A new interpolation method to model thickness,isopachs, extent,and volume of tephra fall deposits     

Qingyuan Yang  Marcus Bursik 《Bulletin of Volcanology》2016,78(10):68

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An Extended CO Source around Comet 29P/Schwassmann-Wachmann 1     

Marcus GunnarssonHans Rickman  M.C. FestouA. Winnberg  G. Tancredi 《Icarus》2002,157(2):309-322

Comet 29P/Schwassmann-Wachmann 1 has been studied during seven days in August 1998 with the SEST submillimeter telescope at ESO, La Silla, Chile. The CO (J=2−1) emission at 230 GHz was mapped by directing the telescope beam at the nucleus and six off-nucleus positions. The CO line profiles exhibit the blue- and redshifted components previously observed by various observers. The strength of the observed lines does not decrease with projected distance to the nucleus as expected if CO molecules were coming from the nucleus only. Instead, the line area is nearly constant throughout the map. This can be explained if CO molecules are being released from both the sunlit side of the nucleus and CO-bearing particles distributed in a shell-like cloud. The extended source must consist of icy grains globally moving toward the Sun at ∼50 m s⁻¹ released ∼30 days before the observations were made. The nuclear and extended sources produce (7±1)×10²⁷ and 2.4×10²⁸ molecules s⁻¹, respectively. Our 1996 observations of the comet (Festou, M., M. Gunnarsson, A. Winnberg, H. Rickman, and G. Tancredi 2001. Icarus150, 140-150) were reexamined using this new two-source model. In this case, the nuclear and extended CO sources produced 10±1×10²⁷ and 2.9×10²⁸ CO molecules s⁻¹, respectively. It is not necessary to postulate night side outgassing, but a large quantity of solid grains has to be expelled into the coma.  相似文献   

Test of AMS 14C dating of pollen concentrates using tephrochronology     

Rewi M. Newnham  Marcus J. Vandergoes  Mark H. Garnett  David J. Lowe  Christine Prior  Peter C. Almond 《第四纪科学杂志》2007,22(1):37-51

Previous attempts to radiocarbon date sediments >10 kyr from the high rainfall region of Westland, New Zealand, a critical location for investigation of interhemispheric patterns of climate change, have been problematic. This study, building on recent work by Vandergoes and Prior ( 2003 ), shows that AMS ¹⁴C dating of pollen concentrates has potential to provide more reliable ages than other sediment constituents, including plant macrofossils. The method was applied to sediments from three sites containing the 22.6k ¹⁴C yr Kawakawa Tephra, which provided an independent test of the ¹⁴C ages. Although some minor laboratory contamination was detected in tests on background standards, the modelled relationship between sample mass and measured ¹⁴C content permitted an appropriate correction to be determined. Improved pollen concentrations derived by density separation between 1.4 and 1.2 specific gravity and sieving in the range 10–50 μm provided either older ages than other fractions of the same sample or, where in situ contamination was not evident, equivalent ages. Differences in degree of in situ contamination between depositional environments indicated that, in Westland, lake sites may be less susceptible to contamination by younger carbon than peat sites, where this process may be facilitated by root penetration into underlying sediments. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Transport of pharmaceutically active compounds in saturated laboratory columns   总被引：1，自引：0，他引：1  

Scheytt T  Mersmann P  Leidig M  Pekdeger A  Heberer T 《Ground water》2004,42(5):767-773

Occurrences of pharmaceutically active compounds in surface water and sewage water have been widely reported. Investigations show the presence of several classes of pharmaceuticals such as antirheumatics (e.g., diclofenac), analgesics (e.g., propyphenazone), and blood lipid regulators (clofibric acid), even in ground water. Compared to their occurrences in surface water, however, the reported incidences of drugs in ground water are much rarer. This may be due to the input, but also to transport processes and degradation in the aquifer. In field studies investigating ground water sampled at a bank infiltration site at Lake Tegel, Berlin, Germany, clofibric acid was found at concentrations up to 290 ng/L, and propyphenazone up to 250 ng/L, whereas concentrations of diclofenac were around the detection limit. The aim of this study was to investigate the ground water transport behavior of the pharmaceuticals clofibric acid, propyphenazone, and diclofenac with a laboratory soil column experiment. Results show that clofibric acid exhibits no degradation and almost no retardation (Rf = 1.1). Diclofenac (Rf = 2.0) and propyphenazone (Rf = 1.6) are retarded, whereas significant degradation was not observed for both pharmaceuticals under the prevailing conditions in the soil column. We conclude that the concentration distribution of the pharmaceuticals at the bank filtration site at Lake Tegel is controlled by sorption, desorption, and input variation, rather than by degradation.  相似文献   

Climate change and energy security: an analysis of policy research     

Marcus DuBois King  Jay Gulledge 《Climatic change》2014,123(1):57-68

The literature on climate change’s impacts on energy security is scattered across disparate fields of research and schools of thought. Much of this literature has been produced outside of the academy by scholars and practitioners working in “think tanks,” government agencies, and international/multilateral institutions. Here we reviewed a selected set of 58 articles and reports primarily from such sources and performed textual analysis of the arguments. Our review of this literature identifies three potential mechanisms for linking climate change and energy security: Climate change may 1) create second-order effects that may exacerbate social instability and disrupt energy systems; 2) directly impact energy supply and/or systems or 3) influence energy security through the effects of climate-related policies. We identify emerging risks to energy security driven by climate mitigation technology choices but find less evidence of climate change’s direct physical impacts. We used both empirical and qualitative selection factors for choosing the grey literature sample. The sources we selected were published in the last 5 years, available through electronic media and were written in language accessible to general policy or academic readers. The organizations that published the literature had performed previous research in the general fields of energy and/or climate change with some analytical content and identified themselves as non-partisan. This literature is particularly valuable to scholars because identifies understudied relationships that can be rigorously assessed through academic tools and methodologies and informs a translational research agenda that will allow scholars to engage with practitioners to address challenges that lie at the nexus of climate change and energy security.  相似文献   

Precipitation trends using in-situ and gridded datasets     

Sharlene Lata Beharry  Ricardo Marcus Clarke  Kishan Kurmarsingh 《Theoretical and Applied Climatology》2014,115(3-4):599-607

Six in situ precipitation time series of varying time periods in the northwestern region and the Global Precipitation Climatology Centre (GPCC) v6 0.5° monthly dataset (1901–2010) were statistically examined for monotonic trends in Trinidad. The Pettit test was used to investigate the abrupt changes in the mean while the Mann–Kendall test was employed to assess the monotonic trends. It was found that three in situ stations and the six grids experienced abrupt changes in the rainfall patterns and that there was an apparent shift in the seasons. In addition, for five out of the six in situ stations no monotonic change was detected in the monthly, seasonal, and annual rainfall patterns. Gradual decreases were detected in the calculated weighted area average for five stations, the GPCCv6 dataset and St. Ann’s time series. The GPCCv6 data indicated that the dry season in the southern Trinidad is becoming drier. Results also suggested that the range between the greatest and lowest recorded rainfall values for some months have increased while others decreased. The gridded dataset appears to give a good representation of the dry season (January to May) rainfall compared with the wet season (June to December) and was found to be negatively biased for the north-western region but may not necessarily be so for the entire island. The results suggested that in the north-western region mirco-climates may exist. It is recommended that further investigations are needed using in situ data.  相似文献   

Influence of model conceptualisation on one-dimensional recharge quantification: Uley South,South Australia     

Carlos M. Ordens  Vincent E. A. Post  Adrian D. Werner  John L. Hutson 《Hydrogeology Journal》2014,22(4):795-805

Model conceptualisation is a key source of uncertainty in one-dimensional recharge modelling. The effects of different conceptualisations on transient recharge predictions for the semi-arid Uley South Basin, South Australia, were investigated. One-dimensional unsaturated zone modelling was used to quantify the effect of variations of (1) lithological complexity of the unsaturated zone, and (2) representation of preferential flow pathways. The simulations considered ranges of water-table depths, vegetation characteristics, and top soil thicknesses representative for the study area. Complex lithological profiles were more sensitive to the selected vegetation characteristics and water-table depth. Scenarios considering runoff infiltration into, and preferential flow through sinkholes resulted in higher and faster recharge rates. A comparison of modelled and field-based recharge estimates indicated that: (1) the model simulated plausible recharge rates, (2) only the models with preferential flow correctly reproduced the timing of recharge, and (3) preferential flow is probably redistributed in the unsaturated zone rather than passing to the water table directly. Because different but equally plausible conceptual models produce widely varying recharge rates, field-based recharge estimates are essential to constrain the modelling results.  相似文献   

Accuracy assessment of georectified aerial photographs: Implications for measuring lateral channel movement in a GIS     

Michael L. Hughes  Patricia F. McDowell  W. Andrew Marcus 《Geomorphology》2006,74(1-4):1-16

Aerial photographs are commonly used to measure planform river channel change. We investigated the sources and implications of georectification error in the measurement of lateral channel movement by testing how the number (6–30) and type (human versus natural landscape features) of ground-control points (GCPs) and the order of the transformation polynomial (first-, second-, and third-order) affected the spatial accuracy of a typical georectified aerial photograph. Error was assessed using the root-mean-square error (RMSE) of the GCPs as well as error in 31 independent test points. The RMSE and the mean and median values of test-point errors were relatively insensitive to the number of GCPs above eight, but the upper range of test-point errors showed marked improvement (i.e., the number of extreme errors was reduced) as more GCPs were used for georectification. Using more GCPs thus improved overall georectification accuracy, but this improvement was not indicated by the RMSE, suggesting that independent test-points located in key areas of interest should be used in addition to RSME to evaluate georectification error.The order of the transformation polynomial also influenced test-point accuracy; the second-order polynomial function yielded the best result for the terrain of the study area. GCP type exerted a less consistent influence on test-point accuracy, suggesting that although hard-edged points (e.g., roof corners) are favored as GCPs, some soft-edged points (e.g., trees) may be used without adding significant error. Based upon these results, we believe that aerial photos of a floodplain landscape similar to that of our study can be consistently georectified to an accuracy of approximately ± 5 m, with 10% chance of greater error. The implications of georectification error for measuring lateral channel movement are demonstrated with a multiple buffer analysis, which documents the inverse relationship between the size of the buffers applied to two channel centerlines and the magnitude of change detected between them. This study demonstrates the importance of using an independent test-point analysis in addition to the RSME to evaluate and treat locational error in channel change studies.  相似文献   

Environmental controls on 10Be‐based catchment‐averaged denudation rates along the western margin of the Peruvian Andes          下载免费PDF全文

Regina Reber  Romain Delunel  Fritz Schlunegger  Camille Litty  Andrea Madella  Naki Akçar  Marcus Christl 《地学学报》2017,29(5):282-293

We present ¹⁰Be‐based basin‐averaged denudation rates for the entire western margin of the Peruvian Andes. Denudation rates range from c. 9 mm ka^?1 to 190 mm ka^?1 and are related neither to the subduction of the Nazca plate nor to the current seismicity along the Pacific coast and the occurrence of raised Quaternary marine terraces. Therefore, we exclude a tectonic control on denudation on a millennial time‐scale. Instead, we explain >60% of the observed denudation rates with a model where erosion rates increase either with mean basin slope angles or with mean annual water discharge. These relationships suggest a strong environmental control on denudation.  相似文献   

Hidden Components in Tropical Seascapes: Deep-Estuary Habitats Support Unique Fish Assemblages     

Michael Bradley  Ronald Baker  Marcus Sheaves 《Estuaries and Coasts》2017,40(4):1195-1206

Tropical coastal seascapes are biodiverse and highly productive systems composed of an interacting mix of habitats. They provide crucial ecosystem services that support people’s livelihoods, yet key components of these seascapes remain unstudied. We know little about the deep (>2 m) subtidal areas of tropical estuaries, because, due to gear restrictions, there have been no detailed studies of the habitats they contain and the fish that use them. Consequently, potentially important functions and linkages with surrounding habitats remain unknown. Using unbaited videos, an approach capable of sampling the full breadth of benthic habitats and whole fish assemblages, we investigated patterns of fish occupancy of the deep subtidal habitats (2–20 m) in one of Australia’s largest tropical estuaries. We identified 19 taxa not previously recorded from estuaries of tropical eastern Australia, along with 36 previously identified estuary taxa. Three recognisable fish assemblages were associated with distinct benthic habitat types: open bottom fine sediment, seagrass and structurally complex rocky areas. In deep water, habitats often overlooked in shallow water become important, and there are sharp differences in habitat function. Deep subtidal habitats are potentially an important zone for direct interaction between estuary and marine fauna, with a range of consequences for intertidal habitat use and nursery ground functioning. The interface between marine areas and the shallow-water estuary may be richer and more complex than previously recognised.  相似文献