High-resolution observations of aggregate flux during a sub-polar North Atlantic spring bloom

An aggregate flux event was observed by ship and by four underwater gliders during the 2008 sub-polar North Atlantic spring bloom experiment (NAB08). At the height of the diatom bloom, aggregates were observed as spikes in measurements of both particulate backscattering coefficient (b_bp) and chlorophyll a fluorescence. Optical sensors on the ship and gliders were cross-calibrated through a series of simultaneous profiles, and b_bp was converted to particulate organic carbon. The aggregates sank as a discrete pulse, with an average sinking rate of ∼75 m d⁻¹; 65% of aggregate backscattering and 90% of chlorophyll fluorescence content was lost between 100 m and 900 m. Mean aggregate organic carbon flux at 100 m in mid-May was estimated at 514 mg C m⁻² d⁻¹, consistent with independent flux estimates. The use of optical spikes observed from gliders provides unprecedented coupled vertical and temporal resolution measurements of an aggregate flux event.     

The largest Au deposits in the St Ives Goldfield (Yilgarn Craton, Western Australia) may be located in a major Neoarchean volcano-sedimentary depo-centre

The largest Neoarchean gold deposits in the world-class St Ives Goldfield, Western Australia, occur in an area known as the Argo–Junction region (e.g. Junction, Argo and Athena). Why this region is so well endowed with large deposits compared with other parts of the St Ives Goldfield is currently unclear, because gold deposits at St Ives are hosted by a variety of lithologic units and were formed during at least three different deformational events. This paper presents an investigation into the stratigraphic architecture and evolution of the Argo–Junction region to assess its implications for gold metallogenesis. The results show that the region’s stratigraphy may be subdivided into five regionally correlatable packages: mafic lavas of the Paringa Basalt; contemporaneously resedimented feldspar-rich pyroclastic debris of the Early Black Flag Group; coarse polymictic volcanic debris of the Late Black Flag Group; thick piles of mafic lavas and sub-volcanic sills of the Athena Basalt and Condenser Dolerite; and the voluminous quartz-rich sedimentary successions of the Early Merougil Group. In the Argo–Junction region, these units have an interpreted maximum thickness of at least 7,130 m, and thus represent an unusually thick accumulation of the Neoarchean volcano-sedimentary successions. It is postulated that major basin-forming structures that were active during deposition and emplacement of the voluminous successions later acted as important conduits during mineralisation. Therefore, a correlation exists between the location of the largest gold deposits in the St Ives Goldfield and the thickest parts of the stratigraphy. Recognition of this association has important implications for camp-scale exploration.     

Quantitative guidance for efficient vertical flow measurements at the sediment–water interface using temperature–depth profiles

Upward discharge to surface water bodies can be quantified using analytical models based on temperature–depth (T-z) profiles. The use of sediment T-z profiles is attractive as discharge estimates can be obtained using point-in-time data that are collected inexpensively and rapidly. Previous studies have identified that T-z methods can only be applied at times of the year when there is significant difference between the streambed–water interface and deeper sediment temperatures (e.g., winter and summer). However, surface water temperatures also vary diurnally, and the influence of these variations on discharge estimates from T-z methods is poorly understood. For this study, synthetic T-z profiles were generated numerically using measured streambed interface temperature data to assess the influence of diurnal temperature variations on discharge estimation and provide insight into the suitable application of T-z methods. Results show that the time of day of data collection can have a substantial influence on vertical flux estimates using T-z methods. For low groundwater discharge fluxes (e.g., 0.1 m d⁻¹), daily transience in streambed temperatures led to relatively large errors in estimated flow magnitude and direction. For higher discharge fluxes (1.5 m d⁻¹), the influence of transient streambed temperatures on discharge estimates was strongly reduced. Discharge estimates from point-in-time T-z profiles were most accurate when the uppermost point in the T-z profile was near the bed interface daily mean (two time periods daily). Where temperature time series data are available, daily averaged T-z profiles can produce accurate discharge estimates across a wide range of discharge rates. Seasonality in shallow groundwater temperature generally had a negligible influence on vertical flow estimates. These findings can be used to plan field campaigns and provide guidance on the optimal application of T-z methods to quantify vertical groundwater discharge to surface water bodies.     

Are galactic GRB models still an option?

The traditional paradigm of a Galactic origin of gamma-ray bursts (GRBs) suffered a major reduction in popularity when BATSE revealed an isotropic but radially inhomogeneous distribution of GRBs. The lack of pronounced galactic anisotropies places severe constraints on models including significant source contributions from the usual disk, bulge, or halo components of the Milky Way. Although models can be designed to preserve the local disk origin, a perhaps more promising approach invokes a very extended Galactic halo. Populating such halos with neutron stars requires very high velocities. Injection of such neutron stars might be restricted to a phase of the early galaxy, or it may continue to the present. We discuss several observational constraints that address the question presented in the title.     

Structural adjustment and the contemporary sub-Saharan African city

Although it has been suggested that structural adjustment policies have slowed Third World urban growth and have stimulated a spatial deconcentration of economic activity, this paper argues that African cities continue to grow and mainly through peri-urban development. This investment comes mainly from domestic sources and migrants' remittances, and tends to be in consumption rather than production. Reasons include cultural factors, lack of confidence in the national economy and in the state's long-term economic objectives, an increasing demand for housing, improvements in intraurban transport, and a desire to spread investment risk among a range of alternatives including housing.     

Livestock development in Somalia

Livestock development in Somalia has mostly focused on the provision of improved veterinary services, water supplies and marketing facilities, whilst range productivity, expressed in terms of the availability of range forage and improved methods and techniques of animal raising, has largely been mismanaged or ignored. This partial development by the government has had some positive consequences. However, there have also been negative consequences, in particular increased animal pressures on the range resources, with the result that Somali rangelands have been increasingly exposed to overgrazing. (formely Research Student in Geography, University of Glasgow)