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.     

DFTopoSim: Modeling Topographically-Controlled Deposition of Subseismic Scale Sandstone Packages Within a Mass Transport Dominated Deep-Water Channel Belt

Facies bodies in geostatistical models of deep-water depositional environments generally represent channel-levee-overbank-lobe morphologies. Such models adequately capture one set of the erosional and depositional processes resulting from turbidity currents traveling downslope to the ocean basin floor. However, depositional morphologies diverge from the straight forward channel-levee-overbank-lobe paradigm when the topography of the slope or the shape of the basin impacts the timing and magnitude of turbidity current deposition. Subaqueous mass-transport-deposits (MTDs) present the need for an exception to the channel-levee-overbank-lobe archetype. Irregular surface topography of subaqueous MTDs can play a primary role in controlling sand deposition from turbidity currents. MTD topography creates mini-basins in which sand accumulates in irregularly-shaped deposits. These accumulations are difficult to laterally correlate using well-log data due to their variable and unpredictable shape and size. Prediction is further complicated because sandstone bodies typical of this setting are difficult to resolve in seismic-reflection data. An event-based model is presented, called DFTopoSim, which simulates debris flows and turbidity currents. The accommodation space on top of and between debris flow lobes is filled in by sand from turbidity currents. When applied to a subsurface case in the Molasse Basin of Upper Austria, DFTopoSim predicts sand packages consistent with observations from core, well, and seismic data and the interpretation of the sedimentologic processes. DFTopoSim expands the set of available geostatistical deep-water depositional models beyond the standard channel-levee-overbank-lobe model.     

Sediment density flow distribution on wave-influenced deltas

Deltas are at the transition between fluvial and marine sedimentary environments where sediment density flows are often triggered during high river discharge events, forming submarine channels and sediment waves. On wave-influenced deltas, longshore currents are particularly efficient at transporting sediment alongshore, reducing the likelihood of sediment density flows from occurring at river mouths. This study describes four deltaic sedimentary systems at different stages of their evolution on a formerly glaciated continental inner shelf of eastern Canada in order to better understand the distribution of sediment density flows on wave-influenced deltas. Three types of settings are recognized as being prone to sediment density flows: (i) in the early stages of wave-influence and on large deltas, converging longshore currents can lead to offshelf sediment transport; (ii) on wave-influenced to wave-dominated deltas, a sandy spit can re-route the river mouth and sediment density flows form where the spit intersects the delta lip; (iii) in advanced stages of wave-dominated deltas and during their demise, rocky headlands are exposed and can intersect the slope, where off-shelf sediment transport occurs. These types of sediment density flows were all characterized by debris flows or surge-type turbidity currents which have limited offshore run-out. More rarely, hyperpycnal flows form at the river mouths, especially where the river incises glaciomarine clays prone to landsliding in the river, which increases fine-grained fluvial suspended sediment concentration. Overall, these results highlight the predominance of fluvial-dominated deltas during a phase of relative sea-level fall combined with high sediment supply. However, as soon as sediment supply diminishes, wave action remobilizes sediment alongshore modifying the distribution and types of sediment density flows occurring on wave-influenced deltas.     

The impact of exceptional events on erosion,bedload transport and channel stability in a step‐pool channel

Sediment transport in the Erlenbach, a small stream with step‐pool morphology in the canton of Schwyz, Switzerland, has been monitored for more than 20 years. During this time three exceptional events (events with high sediment yield and long return times that have a large effect on channel morphology) have impacted the stream and partly or completely rearranged the existing step‐pool morphology. In the aftermath of the events, sediment transport rates at a given discharge and total sediment yield remained elevated for about a year or longer. For the last event, dated on the 20 June 2007, observations of boulder mobility and step destruction were used to interpret channel stability. Boulders with median diameters of up to 135 cm and estimated weights of more than 2·5 tons have moved during the 2007 event. Using hydraulic observations and shear stress calculations boulders up to 65 cm in diameter were predicted to have been fully mobile in peak conditions, even if form resistance and increased critical stresses needed for the initiation of motion in steep streams were taken into account. For two of the events, estimated peak shear stresses at the bed exceeded 1000 Pa, calculated both from observations of the flow hydraulics and from boulder mobility. This suggests that highly energetic flows occur relatively frequently in small, steep streams and that large boulders can be transported by fluvial processes in such streams. The observations have potential significance for hazard risk mitigation, stream engineering and restoration. Copyright © 2009 John Wiley & Sons, Ltd.     

Environmental flows in hydro-economic models

The protection of environmental flows, as a management objective for a regulating agency, needs to be consistent with the aquifer water balance and the degree of resource renewability. A stylized hydro-economic model is used where natural recharge, which sustains environmental flows, is considered both in the aquifer water budget and in the welfare function as ecosystem damage. Groundwater recharge and the associated natural drainage may be neglected for aquifers containing fossil water, where the groundwater is mined. However, when dealing with an aquifer that constitutes a renewable resource, for which recharge is not negligible, natural drainage should explicitly appear in the water budget. In doing so, the optimum path of net extraction rate does not necessarily converge to the recharge rate, but depends on the costs associated with ecosystem damages. The optimal paths and equilibrium values for the water volume and water extraction are analytically derived, and numerical simulations based on the Western La Mancha aquifer (southwest Spain) illustrate the theoretical results of the study.     

Geochemistry of Some Marine Fe–Mn Nodules and Crusts with Respect to Pt Contents

Bulk chemical analyses for Pt and Pd in marine Fe–Mn nodules and crusts from different provenances are presented, together with a wide range of elements. Platinum contents vary from 70–328 ppb, whereas Pd contents extend from 0.6–4.7 ppb only. Bromine and Pb show strong positive correlations with Pt. Lead is remarkably enriched in Fe–Mn precipitates over seawater, but Br is a conservative‐type element in seawater and shows no enrichment in Fe–Mn precipitates. Hence, the Pt–Br–Pb element association combines two elements, Br and Pb, of extremely contrasting enrichment factors in Fe–Mn precipitates.     

Systematics of metal-silicate partitioning for many siderophile elements applied to Earth’s core formation

Superliquidus metal-silicate partitioning was investigated for a number of moderately siderophile (Mo, As, Ge, W, P, Ni, Co), slightly siderophile (Zn, Ga, Mn, V, Cr) and refractory lithophile (Nb, Ta) elements. To provide independent constrains on the effects of temperature, oxygen fugacity and silicate melt composition, isobaric (3 GPa) experiments were conducted in piston cylinder apparatus at temperature between 1600 and 2600 °C, relative oxygen fugacities of IW−1.5 to IW−3.5, and for silicate melt compositions ranging from basalt to peridotite. The effect of pressure was investigated through a combination of piston cylinder and multi-anvil isothermal experiments between 0.5 and 18 GPa at 1900 °C. Oxidation states of siderophile elements in the silicate melt as well as effect of carbon saturation on partitioning are also derived from these results. For some elements (e.g. Ga, Ge, W, V, Zn) the observed temperature dependence does not define trends parallel to those modeled using metal-metal oxide free energy data. We correct partitioning data for solute interactions in the metallic liquid and provide a parameterization utilized in extrapolating these results to the P-T-X conditions proposed by various core formation models. A single-stage core formation model reproduces the mantle abundances of several siderophile elements (Ni, Co, Cr, Mn, Mo, W, Zn) for core-mantle equilibration at pressures from 32 to 42 GPa along the solidus of a deep peridotitic magma ocean (∼3000 K for this pressure range) and oxygen fugacities relevant to the FeO content of the present-day mantle. However, these P-T-fO₂ conditions cannot produce the observed concentrations of Ga, Ge, V, Nb, As and P. For more reducing conditions, the P-T solution domain for single stage core formation occurs at subsolidus conditions and still cannot account for the abundances of Ge, Nb and P. Continuous core formation at the base of a magma ocean at P-T conditions constrained by the peridotite liquidus and fixed fO₂ yields concentrations matching observed values for Ni, Co, Cr, Zn, Mn and W but underestimates the core/mantle partitioning observed for other elements, notably V, which can be reconciled if accretion began under reducing conditions with progressive oxidation to fO₂ conditions consistent with the current concentration of FeO in the mantle as proposed by Wade and Wood (2005). However, neither oxygen fugacity path is capable of accounting for the depletions of Ga and Ge in the Earth’s mantle. To better understand core formation, we need further tests integrating the currently poorly-known effects of light elements and more complex conditions of accretion and differentiation such as giant impacts and incomplete equilibration.     

Shear Wave Anisotropy of the Upper Mantle Beneath the Region from Tingri of Tibet to Golmud of Qinghai

Measurements of shear wave splitting at 43 three-component seismic stationsshow very big difference in anisotropy on both sides of the Indus-Yarlung Zangbo suture(ITS), but little difference on both sides of the older Bangong-Nujiang suture (BNS) and theJinsha River suture (JS) to its north. Obvious discrepancy exists between the anisotropy direc-tion and the superficial tectonic trends, which is not explicable directly by the coherent uppermantle deformation usually supposed to occur in consistency with the trend of a collisional belt.On the other hand, strong spatial relationships are observed from the anisotropy results, such asthe orthogonal directions of anisotropy on both sides of ITS and the good correlation betweenthe region of larger magnitude of anisotropy and the zone of inefficient Sn propagation ofQiangtang as well as the systematic rotation of the directions of anisotropy, which should testifysome much more complicated aspects of the continental convergence mechanism. To the best ofour data, we tend to suppose that the Qinghai-Tibet plateau might result from a mechanismcomplicated by the coexistence of Argand's underthrusting and Dewey's diffuse deformation.     

Inorganic nitrogen acquisition by the tropical seagrass Halophila stipulacea

The tropical seagrass Halophila stipulacea is dominant in most regions of the Indo‐Pacific and the Red Sea and was introduced into the Mediterranean Sea after the opening of the Suez canal. The species is considered invasive in the Mediterranean Sea and has been progressively colonizing new areas westward. Growth and photosynthetic responses of H. stipulacea have been described but no information is yet available on the nitrogen nutrition of the species. Here we simultaneously investigated the uptake kinetics of ammonium and nitrate and the internal translocation of incorporated nitrogen in H. stipulacea using ¹⁵N‐labelled substrates across a range of N_i levels (5, 25, 50 and 100 μm ). The ammonium uptake rates exceeded the nitrate uptake rates 100‐fold, revealing a limited capacity of H. stipulacea to use nitrate as an alternative nitrogen source. The uptake rates of ammonium by leaves and roots were comparable up to 100 μm ¹⁵NH₄Cl. At this concentration, the leaf uptake rate was 1.4‐fold higher (6.22 ± 0.70 μmol·g^?1 DW h^?1) than the root uptake rate (4.54 ± 0.28 μmol·g^?1 DW h^?1). The uptake of ammonium followed Michaelis–Menten kinetics, whereas nitrate uptake rates were relatively constant at all nutrient concentrations. The maximum ammonium uptake rate (V_max) and the half‐saturation constant (K_m) of leaves (9.79 μmol·g^?1 DW h^?1 and 57.95 μm , respectively) were slightly higher than that of roots (6.09 μmol·g^?1DW h^?1 and 30.85 μm , respectively), whereas the affinity coefficients (α = V_max/K_m) for ammonium of leaves (0.17) and roots (0.20) were comparable, a characteristic that is unique among seagrass species. No substantial translocation (<2.5%) of ¹⁵N incorporated as ammonium was detected between plant parts, whereas the translocation of ¹⁵N incorporated as nitrate was higher (40–100%). We conclude that the N_i acquisition strategy of H. stipulacea, characterized by a similar uptake capacity and efficiency of leaves and roots, favors the geographical expansion potential of the species into areas with variable water‐sediment N levels throughout the Mediterranean.