Petrology and petrogenesis of a tertiary bimodal dolerite-peralkaline/subalkaline trachyte/rhyolite dyke association from Lundy,Bristol Channel,UK

The island of Lundy forms the southernmost igneous complex of the British Tertiary Volcanic Province (BTVP) and consists of granite (≈ 90%) emplaced into deformed Devonian sedimentary rocks (Pilton Shale) and associated with a swarm of dykes of dolerite/basalt, minor trachyte and rhyolite composition. The dolerites are of varied olivine basalt composition and are associated with peralkaline trachyte and subalkaline/peralkaline rhyolite with alkali feldspar and quartz ± alkali amphibole ± pyroxene mineralogy. The dyke swarm is therefore an anorogenic bimodal dolerite/basalt–trachyte/rhyolite BTVP association. Although the dyke association is bimodal in major element terms between dolerite/basalt and minor trachyte/rhyolite, the mineralogy and trace element geochemistry indicate that the dykes may be regarded as a cogenetic dolerite—peralkaline trachyte/rhyolite association with minor subalkaline rhyolites. Sr and Nd isotope data indicate derivation of these magmas from a similar BTVP mantle source (with or without minor contamination by Pilton Shale, or possibly Lundy granite). The petrogenesis of the Lundy dyke association is therefore interpreted in terms of extensive fractional crystallization of basaltic magma in a magma chamber of complex geometry below the (exposed) Lundy granite. Fractional crystallization of a representative dolerite magma (olivine ± clinopyroxene ± plagioclase) yields trachyte magma from which the crystallization of alkali feldspar (anorthoclase) ± plagioclase (oligoclase) + Fe–Ti oxide + apatite results in peralkaline rhyolite. Rarer subalkaline rhyolites result from fractionation from a similar dolerite source which did not achieve a peralkaline composition so allowing the crystallization and fractionation of zircon. The basalt–(minor trachyte)/rhyolite bimodality reflects rapid crystallization of basalt magma to trachyte (and rhyolite) over a relatively small temperature interval (mass fraction of melt, F = ≈ 0.15). The rapid high level emplacement of basalt, trachyte and rhyolite dyke magmas is likely to have been associated with the development of a substantial composite bimodal basalt–(minor trachytel)/rhyolite volcano above the BTVP Lundy granite in the Bristol Channel.     

Enabling adaptation? Lessons from the new ‘Green Revolution’ in Malawi and Kenya

This article explores the extent to which efforts to improve productivity of smallholder agriculture through a new ‘Green Revolution’ in Sub Saharan Africa are likely to enhance the capacity of smallholder farmers to adapt to the impacts of climate change. Drawing on empirical material from Malawi and Kenya, the paper finds more conflicts than synergies between the pursuit of higher productivity through the promotion of hybrid maize adoption and crop diversification as a strategy for climate change adaptation. This is despite an oft-assumed causal link between escape from the ‘low maize productivity trap’ and progression towards crop diversification as an adaptive strategy. In both countries, a convergence of interests between governments, donors and seed companies, combined with a historical preference for, and dependence on maize as the primary staple, has led to a narrowing of options for smallholder farmers, undermining the development of adaptive capacities in the longer term. This dynamic is linked to the conflation of market-based variety of agricultural technologies, as viewed ‘from the top down’, with diversity-in-context, as represented by site-specific and locally derived and adapted technologies and institutions that can only be developed ‘from the bottom up’.     

Mariner 9 photometric observations of Mars from November 1971 through March 1972

The large quantity of Mariner 9 television pictures taken at phase angles ranging up to twice those accessible from Earth has been used to describe intergrated photometric properties of Mars. Although frame-to-frame variations emphasize the shortcomings of vidicon cameras when used in a photometric mode, statistical trends have yielded data comparable with Earth-based observations.Analysis of atmospheric parameters over a period of changing opacity, November 1971 through March 1972, has provided time-varying optical depths and light-scattering information. Linear function characterization of the Mars reflectance is clearly discrepant at large incidence or emission angles and at phase angles greater than 40°.     

Diatom paleoecology of Laguna Zoncho,Costa Rica

We analyzed diatoms in a sediment profile from Laguna Zoncho in southern Pacific Costa Rica (lake elevation 1190 m asl, depth 2.6 m, area 0.75 ha) spanning some 3240 cal yr. Diatoms are common in the profile, which we subdivide into three zones. Zone C (3240–1020 cal yr B.P.) is dominated by Staurosira construens var. venter and Aulacoseira spp.; during this time, the lake was dilute and circumneutral. Benthic and acidophilous taxa increase gradually in the upper section of this zone. Zone B (1020–460 cal yr B.P.) almost totally lacks Aulacoseira, and instead is dominated by combinations of Eunotia minor, Encyonema lunatum, Gomphonema gracile, and Pinnularia braunii. Previous pollen and charcoal analysis indicates that this zone falls within the peak of prehistoric agricultural activity at the lake, but diatoms may also reflect climate change. During this period, the lake was likely shallower and more acidic, but not eutrophic. Finally, Zone A (460 cal yr B.P. to AD 1997) begins near a 1.5-cm tephra layer from nearby Volcán Barú; diatom assemblages are dominated by Aulacoseira spp., and suggest deepening of the lake and return to conditions similar to Zone C. This was a time of indigenous population decline and forest recovery in the Zoncho region, probably reflecting the impact of European diseases on the native population, although climate change and impacts of the tephra deposition cannot be wholly discounted.     

Factors contributing to the removal of a marine grass invader (<Emphasis Type="Italic">Spartina anglica</Emphasis>) and subsequent potential for habitat restoration

Our goal is to understand how removal regime and habitat type interact to influence removal success of a marine plant invader and the subsequent potential for restoration. In particular, we investigate the management program designed to eradicate the English cordgrass,Spartina anglica C. E. Hubbard, in marine intertidal habitats of Puget Sound, Washington, United States. Observational and manipulative experiments were used to measure the regrowth (vegetative growth), reinvasion (seedling recruitment), and restoration potential (return to native condition) of invaded habitats. Removal regime (consistent: yearly removal; interrupted: yearly removal with the last year missed) and habitat type (low salinity marsh, mudflat, cobble beach, and high salinity marsh sites) were considered. The response to removal regime was dramatic. Under consistent removal, cordgrass slowly declined but under interrupted removal, there was substantial regrowth of the invader. This pattern results from the resiliency of belowground biomass and the subsequent high aboveground productivity and seedling growth ofS. anglica. We also found that removal success depended on differences among sites that represent different habitat types. Cordgrass regrowth and reinvasion were substantially higher in the low salinity marsh sites where soils have lower salinity. We also found that at the low salinity marsh sites, some restoration of native plants and soil conditions was evident. At mudflat, cobble beach, and high salinity marsh sites, colonization of native vascular plants and algae not normally present, in the absence of the invasion, occurred. Whether these habitats will eventually revert back to the pre-invasion conditions over a longer period of time is unknown.     

The propagation of high frequency internal waves in the Celtic Sea

The continental slope to the south of the Celtic Sea is an area of extremely rough topography and tidal currents of the order of 50cm/s (with components both along and across the slope). This is a region of intense and complicated internal wave and internal tide activity. Historical current meter data from moorings close to the shelf-break show bursts of high frequency, large amplitude internal waves occurring, on average, at either once or twice per M2 tidal cycle. Wave packets at 9 moorings along the shelf-break and further on-shelf are identified using conditional sampling. The paths travelled by these wave packets are calculated using their fluctuation orientation, linear wave theory and the low frequency current. The records are up to 60 days long, allowing the ensemble statistics of propagation direction and wave characteristics to be calculated for a large number of wave packets. This analysis shows that only a fraction of the observed wave packets have orientations consistent with generation by the across-slope barotropic tide. This mechanism accounts for 20% of the wave packets in the north-west Celtic Sea and 29% in the southeast Celtic sea. A similar fraction of the wave packets (23% in the north west and 27% in the south east) have orientations clearly consistent with generation by an along-slope flow over the rough topography on the slope. The remaining wave packets are attributed to generation by tidal flow over topography close to the moorings and possibly internal wave resonance within canyons.     

Mucky carrots and other proxies: Problematising the knowledge-fix for sustainable and ethical consumption

This paper uses evidence from focus groups in England to consider how consumers think about and, more importantly, distinguish foods by both primary and secondary qualities, using both their own judgement but also advice produced by various organisations acting as ‘knowledge intermediaries’, such as independent certification bodies. We thus consider the ‘sorting out’ that consumers do with food, particularly in developing typologies of ‘goodness’ and ‘badness’, and the cues on which they base these judgements, from the material immediacy of ‘mucky carrots’ to the abstract remoteness of organic certification. In particular, we problematise the ‘knowledge-fix’ that underlies attempts to provide knowledge to promote more sustainable and ethical consumption. This raises problems of how consumers give assurance schemes meaning, how ethical and sustainable schemes are subject to re-fetishization and how consumers tend towards increasing scepticism and distrust of such claims, thus making a ‘politics of reconnection’ far from easy.