Late Pleistocene and Early Holocene lake‐level fluctuations in the Lahontan Basin,Nevada: Implications for the distribution of archaeological sites

The Great Basin of the western U.S. contains a rich record of Late Pleistocene and Holocene lake‐level fluctuations as well as an extensive record of human occupation during the same time frame. We compare spatial‐temporal relationships between these records in the Lahontan basin to consider whether lake‐level fluctuations across the Pleistocene‐Holocene transition controlled distribution of archaeological sites. We use the reasonably well‐dated archaeological record from caves and rockshelters as well as results from new pedestrian surveys to investigate this problem. Although lake levels probably reached maximum elevations of about 1230–1235 m in the different subbasins of Lahontan during the Younger Dryas (YD) period, the duration that the lakes occupied the highest levels was brief. Paleoindian and Early Archaic archaeological sites are concentrated on somewhat lower and slightly younger shorelines (_1220–1225 m) that also date from the Younger Dryas period. This study suggests that Paleoindians often concentrated their activities adjacent to large lakes and wetland resources soon after they first entered the Great Basin. © 2008 Wiley Periodicals, Inc.     

Wind erosion of the wind-deposited Navajo Sandstone, USA

Outcrops of the Early Jurassic Navajo Sandstone in southern Utah and northern Arizona, south-western USA are being actively eroded by sand-laden, south-westerly winds. Small-scale stepped topography with risers facing into the wind develops even on steep canyon walls when wind-swept grains strike the rock at a low angle. Photosynthetic, endolithic microbes directly underlie most outcrop surfaces; the crusts formed by these organisms are essential to formation of the small-scale steps. Wind erosion of highlands also forms troughs and pits that are tens of metres across. The pits have deeply scalloped, overhanging walls, and contain central domes surrounded by 'moats' filled with dune sand. Wind erosion of aeolian sandstone is favoured by a positive feedback mechanism in which grains that are liberated from outcrops by impacting particles become a fresh supply of pre-sorted abrasive particles for further attack.     

Comparative Analysis of a Transition Region Bright Point with a Blinker and Coronal Bright Point Using Multiple EIS Emission Lines

Since their discovery 20 year ago, transition region bright points have never been observed spectroscopically. Bright point properties have not been compared with similar transition region and coronal structures. In this work we have investigated three transient quiet Sun brightenings including a transition region bright point (TR BP), a coronal bright point (CBP) and a blinker. We use time-series observations of the extreme-ultraviolet emission lines of a wide range of temperature T (logT=5.3?–?6.4) from the EUV Imaging Spectrometer (EIS) onboard the Hinode satellite. We present the EIS temperature maps and Doppler maps, which are compared with magnetograms from the Michelson Doppler Imager (MDI) onboard the SOHO satellite. Doppler velocities of the TR BP and blinker are ≤?25 km?s^?1, which is typical of transient TR phenomena. The Doppler velocities of the CBP were found to be ≤?20 km?s^?1 with exception of those measured at logT=6.2 where a distinct bi-directional jet is observed. From an EM loci analysis we find evidence of single and double isothermal components in the TR BP and CBP, respectively. TR BP and CBP loci curves are characterized by broad distributions suggesting the existence of unresolved structure. By comparing and contrasting the physical characteristics of the events we find that the BP phenomena are an indication of multi-scaled self-similarity, given the similarities in both their underlying magnetic field configuration and evolution in relation to EUV flux changes. In contrast, the blinker phenomena and the TR BP are sufficiently dissimilar in their observed properties as to constitute different event classes. Our work is an indication that the measurement of similar characteristics across multiple event types holds class-predictive power, and is a significant step towards automated solar atmospheric multi-class classification of unresolved transient EUV sources. Finally, the analysis performed here establishes a connection between solar quiet region CBPs and jets.     

Using Strong Solar Coronal Emission Lines as Coronal Flux Proxies

We investigate the possibility that strong EUV lines observed with the Goddard Solar EUV Rocket Telescope and Spectrograph (SERTS) provide good proxies for estimating the total coronal flux over shorter wavelength ranges. We use coordinated SERTS and Yohkoh observations to obtain both polynomial and power-law fits relating the broad-band soft X-ray fluxes to the intensities of Fexvi 335 Ú and 361 Ú, Fexv 284 Ú and 417 Ú, and Mgix 368 Ú measured with SERTS. We found that the power-law fits best cover the full range of solar conditions from quiet Sun through active region, though not surprisingly the cooler Mgix 368 Ú line proves to be a poor proxy. The quadratic polynomial fits yield fair agreement over a large range for all but the Mgix line. However, the linear fits fail conspicuously when extrapolated into the quiet-Sun regime. The implications of this work for the Heii 304 Ú line formation problem are also briefly considered.     

Seasonal change in the deep atmosphere of Uranus

We present high-resolution radio maps of Uranus, made from data collected in 1994 at wavelengths of 2 and 6 cm, which show large-scale changes occurring deep and rapidly in the troposphere. Brightness features in these maps are significantly different from those observed throughout the 1980's. These differences are not due to the changing viewing geometry, but result from atmospheric changes in the 5 to 50 bar region. All the observations show strong latitudinal variations in absorber abundance and/or temperature, causing the South Pole to appear brighter than lower latitudes. The transition between bright pole and darker latitudes is always near −45°, but between 1989 and 1994 the contrast between the regions increased significantly. This suggests that the large-scale circulation in the upper 50 bars of the uranian Southern Hemisphere changed. Older, disk-averaged microwave observations have suggested that seasonal variability occurs, but these new maps are the first to provide detailed timing and location information which can be used to test dynamical models.     

Superoxide-mediated reduction of organically complexed iron(III): Impact of pH and competing cations (Ca)

The mechanism and kinetics of superoxide-mediated reduction of a variety of organic iron(III) complexes has been investigated over the pH range 7-9. Our experimental results show that the rate of iron(II) formation is a function of pH, ligand type and ligand concentration with the measured rate varying between 0.44 ± 0.07 and 39.25 ± 1.77 pM s⁻¹ in the systems investigated. Additionally, our results show that the presence of competing cations such as Ca²⁺ have a significant impact on iron(II) formation if the organic ligand is strongly complexed by Ca²⁺. Formation of iron(II) occurs by either (or, in some instances, both) reaction of superoxide with inorganic iron(III) after its dissociation from the complex (dissociative reduction) or by direct reaction of superoxide with the complex (non-dissociative reduction). In the presence of weak ligands, dissociative reduction (DR) dominates; however non-dissociative reduction (NDR) becomes important in the presence of either strongly binding ligands or high concentrations of weakly binding ligands. The major factors contributing to the pH dependence of the iron(II) formation rate are the complexation kinetics of inorganic iron(III) (which controls the DR contribution) and the reduction kinetics of the iron(III) complex (which controls the NDR contribution). The relative NDR contribution increases with increasing superoxide and ligand concentration and decreasing pH for all ligands examined. Since iron(II) formation occurring via NDR results in a significantly larger increase in the proportion of iron in free aquated form than does DR, this non-dissociative pathway of superoxide-mediated iron(III) reduction is particularly effective in increasing the lability of iron in aquatic systems.     

Subsurface electric fields of a grounded cable of finite length for both frequency and time domain

Summary The subsurface electric fields of a current-carrying cable are examined for both steady-state and transient situations. Closed form expressions are obtained for two of the electric field components, and a numerical integration is used to obtain the third component. Waveforms for a stepfunction current excitation are displayed. The results have possible application to pulsed downlink communication in mine rescue operations.     

Data reporting norms for 40Ar/39Ar geochronology

Data reported in ⁴⁰Ar/³⁹Ar geochronology studies are commonly insufficient to allow computation of ages. This deficiency renders it difficult to compare ages based on different standards or constants, and often hinders critical evaluation of the results. Herein are presented an enumeration of the data that should be reported in all ⁴⁰Ar/³⁹Ar studies, including a discussion in support of these requirements. The minimum required data are identified and distinguished from parameters that are useful but may be derived from them by calculation. Finally, recommendations are made for metadata needed to document age calculations (e.g., from age spectrum or isochron analyses).