Oxygen isotope analysis of bone and tooth enamel phosphate from paleogene sediments: Experimental techniques and initial results     

M. K. Bera  Kasturi Bhattacharya  A. Sarkar  A. Samanta  Kishor Kumar  Ashok Sahni 《Journal of the Geological Society of India》2010,76(3):275-282

Oxygen isotope composition (δ¹⁸O) of fossil bone and tooth enamel phosphate (bioapatite) is an important tool for estimating the isotopic composition of past environmental water. Lack of analytical facility was a hindrance for studying such bioapatites in spite of large number of fossil materials reported from various geological ages in India. We have established in our laboratory, based on available methods, the chemical procedure for extraction of very small amount (<1000 μg) PO₄ ⁻³ from bioapatite and on-line mass spectrometric measurement of its δ¹⁸O composition by high temperature (∼1450°C) pyrolysis. The achieved precision is ∼± 0.3 ‰ similar to obtained elsewhere, with interlaboratory calibration showing excellent agreement of standard phosphates. Inferred δ¹⁸O values of environmental water, based on the analysis of teeth and bones of sharks, fish and terrestrial mammals from the Paleogene successions of the northwest sub-Himalayan and the Peninsular India show strong correspondence with animal habitats. The freshwater δ¹⁸O values are much depleted having range similar to modern monsoon precipitation. However, owing to our small dataset it is not possible at this stage to infer about the existence of monsoon over the Indian sub-continent during the Eocene-Oligocene time.  相似文献   

Merging circulations on Jupiter: Observed differences between cyclonic and anticyclonic mergers     

John H. Rogers  Hans-Jörg Mettig  Antonio Cidadão  P. Clay Sherrod  Damian Peach 《Icarus》2006,185(1):244-257

The dynamics of mergers of large circulations in Jupiter's atmosphere may permit different models of the atmosphere to be tested. We report well-resolved observations of such events at visible wavelengths: three anticyclonic and three cyclonic events. A merger of anticyclonic white ovals in the South South Temperate domain (2002 March) is compared with the previously reported merger of ovals BE and FA in the South Temperate domain (2000 March). In each case, the two similar-sized ovals converged rapidly once they were separated by less than the sum of their diameters; they orbited around each other anticyclonically during the merger; the merged oval initially had the same rapid drift as the western parent; and, in an unexpected similarity, a cyclonic oval emerged westward from the point of merger. Evidence suggests that a merger of smaller ovals in the North North Temperate domain (2002 February) had similar dynamics. In contrast, mergers of cyclonic ovals in the North Equatorial Belt (‘barges’: 2001 November, 2005 May) proceeded in a different manner. The two parent barges showed no consistent acceleration towards each other as they converged; on contact there was no obvious sign of mutual circulation, and the low-albedo regions had almost passed each other before they finally merged; and the resulting barge had a drift rate intermediate between the two parents, and a length that was greater than either parent. Again, a third such event involving a smaller barge (2002 December) showed many of the same characteristics. These observations define different dynamical behaviour during anticyclonic and cyclonic mergers.  相似文献   

Plasma clouds associated with Comet P/Borrelly dust impacts     

Bruce T. Tsurutani  Douglas R. Clay  B. Dasgupta  Michael Henry  Stewart Moses 《Icarus》2004,167(1):89-99

The NASA DS1 spacecraft encountered Comet P/Borrelly on September 22, 2001 at a distance of ∼2171 km on the sunward side of the comet. The flyby speed was ∼16.5 km s⁻¹. Using high temporal resolution (50 μs) absolute electric field amplitude measurements from a ∼1 m dipole antenna, new features of plasma clouds created by cometary dust impacts have been detected. The pulses have 1/e exponential decays of ∼650 μs duration, exponentially shaped overshoots with rise times of ∼2 ms, and exponential-shaped overshoot decay times of ∼10 ms. Assuming a plasma temperature of 10⁴ K, these pulse features have been explained as plasma cloud space charge effects from the electron, proton and heavy ion portions of the clouds passing the antenna. Complex pulse shapes were also detected. These are believed to be due to either plasma cloud scattering off of the spacecraft, or to secondary impacts. Small electric pulses of duration 10-15 ms of cometary origin were detected but are presently unexplained. The electric component of the plasma wave spectra at closest approach had an f^−2.4 power law shape from 10 Hz to 1 kHz. The electron cyclotron frequency was approximately 1 kHz. One possible explanation of the wave spectrum is that whistler mode waves associated with phase steepened cometary plasma waves are dispersed, leading to the broad spectrum. Finally, based on the present results, a new type of low-cost, large-area dust detector is proposed.  相似文献   

Modeling forest fire risk in the northeast of Iran using remote sensing and GIS techniques   总被引：3，自引：1，他引：2  

Hamed Adab  Kasturi Devi Kanniah  Karim Solaimani 《Natural Hazards》2013,65(3):1723-1743

Fire in forested areas can be regarded as an environmental disaster which is triggered by either natural forces or anthropogenic activities. Fires are one of the major hazards in forested and grassland areas in the north of Iran. Control of fire is difficult, but it is feasible to map fire risk by geospatial technologies and thereby minimize the frequency of fire occurrences and damages caused by fire. The fire risk models provide a suitable concept to understand characterization of fire risk. Some models are map based, and they combine effectively different forest fire–causing variables with remote sensing data in a GIS environment for identifying and mapping forest fire risk. In this study, Structural Fire Index, Fire Risk Index, and a new index called Hybrid Fire Index were used to delineate fire risk in northeastern Iran that is subjected to frequent forest fire. Vegetation moisture, slope, aspect, elevation, distance from roads, and vicinity to settlements were used as the factors influencing accidental fire starts. These indices were set up by assigning subjective weight values to the classes of the layers based on their sensitivity ratio to fire. Hot spots data derived from MODIS satellite sensor were used to validate the indices. Assessment of the indices with receiver operating characteristic (ROC) curves shows that 76.7 % accuracy of the HFI outperformed the other two indices. According to the Hybrid Fire Index, 57.5 % of the study area is located under high-risk zone, 33 % in medium-risk zone, and the remaining 9.5 % area is located in low-risk zone.  相似文献   

Carbon dioxide fluxes and DOC concentrations of eroding blanket peat gullies   总被引：1，自引：0，他引：1  

Gareth D. Clay  Simon Dixon  Martin G. Evans  James G. Rowson  Fred Worrall 《地球表面变化过程与地形》2012,37(5):562-571

UK peatlands are affected by severe gully erosion with consequent impacts on ecosystem services from these areas. Incision into the peat can damage the vegetation and hydrology and lead to increases in carbon loss and sediment transfer downstream. Gullies represent then a conduit for and a hotspot of carbon loss but the relatively high water tables of gullies have meant that they have been identified as areas with a high restoration potential because of easily restored peat‐forming conditions. This study uses a series of gully sites, subject to different restoration interventions, to investigate differences in carbon pathways (DOC, CO₂) and hydrology between restoration strategies and gully position. The results show that the position within the gully (interfluve, gully side, or gully floor) does not significantly affect water quality but that it plays a significant role in CO₂ exchange. Gully floors are areas of high photosynthesis and ecosystem respiration, though net ecosystem exchange is not significantly different across the gully. While gully position plays a role in the cycling of some carbon species, this study highlights the importance of vegetation as a key control on carbon cycling. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Garnet peridotite from Colorado Plateau ultramafic diatremes: Hydrates,carbonates, and comparative geothermometry     

W. Clay Hunter  Douglas Smith 《Contributions to Mineralogy and Petrology》1981,76(3):312-320

Crystal fragments of pyrope from diatremes of ultramafic microbreccia in the Navajo Province of the Colorado Plateau contain inclusions of olivine, pyroxene, spinel, chlorite, amphibole, chlorapatite, and dolomite. The included suite supports earlier hypotheses that hydrous phases and carbonates were primary parts of some garnet peridotite assemblages in the Plateau lithosphere. Garnets with spinel and orthopyroxene inclusions likely all were sampled at pressures less than 36 kb and perhaps as low as 15–20 kb; no evidence was found for inclusions from greater depths. Temperature estimates are 800°–900° C for garnet-clinopyroxene equilibration, but only 500°–700° C for garnetolivine equilibration. Inherent differences between geothermometry methods account for only part of the discrepancy. Pronounced Fe-Mg zoning in garnet at olivine contacts and the lack of such zoning at clinopyroxene contacts are evidence that the difference in part relates to relative reequilibration rates with cooling. The garnet-olivine temperature estimates may be the best approximations to mantle temperatures before eruption. Our data are compatible both with the hypothesis that the garnet peridotite was emplaced in the mantle by large-scale, horizontal transport in the lithosphere and with the hypothesis that rocks were sampled from Precambrian lithosphere cooled to temperatures like those along a low heat flow geotherm. Discordances between the geothermometers here and in other lherzolite localities may be keys to evaluating tectonic histories of lherzolite masses.  相似文献   

Sonar echo statistics as a remote-sensing tool: Volume and seafloor     

Stanton  T. Clay  C. 《Oceanic Engineering, IEEE Journal of》1986,11(1):79-96

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粘土矿物对环境污染的防治作用   总被引：10，自引：1，他引：9  

鲁春霞  于云江  吴俊平 《中国沙漠》1999

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Estuaries of the South Atlantic coast of North America: Their geographical signatures     

Richard Dame  Merryl Alber  Dennis Allen  Michael Mallin  Clay Montague  Alan Lewitus  Alice Chalmers  Robert Gardner  Craig Gilman  Björn Kjerfve  Jay Pinckney  Ned Smith 《Estuaries and Coasts》2000,23(6):793-819

Estuaries of the southeastern Atlantic coastal plain are dominated by shallow meso-tidal bar-built systems interspersed with shallow sounds and both low flow coastal plain and high flow piedmont riverine systems. Three general geographical areas can be discriminated: the sounds of North Carolina; the alternating series of riverine and ocean dominated bar-built systems of South Carolina, Georgia, and northeast Florida, and the subtropical bar-built estuaries of the Florida southeast coast. The regional climate ranges from temperate to subtropical with sea level rise and hurricanes having a major impact on the region's estuaries because of its low and relatively flat geomorphology. Primary production is highest in the central region. Seagrasses are common in the northern and southern most systems, while intertidal salt marshes composed ofSpartina alterniflora reach their greatest extent and productivity in South Carolina and Georgia. Nuisance blooms (cyanobacteria, dinoflagellates, and cryptomonads) occur more frequently in the northern and extreme southern parts of the region. Fishery catches are highest in the North Carolina and Florida areas. Human population growth with its associated urbanization reaches a maximum in Florida and it is thought that the long-term sustainability of the Florida coast for human habitation will be lost within the next 25 years. Tidal flushing appears to play an important role in mitigating anthropogenic inputs in systems of moderate to high tidal range, i.e., the South Carolina and Georgia coasts. The most pressing environmental problems for the estuaries of the southeastern Atlantic coast seem to be nutrient loading and poor land use in North Carolina and high human population density and growth in Florida. The future utilization of these estuarine systems and their services will depend on the development of improved management strategies based on improved data quality.  相似文献   

RoboNet‐II: Follow‐up observations of microlensing events with a robotic network of telescopes     

Y. Tsapras  R. Street  K. Horne  C. Snodgrass  M. Dominik  A. Allan  I. Steele  D.M. Bramich  E.S. Saunders  N. Rattenbury  C. Mottram  S. Fraser  N. Clay  M. Burgdorf  M. Bode  T.A. Lister  E. Hawkins  J.P. Beaulieu  P. Fouqu  M. Albrow  J. Menzies  A. Cassan  D. Dominis‐Prester 《Astronomische Nachrichten》2009,330(1):4-11

RoboNet‐II uses a global network of robotic telescopes to perform follow‐up observations of microlensing events in the Galactic Bulge. The current network consists of three 2 m telescopes located in Hawaii and Australia (owned by Las Cumbres Observatory) and the Canary Islands (owned by Liverpool John Moores University). In future years the network will be expanded by deploying clusters of 1 m telescopes in other suitable locations. A principal scientific aim of the RoboNet‐II project is the detection of cool extra‐solar planets by the method of gravitational microlensing. These detections will provide crucial constraints to models of planetary formation and orbital migration. RoboNet‐II acts in coordination with the PLANET microlensing follow‐up network and uses an optimization algorithm (“web‐PLOP”) to select the targets and a distributed scheduling paradigm (eSTAR) to execute the observations. Continuous automated assessment of the observations and anomaly detection is provided by the ARTEMiS system (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献