On the relationship of thunderstorm ice hydrometeor characteristics and total lightning measurements

Satellite-borne and ground-based devices for the detection of lightning offer the opportunity to explore relationships–on all significant scales up to global–between lightning frequency, f, and other thundercloud parameters. Calculations predict that f is proportional to the product of the downflux p of solid precipitation and the upward mass flux, I, of ice crystals. This prediction has received support from limited computational studies. The physical reasons for such a relationship are explained in terms of the paramount role of ice in the electrification of thunderstorms. Herein, this prediction is subjected to further, preliminary examination through analysis of lightning and dual-polarimetric radar data collected during the STERAO experiment conducted in Northern Colorado during the summer of 1996. The analysis has yielded some highly provisional support for this flux hypothesis. Computed trends of radar derived hydrometeor fractions of solid precipitation and small ice show correlation to the total lightning frequency and raise the possibility of determining values of p and/or I from lightning measurements.It is shown that the extent to which the observed correlations between f and both solid precipitation and small ice trends are or are not strong can provide an indication as to whether the lightning activity is limited by the available concentrations of precipitating or non-precipitating ice in the upper regions of the charging zone of the thundercloud, where most of the charge transfer occurs. It is demonstrated that the most accurate determinations of precipitation rate p from measurements of lighting frequency f are likely to be for conditions where the field-growth is limited by the availability of graupel pellets. It is shown that the simultaneous time variations of f and solid precipitation trends of the type obtained in the STERAO experiment could enable us to determine the nature of the dominant glaciation process operative in the thunderclouds studied.     

'They don't like girls hanging around there': conflicts over recreational space in rural Northamptonshire

This paper provides new insights into girls' use of recreational spaces within rural areas. We draw upon data from in-depth discussion work with 10–14 year old girls undertaken in rural Northamptonshire to show how conflict between adults and children, rival groups of children, and boys and girls influences the social ownership of recreational spaces. In contrast to the rural childhood myth, we disclose geographies of anxiety, tension anddisharmony.     

Lithological and spatial controls on the distribution of quartz veins in andesite- and rhyolite-hosted epithermal Au–Ag deposits of the Hauraki Goldfield, New Zealand

Vein distributions in line samples from four epithermal Au–Ag deposits of the Hauraki Goldfield were logged and quantified by vein spacing, vein density, vein thickness and percentage of vein extension. One deposit is hosted in andesite lavas (Martha Hill), one in andesite lavas and dacite porphyry, dacitic tuffs and pyroclastic breccias (Golden Cross), and two in rhyolite lavas and rhyolitic tuffs with minor andesite lavas or andesite dikes (Ohui and Wharekirauponga). The vein systems in these deposits form fault-controlled arrays of extensional veins. Vein spacing distributions are non-fractal over two to three orders of magnitude (1 mm to 5 m), and therefore fractal dimension statistics are not applicable. The coefficient of variation (C_v) of vein spacing was used as a measure of the degree of vein clustering. Rock type has a marked influence on vein spacing distributions, with veining in rhyolite lava having lower average thickness and percentage extension, but a generally higher degree of vein clustering compared with veining in andesite lava in the same deposit. Vein spacing distributions in well-jointed lithologies, mainly andesite lava, have C_v values (0.8–1.2) that are indicative of anticlustered to weakly clustered patterns, particularly in the vein stockwork of the upper part of the Golden Cross deposit. These C_v values are consistent with field observations that joints are a major control on vein spacing. In the poorly jointed dacitic and rhyolitic rocks, the veins are weakly to strongly clustered as shown by higher C_v values (1.2–2.4), and are commonly associated with normal faults. Overall, andesite lava and dacite porphyry and pyroclastics host thicker and more persistent veins than rhyolite lava and tuff. These larger veins contain significant volumes of high-grade gold mineralisation. The higher chemical reactivity to hydrothermal fluids of andesite and dacite compared with rhyolite may have aided propagation and thickening of the veins in andesite-hosted deposits. Within an individual epithermal deposit, location close to thick veins, representing major fluid conduits, commonly overrides the effect of different lithologies. Sites that are deeper and located within or adjacent to major vein structures have higher average vein thickness, percentage extension and degree of vein clustering. Systematic collection and analysis of vein spacing, thickness and density data can be used to define trends that are useful in the exploration of gold-bearing epithermal vein deposits. Received: 25 August 1998 / Accepted: 23 December 1999     

Microphytobenthos: The ecological role of the “secret garden” of unvegetated,shallow-water marine habitats. II. role in sediment stability and shallow-water food webs

The microphytobenthos form an important component of all shallow-water ecosystems where enough light reaches the sediment surface to support appreciable primary production. Although less conspicuous than macroalgae or vascular plants, the microphytobenthos can contribute significantly to primary production and can modify habitat characteristics. The microphytobenthos alter sediment properties (e.g., erodibility) both directly, in the extreme forming a mat or scum on the sediment surface, and indirectly by modifying the activities of benthic infauna (e.g., pelletization, burrowing, tube building, and sediment tracking). Carbon dioxide fixed by the microphytobenthos supports higher, grazing trophic levels. These include deposit-feeding and suspension-feeding macrofauna as well as meiofauna and microfauna. Quantitative relations between the feeding and growth rates of macrofauna and the abundance of microphytobenthos and suspended organic matter (i.e., functional responses) are reviewed. Given the current state of knowledge of the direct and indirect interactions involving trophic dynamics, sediment properties, and benthic microalgae, we argue for reductionist studies of particular interactions as distinct entities. This is a prerequisite for the emergence of a comprehensive picture of unvegetated ecosystems and the ability to predict their responses to man’s activities. *** DIRECT SUPPORT *** A01BY074 00005     

Temperatures of serpentinization of ultramafic rocks based on O18/O16 fractionation between coexisting serpentine and magnetite

Five lizardite-chrysotile type serpentinites from California, Guatemala and the Dominican Republic show oxygen isotope fractionations of 15.1 to 12.9 per mil between coexisting serpentine and magnetite (O¹⁸ magnetite=–7.6 to –4.6 per mil relative to SMOW). Nine antigorites (mainly from Vermont and S. E. Pennsylvania) show distinctly smaller fractionations of 8.7 to 4.8 per mil (O¹⁸ magnetite=–2.6 to +1.7 per mil). Two lizardite and chrysotile serpentinites dredged from the Mid-Atlantic Ridge exhibit fractionations of 10.0 and 12.4 per mil (O¹⁸ magnetite=–6.8 and –7.9 per mil, respectively), whereas an oceanic antigorite shows a value of 8.2 per mil (O¹⁸ magnetite=–6.2). These data all clearly indicate that the antigorites formed at higher temperatures than the chrysotilelizardites. Electron microprobe analyses of magnetites from the above samples show that they are chemically homogeneous and essentially pure Fe₃O₂. However, some magnetites from certain other samples that show a wide variation of Cr content also give very erratic oxygen isotopic results, suggesting non-equilibrium. An approximate serpentine-magnetite geothermometer curve was constructed by (1) extrapolation of observed O¹⁸ fractionations between coexisting chlorites and Fe-Ti oxides in low-grade pelitic schists whose isotopic temperatures are known from the quartz-muscovite O¹⁸ geothermometer, and (2) estimates of the O¹⁸ fractionation factor between chlorite and serpentine (assumed to be equal to unity). This serpentine-magnetite geothermometer suggests approximate equilibrium temperatures as follows: continental lizardite-chrysotile, 85° to 115° C; oceanic lizardite and chrysotile, 130° C and 185° C, respectively; oceanic antigorite, 235° C; and continental antigorites, 220° to 460° C.Contribution No. 2029 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91109.     

The oxygen isotope geochemistry of igneous rocks

Oxygen isotope analyses have been obtained for 443 igneous rock and mineral samples from various localities throughout the world. Detailed studies were made on the Medicine Lake, Newberry, Lassen, Clear Lake, S. E. Guatemala, Hawaii and Easter I. volcanic complexes and on the Bushveld, Muskox, Kiglapait, Guadalupe, Duluth, Nain, Egersund, Lac St. Jean, Laramie, Skaergaard, Mull, Skye, Ardnamurchan and Alta, Utah plutonic complexes, as well as upon several of the zoned ultramafic intrusions of S. E. Alaska. Basalts, gabbros, syenites and andesites are very uniform in O¹⁸/O¹⁶, commonly with δ-values of 5.5 to 7.0 per mil. Many rhyolite obsidians, particularly those from oceanic areas and the Pacific Coast of the United States, also lie in this range; this indicates that such obsidians are differentiates of basaltic or andesitic magma at high temperatures (about 1,000° C). They cannot represent melted sialic crust. The only plutonic granites with such low δ-values are some of the hypersolvus variety, suggesting that these also might form by fractional crystallization. Obsidians from the continental interior, east of the quartz-diorite line, have higher δ-values. This is compatible with their having assimilated O¹⁸-rich sialic crust. A correlation generally exists between the O¹⁸/O¹⁶ ratios of SiO₂-rich differentiates and the chemical trends in volcanic complexes. High O¹⁸/O¹⁶ ratios accompany those trends having the lower Fe/Mg ratios, while ferrogabbro trends are associated with depletion in O¹⁸. Variations in oxygen fugacity may be responsible for these effects, as abundant early precipitation of magnetite should lead to both O¹⁸-enrichment and Fe-depletion in later differentiates. Plutonic granites have higher O¹⁸/O¹⁶ ratios than their volcanic equivalents, because (a) their differentiation occurred at much lower temperatures, or (b) they are in large part derived from O¹⁸-rich sialic crust by partial melting or assimilation. Also, the oxygen isotope fractionations among coexisting minerals are distinctly larger in plutonic rocks than in volcanic rocks. This is in keeping with their lower crystallization temperatures and their longer cooling history, which promotes post-crystallization oxygen isotope exchange. Hydrated obsidians and perlites have δO¹⁸-values that are much different from their primary, magmatic values. A correlation exists between D/H and O¹⁸/O¹⁶ ratios in hydrated volcanic glass from the western U.S.A., proving that the isotopic compositions are a result of exchange with meteoric waters. The O¹⁸ contents of the glasses appear to be about 25 per mil higher than their associated waters; hence, these hydrated glasses have not simply absorbed H₂O, but they have exchanged with large quantities of it. The igneous rocks from Mull, Skye, Ardnamurchan and the Skaergaard intrusion are all abnormally depleted in O¹⁸ relative to “normal” igneous rocks. This is a result of their having exchanged at high temperatures with meteoric water that was apparently abundant in the highly jointed plateau lavas into which these igneous rocks were intruded. In part, this exchange occurred with liquid magma and in part with the crystalline rock; in the latter case the feldspar was more easily exchanged and has become much more depleted in O¹⁸ than has coexisting quartz or pyroxene. The later differentiates of the Muskox intrusion are markedly O¹⁸-rich, but this is not a result of fractional crystallization. It is in large part a result of deuteric exchange between feldspars and an oxygen-bearing fluid (H₂O ?) that was either O¹⁸-rich or had a relatively low temperature. This phenomenon was also observed in a number of granophyres from other localities, particularly those containing brick-red alkali feldspar. The exchanged feldspars in all these examples are turbid or cloudy, and may be filled with hematite dust. It is concluded that most such feldspar in nature is the result of deuteric exchange and is probably drastically out of oxygen isotopic equilibrium with its coexisting quartz.     

The right to say: the development of youth councils/forums within the UK

Summary Article 12 of the United Nations Convention on the Rights of the Child makes explicit reference to children's right to say what they think about matters relating to the quality of their lives, and to have those opinions taken into account in accordance with their levels of competence and maturity. Despite the commitment of the UK Government to this and other similar initiatives designed to empower young people, a culture of non-participation is endemic within the UK in the context of environmental planning. Young people are seemingly invisible on the landscape. This paper reviews the case for children's active involvement in their environmental future and considers attempts to engage young people through an incipient structure of youth councils and forums.     

Partitioning of Fe and Mn between ilmenite and olivine at 1100 °C: constraints on the thermodynamic mixing properties of (Fe, Mn)TiO3 ilmenite solid solutions

The partitioning of Fe²⁺ and Mn²⁺ between (Fe, Mn)TiO₃ and (Fe, Mn)₂SiO₄ solid solutions in the system FeO-MnO-TiO₂-SiO₂ has been experimentally investigated at 1100 ^∘C and pressures of 1 bar and 25 kbar, over a wide range of Fe/Mn ratios, using electron microprobe analysis of quenched run products. The ilmenite solid solution in this system is within analytical uncertainty a simple binary between FeTiO₃ and MnTiO₃, but the olivine solid solution appears to contain up to 2.5 wt% TiO₂. The Fe-Mn partitioning results constrain precisely the difference in the thermodynamic mixing properties of the two solid solutions. If the mixing properties of (Fe, Mn)₂SiO₄ solid solutions are assumed to be ideal, as experimentally determined by Schwerdtfeger and Muan (1966), then the ilmenite is a regular, symmetric solution with W ^ilm _Fe-Mn=1.8±0.1 kJ mol⁻¹. The quoted uncertainty does not include the contribution from the uncertainty in the mixing properties of the olivine solution, which is estimated to be ±1.8 kJ mol⁻¹, and which therefore dominates the uncertainty in the present results. Nevertheless, this result is in good agreement with the previous experimental study of O'Neill et al. (1989), who obtained W ^ilm _Fe-Mn=2.2±0.3 kJ mol⁻¹ from an independent method. The results provide another item of empirical evidence supporting the proposition that solid solutions between isostructural end-members, in which order-disorder effects are not important, generally have simple thermodynamic mixing properties, with little asymmetry, modest excess entropies, and excess enthalpies approximately proportional to the difference in the molar volumes of the end-members. Received: 11 February 1998 / Accepted: 29 June 1998     

Volcanism and vertical tectonics in the Pacific Basin related to global Cretaceous transgressions

The dominance of volcanic processes and the importance of vertical tectonics in the geological evolution of the Pacific Basin has been recognised since the time of Charles Darwin. Data gathered on several legs of the Deep Sea Drilling Project (DSDP) and numerous marine expeditions in the past decade have confirmed Menard's postulate that the Pacific Basin was the scene of volcanism on an enormous scale in Mesozoic time. Widespread mid-plate volcanism between ～110 and 70 m.y. B.P. characterised the area bounded by the Line Islands, the Mid-Pacific Mountains and the Nauru Basin-Marshall Islands. Heating of the Pacific lithospheric plate during this period of volcanism resulted in regional uplift and the bathymetric evolution of the area diverged significantly from a “normal” Parsons-Sclater subsidence curve. The Farallon plate, now almost entirely subducted, was also the scene of mid-plate volcanism that produced such features as the Nicoya Plateau now found as an allochthonous ophiolitic terrain landward of the middle America trench. Large, benthonic, reef-associated foraminifera comprising a pseudorbitoid fauna, hitherto considered to be largely restricted to Central America, have now been additionally recorded from DSDP Sites 165, 315 and 316 in the Line Islands, Site 462 in the Nauru Basin, and in New Guinea. The distribution of this fauna, of Campanian/Maastrichtian age, is interpreted as indicating “stepping stone” connections (aseismic ridges, plateaus and seamounts) between the Caribbean, Farallon, and Pacific plates 70–80 m.y. B.P. Similarities between the geology of the Nauru Basin and the Caribbean Ocean crust reinforce the interpretation of the latter as a former part of the Farallon plate. Estimates of the sea-level and continental freeboard change caused by the thermally induced uplift of the Pacific and Farallon plates, as well as substantial areas in the Atlantic and Indian Ocean Basins, indicate that such shallowing of the sea floor could have been the major factor in causing global Cretaceous transgressions.