Biochemical processes in sagebrush ecosystems: Interactions with terrain

The objectives of a biogeochemical study of sagebrush ecosystems in Wyoming and their interactions with terrain are as follows: to describe the vegetational pattern on the landscape and elucidate controlling variables, to measure the soil properties and chemical cycling properties associated with the vegetation units, to associate soil properties with vegetation properties as measured on the ground, to develop remote sensing capabilities for vegetation and surface characteristics of the sagebrush landscape, to develop a system of sensing snow cover and indexing seasonal soil to moisture; and to develop relationships between temporal Thematic Mapper (TM) data and vegetation phenological state

Extremely low long‐term erosion rates around the Gamburtsev Mountains in interior East Antarctica

The high elevation and rugged relief (>3 km) of the Gamburtsev Subglacial Mountains (GSM) have long been considered enigmatic. Orogenesis normally occurs near plate boundaries, not cratonic interiors, and large‐scale tectonic activity last occurred in East Antarctica during the Pan‐African (480–600 Ma). We sampled detrital apatite from Eocene sands in Prydz Bay at the terminus of the Lambert Graben, which drained a large pre‐glacial basin including the northern Gamburtsev Mountains. Apatite fission‐track and (U‐Th)/He cooling ages constrain bedrock erosion rates throughout the catchment. We double‐dated apatites to resolve individual cooling histories. Erosion was very slow, averaging 0.01–0.02 km/Myr for >250 Myr, supporting the preservation of high elevation in interior East Antarctica since at least the cessation of Permian rifting. Long‐term topographic preservation lends credence to postulated high‐elevation mountain ice caps in East Antarctica since at least the Cretaceous and to the idea that cold‐based glaciation can preserve tectonically inactive topography

Coupled spatial variations in precipitation and long-term erosion rates across the Washington Cascades

Past studies of tectonically active mountain ranges have suggested strong coupling and feedbacks between climate, tectonics and topography(1 - 5). For example, rock uplift generates topographic relief, thereby enhancing precipitation, which focuses erosion and in turn influences rates and spatial patterns of further rock uplift. Although theoretical links between climate, erosion and uplift have received much attention(2,6 - 10), few studies have shown convincing correlations between observable indices of these processes on mountain- range scales(11,12). Here we show that strongly varying long- term(> 10(6) - 10(7) yr) erosion rates inferred from apatite ( U - Th)/ He cooling ages across the Cascades mountains of Washington state closely track modern mean annual precipitation rates. Erosion and precipitation rates vary over an order of magnitude across the range with maxima of 0.33 mm yr(-1) and 3.5 m yr(-1), respectively, with both maxima located 50 km west ( windward) of the topographic crest of the range. These data demonstrate a strong coupling between precipitation and long- term erosion rates on the mountain- range scale. If the range is currently in topographic steady state, rock uplift on the west flank is three to ten times faster than elsewhere in the range, possibly in response to climatically focused erosion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62817/1/nature02111.pd

Nonradiative Electronic Deexcitation Time Scales in Metal Clusters

The life-times due to Auger-electron emission for a hole on a deep electronic shell of neutral and charged sodium clusters are studied for different sizes. We consider spherical clusters and calculate the Auger-transition probabilities using the energy levels and wave functions calculated in the Local-Density-Approximation (LDA). We obtain that Auger emission processes are energetically not allowed for neutral and positively charged sodium clusters. In general, the Auger probabilities in small Na$_N^-$ clusters are remarkably different from the atomic ones and exhibit a rich size dependence. The Auger decay times of most of the cluster sizes studied are orders of magnitude larger than in atoms and might be comparable with typical fragmentation times.Comment: 11 pages, 4 figures. Accepted for publication in Phys. Rev.

The CARMENES search for exoplanets around M dwarfs - Photospheric parameters of target stars from high-resolution spectroscopy

The new CARMENES instrument comprises two high-resolution and high-stability spectrographs that are used to search for habitable planets around M dwarfs in the visible and near-infrared regime via the Doppler technique. Characterising our target sample is important for constraining the physical properties of any planetary systems that are detected. The aim of this paper is to determine the fundamental stellar parameters of the CARMENES M-dwarf target sample from high-resolution spectra observed with CARMENES. We also include several M-dwarf spectra observed with other high-resolution spectrographs, that is CAFE, FEROS, and HRS, for completeness. We used a {chi}^2 method to derive the stellar parameters effective temperature T_eff, surface gravity log g, and metallicity [Fe/H] of the target stars by fitting the most recent version of the PHOENIX-ACES models to high-resolution spectroscopic data. These stellar atmosphere models incorporate a new equation of state to describe spectral features of low-temperature stellar atmospheres. Since T_eff, log g, and [Fe/H] show degeneracies, the surface gravity is determined independently using stellar evolutionary models. We derive the stellar parameters for a total of 300 stars. The fits achieve very good agreement between the PHOENIX models and observed spectra. We estimate that our method provides parameters with uncertainties of {sigma} T_eff = 51 K, {sigma} log g = 0.07, and {sigma} [Fe/H] = 0.16, and show that atmosphere models for low-mass stars have significantly improved in the last years. Our work also provides an independent test of the new PHOENIX-ACES models, and a comparison for other methods using low-resolution spectra. In particular, our effective temperatures agree well with literature values, while metallicities determined with our method exhibit a larger spread when compared to literature results

Major Miocene exhumation by fault-propagation folding within a metamorphosed, early Paleozoic thrust belt: Northwestern Argentina

The central Andean retroarc thrust belt is characterized by a southward transition at ∼22°S in structural style (thin-skinned in Bolivia, thick-skinned in Argentina) and apparent magnitude of Cenozoic shortening (>100 km more in the north). With the aim of evaluating the abruptness and cause of this transition, we conducted a geological and geo-thermochronological study of the Cachi Range (∼24–25°S), which is a prominent topographic feature at this latitude. Our U-Pb detrital zircon results from the oldest exposed rocks (Puncoviscana Formation) constrain deposition to mainly Cambrian time, followed by major, Cambro-Ordovician shortening and ∼484 Ma magmatism. Later, Cretaceous rift faults were locally inverted during Cenozoic shortening. Coupled with previous work, our new (U-Th)/He zircon results require 8–10 km of Miocene exhumation that was likely associated with fault-propagation folding within the Cachi Range. After Miocene shortening, displacement on sinistral strike-slip faults demonstrates a change in stress state to a non-vertically orientedσ3. This change in stress state may result from an increase in gravitational potential energy in response to significant crustal thickening and/or lithospheric root removal. Our finding of localized Cenozoic shortening in the Cachi Range increases the estimate of the local magnitude of shortening, but still suggests that significantly less shortening was accommodated south of the thin-skinned Bolivian fold-thrust belt. Our results also underscore the importance of the pre-existing stratigraphic and structural architecture in orogens in influencing the style of subsequent deformation.Fil: Pearson, D. M.. University Of Arizona; Estados Unidos. University Of Idaho; Estados UnidosFil: Kapp, P.. University Of Arizona; Estados UnidosFil: Reiners, P. W.. University Of Arizona; Estados UnidosFil: Gehrels, G. E.. University Of Arizona; Estados UnidosFil: Ducea, M. N.. University Of Arizona; Estados Unidos. University of Bucharest; RumaniaFil: Pullen, A.. University Of Arizona; Estados Unidos. University of Rochester; Estados UnidosFil: Otamendi, Juan Enrique. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Departamento de Geologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Alonso, Ricardo Narciso. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

The Rigidly Rotating Magnetosphere of Sigma Ori E

We attempt to characterize the observed variability of the magnetic helium-strong star sigma Ori E in terms of a recently developed rigidly rotating magnetosphere model. This model predicts the accumulation of circumstellar plasma in two co-rotating clouds, situated in magnetohydrostatic equilibrium at the intersection between magnetic and rotational equators. We find that the model can reproduce well the periodic modulations observed in the star's light curve, H alpha emission-line profile, and longitudinal field strength, confirming that it furnishes an essentially correct, quantitative description of the star's magnetically controlled circumstellar environment.Comment: 4 pages, 3 figures, accepted by Ap