D.R. Sherrod, W.E. Scott, P.H. Stauffer (eds): A volcano rekindled: the renewed eruption of Mount St. Helens, 2004–2006
USGS Prof. Paper 1750, 2009. 856 pp, plus DVD with appended data and figures, $50 printed, downloadable for free     

William I. Rose 《Bulletin of Volcanology》2010,72(3):373

  相似文献   

Magnetic susceptibility as a proxy for rainfall: Worldwide data from tropical and temperate climate     

William L. Balsam  Brooks B. Ellwood  Junfeng Ji  Earle R. Williams  Xiaoyong Long  Ahmed El Hassani 《Quaternary Science Reviews》2011,30(19-20):2732-2744

The magnetic susceptibility of soils has been linked with climate, mainly through rainfall, by numerous investigators. For this study we assembled a worldwide dataset of 272 samples, both published and new, to determine the nature of the relationship between MS and rainfall. On a worldwide basis there is a crude relationship (r² = 0.265) between MS and rainfall. MS increases with increasing rainfall from about 200 mm/yr to 1000–1200 mm/yr. Above 1200 mm/yr, MS decreases as rainfall increases up to about 2000 mm/yr. Under arid and semi-arid conditions, below about 200 mm/yr of rainfall, MS and rainfall exhibit no relationship, likely the result of limited pedogenic activity.When tropical and temperate localities are analyzed separately, the correlation between MS and rainfall exhibits a dramatic improvement, r² = 0.568 and 0.520, respectively. For similar amounts of rainfall tropical localities generally exhibit lower MS values which may be related to differences in the seasonal variation of rainfall. Because the soil environment is highly variable, it is unlikely that a global or even regional equation could accurately estimate rainfall from MS. Using data from Morocco and Mali we demonstrate that local equations using only MS to estimate rainfall produce reasonable results, r² = 0.700 for Morocco and 0.611 for Mali. However, a single independent variable is unlikely to capture the variability of the complex soil system. To the local equations described above we experimented with adding several independent variables in addition to MS including diffuse reflectance spectral data (DRS), x-ray diffraction (XRD), and x-ray fluorescence (XRF). For DRS data, % reflectance and red, yellow, and near-infrared wavelengths appear important; for XRD illite and kaolinite counts are important whereas for XRF Fe₂O₃ is important. The addition of these other independent variables dramatically improves prediction quality. In the case of the Mali transect, estimating rainfall from these variables produces an r² that exceeds 0.9. Based on these data we conclude that MS has the potential to be a reasonable proxy of rainfall for mean annual precipitation values from 200 to 2000 mm/yr, especially if local equations are used. Predictions can be improved by including other independent variables that show sensitivity to climate and are related to MS through the chemistry of the weathering process; we included DRS, XRD, and XRF data with good results.  相似文献   

Influence of antecedent soil moisture on hydraulic conductivity in a series of texture‐contrast soils     

Marcus A. Hardie  Richard B. Doyle  William E. Cotching  Kathrin Mattern  Shaun Lisson 《水文研究》2012,26(20):3079-3091

Antecedent soil moisture significantly influenced the hydraulic conductivity of the A1, A2e and B21 horizons in a series of strong texture‐contrast soils. Tension infiltration at six supply potentials demonstrated that in the A1 horizon, hydraulic conductivity was significantly lower in the ‘wet’ treatment than in the ‘dry’ treatment. However in the A2e horizon, micropore and mesopore hydraulic conductivity was lower in the ‘dry’ treatment than the ‘wet’ treatment, which was attributed to the precipitation of soluble amorphous silica. In the B21 horizon, desiccation of vertic clays resulted in the formation of shrinkage cracks which significantly increased near‐saturated hydraulic conductivity and prevented the development of subsurface lateral flow in the ‘dry’ treatment. In the ‘wet’ treatment, the difference between the hydraulic conductivity of the A1 and B21 horizons was reduced; however, lateral flow still occurred in the A1 horizon due to difficulty displacing existing soil water further down the soil profile. Results demonstrate the need to account for temporal variation in soil porosity and hydraulic conductivity in soil‐water model conceptualisation and parameterisation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Development and deployment of a deep-sea Raman probe for measurement of pore water geochemistry     

Xin Zhang  Peter M. Walz  William J. Kirkwood  Keith C. Hester  William Ussler  Edward T. Peltzer  Peter G. Brewer 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(2):297-306

We have developed, deployed, and tested a novel probe for study of the geochemistry of sediment pore waters based upon Raman spectroscopy. The Raman technique has already been used successfully for in situ measurements of targets of scientific interest including gas and hydrothermal vents and complex gas hydrates, but sediment geochemistry has so far been an intractable problem since the sediments themselves are strongly fluorescent and typically only very small sample volumes are obtainable. The 35 cm long probe extracts pore fluids through a 10 μm sintered metallic frit and draws the sample through a 2 mm diameter channel into a sapphire windowed optical cell within which the laser beam is focused and the spectrum recorded. The dead volume of the system is ～1 ml and the instrument is ROV deployable with activation of probe insertion and sample withdrawal under direct operator control. The unique features of this mode of detection include observation of the sulfate gradient in marine pore waters as an indicator of diagenesis, direct measurement of the dissolved sulfide species H₂S and HS^?, and measurement of dissolved methane; all of which are of primary geochemical interest. Quantitative analysis is achieved by area ratio to known water peaks and from standard calibration curves with a precision of ±5%. We find only very small fluorescence from pore waters measured in situ, but observe rapid increases in fluorescence from cores returned to the surface and exposed to oxygen.  相似文献   

DEVELOPMENT AND THE IMMINENT DEMISE OF THE AMAZON RAIN FOREST*     

William M. Denevan 《The Professional geographer》1973,25(2):130-135

  相似文献   

Deep Hubble space telescope ultraviolet imaging of the M87 jet     

Juan P. Madrid  William B. Sparks  D. E. Harris  Eric S. Perlman  Duccio Macchetto  John Biretta 《Astrophysics and Space Science》2007,311(1-3):329-333

Near-ultraviolet imaging with HST offers the best possible spatial resolution currently available for optical/UV astronomical imaging. The giant elliptical galaxy M87 hosts one of the most spectacular, best studied and nearest (d=16 Mpc) galactic-scale relativistic (synchrotron emitting plasma) jets. We have extracted from the HST archive all 220 nm images of the jet of M87, taken with the STIS MAMA camera and co-added them to provide the deepest image ever at this wavelength. The combination of highest spatial resolution and long integration time, 42500 seconds, reveals a wealth of complex structure, knots, filaments and shocks. We compare this image with deep X-ray observations obtained with the Chandra X-ray telescope.  相似文献   

Carbon dioxide and carbon monoxide photoproduction quantum yields in the Delaware Estuary     

Emily M. White  David J. Kieber  Jane Sherrard  William L. Miller  Kenneth Mopper 《Marine Chemistry》2010,118(1-2):11-21

Photochemical mineralization of dissolved organic matter (DOM) plays an important role in the cycling of carbon in estuarine systems. A key to modeling this process is knowledge of apparent quantum yields (AQYs) for the photochemical products. Here we determined spectral AQYs for carbon dioxide (CO₂) and carbon monoxide (CO), the main products of DOM photomineralization, along the main axis of the Delaware Estuary. Apparent quantum yields for CO₂ photoproduction were determined shipboard using a multi-spectral irradiation system. Carbon monoxide AQYs were determined in stored samples by employing a narrow band spectral irradiation system. A single AQY spectrum described carbon dioxide photochemical production within the estuary whereas CO AQY spectra varied with salinity, suggesting different precursors and mechanisms for the production of these two species. CO₂ AQYs were used along with shipboard measurements of DOM absorbance and solar irradiance to calculate photoproduction rates. Calculated CO₂ photoproduction rates agreed with directly measured rates (2 to 4 μM CO₂ d^? 1) within experimental error, supporting the further development and use of AQYs to calculate regional-scale photochemical fluxes.  相似文献   

Dissolution kinetics of biogenic silica collected from the water column and sediments of three Southern California borderland basins     

Tao Cheng  Douglas E. Hammond  William M. Berelson  Janet G. Hering  Suvasis Dixit 《Marine Chemistry》2009,113(1-2):41-49

Understanding biogenic silica (bSi) dissolution kinetics in margin environments is important in assessing the global silicon cycle, a cycle closely linked to the global carbon cycle. This understanding is also essential to answer the question of whether bSi content in marine sediment is a valid indicator of productivity in the overlying surface ocean. In this study, plankton tow, sediment trap, and sediment samples were collected at sites in three Southern California borderland basins. Batch dissolution experiments with plankton tow and sediment trap materials (conducted in the laboratory at 22 °C) showed linear dissolution kinetics, from which mean dissolution rate constants of 0.05 d^? 1 for plankton tow samples and 0.07 d^? 1 for sediment trap samples could be calculated. The dissolution rate constants for both types of samples showed seasonal variability but not the same seasonal patterns. Faster dissolution was observed with sediment trap samples collected at 800 m than at 550 m. With sediment multi-core samples, non-linear dissolution kinetics was observed, which complicates the direct comparison of dissolution rates. Nonetheless, dissolution appeared to be slower for the sediments samples than for samples collected from the water column and to decrease with depth in the sediments. Rate constants for surface sediment (0–0.5 cm) were at least 3–5 times less, and sediments at depths > 2 cm had rate constants at least 6–13 times less than those for material sinking to the sediment surface at these sites. Dissolution experiments conducted with Santa Barbara Basin surface sediment samples amended with dissolved aluminum (Al) and San Pedro Basin trap samples amended with enriched detrital materials (obtained by leaching bSi from sediment samples) suggested that dissolution was inhibited by Al and that the sediments from the different basins varied in the extent of Al release.  相似文献   

The case for human causes of increased atmospheric CH₄ over the last 5000 years     

William F. Ruddiman  Jonathan S. Thomson 《Quaternary Science Reviews》2001,20(18)

We propose that humans significantly altered atmospheric CH₄ levels after 5000 years BP and that anthropogenic inputs just prior to the industrial revolution accounted for up to 25% of the CH₄ level of 725 ppb (parts per billion). We base this hypothesis on three arguments: (1) the 100 ppb increase in atmospheric CH₄ that occurred after 5000 years BP follows a pattern unprecedented in any prior orbitally driven change in the ice-core record; (2) non-anthropogenic explanations for this increase (expansion of boreal peat lands or tropical wetlands) are inconsistent with existing evidence; and (3) inefficient early rice farming is a quantitatively plausible means of producing anomalously large CH₄ inputs to the atmosphere prior to the industrial revolution. If the areas flooded for farming harbored abundant CH₄-producing weeds, disproportionately large amounts of CH₄ would have been produced in feeding relatively small pre-industrial populations.  相似文献   

Proterozoic low-sulfidation epithermal Au-Ag mineralization in the Mallery Lake area, Nunavut, Canada   总被引：2，自引：0，他引：2  

William Turner  Jeremy Richards  Bruce Nesbitt  Karlis Muehlenbachs  John Biczok 《Mineralium Deposita》2001,36(5):442-457

The Mallery Lake area contains pristine examples of ancient precious metal-bearing low-sulfidation epithermal deposits. The deposits are hosted by rhyolitic flows of the Early Proterozoic Pitz Formation, but are themselves apparently of Middle Proterozoic age. Gold mineralization occurs in stockwork quartz veins that cut the rhyolites, and highest gold grades (up to 24 g/t over 30 cm) occur in the Chalcedonic Stockwork Zone. Quartz veining occurs in two main types: barren A veins, characterized by fine- to coarse-grained comb quartz, with fluorite, calcite, and/or adularia; and mineralized B veins, characterized by banded chalcedonic silica and fine-grained quartz, locally intergrown with fine-grained gold or electrum. A third type of quartz vein (C), which crosscuts B veins at one locality, is characterized by microcrystalline quartz intergrown with fine-grained hematite and rare electrum. Fluid inclusions in the veins occur in two distinct assemblages. Assemblage 1 inclusions represent a moderate temperature (Th=150 to 220 °C), low salinity (~1 eq. wt% NaCl, with trace CO₂), locally boiling fluid; this fluid type is found in both A and B veins and is thought to have been responsible for Au-Ag transport and deposition. Assemblage 2 inclusions represent a lower temperature (Th=90 to 150 °C), high salinity calcic brine (23 to 31 wt% CaCl₂-NaCl), which occurs as primary inclusions only in the barren A veins. Assemblage 1 and 2 inclusions occur in alternating quartz growth bands in the A-type veins, where they appear to represent alternating fluxes of dilute fluid and local saline groundwater. No workable primary fluid inclusions were observed in the C veins. The A-vein quartz yields '¹⁸O values from 8.3 to 14.5‰ (average=10.9ǃ.7‰ [1C], n=30), whereas '¹⁸O values for B-vein quartz range from 11.2 to 14.0‰ (average=13.0ǂ.9‰, n=12). Calculated '¹⁸O_H2O values for the dilute mineralizing fluid from B veins range from -2.6 to 0.2‰ (average=-0.8ǂ.9‰, n=12) and are consistent with a dominantly meteoric origin. No values could be calculated for the brine, however, because all A-vein quartz samples contain mixed fluid inclusion populations. However, the fact that A-vein quartz samples extend to lower '¹⁸O values than the B veins suggests that the brine had a lighter isotopic signature relative to the dilute fluid. Hydrogen isotopic ratios of fluid inclusion waters extracted from eleven quartz samples of both vein types range from 'D_FI=-56 to -134‰, but show no particular correlation with vein type. In most respects, the mineralogical and fluid characteristics of the Mallery Lake system are comparable to those of Phanerozoic low-sulfidation deposits, and although the presence of high salinity brines is unusual in such deposits, it is not unknown (e.g., Creede, Colorado). In addition, one of the few other examples of well-preserved, Precambrian, low-sulfidation epithermal deposits, from the Central Pilbara tectonic zone, Australia, contains a similarly bimodal fluid assemblage. The significance of these saline brines is not clear, but from this study we infer that they were not directly involved with Au-Ag transport or deposition.  相似文献