This study was undertaken to determine how long baited hooks are within the known diving ranges of seabirds. During the vessel's normal fishing operations the unweighted baited hooks reached a mean depth of 5.57 m, 30 s after being deployed. The tori line aerial section covered the longline for a mean time of 29.3 s. With the addition of a 60 g lead swivel, the mean baited hook depth attained more than doubled to 13.44 m, and a further trial using a lead core cord in the snood configuration showed a small but significant increase in hook depth over the unweighted control (7.27 m). An increase in wind speed caused the baited hooks to sink faster (0.54 m for each Beaufort unit increase in wind speed). There was also evidence that the apparent wind direction while the vessel is setting also has an effect on the depths realised, but swell height had no detectable effect. The temperature of the bait also significantly affected the hook depth: partially thawed baits sank faster than thawed baits. A 1°C rise in bait temperature reduced the depth by 0.19 m. During normal line setting on this vessel using unweighted branchlines and a tori line, a considerable proportion of the baited hooks are within the known diving range of sooty shearwaters (Puffinus griseus), white chinned petrels (Procellaria aequinoctialis), shy albatross (Thalassarche cauta), black browed albatross (T. melanophrys), grey headed albatross (T. chrysostoma), and light mantled sooty albatross (Phoebetria palpebrata). The addition of a 60 g weight removes the baited hooks from the recorded diving range of all of these species except sooty shearwaters. Investigating the behaviour of different gear configurations along with evaluating the effect that environmental conditions have on the deployment of a longline will greatly add to our understanding of why some seabirds are caught.  相似文献   

Using fine‐scale catch predictions to examine spatial variation in growth and catchability of Panulirus cygnus along the west coast of Australia     

Simon De Lestang  Nick Caputi  Roy Melville‐Smith 《新西兰海洋与淡水研究杂志》2013,47(1):443-455

Puerulus settlement has been monitored throughout the western rock lobster Panulirus cygnus fishery for nearly 40 years. These data, in combination with indices of effort and water temperature, were used to produce recruitment‐catch relationships for each 1° transect of latitude in the coastal part of this fishery from Kalbarri to Cape Leeuwin, as well as at the offshore Abrolhos Islands (total of eight transects). The fine spatial scales of these models provided estimates of certain life history traits that are known to affect lobster catches between adjacent fishing ports. This catch modelling showed that the proportions of 3‐ and 4‐year‐old post‐settlement lobsters contributing to the catches varied markedly from the southern to northern transects, suggesting that juvenile lobsters grow substantially faster in the warmer northern and offshore waters of this fishery. These proportions provide accurate estimates of juvenile growth rates, which are vital in the construction of location‐specific growth algorithms required by the age‐structured models used in the management of this fishery. Model estimates of density‐dependent mortality were greater in the more densely populated centre of the fishery and markedly lower at the northern and southern limits of this species distribution. Annual increases in fishing efficiency were also found to be lowest at the northern and southern extremes of the fishery and greatest in the centre of the fishery, where technology advances and increased fleet mobility have enabled the fleet to increase efficiency by 1–3% each year. Catchability (q) was found to be most influenced by water temperatures in the cooler southern transects, whereas at the Abrolhos Islands, changes in water temperature produced almost no discernable change in q. The catch modelling was also used to quantify the impact of management changes introduced in the 1993/94 fishing season. Increased protection of female lobsters and an 18% pot reduction resulted in a 3–4% permanent reduction in the catch rates of lobsters throughout most of the coastal fishery, whereas at the offshore Abrolhos Islands, catch rates increased by c. 20%, presumably owing to a reduction in the level of pot saturation.  相似文献   

Washed with Sun: Landscape and the Making of White South Africa – By Jeremy Foster     

David  Simon 《The Geographical journal》2009,175(3):239-240

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Remarkable geochemical changes and degassing at Voui crater lake,Ambae volcano,Vanuatu     

Philipson Bani  Clive Oppenheimer  Johan C. Varekamp  Thomas Quinou  Michel Lardy  Simon Carn 《Journal of Volcanology and Geothermal Research》2009

Ambae (also known as Aoba), is a 38 × 16 km² lozenge-shaped island volcano with a coastal population of around 10 000. At the summit of the volcano is lake Voui — one of the largest active crater lakes worldwide, with 40 × 10⁶ m³ of acidic water perched 1400 m a.s.l. After more than 300 years of dormancy, Ambae volcano reawakened with phreatic eruptions through Voui in 1995, and culminating in a series of surtseyan eruptions in 2005, followed by a rapid and spectacular colour change of the lake from light blue to red in 2006. Integrating lake water chemistry with new measurements of SO₂ emissions from the volcano during the 2005–2006 eruptive period helps to explain the unusual and spectacular volcanic activity of Ambae — initially, a degassed magma approached the lake bed and triggered the surtseyan eruption. Depressurization of the conduit facilitated ascent of volatile-rich magma from the deeper plumbing system. The construction of a cone during eruption and the high degassing destabilised the equilibrium of lake stratification leading to a limnic event and subsequently the spectacular colour change.  相似文献   

On the Use of Hydrological Models and Satellite Data to Study the Water Budget of River Basins Affected by Human Activities: Examples from the Garonne Basin of France     

Eric Martin  Simon Gascoin  Youen Grusson  Clément Murgue  Mélanie Bardeau  François Anctil  Sylvain Ferrant  Romain Lardy  Patrick Le Moigne  Delphine Leenhardt  Vincent Rivalland  José-Miguel Sánchez Pérez  Sabine Sauvage  Olivier Therond 《Surveys in Geophysics》2016,37(2):223-247

Natural and anthropogenic forcing factors and their changes significantly impact water resources in many river basins around the world. Information on such changes can be derived from fine scale in situ and satellite observations, used in combination with hydrological models. The latter need to account for hydrological changes caused by human activities to correctly estimate the actual water resource. In this study, we consider the catchment area of the Garonne river (in France) to investigate the capabilities of space-based observations and up-to-date hydrological modeling in estimating water resources of a river basin modified by human activities and a changing climate. Using the ISBA–MODCOU and SWAT hydrological models, we find that the water resources of the Garonne basin display a negative climate trend since 1960. The snow component of the two models is validated using the moderate-resolution imaging spectroradiometer snow cover extent climatology. Crop sowing dates based on remote sensing studies are also considered in the validation procedure. Use of this dataset improves the simulated evapotranspiration and river discharge amounts when compared to conventional data. Finally, we investigate the benefit of using the MAELIA multi-agent model that accounts for a realistic agricultural and management scenario. Among other results, we find that changes in crop systems have significant impacts on water uptake for agriculture. This work constitutes a basis for the construction of a future modeling framework of the sociological and hydrological system of the Garonne river region.  相似文献