Dynamics of the plasmasphere in the dusk sector as observed in the outer ionosphere

Summary Direct measurements of the thermal plasma parameters in the topside ionosphere reveal variations of the plasmasphere boundary in the dusk sector. The ACTIVE satellite's near-polar orbits at altitudes of 500 – 1800 km around winter solstice 1989 were used to study the bulge region of the plasmasphere during intervals with different levels of geomagnetic agitation. The narrow, sharply defined trough in electron concentration corresponding to the plasmapause under quiet conditions situated at L = 6 – 7 moved to lower L-values with increasing geomagnetic activity. This narrow trough can be found in all main ion constituents. During periods of moderate geomagnetic activity, following the onset of a weak magnetic storm, a portion of the plasmaspheric bulge region was separated from the main plasmaspheric body. This can be seen in the outer ionosphere as an inner narrow trough at lower L-value. Troughs in light ions need no longer coincide with this in electron concentration. He⁺ is the most sensitive constituent reflecting the dusk sector plasmaspheric situation at this altitude.Dedicated to the Memory of Professor Karel P     

Paleogeothermal gradient in the boskovice furrow

Summary A coalification data set from the first seam of the Rosice-Oslavany coal district in the Boskovice furrow was used to estimate the temperature gradient prevailing within the furrow during Autunian sedimentation. An appreciable scatter of the data reflects the complicated history of the sedimentary region. The northern part of the district displays a higher degree of coalification. The results of the evaluation suggest that the region ceased to subside in the upper Autunian, and that the extent of the post-Autunian erosion does not exceed 500 metres. This version of the burial history, which is consistent with geological data, yields a temperature paleogradient of 76 mK/m for the northern part and of 72 mK/m for the southern part of the district. The gradients estimated are higher than those prevailing during the Carboniferous sedimentation in the Central Bohemian Basin (45 – 53 mK/m), lower than values found for the Ostrava Formation in the Upper Silesian Basin during its Namurian A sedimentation (about 95 mK/m), but comparable with values evaluated for the Karviná Formation of the same basin deposited during the Namurian B - C and Westphalian A (60 – 77 mK/m).Dedicated to the Memory of Professor Karel P     

A rural “eye” in the Capital: Tuti Island,Khartoum, Sudan

Islands at strategic points have often become the core of a modern city, or have been developed as historic heritage sites. This has been especially true when the settlers have been strangers in the land. This paper examines why such a situation has not occurred with Tuti Island at the confluence of the White and Blue Niles in the centre of Sudan's Three Towns capital, even though the first permanent inhabitants at the confluence were strangers and chose Tuti Island for their first settlement. The paper questions whether Tuti can survive as a green eye in its present form with the increasing pressures from the urban areas surrounding it.     

Behavioural-geographical aspects of environmental quality

The behavioural approach in human geography accentuates the view of quality of the environment through man and his value orientations. The quality of environment from the point of view of human experience raises behavioural-geographical questions that are the core of the presented topic. Aspects of environmental imaginations and sensations as well as human value system are presented as variables affecting the structure of the perceived environment and human spatial behaviour. In this context, the authors present results of two behavioural studies that correspond to new models of man and environment from the viewpoint of a behavioural approach. The suggested humanistic approach in behavioural geography emphasizes above all the emotional aspect of the relationship between man and environment, which through environmental values, spatial sensations, and meanings, leads to human spatial behaviour.     

Seismic hazard of Egypt

Earthquake hazard parameters such as maximum expected magnitude,M _max, annual activity rate,, andb value of the Gutenberg-Richter relation have been evaluated for two regions of Egypt. The applied maximum likelihood method permits the combination of both historical and instrumental data. The catalogue used covers earthquakes with magnitude 3 from the time interval 320–1987. The uncertainties in magnitude estimates and threshold of completeness were taken into account. The hazard parameter determination is performed for two study areas. The first area, Gulf of Suez, has higher seismicity level than the second, all other active zones in Egypt.b-values of 1.2 ± 0.1 and 1.0 ± 0.1 are obtained for the two areas, respectively. The number of annually expected earthquakes with magnitude 3 is much larger in the Gulf of Suez, 39 ± 2 than in the other areas, 6.1 ± 0.5. The maximum expected magnitude is calculated to be 6.5 ± 0.4 for a time span of 209 years for the Gulf of Suez and 6.1 ± 0.3 for a time span of 1667 years for the remaining active areas in Egypt. Respective periods of 10 and 20 years were reported for earthquakes of magnitude 5.0 for the two subareas.     

Blind prediction of the site effects at Ashigara Valley,Japan, and its comparison with reality

Weak and strong ground motions were numerically predicted for three stations of the Ashigara Valley test site. The prediction was based on the records from a rock-outcrop station, one weak-motion record from a surface-sediments station, and the standard geotechnical model. The data were provided by the Japanese Working Group on the Effects of Surface Geology as a part of an international experiment. The finite-difference method for SH waves in a 2-D linear viscoelastic medium (a causalQ model) was employed.Comparison with the real records shows that at two stations the predictions fit better than at the third one. Strangely, the two better predictions were for stations situated at larger distances from the reference rock station (one station was on the surface, the other in a borehole). The strong ground motion (the peak acceleration of about 200 cm s^–2) was not predicted qualitatively worse than the weak motion (8 cm s^–2). A less sophisticated second prediction (not submitted during the experiment), in which we did not attempt to fit the available weak-motion record at the sedimentary station, agrees with the reality significantly better.     

Towards a political geography of United Nations peacekeeping: Some considerations

Peacekeeping missions should be viewed from various political and spatial perspectives. Firstly, there is the macro-level perspective of the UN Organization itself, particularly the respective interests of the most powerful members of the UN and permanent seat holders on the Security Council. Secondly, there are the national perspectives of the various resources and troop-contributing states to specific UN operations. Thirdly, there are the interests of the conflicting parties themselves, including governments, national armies, local militia groups, factional political leaders and local communities. An analysis of UN peacekeeping involves a complex multi-dimensional geopolitical framework that incorporates the linkages and contradictions between all these differing perspectives, from macro to micro-spatial scales. Peacekeepers themselves are not passive figures in the political and human landscapes within which they operate. Many of the activities of UN blue helmets alter landscapes and conflict scenarios. Whilst some of these changes are deliberate, such as the creation of demilitarized zones, many are unforeseen and less visible, such as the ways in which local civilian populations are affected by the presence of large numbers of foreign peacekeepers. This paper examines some of the political, social and economic consequences of peacekeeping missions in places as diverse as Cambodia, Somalia, the Lebanon and Cyprus.     

Multiple Isotopic Components in Quaternary Volcanic Rocks of the Cascade Arc near Crater Lake, Oregon

Quaternary lavas and pyroclastic rocks of Mount Mazama, CraterLake caldera, and the surrounding area have variable Sr, Nd,and Pb isotopic compositions. High-alumina olivine tholeiites(HAOT) have ⁸⁷Sr/⁸⁶Sr ratios of 0.70346–0.70364; basalticandesite, 0–70349–0.70372; shoshonitic basalticandesite, 0.70374–0.70388; and andesite, 0.70324–0.70383.Dacites of Mount Mazama have ⁸⁷Sr/⁸⁶Sr ratios of 0.70348–0.70373.Most rhyodacites converge on 0.7037. However, rhyodacite ofthe caldera-forming, climactic eruption has ⁸⁷Sr/⁸⁶Sr=0.70354because of an admixed low-⁸⁷Sr/⁸⁶Sr component. Andesitic tomafic-cumulate scoriae of the climactic eruption, and enclavesin preclimactic rhyodacites, cluster in two groups but shownearly the entire ⁸⁷Sr/⁸⁶Sr range of the data set, confirmingpreviously suggested introduction of diverse parental magmasinto the growing climactic chamber. Pb and Nd isotope ratiosdisplay less variation (²⁰⁶Pb/²⁰⁴Pb= 18.838–18.967, ²⁰⁷Pb/²⁰⁴Pb=15.556–15.616,²⁰⁸Pb/²⁰⁴Pb=38.405–38.619; _Nd= +3.9 to +6.1) and generallycovary with ⁸⁷Sr/⁸⁶ Sr ratios. Radiogenic isotope data fromCrater Lake plot with published data for other Cascade volcanoeson isotope ratio correlation diagrams. The isotopic data for the Crater Lake area require sources ofprimitive magmas to consist of depleted mantle and a subductioncomponent, introduced in variable quantity to the depleted mantlewedge. Variable degrees of melting of this heterogeneous mantle,possibly at different depths, produced the diversity of isotopiccompositions and large-ion lithophile element (LILE) abundancesin primitive magmas. Trace element ratios do not indicate presenceof an ocean island basalt (OIB) source component that has beenreported in lavas of some other Cascade volcanoes. Crustal contamination may have affected isotope ratios and LILEconcentrations in evolved HAOT, where initial LILE concentrationswere low. Contamination is more difficult to detect in the calcalkalinelavas because of their higher LILE concentrations and the smallisotopic contrast with likely contaminants, such as mid- tolower-crustal rocks thought to be equivalents of igneous rocksof the Klamath Mountains and associated lower crust. Crustalassimilation appears to be required for calcalkaline rocks onlyby ¹⁸O values, which vary from lows of +5.6 to + 6.0% in HAOTand primitive basaltic andesites to a high of +7.0% in dacite,a range that is too high to be explained by plagioclase-dominatedclosed-system fractional crystallization. Elevated ¹⁸O valuesof differentiated lavas may be attributed to interaction withrelatively ¹⁸O-rich, ⁸⁷Sr-poor crustal rocks. Variably fused granitoid blocks ejected in the climactic eruption,and rarely in late Pleistocene eruptive units, have ¹⁸Opl of–3.4 to +6.5% and ¹⁸O_qz of –2.2 to +8.0% but haveSr, Nd, and Pb isotope ratios similar to volcanic rocks (e.g.⁸⁷Sr/⁸⁶Sr0.7037). Rb and Sr data for glass separates from granodioritessuggest that the source pluton is Miocene. Glass from granodioritehas ⁸⁷Sr/⁸⁶Sr ratios as high as 0.70617. Oxygen isotope fractionationbetween quartz, plagioclase, and glass indicates requilibrationof O isotopes at magmatic temperatures, after ¹⁸O/¹⁶O had beenlowered by exchange with meteoric hydrothermal fluids. Unmeltedgranodiorite xenoliths from pre-climactic eruptive units have¹⁸O values that are consistent with onset of hydrothermal exchangeearly during growth of the climactic magma chamber. Assimilationof such upper-crustal granodiorite apparently lowered ¹⁸O valuesof rhyodacites without significantly affecting their magmaticcompositions in other ways.     

Aqueous alteration of the Bali CV3 chondrite: evidence from mineralogy, mineral chemistry, and oxygen isotopic compositions

A petrographic, geochemical, and oxygen isotopic study of the Bali CV3 carbonaceous chondrite revealed that the meteorite has undergone extensive deformation and aqueous alteration on its parent body. Deformation textures are common and include flattened chondrules, a well-developed foliation, and the presence of distinctive (100) planar defects in olivine. The occurrence of alteration products associated with the planar defects indicates that the deformation features formed prior to the episode of aqueous alteration. The secondary minerals produced during the alteration event include well-crystallized Mg-rich saponite, framboidal magnetite, and Ca-phosphates. The alteration products are not homogeneously distributed throughout the meteorite, but occur in regions adjacent to relatively unaltered material, such as veins of altered material following the foliation. The alteration assemblage formed under oxidizing conditions at relatively low temperatures (<100 degrees C). Altered regions in Bali have higher Na, Ca, and P contents than unaltered regions which suggests that the fluid phase carried significant dissolved solids. Oxygen isotopic compositions for unaltered regions in Bali fall within the field for other CV3 whole-rocks, however, the oxygen isotopic compositions of the heavily altered material lie in the region for the CM and CR chondrites. The heavy-isotope enrichment of the altered regions in Bali suggest alteration conditions similar to those for the petrographic type-2 carbonaceous chondrites.     

Carbon isotopic fractionation in lipids from methanotrophic bacteria: relevance for interpretation of the geochemical record of biomarkers

Experiments with cultured aerobic methane oxidising bacteria confirm that their biomarker lipids will be significantly depleted in 13C compared to the substrate. The methanotrophic bacteria Methylococcus capsulatus and Methylomonas methanica, grown on methane and using the RuMP cycle for carbon assimilation, show maximum 13C fractionation of approximately 30% in the resultant biomass. In M. capsulatus, the maximum fractionation is observed in the earliest part of the exponential growth stage and decreases to approximately 16% as cells approach stationary phase. This change may be associated with a shift from the particulate form to the soluble form of the methane monooxygenase enzyme. Less than maximum fractionation is observed when cells are grown with reduced methane availability. Biomass of M. capsulatus grown on methanol was depleted by 9% compared to the substrate. Additional strong 13C fractionation takes place during polyisoprenoid biosynthesis in methanotrophs. The delta 13C values of individual hopanoid and steroid biomarkers produced by these organisms were as much as l0% more negative than total biomass. In individual cultures, squalene was 13C-enriched by as much as 14% compared to the triterpane skeleton of bacteriohopaneaminopentol. Much of the isotopic dispersion in lipid metabolites could be attributed to shifts in their relative abundances, combined with an overall reduction in fractionation during the growth cycle. In cells grown on methanol, where there was no apparent effect of growth stage on overall fractionation there were still significant isotopic differences between closely related lipids including a 5.3% difference between the hopane and 3 beta-methylhopane skeletons. Hopane and sterane polyisoprenoids were also 13C-depleted compared to fatty acids. These observations have significant implications for the interpretation of specific compound isotopic signatures now being measured for hydrocarbons and other lipids present in sediments and petroleum. In particular, biomarker lipids produced by a single organism do not necessarily have the same carbon isotopic composition.