Processing and analysis of commercial satellite image data of the nuclear accident near Chernobyl U.S.S.R. (U.S. geological survey bulletin 1785)     

Frank G. Sadowski  Steven J. Covington 《国际地球制图》2013,28(3)

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Hydromagnetic waves in a thin rotating spherical shell     

Steven D. London 《地球物理与天体物理流体动力学》2013,107(6):616-628

We consider an electrically conducting fluid confined to a thin rotating spherical shell in which the Elsasser and magnetic Reynolds numbers are assumed to be large while the Rossby number is assumed to vanish in an appropriate limit. This may be taken as a simple model for a possible stable layer at the top of the Earth's outer core. It may also be a model for the thin shells which are thought to be a source of the magnetic fields of some planets such as Mercury or Uranus. Linear hydromagnetic waves are studied using a multiple scale asymptotic scheme in which boundary layers and the associated boundary conditions determine the structure of the waves. These waves are assumed to be of the form of an asymptotic series expanded about an ambient magnetic field which vanishes on the equatorial plane and velocity and pressure fields which do not. They take the form of short wave, slowly varying wave trains. The results are compared to the author's previous work on such waves in cylindrical geometry in which the boundary conditions play no role. The approximation obtained is significantly different from that obtained in the previous work in that an essential singularity appears at the equator and nonequatorial wave regions appear.  相似文献   

Using DNA‐Stable Isotope Probing to Identify MTBE‐ and TBA‐Degrading Microorganisms in Contaminated Groundwater     

Katherine C. Key  Kerry L. Sublette  Kathleen Duncan  Douglas M. Mackay  Kate M. Scow  Dora Ogles 《Ground Water Monitoring & Remediation》2013,33(4):57-68

Although the anaerobic biodegradation of methyl tert‐butyl ether (MTBE) and tert‐butyl alcohol (TBA) has been documented in the laboratory and the field, knowledge of the microorganisms and mechanisms involved is still lacking. In this study, DNA‐stable isotope probing (SIP) was used to identify microorganisms involved in anaerobic fuel oxygenate biodegradation in a sulfate‐reducing MTBE and TBA plume. Microorganisms were collected in the field using Bio‐Sep® beads amended with ¹³C₅‐MTBE, ¹³C₁‐MTBE (only methoxy carbon labeled), or ¹³C₄‐TBA. ¹³C‐DNA and ¹²C‐DNA extracted from the Bio‐Sep beads were cloned and 16S rRNA gene sequences were used to identify the indigenous microorganisms involved in degrading the methoxy group of MTBE and the tert‐butyl group of MTBE and TBA. Results indicated that microorganisms were actively degrading ¹³C‐labeled MTBE and TBA in situ and the ¹³C was incorporated into their DNA. Several sequences related to known MTBE‐ and TBA‐degraders in the Burkholderiales and the Sphingomonadales orders were detected in all three ¹³C clone libraries and were likely to be primary degraders at the site. Sequences related to sulfate‐reducing bacteria and iron‐reducers, such as Geobacter and Geothrix, were only detected in the clone libraries where MTBE and TBA were fully labeled with ¹³C, suggesting that they were involved in processing carbon from the tert‐butyl group. Sequences similar to the Pseudomonas genus predominated in the clone library where only the methoxy carbon of MTBE was labeled with ¹³C. It is likely that members of this genus were secondary degraders cross‐feeding on ¹³C‐labeled metabolites such as acetate.  相似文献   

EFFECT OF VIEWING GEOMETRY ON REMOTELY SENSED NET RADIATION MEASUREMENTS FOR VEGETATED AND NON-VEGETATED SURFACES     

Douglas G. Goodin 《自然地理学》2013,34(6):557-572

Increased use of remotely sensed data for estimation of land-surface climatological variables such as the radiation and energy balance has underscored the need to understand errors inherent in remote sensing systems. The effects of viewing geometry on the signal received at the sensor have been examined for a variety of surface types, but systematic study of how sensor viewing geometry may introduce error into remote measurements of surface climate parameters is lacking. In this paper, close-range remote sensing is used to assess error caused by viewing geometry in remote measurements of net radiation, an important surface climate variable. Estimates of net radiation were made by inserting remotely sensed values of albedo and surface temperature into the surface radiation budget equation. Two contrasting surfaces, one vegetated and one bare, were evaluated at seven view angles and five azimuth angles. The remote net radiation measurements for each combination of view and azimuth angle then were compared to reference measurements to assess error. Results indicate that, under cloud-free conditions, view angle can affect measurement accuracy substantially, and that off-nadir view angles ranging from 15° to 30° in the forward-scatter direction are optimal. The potential impact of these findings on studies of the spatial variation of the surface radiation budget from spaceborne remote sensing platforms is discussed. [Key words: land-surface climatology, remote sensing, radiation budget, net radiation.]  相似文献   

PREDICTING ABOVE-GROUND NET PRIMARY PRODUCTIVITY OF TROPICAL RAINFORESTS FROM EVAPOTRANSPIRATION DATA     

Stanley R. Herwitz  Steven M. Friedland 《自然地理学》2013,34(1):18-25

The relationship between above-ground net primary productivity (ANPP) and actual evapotranspiration (AE) has been previously shown by Rosenzweig (1968) to be significant for a variety of mainly temperate terrestrial ecosystems. Our study of ANPP and AE data from the humid tropics showed that AE remains a useful predictor of ANPP in tropical rainforest environments. However, we also noted that 80% of the tropical rainforest data points were depressed below Rosenzweig's original regression line. We attribute these lower-than-predicted ANPP values to transpiration losses and rainfall interception losses that do not result in a corresponding production of biomass.  相似文献   

Contrasting the effects of climatic, nutrient, and oxygen dynamics on subfossil chironomid assemblages: a paleolimnological experiment from eutrophic High Arctic ponds     

Emily M. Stewart  Neal Michelutti  Jules M. Blais  Mark L. Mallory  Marianne S. V. Douglas  John P. Smol 《Journal of Paleolimnology》2013,49(2):205-219

Nutrients from the waste products of large seabird colonies can enter freshwater ecosystems, markedly altering water quality and biotic assemblages, especially in nutrient-poor regions like the Canadian High Arctic. Here, we investigate the influence of nutrient-rich seabird wastes on freshwater larval chironomid assemblages from two distinct seabird colonies. The study sites include four ponds dominated by northern fulmars (Fulmarus glacialis) at Cape Vera, Devon Island, as well as one pond near a large group of common eider ducks (Somateria mollissima borealis) on Tern Island (unofficial name) near Cornwallis Island, Nunavut. The rare combination of nutrient-enriched and well-oxygenated waters allowed us to contrast the effects of nutrients, oxygen, and temperature on chironomid community structure in shallow Arctic ponds using sediment cores. Despite highly elevated nutrient levels, the subfossil assemblages were dominated by cold stenotherms typical of oligotrophic waters. Although nutrient inputs appear to have increased chironomid head capsule numbers due to enhanced food availability, the fertilization had little direct effect on assemblage composition, at least at the taxonomic level achievable based on fossil material. The presence of low abundances of eutrophic/anoxic taxa, such as Chironomus plumosus-type, suggests that biogeographic barriers to dispersal are not influencing the assemblages. These data demonstrate that, in the presence of high concentrations of dissolved oxygen, nutrient enrichment had little direct effect on chironomid community composition in shallow Arctic ponds.  相似文献   

Calving retreat and proglacial lake growth at Hooker Glacier,Southern Alps,New Zealand     

Clare M. Robertson  Martin S. Brook  Kat A. Holt  Ian C. Fuller  Douglas I. Benn 《New Zealand geographer》2013,69(1):14-25

Hooker Glacier in the central Southern Alps of New Zealand has undergone significant downwasting and recession (～2.14 km) during the last two centuries. High retreat rates (51 m a^?1 1986–2001, 43 m a^?1 2001–2011) have produced a large (1.22 km²) proglacial lake. We present a retreat scenario for Hooker Glacier. A retreat scenario predicts that the glacier terminus will stabilise >3 km up‐valley of the current lake outlet after 2028 when ice velocity equals calving rate.  相似文献   

Heterogeneous redox conditions, arsenic mobility, and groundwater flow in a fractured-rock aquifer near a waste repository site in New Hampshire, USA     

Philip T. Harte  Joseph D. Ayotte  Andrew Hoffman  Kinga M. Révész  Marcel Belaval  Steven Lamb  J. K. B?hlke 《Hydrogeology Journal》2012,20(6):1189-1201

Anthropogenic sources of carbon from landfill or waste leachate can promote reductive dissolution of in situ arsenic (As) and enhance the mobility of As in groundwater. Groundwater from residential-supply wells in a fractured crystalline-rock aquifer adjacent to a Superfund site in Raymond, New Hampshire, USA, showed evidence of locally enhanced As mobilization in relatively reducing (mixed oxic-anoxic to anoxic) conditions as determined by redox classification and other lines of evidence. Redox classification was determined from geochemical indicators based on threshold concentrations of dissolved oxygen (DO), nitrate (NO ₃ ^– ), iron (Fe²⁺), manganese (Mn²⁺), and sulfate (SO ₄ ^2– ). Redox conditions were evaluated also based on methane (CH₄), excess nitrogen gas (N₂) from denitrification, the oxidation state of dissolved As speciation (As(III) and As(V)), and several stable isotope ratios. Samples from the residential-supply wells primarily exhibit mixed redox conditions, as most have long open boreholes (typically 50–100?m) that receive water from multiple discrete fractures with contrasting groundwater chemistry and redox conditions. The methods employed in this study can be used at other sites to gauge redox conditions and the potential for As mobilization in complex fractured crystalline-rock aquifers where multiple lines of evidence are likely needed to understand As occurrence, mobility, and transport.  相似文献   

Constraining pathways of microbial mediation for carbonate concretions of the Miocene Monterey Formation using carbonate-associated sulfate     

Sean J. Loyd  William M. Berelson  Timothy W. Lyons  Douglas E. Hammond  Frank A. Corsetti 《Geochimica et cosmochimica acta》2012

Carbonate concretions can form as a result of organic matter degradation within sediments. However, the ability to determine specific processes and timing relationships to particular concretions has remained elusive. Previously employed proxies (e.g., carbon and oxygen isotopes) cannot uniquely distinguish among diagenetic alkalinity sources generated by microbial oxidation of organic matter using oxygen, nitrate, metal oxides, and sulfate as electron acceptors, in addition to degradation by thermal decarboxylation. Here, we employ concentrations of carbonate-associated sulfate (CAS) and δ³⁴S_CAS (along with more traditional approaches) to determine the specific nature of concretion authigenesis within the Miocene Monterey Formation.Integrated geochemical analyses reveal that at least three specific organo-diagenetic reaction pathways can be tied to concretion formation and that these reactions are largely sample-site specific. One calcitic concretion from the Phosphatic Shale Member at Naples Beach yields δ³⁴S_CAS values near Miocene seawater sulfate (～+22‰ VCDT), abundant CAS (ca. 1000 ppm), depleted δ¹³C_carb (～?11‰ VPDB), and very low concentrations of Fe (ca. 700 ppm) and Mn (ca. 15 ppm)—characteristics most consistent with shallow formation in association with organic matter degradation by nitrate, iron-oxides and/or minor sulfate reduction. Cemented concretionary layers of the Phosphatic Shale Member at Shell Beach display elevated δ³⁴S_CAS (up to ～+37‰), CAS concentrations of ～600 ppm, mildly depleted δ¹³C_carb (～?6‰), moderate amounts of Mn (ca. 250 ppm), and relatively low Fe (ca. 1700 ppm), indicative of formation in sediments dominated by sulfate reduction. Finally, concretions within a siliceous host at Montaña de Oro and Naples Beach show minimal CAS concentrations, positive δ¹³C values, and the highest concentrations of Fe (ca. 11,300 ppm) and Mn (ca. 440 ppm), consistent with formation in sediments experiencing methanogenesis in a highly reducing environment. This study highlights the promise in combining CAS analysis with more traditional techniques to differentiate among diagenetic reactions as preserved in the geologic record and shows potential for unraveling subsurface biospheric processes in ancient samples with a high degree of specificity.  相似文献   

The OSL chronology of eolian sand deposition in a perched dune field along the northwestern shore of Lower Michigan     

Bradley E. Blumer  Alan F. Arbogast  Steven L. Forman 《Quaternary Research》2012,77(3):445-455

Extensive coastal dunes occur in the Great Lakes region of North America, including northwestern Michigan where some are perched on high (~ 100 m) bluffs. This study focuses on such a system at Arcadia Dunes and is the first to systematically generate optical ages from stratigraphic sections containing buried soils. Dune growth began ca. 4.5 ka during the Nipissing high lake stand and continued episodically thereafter, with periods of increased sand supply at ca. 3.5 ka and ca. 1.7 ka. The most volumetrically dominant phase of dune growth began ca. 1.0 ka and continued intermittently for about 500 years. It may have begun due to the combined effects of a high lake phase, potential changes in lake hydrodynamics with final isostatic separation of Lake Superior from Lakes Michigan and Huron, and increased drought and hydrologic variability associated with the Medieval Warm Period. Thus, this latest eolian phase likely reflects multiple processes associated with Great Lakes water level and climate variability that may also explain older eolian depositional events. Comparison of Arcadia ages and calendar corrected ¹⁴C ages from previous studies indicate broad chronological agreement between events at all sites, although it appears that dune growth began later at Arcadia.  相似文献