Spatial and temporal variation of organic carbon in the northern South China Sea revealed by sedimentary records   总被引：2，自引：0，他引：2  

Jianfang Hu  Xuesong Sun  Ping'an Peng  Gan Zhang  Allan R. Chivas 《Quaternary International》2009,206(1-2):46

Three sediment cores were taken from the Pearl River estuary and adjacent northern South China Sea (SCS). These sediment cores span the time interval 1900–2000 AD. The stratigraphy of the concentration, the ratio of total organic carbon (TOC) to total nitrogen (TN) and stable isotope (δ¹³C_org) of organic carbon (OC) from three high-resolution sediment cores were analyzed. The stratigraphic profiles of OC concentration, TOC/TN ratios and δ¹³C_org for the near past 100 yrs indicate that terrestrial organic matter decreases from 68.3% to 27.4% of the TOC in the Pearl River estuary, while Dapeng Bay (offshore east of Hong Kong) apparently had throughout little terrestrial organic matter input. The highest deposited OC occurs at the Humen River mouth and the OC concentrations are higher in the outer estuary than in the inner shelf of the northern SCS. The deposited OC at the River mouth increased with time, which could be caused by the high precipitation of land-derived organic matter and the high input of terrestrial organic matter, which is likely related to the rapid urbanization and industrial development in the Pearl River Delta since the 1970s. The OC concentrations did not exhibit an obvious increase with time in most areas of the Pear River estuary and adjacent inner shelf of the SCS, but the algal-derived OC concentration inferred from the δ¹³C_org values increased with time especially from 1980 to 2000 in the outer Pearl River estuary and Dapeng Bay. This increase is presumably caused by enhanced primary marine productivity supported by higher anthropogenic nutrient inputs.  相似文献   

Procedures for woody vegetation surveys in the Kazgail rural council area,Kordofan, Sudan     

Allan Falconer  Matthew D. Cross  Donald G. Orr 《国际地球制图》2013,28(3):49-58

Efforts to reforest parts of the Kordofan Province of Sudan are receiving support from international development agencies. These efforts include planning and implementing reforestation activities that require the collection of natural resources and socioeconomic data, and the preparation of base maps. A combination of remote sensing, geographic information system and global positioning systems procedures are used in this study to meet these requirements.

Remote sensing techniques were used to provide base maps and to guide the compilation of vegetation resources maps. These techniques provided a rapid and efficient method for documenting available resources. Pocket‐sized global positioning system units were used to establish the location of field data collected for mapping and resource analysis. A microcomputer data management system tabulated and displayed the field data. The resulting system for data analysis, management, and planning has been adopted for the mapping and inventory of the Gum Belt of Sudan.  相似文献   

Differences in the neighborhood: Structural variations in the carapace of shore crabs Carcinus maenas (Decapoda: Portunidae)     

Allan T. Souza  Martina I. Ilarri  Joana Campos  João C. Marques  Irene Martins 《Estuarine, Coastal and Shelf Science》2011

The present study compared the carapace structure of Carcinus maenas in two nearby sites (2 km apart) within Minho estuary, submitted to different physicochemical and ecological conditions (water temperature, pH, crabs’ density and sex ratio). The carapace structure of the carapace and chelae of the crabs presented significant differences between sampling sites (t-test; p < 0.01). The SIMPER analysis revealed that the Weight/CW and Thickness/CW ratios explained all the dissimilarities found among sites. Overall, the male carapace was proportionally thicker at station 2 (t-test; p < 0.01), while the female carapace was proportionally thicker at station 1 (t-test; p < 0.001). A thicker carapace can be advantageous when competing for food or a sexual partner. We hypothetized that, since at station 2, the density of individuals was twice higher than at station 1, it is likely that agonistic encounters are more frequent, thus favouring a thicker carapace.  相似文献   

Petrography,mineral chemistry,and crystallization history of olivine‐phyric shergottite NWA 6234: A new melt composition     

Juliane Gross  Justin Filiberto  Christopher D. K. Herd  Mohit Melwani Daswani  Susanne P. Schwenzer  Allan H. Treiman 《Meteoritics & planetary science》2013,48(5):854-871

Knowledge of Martian igneous and mantle compositions is crucial for understanding Mars' mantle evolution, including early differentiation, mantle convection, and the chemical alteration at the surface. Primitive magmas provide the most direct information about their mantle source regions, but most Martian meteorites either contain cumulate olivine or crystallized from fractionated melts. The new Martian meteorite Northwest Africa (NWA) 6234 is an olivine‐phyric shergottite. Its most magnesian olivine cores (Fo₇₈) are in Mg‐Fe equilibrium with a magma of the bulk rock composition, suggesting that it represents a melt composition. Thermochemical calculations show that NWA 6234 not only represents a melt composition but is a primitive melt derived from an approximately Fo₈₀ mantle. Thus, NWA 6234 is similar to NWA 5789 and Y 980459 in the sense that all three are olivine‐phyric shergottites and represent primitive magma compositions. However, NWA 6234 is of special significance because it represents the first olivine‐phyric shergottite from a primitive ferroan magma. On the basis of Al/Ti ratio of pyroxenes in NWA 6234, the minor components in olivine and merrillite, and phosphorus zoning of olivine, we infer that the rock crystallized completely at pressures consistent with conditions in Mars' upper crust. The textural intergrowths of the two phosphates (merrillite and apatite) indicate that at a very last stage of crystallization, merrillite reacted with an OH‐Cl‐F‐rich melt to form apatite. As this meteorite crystallized completely at depth and never erupted, it is likely that its apatite compositions represent snapshots of the volatile ratios of the source region without being affected by degassing processes, which contain high OH‐F content.  相似文献   

From mush to eruption in centuries: assembly of the super-sized Oruanui magma body     

Aidan S. R. Allan  Daniel J. Morgan  Colin J. N. Wilson  Marc-Alban Millet 《Contributions to Mineralogy and Petrology》2013,166(1):143-164

The magmatic systems that give rise to voluminous crystal-poor rhyolite magma bodies can be considered to operate on two contrasting timescales: Those governed by longer-term processes by which a magma acquires its chemical and isotopic characteristics (e.g., fractional crystallisation and assimilation), and those operating at shorter timescales during the physical accumulation of the melt-dominant magma body that finally erupts. We explore the compositional and textural relationships between amphibole and orthopyroxene crystals from the 25.4 ka, 530 km³ (magma) Oruanui eruption products (Taupo volcano, New Zealand) to investigate how processes related to the physical assembly of the pre-eruptive magma body are represented in the crystal record. Over 90 % of orthopyroxenes from the volumetrically dominant high-SiO₂ (>74 wt%) rhyolite pumices record textural evidence for a significant disequilibrium event (partial dissolution ± resorption of cores and interiors) prior to the growth of 40–500 μm thick rim zones. This dissolution/regrowth history of orthopyroxene is recorded in the chemistry of co-crystallising amphiboles as a prominent inflection in the concentrations of Mn and Zn, two elements notably enriched in orthopyroxene relative to amphibole. Textural and chemical features, linked with in situ thermobarometric estimates, indicate that a major decompression event preceded the formation of the melt-dominant body. The decompression event is inferred to represent the extraction of large volumes of melt plus crystals from the Oruanui crystal mush/source zone at pressures of 140–300 MPa (~6–12 km depth). Orthopyroxene underwent partial dissolution during ascent before reestablishing in the melt-dominant magma body at pressures of 90–140 MPa (~3.5–6 km). We model Fe–Mg diffusion across the core-rim boundaries along the crystallographic a or b-axes to constrain the timing of this decompression event, which marked establishment of the melt-dominant magma body. Maximum modelled ages indicate that this event did not begin until ~1,600 years before eruption, consistent with constraints from zircon model-age spectra. Once extraction began, it underwent runaway acceleration with a peak extraction age of ~230 years, followed by an apparent period of stasis of ~60 years prior to eruption. The rapidity of the extraction and accumulation processes implies the involvement of a dynamic driving force which, in the rifted continental arc setting of the Taupo Volcanic Zone, seems likely to be represented by magma-assisted extensional tectonic processes.  相似文献   

Quantifying preferential flow in soils: A review of different techniques   总被引：19，自引：0，他引：19  

Suzanne E. Allaire  Stphanie Roulier  Allan J. Cessna 《Journal of Hydrology》2009,378(1-2):179-204

Preferential flow (PF) in soil has both environmental and human health implications since it favours contaminant transport to groundwater without interaction with the chemically and biologically reactive upper layer of soil. PF is, however, difficult to measure and quantify. This paper reviews laboratory and field techniques, such as breakthrough curves, dye tracing, and scanning techniques, for evaluating PF in soil at different scales. Advanced technologies, such as scanning techniques, have increased our capability to quantify transport processes within the soil with minimal soil disturbance. Important issues with respect to quantifying PF concern large-scale studies, frozen soil conditions, tracing techniques for particles and gases, a lack of simple mathematical tools for interpreting field data, and the lack of a systematic approach for comparing PF data resulting from different measurement techniques. Also, more research is required to quantify the relative importance of the various PF processes that occur in soil rather than the integrated result of all PF processes in soils.  相似文献   

The eSTAR network – agent architectures for astronomy     

A. Allan  T. Naylor  E. S. Saunders 《Astronomische Nachrichten》2006,327(8):767-770

The eSTAR Project uses intelligent agent technologies to carry out resource discovery, submit observation requests and analyze the reduced data returned from a meta‐network of robotic telescopes. Linking ground based telescopes with astronomical satellites, and using the emerging field of intelligent agent architectures to provide crucial autonomous decision making in software, the project has succeeded in combining data archives and research class telescopes, along with distributed computing nodes, to build an ad‐hoc peer‐to‐peer heterogeneous network of resources. We present the current operations paradigm of the eSTAR network and describe the direction in which the project intends to develop over the next few years. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Laterites and paleoclimates. Weathering processes and anthropogenic impact   总被引：2，自引：0，他引：2  

Jean-Luc Probst  Allan R. Chivas  Jeff Wilson 《Chemical Geology》2000,170(1-4):1-3

  相似文献   

Seasonal Variability of Northern Hemisphere Snow Extent Using Visible Satellite Data     

David A. Robinson  Allan Frei 《The Professional geographer》2000,52(2):307-315

In this paper we use a satellite‐derived data set to explore spatial and temporal variations of snow extent across Northern Hemisphere continents during the last three decades. These weekly visible‐wavelength satellite maps of Northern Hemisphere snow extent produced by the National Oceanic and Atmospheric Administration constitute the longest consistently‐derived satellite record of any environmental variable. We document the considerable intra‐annual variability of snow extent, and show that during each month, fluctuations over relatively small areas are responsible for the majority of the year‐to‐year variability. Regions that cover less than 6% of Northern Hemisphere lands north of 20°N explain 62% Ã Â Ã Â 92% of the interannual variance across the continents. On average, snow was more extensive across both Eurasia and North America from the 1970s to middle 1980s than during the late 1980s to late 1990s. During late winter, spring and summer, snow extent has decreased since the middle 1980s, while during fall to middle winter, snow extent has remained relatively constant. Accurate information on continental snow extent is critical for weather and hydrologic forecasting; for understanding hemispheric‐scale atmospheric circulation, thermal variations, and regional snow extent; and for using snow as a credible indicator of climate variability and change.  相似文献   

The labour-market impact of migration to rural areas     

Allan M. Findlay  David Short  Aileen Stockdale 《Applied geography (Sevenoaks, England)》2000,20(4):257

An economic audit of the labour-market impact of in-migration to rural Scotland provides evidence that migrants make rather than take jobs. A survey of 689 households in six study areas selected from across rural Scotland provides the basis for examining the scale and nature of job growth associated with in-migration. Job multipliers are calculated by migrant type and by economic sector.  相似文献