Introduction     

Wim Ostendorf  Larry Bourne  Denise Pumain 《GeoJournal》1997,43(4):303-305

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The exact solution of the time-harmonic wave equation for a linear velocity profile     

Boris N. Kuvshinov  Wim A. Mulder 《Geophysical Journal International》2006,167(2):659-662

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Recent rapid salinity rise in three East Antarctic lakes   总被引：1，自引：0，他引：1  

Donna Roberts  Dominic A. Hodgson  Andrew McMinn  Elie Verleyen  Bruce Terry  Christine Corbett  Wim Vyverman 《Journal of Paleolimnology》2006,36(4):385-406

Research in East Antarctica has shown several recent environmental changes that may be linked to human impacts on climate. In order to detect the influence and context of these changes on coastal aquatic ecosystems we examined lake sediment cores from three lakes in the Windmill Islands, East Antarctica; Beall Lake, Holl Lake and ȁ8Lake Mȁ9. Cores were sectioned at␣2.5 mm intervals. Their diatom species composition was examined to detect changes in lake salinity using a diatom-salinity transfer function, and their algal pigment content was examined to detect photoautotrophic community responses to environmental change. Results showed that Holl Lake originated in a depression exposed by Holocene recession of the continental ice sheet and that Beall Lake and Lake M originated as isolated marine basins formed by changes in relative sea level. A general late Holocene trend of declining lake salinity was evident in all three lakes, interrupted by one short-term high salinity event in Beall Lake. This is consistent with a long-term positive moisture balance. This general decline in salinity has been followed by a remarkable recent rapid increase in salinity in all three lakes in the last few decades. We speculate that this rapid increase in salinity might be linked to changes taking place in the region including feedbacks resulting from decreasing sea ice extent as recorded in the nearby Law Dome ice core, and positive feedbacks in the catchments whereby reduced snow cover has led to decreased albedo, which in turn has caused increased evaporation and sublimation. Collectively these changes have shifted the lakes across a threshold from positive to negative moisture balance. A minor, but not rapid shift in the abundance of diatom pigments relative to pigments from green algae and cyanobacteria was also detected suggesting that some changes in photoautotrophic community composition have occurred. Measurements of modern nutrient levels are also higher than would be expected in Beall Lake and Holl Lake, given the extremely low sediment accumulation rates. This may be associated with a c. 300% increase in the population of Adélie penguins in the Windmill Islands recorded since the 1950s, or may a first signs of a rapid increase in catchment development and associated lake productivity as experienced in Antarctic and Arctic lakes subject to recent rapid regional warming. The most marked feature of the records is the rapid increase in salinity in all three lakes in␣the last few decades, which has occurred in lakes both with and without resident penguin populations.Dominic A. Hodgson and Donna Roberts contributed equally to this work  相似文献   

Alterations in guano phosphates and mio-pliocene carbonates of table mountain Santa Barbara,Curacao     

Ton Ten Have  Wim Heijnen  Enno Nickel 《Sedimentary Geology》1982,31(2):141-165

The Table Mountain Santa Barbara, consisting of the Mio-Pliocene Seroe Domi Limestone Formation, was probably covered with a guano layer in the Pleistocene (?). Solutions, carrying guano-derived phosphate, percolated downwards, resulting in partial phosphatization of the underlying limestones. Only two phosphate minerals are present in the Table Mountain: apatite, and whitlockite.Phosphatization includes both replacement of the original carbonate or (pre-phosphate) dolomite, and cementation in primary- as well as secondary porosity (cryptocrystalline, isotropic phosphate cement, (micro)crystalline apatite, isopachous apatite fringe cement, multiple-zoned apatite crusts, rhombic whitlockite cements). Two factors controlled the final distribution of the phosphate within the Table Mountain. Firstly, changing positions of the sea level (and, therefore, of the diagenetic environments) determined the overall distribution of the phosphatized interval, a horizontal layer (98–128 m above sea level) sandwiched between two non-phosphatized limestone units.Original carbonate facies and -mineralogy was the second controlling factor causing the final variations in degree of phosphatization. The limestones comprise two lithofacies: (a) coralliferous limestone lenses erratically distributed amidst; and (b) micritic limestones. These coralliferous limestones are phosphatized preferentially forming so-called “phosphate pockets”, sharply outlined within a non-phosphatized micritic limestone “host”. These pockets are characteristically organized into five zones which are described in detail. Higher original porosity/permeability of the coralliferous limestone lenses as compared to the micrites, additionally enhanced by a phase of pre-phosphate dolomitization, determined preferential phosphatization of this facies type.A second controlling factor was the original carbonate mineralogy and resulting dia-  相似文献   

Improved collection of rooftop micrometeorites through optimized extraction methods: The Budel collection     

Guido Jonker  Roel van Elsas  Jeroen H. J. L. van der Lubbe  Wim van Westrenen 《Meteoritics & planetary science》2023,58(4):463-479

The scientific value of micrometeorites collected from deep-sea sediments or glacial deposits can be limited by poorly constrained accumulation times or severe alteration, coupled with a complex infrastructure of sampling expeditions. Collecting micrometeorites from rooftops has recently become a feasible alternative, but extraction methods have not been optimized or standardized to date. Here, we show that existing methods for the recovery of melted cosmic spherules (CSs) can be strongly improved by using a sequence of mineral separation techniques, including shape separation with an asymmetric vibrator and heavy liquid density separation with overflow centrifuges. We retrieved 1006 micrometeorites from the gutter of a barn in Budel, the Netherlands. Particle diameters are 80–515 μm, with the major mode at 130 μm and a slope exponent of −4.88. Differences in size distributions among various types of CSs indicate a multi-source influx, with CS textures controlled by their parent body's mineralogy and orbital parameters. Repeated sampling of the rooftop after accumulation times of 959 and 333 days allows for a time-integrated global mass flux estimate of 472 t year⁻¹. This estimate is notably higher than previous rooftop-based estimates but is still severely affected by micrometeorite loss from the gutter through drainage. The mass flux peaks at an equivalent particle diameter of ~200 μm. The Budel collection is the first rooftop collection to contain abundant vitreous micrometeorites and include the coarse-grained S-type CS class. Unmelted and I-type micrometeorites remain difficult to extract from rooftop samples. Vitreous micrometeorites display various stages of weathering, showing that severe alteration of glass can progress at a faster rate in populated regions than previously assumed. This study demonstrates that methodological adjustments can drastically increase the scientific potential of rooftop micrometeorite collections.  相似文献   

Agricultural land partitioning model based on irrigation efficiency using a multi‐objective artificial bee colony algorithm     

Mehrdad Bijandi  Mohammad Karimi  Bahman Farhadi Bansouleh  Wim van der Knaap 《Transactions in GIS》2021,25(1):551-574

In the process of agricultural land consolidation, the land parcels are optimally redesigned and rearranged in such a way that the dimensions of the resulting parcels are proportional to agricultural criteria such as irrigation discharge, soil texture, and cropping pattern. Besides these criteria, spatial factors like slope, road accessibility, volume of earthwork, and geometrical factors such as size and shape of parcels are also included in the design process of agricultural land partitioning. In this study, a land partitioning model was proposed using a multi‐objective artificial bee colony algorithm (MOABC‐LP) taking into consideration the mentioned factors. Initially, a feasible dimension range of parcels in a block was calculated based on irrigation efficiency. Two partitioning layouts were defined according to the topography and geometry of blocks. The proposed method was applied to a real study area and the results suggest that the land partitioning plan obtained by the MOABC‐LP model, in comparison with a designer's plan, not only makes the shape and size of parcels more compatible with the topographical and agricultural conditions of each block, but also reduces their cut‐and‐fill ratio.  相似文献   

Planktonic diatom communities in temperate South-Central Chilean lakes with a focus on Asterionella formosa and the genus Aulacoseira     

Van de Vyver  Evelien  Pinseel  Eveline  Verleyen  Elie  Vanormelingen  Pieter  Van Wichelen  Jeroen  de Jong  Rixt  Urrutia  Roberto  Vyverman  Wim 《Journal of Paleolimnology》2022,68(3):279-296

Journal of Paleolimnology - Paleolimnological records from temperate South-Central Chilean lakes revealed a recent and marked increase in the relative abundances of the key-planktonic diatom...  相似文献   

HEIFE非均匀陆面上区域能量平衡研究   总被引：8，自引：1，他引：7  

马耀明  王介民  Massimo Menenti  Wim Bastiaanssen 《气候与环境研究》1997,2(3):293-301

卫星遥感在研究非均匀陆面上地－气间能量和水循环过程时有其独到的作用。本文介绍了一种利用陆地资源卫星ＴＭ资料进行非均匀陆面上区域能量平衡研究的参数化方案。以两个景的ＴＭ资料（１９９１年７月９日,夏季;１９９１年１０月２９日,近冬季）为个例,结合“黑河实验”（ＨＥＩＦＥ）期间的地面观测资料分析研究了实验区非均匀陆面上地表特征参数（地表反射率、标准化差值植被指数和地表温度）及能量平衡各分量（地表净辐射通量、土壤热通量、感热和潜热通量）的区域分布及季节差异,同时将所得的结果与地面观测的“真值”作了比较。结果表明：（１）由于黑河实验区下垫面状况十分复杂,戈壁、沙漠与绿洲交错分布,故在整个实验区内各地表特征参数及能量平衡各分量的分布范围亦比较宽;（２）地表特征参数及能量平衡各分量在实验区的绿洲、戈壁及沙漠上各有其特定的代表值;（３）地表能量平衡各分量的区域平均值在整个实验区内基本平衡;（４）夏季与近冬季的地表特征参数及能量平衡各分量的分布特征存在着显著差异。所得的这些结果与地面观测的“真值”和局地研究的结论基本一致。这些分析对非均匀下垫面中尺度模式陆面过程参数化方案的建立以及模式预报效果的检验都具有不可缺少的重要意义。  相似文献   

Distinct patterns of bank erosion in a navigable regulated river     

Gonzalo Duró  Alessandra Crosato  Maarten G. Kleinhans  Timotheus G. Winkels  Hessel A.G. Woolderink  Wim S.J. Uijttewaal 《地球表面变化过程与地形》2020,45(2):361-374

Distinct bankline patterns appeared after the removal of protection works along a navigable reach of the Meuse River. A series of oblique embayments now dominate the riverine landscape after ten years of bank erosion, but their location and asymmetry cannot be explained yet. This work analyses and integrates field measurements of flow, ship waves, bank composition, bed topography and historical maps to explain the observed patterns along two reaches of the river. An extraordinary low-water-level event generated by a ship accident provided the unique opportunity to also analyse the subaqueous bank topography. The results indicate that the formation of oblique embayments arises from the combination of floodplain heterogeneity, structured by scroll-bar deposits, and the regulation of water levels, resulting in ship-wave attack at a narrow range of bank elevation for 70% of the time. Substrate erodibility acts on the effectiveness of trees to slow down local bank erosion rates, which is possibly enhanced by a positive feedback between woody roots and cohesive soil. The strong regulation of water levels and the waves generated by the intense ship traffic produce an increasingly long mildly-sloping terrace at the bank toe and progressively dominate the bank erosion process. This study demonstrates the important role of floodplain and scroll bar formation in shaping later bank erosion, which has implications for predictive numerical models, restoration strategies, and understanding the role of vegetation in bank erosion processes. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献