Antarctic Ice‐Core Water (USGS49) – A New Isotopic Reference Material for δ2H and δ18O Measurements of Water

As a result of the scarcity of isotopic reference waters for daily use, a new secondary isotopic reference material for international distribution has been prepared from ice‐core water from the Amundsen–Scott South Pole Station. This isotopic reference material, designated as USGS49, was filtered, homogenised, loaded into glass ampoules, sealed with a torch, autoclaved to eliminate biological activity and measured by dual‐inlet isotope‐ratio mass spectrometry. The δ²H and δ¹⁸O values of USGS49 are ?394.7 ± 0.4 and ?50.55 ± 0.04 mUr (where mUr = 0.001 = ‰), respectively, relative to VSMOW, on scales normalised such that the δ²H and δ¹⁸O values of SLAP reference water are, respectively, ?428 and ?55.5 mUr. Each uncertainty is an estimated expanded uncertainty (U = 2u_c) about the reference value that provides an interval that has about a 95% probability of encompassing the true value. This isotopic reference material is intended as one of two isotopic reference waters for daily normalisation of stable hydrogen and oxygen isotopic analysis of water with an isotope‐ratio mass spectrometer or a laser absorption spectrometer. It is available by the case of 144 glass ampoules or as a set of sixteen glass ampoules containing 5 ml of water in each ampoule.     

A novel nuclear forensic tool involving deposit type normalized rare earth element signatures

Identifying the provenance of uranium‐rich materials is a critical objective of nuclear forensic analysis. Rare earth element (REE) distributions within uranium ores are well‐established forensic indicators, but quantifying and correlating trace element signatures for U ores to known deposits has thus far involved intricate statistical analyses. This study reports average chondrite normalized (CN)‐REE signatures for important U deposit types worldwide, which are then employed to evaluate U ore paragenesis using a simple linear regression analysis. This technique provides a straightforward method that can aid in determining the deposit type of U ores based on their REE abundances, and combined with other forensic indicators (e.g. radiogenic isotope signatures) can provide essential provenance information for nuclear materials.     

Thermodynamics and civilization: from ancient rivers to fossil fuel energy servants

Civilization can be at least partially determined by climatic constraints upon net primary productivity and heat dissipation from the human body (Kleidon 2009). I discuss how these “metabolic” limitations were historically overcome: first, because large rivers in dry regions provided water to ancient civilizations; second, because fossil fuel energy servants working externally to muscle-limited bodies have produced economic well-being in a number of world areas.     

Reconstruction of the hydrothermal history of the Cu–Ag vein-type mineralisation at Dikulushi, Kundelungu foreland, Katanga, D.R. Congo

The Kundelungu foreland, north of the Lufilian arc in the Democratic Republic of Congo, contains a number of various vein-type and stratiform copper mineralisations. The geodynamic context and metallogenesis of these mineral occurrences remain enigmatic. Currently, the vein-type Cu–Ag ore deposit at Dikulushi is the most significant deposit in the region. Mineralisation at Dikulushi comprises two major styles: 1) a polysulphide assemblage (Zn–Pb–Fe–Cu–As) within brecciated rocks along an anticlinal closure; and 2) a vein-hosted Cu–Ag assemblage. Petrographic and fluid inclusion studies indicate that the early Zn–Pb–Fe–Cu–As assemblage formed from a high-salinity Ca–Na–Cl fluid of modest temperature (135–172 °C). The later, economically more significant vein-related Cu–Ag mineralisation formed from intermediate salinity, lower temperature (46–82 °C) Na–Cl fluids. Weathering of the sulphide minerals resulted in a supergene enrichment with the formation of secondary Cu-minerals.     

Spatial characterization of land surface energy fluxes and uncertainty estimation at the Salar de Atacama,Northern Chile

We use Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) data to estimate spatial energy flux and evaporation distributions at the Salar de Atacama, a playa in Northern Chile. Our approach incorporates ASTER surface kinetic temperature, emissivity, and reflectance data, ground-based meteorological measurements, and empirical parameters. Energy flux distributions are estimated using either spatially constant or spatially distributed values of model parameters, with spatially distributed parameters assigned separately to each land cover category in an image classification. We test the sensitivity of energy budget calculations to state variable and parameter values by conducting Monte Carlo simulations for regions with ground energy budget measurements. Results show that assigning spatially distributed model parameters via land cover classifications yields significant improvements to ground and sensible heat flux predictions. Latent heat fluxes cannot, however, be predicted with sufficient accuracy to allow estimation of area-integrated evaporative moisture loss at this low-evaporation playa.     

Evaporation and land surface energy budget at the Salar de Atacama, Northern Chile

Playa systems are driven by evaporation processes, yet the mechanisms by which evaporation occurs through playa salt crusts are still poorly understood. In this study we examine playa evaporation as it relates to land surface energy fluxes, salt crust characteristics, groundwater and climate at the Salar de Atacama, a 3000 km² playa in northern Chile containing a uniquely broad range of salt crust types. Land surface energy budget measurements were taken at eight representative sites on this playa during winter (August 2001) and summer (January 2002) seasons. Measured values of net all-wave radiation were highest at vegetated and rough halite crust sites and lowest over smooth, highly reflective salt crusts. Over most of the Salar de Atacama, net radiation was dissipated by means of soil and sensible heat fluxes. Dry salt crusts tended to heat and cool very quickly, whereas soil heating and cooling occurred more gradually at wetter vegetated sites. Sensible heating was strongly linked to wind patterns, with highest sensible heat fluxes occurring on summer days with strong afternoon winds. Very little energy available at the land surface was used to evaporate water. Eddy covariance measurements could only constrain evaporation rates to within 0.1 mm d⁻¹, and some measured evaporation rates were less than this margin of uncertainty. Evaporation rates ranged from 0.1 to 1.1 mm d⁻¹ in smooth salt crusts around the margin of the salar and from 0.4 to 2.8 mm d⁻¹ in vegetated areas. No evaporation was detected from the rugged halite salt crust that covers the interior of the salar, though the depth to groundwater is less than 1 m in this area. These crusts therefore represent a previously unrecorded end member condition in which the salt crusts form a practically impermeable barrier to evaporation.     

The microwave opacity of Saturn's rings at wavelengths of 3.6 and 13 cm from Voyager 1 radio occultation

Radio occultation observations of Saturn's rings with Voyager 1 provided independent measurements of complex (amplitude and phase) microwave extinction and near-forward scattering cross section of the rings at wavelengths (λ) of 3.6 and 13 cm. The ring opening was 5.9°. The normal microwave opacities, τ[3.6] and τ[13], provide a measure of the total cross-sectional area of particles larger than about 1 and 4 cm radius, respectively. Ring C exhibits gently undulating (～ 1000 km) structure of normal opacity τ[3.6] ? 0.25 except for several narrow imbedded ringlets of less than about 100 km width and τ[3.6] ～ 0.5 to 1.0. The normalized differential opacity Δτ/τ[3.6], where Δτ = τ[3.6] ? τ[13], is about 0.3 over most of ring C, indicating a substantial fraction of centimeter-size particles. Some narrow imbedded ringlets show marked increases in Δτ/τ[3.6] near their edges, implying an enhancement in the relative population of centimeter-size and smaller particles at those locations. In the Cassini division, several sharply defined gaps separate regions of opacity τ ～ 0.08 and τ ～ 0.25; the opacity in the Cassini Division appears to be nearly independent of λ. The boundary features at the outer edges of ring C and the Cassini Division are remarkably similar in width and opacity profile, suggesting a similar dynamical control. Ring A appears to be nearly homogeneous over much of its width with 0.6 < τ[3.6] < 0.8 but with considerable thickening, to τ[3.6] ～ 1.0, near its inner boundary with the Cassini division. Normalized differential opacity decreases from ～0.3 at the inner and outer edges of ring A to Δτ/τ[3.6] ～ 0 at a point about one-third of the distance from the inner edge to the outer. The inner one-fourth of ring B has τ[3.6] ～ 1.0, except very near the boundary with ring C, where it is greater. The outer three-fourths of ring B has $\text{τ[3.6] ? 1.2}$. The differential opacity for the inner one-fourth of ring B is Δτ/τ[3.6] ～ 0.15. There are no gaps in ring B exceeding about 2 km in width. Ring F was observed at 3.6 cm as a single ringlet of radial width $\text{? 2}\text{km}$, but was not detected in 13 cm data.     

An Evaluation of Four Different Wavelet Decomposition Procedures for Spatial Feature Discrimination in Urban Areas

Texture or spatial arrangement of neighborhood objects and features plays an important role in the human visual system for pattern recognition and image classification. The traditional spectral–based image processing techniques have proven inadequate for urban land use and land cover mapping from images acquired by the current generation of fine–resolution satellites. This is because of the high frequency spatial arrangements or complex nature of urban features. There is a need for an effective algorithm to digitally classify urban land use and land cover categories using high–resolution image data. Recent studies using wavelet transforms for texture analysis have generally reported better accuracy. Based on a high–resolution ATLAS image, this study illustrates four different wavelet decomposition procedures – the standard, horizontal, vertical, and diagonal decompositions – for urban land use and land cover feature extraction with the use of 33×33 pixel samples. The standard decomposition approach was found to be the most efficient approach in urban texture analysis and classification. For comparison purposes and to better evaluate the accuracy of wavelet approaches in image classification, spatial autocorrelation techniques (Moran's I and Geary's C ) and the spatial co–occurrence matrix method were also examined. The results suggest that the wavelet transform approach is superior to all other approaches.     

Unsaturated zones as archives of past climates: toward a new proxy for continental regions

Natural chemical and isotopic tracers contained in unsaturated-zone moisture profiles are being developed as potential new archives for reconstructing recharge history, as well as palaeoclimatic or palaeobotanical conditions over time scales ranging from 20–120,000 years. Results worldwide to date are reviewed, and examples from northern Africa and the western USA are discussed in detail. Encouraging results are obtained from relatively homogeneous deposits such as Quaternary dune sands, where Cl profiles are compared both with the instrumental record, such as rainfall and river-gauging records, and ³H profiles. Model studies have helped to define the persistence time of unsaturated-zone signals, where evidence of a 20-year event such as the Sahel drought may persist for 1,000 years. Significant questions remain regarding the assumptions used in interpreting profiles, particularly the extent to which preferential flow may occur, transient flow phenomena, and stability of tracer-input function. Unsaturated zones that exhibit strong preferential flow are probably unsuitable as archives. Questions remain also on the assumption that flow remains downward, especially in deep unsaturated zones where non-isothermal vapour transport may occur. Estimation of depositional flux for Cl and other parameters is probably the greatest source of uncertainty, both at the spatial scale and also in the long term. Advances are being made in all areas, however, and the use of multiple tracers (chemical, especially Cl and NO₃) and isotopic signals (δ¹⁸O, δ²H, ³⁶Cl), together with soil hydraulic properties, is promising for palaeohydrological reconstruction. Electronic Publication