The Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission

The Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission spacecraft is described, including the experiment objectives, system design, performance, and modes of operation. The instrument operates in the wavelength range 1150–3600 Å with better than 2 arc sec spatial resolution, raster range 256 × 256 arc sec², and 20 mÅ spectral resolution in second order. Observations can be made with specific sets of 4 lines simultaneously, or with both sides of 2 lines simultaneously for velocity and polarization. A rotatable retarder can be inserted into the spectrometer beam for measurement of Zeeman splitting and linear polarization in the transition region and chromosphere.Currently at MMTO, University of Arizona, Tucson, Ariz. 85721, U.S.A.     

The impact of taphonomic processes on interpreting paleoecologic changes in large lake ecosystems: ostracodes in Lakes Tanganyika and Malawi

Nonmarine ostracodes are often used as proxy indicators for the biotic response to climate as well as anthropogenic changes in large lakes. Their large numbers, small size and sensitivities to environmental conditions make them ideal for assessing how organisms respond to environmental perturbations. However, little is known about the various taphonomic processes related to preserving these organisms in the lacustrine fossil record. Without understanding the amount of time averaging associated with these assemblages, any interpretation of their biodiversity and paleoecology may be problematic.To address these issues, we conducted actualistic experiments to determine transport, time-averaging, and the amount of taphonomic bias in ostracode sub-fossil assemblages. Sand transport experiments revealed significant mixing at all sites at shallower depths and significant mixing on rocky substrates but not sandy ones. Comparisons with ostracode material collected along the experimental transects support this model and demonstrate time averaging in both the sandy and rocky substrates. Preservational models were derived from the experimental data and applied to interpreting the paleobiologic record of ostracodes from piston cores in both Lake Tanganyika and Malawi. The core record reveals assemblages that have undergone significant time-averaging, and in the case of Lake Malawi, preservational degradation. In the core examined from Tanganyika, most assemblages resemble the time-averaged experimental model with respect to species richness, percentage of articulated shells and heavy bias towards adult dead individuals. In the Malawi cores, most of the valves were preserved only as internal molds. The taphonomic signature of these samples resemble the time-averaged assemblages of Tanganyika cores, even though carapaces are not often present.Both the experimental and live/dead valve data suggest significant time-averaging and transport, smearing seasonal-yearly data in some environments involved in using ostracodes to assess biotic changes as a result of climate and or anthropogenically-induced environmental change. Ostracode species richness estimates were impacted by time averaging because transport of dead valve material occurs at high percentages in the shallow depths and on the rocky substrates, suggesting that the ostracode death assemblages in these areas will not reflect living populations. In addition, ecologic models based only upon death assemblages will be less resolved than those based upon live assemblages. A time averaging index was derived using the % dead juveniles ratio, as well as sedimentation rate and information on the population dynamics, if known.     

The relationship of total dissolved solids measurements to bulk electrical conductivity in an aquifer contaminated with hydrocarbon

A recent conceptual model links higher bulk conductivities at hydrocarbon impacted sites to higher total dissolved solids (TDS) resulting from enhanced mineral weathering due to acids produced during biodegradation. In this study, we evaluated the above model by investigating the vertical distribution of bulk conductivity, TDS, and specific conductance in groundwater. The results showed higher TDS at contaminated locations consistent with the above model. Further, steep vertical gradients in bulk conductivity and TDS suggest vertical and spatial heterogeneity at the site. We observed that at fluid conductivities <40 mS/m, bulk conductivity was inversely related to fluid conductivity, but at fluid conductivities >40 mS/m, bulk conductivity increased with increasing fluid conductivity. However, at fluid conductivities >80 mS/m, bulk conductivities increased without a corresponding increase in fluid conductivity, resulting in a poor correlation between bulk conductivity and fluid conductivity for the contaminated samples. This suggests that electrolytic conductivity was not completely responsible for the observed variability in bulk conductivity. We suggest two possible reasons for the inverse relationship at low fluid conductivity and poor positive correlation at high fluid conductivity: (1) geochemical heterogeneity due to biological processes not captured at a scale comparable to the bulk conductivity measurement and (2) variability in the surface conductivity, consistent with a simple petrophysical model that suggests higher surface conductivity for contaminated sediments. We conclude that biodegradation processes can impact both electrolytic and surface conduction properties of contaminated sediments and these two factors can account for the higher bulk conductivities observed in sediments impacted by hydrocarbon.     

Chemical and thermal zonation in a mildly alkaline magma system Infiernito Caldera,Trans-Pecos Texas

Postcollapse lavas of the Infiernito caldera grade stratigraphically upward from nearly aphyric, high-silica rhyolite (76% SiO₂) to highly prophyritic trachyte (62% SiO₂). Plagioclase, clinopyroxene, orthopyroxene, magnetite, ilmenite, and apatite occur as phenocrysts throughout the sequence. Sanidine, biotite, and zircon are present in rocks with more than about 67% SiO₂. Major and trace elements show continuous variations from 62 to 76% SiO₂. Modeling supports fractional crystallization of the observed phenocrysts as the dominant process in generating the chemical variation.Temperatures calculated from coexisting feldspars, pyroxenes, and Fe-Ti oxides agree and indicate crystallization from slightly more than 1100° C in the most mafic trachyte to 800° C in high-silica rhyolite. The compositional zonation probably arose through crystallization against the chilled margin of the magma chamber and consequent rise of more evolved and therefore less dense liquid.Mineral compositions vary regularly with rock composition, but also suggest minor mixing and assimilation of wall rock or fluids derived from wall rock. Mixing between liquids of slightly different compositions is indicated by different compositions of individual pyroxene phenocrysts in single samples. Liquid-solid mixing is indicated by mineral compositions of glomerocrysts and some phenocrysts that apparently crystallized in generally more evolved liquids at lower temperature and higher oxygen fugacity than represented by the rocks in which they now reside. Glomerocrysts probably crystallized against the chilled margin of the magma chamber and were torn from the wall as the liquid rose during progressive stages of eruption. Assimilation is indicated by rise of oxygen fugacity relative to a buffer from more mafic to more silicic rocks.Calculation of density and viscosity from the compositional and mineralogical data indicates that the magma chamber was stably stratified; lower temperature but more evolved, thus less dense, rhyolite overlay higher temperature, less evolved, and therefore more dense, progressively more mafic liquids. The continuity in rock and mineral compositions and calculated temperature, viscosity, and density indicate that compositional gradation in the magma chamber was smoothly continuous; any compositional gaps must have been no greater than about 2% SiO₂.     

Fugitive emissions from Norwegian oil and gas production

Fugitive hydrocarbon emissions from oil and gas production, always a safety concern, are currently a growing environmental and economic concern. Fugitive emissions from the offshore industry comprise mainly methane, which has an atmospheric warming contribution of approximately 14 times that of CO₂, and Volatile Organic Compounds (VOCs), which have an atmospheric warming contribution of around twice that of CO₂.

Current studies indicate that fugitive emissions are approximately equivalent to 0.02% of the total gas produced in 1992 on the Norwegian Continental Shelf. A positive downward trend in fugitive emissions from oil and gas production has been identified and attributed to advances in technology and changes in design and operating philosophy.     

‘It’s more than just what it is’: Defetishising commodities, expanding fields, mobilising change…

Commodity geographies are politically weak. Geographical pedagogy isn’t particularly engaging. Radical geography should make connections. But it rarely leaves room for interpretation. Too much seems to be too didactic. And to preach to the converted. That’s a problem that needs attention. So, is it possible to develop a radical, less didactic, geography? With research funding, publication and teaching the way they are? To engage more students, more heartily, in the issues studied? To promote social justice, critical citizenship, and participatory democracy? But not by setting out the right ways to think, be, or act. Some film-makers, artists and writers have been able to do this. It seems. Subtly and cleverly. Through projects attempting to de-fetishise commodities. But their politics have been placed largely in the background, between the lines of, or separated out from, the presentation of scenes, things, relations, bodies, lives and voices. Seen and unseen elements of their audiences’ lives. Re-connected. Perhaps. Through communication strategies giving audiences something to think about and to think with, to argue about and to argue with. Putting themselves in the picture, in the process. These less didactic materials may be difficult to master for an exam or an essay. They may not make it clear who or what’s right or wrong or what audiences are supposed to do. But they could engage them in less direct ways. When they’re shopping for petrol or fish, or when they’re doing or thinking about completely different things. Things that may not even come under the heading of ‘production’ or ‘consumption’. This approach might be labelled as ‘weak’, ‘relativist’, a bit too ‘cultural’ ‘post-modern’, or ‘defunct’. But it’s an approach that may be radical in effect because its ‘politics’ aren’t so straightforward or ‘up front’. This paper is about changing relationships between research, writing, teaching, learning and assessment; expanding fields of commodity geographies to include classrooms as sites not only of ‘instruction’, but also of learning, for researchers and their students¹; showing how such learning might usefully shape research and writing elsewhere in these fields for those engaged in this defetishising project.