Aeromagnetic map constrains cratonization of the Arabian Shield

A new aeromagnetic map together with new geological and geochronological data has led to a reinterpretation of the geological history of the Arabian Shield.
The magnetic anomalies outline an orogenic complex containing a network of mostly left-lateral strike-slip faults, including the Nabitah Belt and several peripheral mountain ranges. Oblique accretion resulted in obliteration of early volcanic-arc magnetic fabrics, which were almost completely replaced by a NW–SE magnetic fabric in the northern Shield; the southern Shield, however, reveals extensive E–W anomalies related to post-accretion magmatic intrusions. This complex web of orogenic zones is intimately associated with synchronous molasse basins that formed 680–610 Ma.
The distribution and chronology of orogenic zones, related to the closing of East and West Gondwana, brings into question several earlier assumptions, such as high continental growth rates, palaeogeodynamic reconstructions, the definitions of the Nabitah and Najd faults, and the significance of molasse basins.     

Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: I. An introduction to the project

We investigated paleolimnological records from a series of river deltas around the northeastern rim of Lake Tanganyika, East Africa (Tanzania and Burundi) in order to understand the history of anthropogenic activity in the lakes catchment over the last several centuries, and to determine the impact of these activities on the biodiversity of littoral and sublittoral lake communities. Sediment pollution caused by increased rates of soil erosion in deforested watersheds has caused significant changes in aquatic communities along much of the lakes shoreline. We analyzed the effects of sediment discharge on biodiversity around six deltas or delta complexes on the east coast of Lake Tanganyika: the Lubulungu River delta, Kabesi River delta, Nyasanga/Kahama River deltas, and Mwamgongo River delta in Tanzania; and the Nyamuseni River delta and Karonge/Kirasa River deltas in Burundi. Collectively, these deltas and their associated rivers were chosen to represent a spectrum of drainage-basin sizes and disturbance levels. By comparing deltas that are similar in watershed attributes (other than disturbance levels), our goal was to explore a series of historical experiments at the watershed scale, with which we could more clearly evaluate hypotheses of land use or other effects on nearshore ecosystems. Here we discuss these deltas, their geologic and physiographic characteristics, and the field procedures used for coring and sampling the deltas, and various indicators of anthropogenic impact.     

Physical controls and resulting morphological forms of Quaternary ice-contact volcanoes in western Canada

Volcanism in association with large quantities of ice manifests itself in a variety of morphological forms developed under differing physical conditions. These physical conditions include the location, amount, thickness, and type of confining ice, the location and quantity of trapped water, and the surrounding topography. Ice in the form of thick continental ice sheets, thinner alpine glaciers or even perennial accumulations of snow can influence the resulting morphological form of the volcano. The chemical composition of the erupting magma, effusion rate and total erupted volume will also affect the shape of the resulting edifice. Quaternary volcanoes influenced by many of these factors are found in western Canada. The morphological forms range from tuyas to subglacial mounds to stratovolcanoes. This paper provides a review of ice-contact volcanism and volcanic products formed in these environments using Canadian examples for illustration.     

Intrinsic correlation of galaxy shapes: implications for weak lensing measurements

Weak gravitational lensing is now established as a powerful method to measure mass fluctuations in the universe. It relies on the measurement of small coherent distortions of the images of background galaxies. Even low-level correlations in the intrinsic shapes of galaxies could however produce a significant spurious lensing signal. These correlations are also interesting in their own right, since their detection would constrain models of galaxy formation. Using     haloes found in N -body simulations, we compute the correlation functions of the intrinsic ellipticity of spiral galaxies assuming that the disc is perpendicular to the angular momentum of the dark matter halo. We also consider a simple model for elliptical galaxies, in which the shape of the dark matter halo is assumed to be the same as that of the light. For deep lensing surveys with median redshifts ∼1, we find that intrinsic correlations of ∼10⁻⁴ on angular scales     are generally below the expected lensing signal, and contribute only a small fraction of the excess signals reported on these scales. On larger scales we find limits to the intrinsic correlation function at a level ∼10⁻⁵, which gives a (model-dependent) range of separations for which the intrinsic signal is about an order of magnitude below the ellipticity correlation function expected from weak lensing. Intrinsic correlations are thus negligible on these scales for dedicated weak lensing surveys. For wider but shallower surveys such as SuperCOSMOS, APM and SDSS, we cannot exclude the possibility that intrinsic correlations could dominate the lensing signal. We discuss how such surveys could be used to calibrate the importance of this effect, as well as study spin–spin correlations of spiral galaxies.     

The late-glacial and early-Holocene palaeoecology of cladoceran microfossil assemblages at Kråkenes, western Norway, with a quantitative reconstruction of temperature changes

Cladoceran microfossil remains were analysed from a sediment core taken from a lake basin at Kråkenes, western Norway. The sequence included immediate post-glacial conditions (ca. 12,300 ¹⁴C BP), the Allerod, Younger Dryas, and early Holocene to approximately 8,500 ¹⁴C BP. The interpretation of changes in the cladoceran assemblages is based on the known ecology of the taxa, the documented environmental history of the study sequence, the variations in the organic content of the sediment, the radiocarbon dates, and the results of analyses of other biotic groups, including diatoms, macrophytes, and chironomids. In addition, a quantitative reconstruction of changes in air temperature is presented for the study period. This reconstruction is based on transfer functions developed from a separate Swiss surface-sediment cladoceran data set.The cladoceran assemblages throughout the sequence are dominated by littoral chydorid taxa. Bosmina, Daphnia, and Simocephalus represent the open-water component of the zooplankton. Chydorus piger and Daphnia were the only immediate post-glacial pioneer taxa. A rapid proliferation of the open-water and littoral cladoceran taxa began with the onset of the Allerod and persisted for approximately 1,000 yrs. At the start of the Younger Dryas a local glacier formed and drained into the lake, causing a sudden decline in chydorid diversity, with only Chydorus sphaericus and Acroperus harpae persisting throughout this period. Chydorid diversity started to recover in the upper Younger Dryas and continued in the early Holocene. Progressive acidification and oligotrophication are also discernible from the cladoceran assemblages present in the Holocene.The reconstructed mean summer air temperature was from 8-21 °C, with prediction errors of 1.8-2.5 °C. The Allerod was only slightly warmer than the Younger Dryas period, but a progressive increase in temperature is apparent during the early Holocene. In conclusion, the results of this study provide a further demonstration of the value of cladocera as indicators of a variety of palaeoenvironmental parameters, including temperature.     

Hydrologic changes resulting from urban cover in seasonally snow‐covered catchments

There are few multibasin analyses of the effects of urban land cover on seasonal stream flow patterns within northern watersheds where winter snow cover is the norm. In this study, the effects of urban cover on stream flow were evaluated at nine catchments in southern Ontario, Canada, which vary greatly in urban impervious cover (1–84%) but cluster into two groups having ≥54% urban impervious area (‘urban’) and ≤11% impervious cover (‘rural’), respectively. Annual and seasonal run‐off totals (millimetres) were similar between the rural and urban groups and were relatively insensitive to urban cover. Instead, urban streams had significantly greater high flow frequency, flow variability and quickflow and lower baseflow compared with rural streams. Furthermore, differences in high flow frequency between urban and rural stream groups were largest in the summer and fall and less extreme in the winter and spring, perhaps because of the homogenizing effect of winter snow cover, frozen ground and spring melt on surface imperviousness. Although the clear clustering of streams into urban and rural groups precluded the identification of a threshold above which urban cover is the primary cause of flow differences, relatively high extreme flow frequency and flow variability in the two most urbanized of the rural streams (10–11% impervious) suggest that it may lie close to this range. Furthermore, whereas total run‐off volumes were not affected by urban cover, increases in stream flashiness and a greater frequency of high flow events particularly during the summer and fall may negatively impact stream biota and favour the transfer of surface‐deposited pollutants to urban streams. Copyright © 2014 John Wiley & Sons, Ltd.     

Incorporating landscape features to obtain an object‐oriented landscape drainage network representing the connectivity of surface flow pathways over rural catchments

A topological representation of a rural catchment is proposed here in addition to the generally used topographic drainage network. This is an object‐oriented representation based on the identification of the inlets and outlets for surface water flow on each farmer's field (or plot) and their respective contributing areas and relationships. It represents the catchment as a set of independent plot outlet trees reaching the stream, while a given plot outlet tree represents the pattern of surface flow relationships between individual plots. In the present study, we propose to implement functions related to linear and surface elements of the landscape, such as hedges or road networks, or land use, to obtain what we call a landscape drainage network which delineates the effective contributing area to the stream, thus characterizing its topological structure. Landscape elements modify flow pathways and/or favour water infiltration, thus reducing the area contributing to the surface yield and modifying the structure of the plot outlet trees. This method is applied to a 4·4‐km² catchment area comprising 43 955 pixels and 312 plots. While the full set of 164 plot outlet trees, with an average of 7 plots per tree, covers 100% of the total surface area of the catchment, the landscape drainage network comprises no more than 37 plot outlet trees with an average of 2 plots per tree, accounting for 52 and 7% of the catchment surface area, when taking account of linear elements and land use, respectively. This topological representation can be easily adapted to changes in land use and land infrastructure, and provides a simple and functional display for intercomparison of catchments and decision support regarding landscape and water management. Copyright © 2011 John Wiley & Sons, Ltd.