Recent changes in the level of Lake Naivasha,Kenya, as an indicator of equatorial westerlies over East Africa

A previously unpublished record of lake levels from Lake Naivasha, Kenya from 1880 to 1976 has been analysed and shows little similarity to the level record from nearby Lake Victoria. Level changes from year to year of the two lakes show no significant correlation (at 5%) and spectral analysis of the two records shows no common significant peaks. Both lakes show significant correlations between their level changes and the strength of the North Atlantic winter circulation, with the correlation coefficients in opposing directions indicating important, but different, large scale climatic links.Lake Naivasha's major level increases occur during May and September. Lake Victoria's level increases mainly in May with a small December increase. East African rainfall is generally during April and November, corresponding with Lake Victoria's changes. Rainfall records from Kenyan highland areas, however, show an August rainfall peak and little rainfall in November. Rainfall amounts from Equator, a highland meteorological station, for July, August and September are highly correlated (at 1% significance level) with the change in Naivasha's level during September. Winds at the highland stations are westerly during August while the lower level stations experience the drier S.E. Trades. The level changes of Lake Naivasha indicate changes in the extent of the penetration of moist air from West Africa between the Trade winds and the 200 mb easterly jet.     

Water-poverty relationships in the coastal town of Mbour (Senegal): Relevance of GIS for decision support

Coastal area is always a zone with complex problems. Due to the attraction they exert, are facing many social problems. Therefore, a coastal city is usually a city with problems. Its extension, caused by the influx of people from different backgrounds, creates an increased demand for services. One of the problems frequently encountered, especially in Senegal, is access to water. The problem of access to water is poorly treated, without being correlated with the urban evolution, i.e. with increasing population and demand growth. The water resource is facing numerous complications such as the lack of integrated management, integration issues at the governance level, where the local factor is often forgotten.The town of Mbour, object of our study, does not come out of that lot, being an attractive coastal city, from an African country. This indicates the need for an integrated management oriented from local to a global basis and not vice versa. The study presented in this paper indicates that a large proportion of the population has not access to a verified drinking water system and uses water from wells or standpipes. Half of the surveyed population (50%) has no access to a water supply system. The water poverty map of the town overlaps with that of the general poverty excepting few neighborhoods. This means that even areas that are not affected by poverty have a very low or poor access to water, which so far remains the perverse effect of the reform of the Senegalese water sector in 1995.     

汶川地震同震滑坡物质在震区的滞留和运移及其对龙门山地形演化的影响

2008年M_W7.9汶川地震导致龙门山断裂发生强烈地壳变形,同时引发的巨量同震滑坡加速了该地区的地表剥蚀和河流侵蚀.然而,目前尚缺少系统的数据定量研究滑坡物质的运移以及河流侵蚀速率随时间的演化规律,这些对理解龙门山前缘物质的再分配以及强震对活动造山带地形塑造的作用至关重要.为此,本研究在汶川地震后的6年间,对震区沱江上游3条支流湔江、石亭江、绵远河流域进行了多期次的定点现代河沙采样.通过系统测量河沙中的石英¹⁰Be浓度,并与震前已发表的数据进行对比,发现如下基本特点：（1）震后河沙¹⁰Be浓度均有明显降低,表明同震滑坡物质对河沙的稀释作用;（2）震后河流对河沙的运移量增加为震前的1.3~18.5倍,因此震后龙门山地区侵蚀速率短期显著增加;（3）初步估计得到汶川地震产生的滑坡物质被完全运移出造山带所需要的时间至少为100~4000年,接近龙门山地区强震复发周期;（4）震间和同震产生的构造变形和地表剥蚀在空间上具有互补性.考虑到地表剥蚀引起的地壳均衡反弹效应,认为类似汶川地震的强震有利于龙门山的隆升.认识震前、震时和震后的地壳变形及侵蚀过程有助于更好地理解单次强震事件对高原边界龙门山地形演化的作用.

     

‘Paleoenvironmental study of modern charcoal making activity on forest soils in the Northern Vosges Mountains (Bitche,France): A multidisciplinary study of two remaining charcoal platforms and associated soils sequences’

This multidisciplinary study aims to decipher the impact of ancient charcoal production on past and present-day soils in the northern Vosges Mountains. Soil observations in the field and laboratory were complemented by charcoal and phytolith studies on large thin sections, molecular analyses of organic pollutants, and phytolith analysis on bulk samples. The complex technosol platform records an ancient natural soil sequence buried by a human-made platform on which charcoal accumulated. The current upslope soil is an entic Podzol. Palaeoecological data collected in the buried soil are reliable owing to low bioactivity due to soil acidity. Podzolisation predated the platform construction. The presence of ashes induced low soil alkalisation developed in the charcoal hearth remains and appears to have generated the migration of subsequent iron/clay/organic bands throughout the platform sediment and the buried soil. Charcoal studied in thin sections revealed mainly Quercus and Fagus taxa. Phytolith studies suggest that a less dense or degraded forest preceded platform construction, probably due to former woodland coppicing or earlier disorganised wood gathering. The specific distribution of polycyclic aromatic hydrocarbons sorbed on charcoal has persisted in soils throughout centuries, but we have no evidence that charcoal-making activities contributed to diffuse global pollution.     

Quantification and isotopic analysis of nitrogen in rocks at the ppm level using sealed tube combustion technique: A prelude to the study of altered oceanic crust

The present paper reports recent improvements in sealed tube combustion technique used for the determination of N isotopic composition in various rocks characterized by low N contents (i.e. few ppm). Nitrogen is extracted from samples by combustion in quartz tubes sealed under vacuum. The nitrogen gas purified using Cu, CuO and CaO, is quantified as dinitrogen N₂ by capacitance manometry in ultra-high vacuum line. Nitrogen isotopic analysis is performed on a triple-collector static vacuum mass spectrometer, allowing measurement of nanomole quantity of N₂. Nitrogen amount and isotopic composition of the analytical blanks are low and describe Gaussian distribution with mean values of 0.65 ± 0.30 nmol N and − 3.7‰ ± 2.7‰, respectively (2σ). Systematic analyses of international and internal standards demonstrate that this technique provides accurate and precise results. The precision on N content and isotopic composition are better than ± 8% and ± 0.5‰ respectively, even for samples containing less than 2 ppm N. The sealed tube combustion technique is shown to apply successfully to rocks of various lithologies such as metagabbros, metaperidotites and altered basalts. It is thus suitable for studying oceanic crust in a perspective to better constrain N exchanges between Earth mantle and surface reservoirs. The investigation can also be extended to analysis of small size samples, particularly when little sample exists and when high spatial resolution is required.     

Some Aspects of Diet and Foraging Behavior of Octopus dofleini Wülker, 1910 in its Northernmost Range

Abstract. Diet and foraging behavior of Octopus dofleini in Prince William Sound and Port Graham, Alaska, were studied from collections of den litter, measurements of octopuses and estimates of live prey abundance. Based on 193 den collections from depths of - 31 to + 1.3 m, a diet of hard-bodied prey could be identified. The five most common litter species made up 80% of the litter remains, with nearly 30 species of various taxa malung up the rest. The proportions of major hard-bodied prey species in each litter pile significantly differed with depth of den, associated substrata, presence of cobble and geographical location but not with the presence of boulders or outcrop, the density of kelp or season of litter collection. Octopus weight was not significantly correlated with the size of prey remains although O. dofleini may take a wide range of prey sizes once it reaches 2.5 kg. O. dofleini was more likely to be found at sites with crabs, although no litter species was significantly preferred over its estimated abundance, and one species was significantly avoided. These results suggest that O. dofleini includes suitable bivalve and crab species in its diet in relation to live abundance, while at the same time exercising an element of selectivity, as some species were actively avoided. Comparison of litter remains from the northern-most range of O. dofleini with those published for British Columbia show that diet breadth was similar, but the identity of major hard-bodied prey species was very different for Alaskan octopuses.     

Post‐stack stratigraphic inversion workflow applied to carbon dioxide storage: application to the saline aquifer of Sleipner field‡

In the Norwegian North Sea, the Sleipner field produces gas with a high CO₂ content. For environmental reasons, since 1996, more than 11 Mt of this carbon dioxide (CO₂) have been injected in the Utsira Sand saline aquifer located above the hydrocarbon reservoir. A series of seven 3D seismic surveys were recorded to monitor the CO₂ plume evolution. With this case study, time‐lapse seismics have been shown to be successful in mapping the spread of CO₂ over the past decade and to ensure the integrity of the overburden. Stratigraphic inversion of seismic data is currently used in the petroleum industry for quantitative reservoir characterization and enhanced oil recovery. Now it may also be used to evaluate the expansion of a CO₂ plume in an underground reservoir. The aim of this study is to estimate the P‐wave impedances via a Bayesian model‐based stratigraphic inversion. We have focused our study on the 1994 vintage before CO₂ injection and the 2006 vintage carried out after a CO₂ injection of 8.4 Mt. In spite of some difficulties due to the lack of time‐lapse well log data on the interest area, the full application of our inversion workflow allowed us to obtain, for the first time to our knowledge, 3D impedance cubes including the Utsira Sand. These results can be used to better characterize the spreading of CO₂ in a reservoir. With the post‐stack inversion workflow applied to CO₂ storage, we point out the importance of the a priori model and the issue to obtain coherent results between sequential inversions of different seismic vintages. The stacking velocity workflow that yields the migration model and the a priori model, specific to each vintage, can induce a slight inconsistency in the results.     

Sulfide petrology of four nakhlites: Northwest Africa 817, Northwest Africa 998, Nakhla,and Governador Valadares

Abstract– The nakhlites contain small proportions of Cu‐Fe‐Ni sulfide minerals; we have studied these sulfides in Northwest Africa (NWA) 998, Nakhla, Governador Valadares, and NWA 817 with optical microscopy, scanning electron microscope, and electron microprobe. Modal abundances of magmatic sulfides, as estimated by image analysis on thin section, are uniformly low (0.02 to 0.05 ± 0.03 vol%), i.e., a factor 5 lower than in shergottites. Sulfides occur within the glassy mesostasis, as composite two‐phase Fe‐Ti oxide‐sulfide grains, intimately associated with interstitial grains or locally enclosed in postcumulus melt inclusions (e.g., Governador Valadares) in olivine. They exhibit a uniform low‐Ni monoclinic pyrrhotite composition ± chalcopyrite. There is a gradation of sulfide grain sizes and textures across the nakhlites flow(s): droplets in NWA 817; resorbed blebs in Governador Valadares; more massive, true intercumulus blebs in Nakhla and NWA 998. These nakhlites also show evidence for sulfide weathering. Hot desert finds (e.g., NWA 998 and NWA 817) show a few percent fracture‐filling iron (oxy) hydroxides of likely terrestrial origin. Original sulfides are 50% altered in our NWA 998 section, with iron (oxy) hydroxides at grain boundaries and as complete pseudomorphs. The compositions of unaltered pyrrhotites are homogeneous, close to that of the monoclinic endmember Fe₇S₈, and are too sulfur‐rich to have been in chemical equilibrium with the late magmatic redox state fixed by the fayalite‐magnetite‐quartz buffer. Therefore, the compositions of the pyrrhotites must have been altered during the later stages of magmatic crystallization, by assimilation of S‐rich regolith and hydrothermal circulation.