The CM carbonaceous chondrite regolith Diepenveen     

Marco Langbroek  Peter Jenniskens  Leo M. Kriegsman  Henk Nieuwenhuis  Niek De Kort  Jacob Kuiper  Wim Van Westrenen  Michael E. Zolensky  Karen Ziegler  Qing‐Zhu Yin  Matthew E. Sanborn  Josh Wimpenny  Akane Yamakawa  Sebastiaan J. De Vet  Matthias M. M. Meier  Kees C. Welten  Kunihiko Nishiizumi  Marc W. Caffee  Aaron S. Burton  Jason P. Dworkin  Daniel P. Glavin  Qinghao Wu  Richard N. Zare  Alexander Ruf  Mourad Harir  Philippe Schmitt‐Kopplin   《Meteoritics & planetary science》2019,54(7):1431-1461

A carbonaceous chondrite was recovered immediately after the fall near the village of Diepenveen in the Netherlands on October 27, 1873, but came to light only in 2012. Analysis of sodium and poly‐aromatic hydrocarbon content suggests little contamination from handling. Diepenveen is a regolith breccia with an overall petrology consistent with a CM classification. Unlike most other CM chondrites, the bulk oxygen isotopes are extremely ¹⁶O rich, apparently dominated by the signature of anhydrous minerals, distributed on a steep slope pointing to the domain of intrinsic CM water. A small subset plots closer to the normal CM regime, on a parallel line 2 ‰ lower in δ¹⁷O. Different lithologies in Diepenveen experienced varying levels of aqueous alteration processing, being less aqueously altered at places rather than more heated. The presence of an agglutinate grain and the properties of methanol‐soluble organic compounds point to active impact processing of some of the clasts. Diepenveen belongs to a CM clan with ~5 Ma CRE age, longer than most other CM chondrites, and has a relatively young K‐Ar resetting age of ~1.5 Ga. As a CM chondrite, Diepenveen may be representative of samples soon to be returned from the surface of asteroid (162173) Ryugu by the Hayabusa2 spacecraft.  相似文献   

Extreme storm surge modelling in the North Sea     

Nina Ridder  Hylke de Vries  Sybren Drijfhout  Henk van den Brink  Erik van Meijgaard  Hans de Vries 《Ocean Dynamics》2018,68(2):255-272

This study shows that storm surge model performance in the North Sea is mostly unaffected by the application of temporal variations of surface drag due to changes in sea state provided the choice of a suitable constant Charnock parameter in the sea-state-independent case. Including essential meteorological features on smaller scales and minimising interpolation errors by increasing forcing data resolution are shown to be more important for the improvement of model performance particularly at the high tail of the probability distribution. This is found in a modelling study using WAQUA/DCSMv5 by evaluating the influence of a realistic air-sea momentum transfer parameterization and comparing it to the influence of changes in the spatial and temporal resolution of the applied forcing fields in an effort to support the improvement of impact and climate analysis studies. Particular attention is given to the representation of extreme water levels over the past decades based on the example of the Netherlands. For this, WAQUA/DCSMv5 is forced with ERA-Interim reanalysis data. Model results are obtained from a set of different forcing fields, which either (i) include a wave-state-dependent Charnock parameter or (ii) apply a constant Charnock parameter (α _{C h} =?0.032) tuned for young sea states in the North Sea, but differ in their spatial and/or temporal resolution. Increasing forcing field resolution from roughly 79 to 12 km through dynamically downscaling can reduce the modelled low bias, depending on coastal station, by up to 0.25 m for the modelled extreme water levels with a 1-year return period and between 0.1 m and 0.5 m for extreme surge heights.  相似文献   

Can the Scheldt River Estuary become hyperturbid?     

Dijkstra  Yoeri M.  Schuttelaars  Henk M.  Schramkowski  George P. 《Ocean Dynamics》2019,69(7):809-827

Ocean Dynamics - We investigate the hypothesis by Winterwerp and Wang (Ocean Dyn 63:1279–1292, 2013) that channel deepening in the Scheldt River Estuary could lead to a large increase in...  相似文献   

Evaluation of WaPOR V2 evapotranspiration products across Africa     

Megan L. Blatchford  Chris M. Mannaerts  Sammy M. Njuki  Hamideh Nouri  Yijian Zeng  Henk Pelgrum  Steven Wonink  Poolad Karimi 《水文研究》2020,34(15):3200-3221

The Food and Agricultural Organization of the United Nations (FAO) portal to monitor water productivity through open-access of remotely sensed derived data (WaPOR) offers continuous actual evapotranspiration and interception (ETIa-WPR) data at a 10-day basis across Africa and the Middle East from 2009 onwards at three spatial resolutions. The continental level (250 m) covers Africa and the Middle East (L1). The national level (100 m) covers 21 countries and 4 river basins (L2). The third level (30 m) covers eight irrigation areas (L3). To quantify the uncertainty of WaPOR version 2 (V2.0) ETIa-WPR in Africa, we used a number of validation methods. We checked the physical consistency against water availability and the long-term water balance and then verify the continental spatial and temporal trends for the major climates in Africa. We directly validated ETIa-WPR against in situ data of 14 eddy covariance stations (EC). Finally, we checked the level consistency between the different spatial resolutions. Our findings indicate that ETIa-WPR is performing well, but with some noticeable overestimation. The ETIa-WPR is showing expected spatial and temporal consistency with respect to climate classes. ETIa-WPR shows mixed results at point scale as compared to EC flux towers with an overall correlation of 0.71, and a root mean square error of 1.2 mm/day. The level consistency is very high between L1 and L2. However, the consistency between L1 and L3 varies significantly between irrigation areas. In rainfed areas, the ETIa-WPR is overestimating at low ETIa-WPR and underestimating when ETIa is high. In irrigated areas, ETIa-WPR values appear to be consistently overestimating ETa. The relative soil moisture content (SMC), the input of quality layers and local advection effects were some of the identified causes. The quality assessment of ETIa-WPR product is enhanced by combining multiple evaluation methods. Based on the results, the ETIa-WPR dataset is of enough quality to contribute to the understanding and monitoring of local and continental water processes and water management.  相似文献   

Process-based modeling of the overflow-induced growth of erosional channels     

Thieu Quang Tuan  Marcel J.F. Stive  Henk Jan Verhagen  Paul J. Visser 《Coastal Engineering》2008

A new process-based approach is introduced for a more efficient computation of the overflow-induced growth of an erosional channel in a non-cohesive homogeneous narrow landmass such as the breach growth in a sand-dike. The approach is easy to incorporate in a 1D/2DV morphodynamic model to compute the channel growth both vertically and laterally.  相似文献   

Holocene seasonal sea‐surface temperature variations in the southern Adriatic Sea inferred from a multiproxy approach     

Francesca Sangiorgi  Lucilla Capotondi  Nathalie Combourieu Nebout  Luigi Vigliotti  Henk Brinkhuis  Simona Giunta  Andr F. Lotter  Caterina Morigi  Alessandra Negri  Gert‐Jan Reichart 《第四纪科学杂志》2003,18(8):723-732

Holocene cooling events have been reconstructed for the southern Adriatic Sea (central Mediterranean) by means of analyses of organic walled dinoflagellate cysts, planktonic foraminifera, oxygen isotopes, calcareous nanoplankton, alkenones and pollen from a sediment core. Two cooling events have been detected, during which sea‐surface temperatures (SSTs) were ca. 2°C lower. Unravelling the SST signal into dominant seasonal components suggests maximum winter cooling of 2°C at around 6.0 ka, whereas the cooling at ca. 3.0 ka might be the result of a spring temperature cooling of 2–3°C. The events, lasting several hundred years, are apparently synchronous with those in the Aegean Sea, where they have been related to known cooling events from the Greenland ice‐core record. A distinct interruption in Adriatic Sea sapropel S1 is not clearly accompanied by a local drop in winter temperatures, but seems to be forced by ventilation, which probably occurred earlier in the Aegean Sea and was subsequently transmitted to the Adriatic Sea. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Mapping East African tropical forests and woodlands — A comparison of classifiers     

Grace Nangendo  Andrew K. Skidmore  Henk van Oosten 《ISPRS Journal of Photogrammetry and Remote Sensing》2007,61(6):393-404

In mapping the forest–woodland–savannah mosaic of Budongo Forest Reserve, Uganda, four classification methods were compared, i.e. Maximum Likelihood classifier (MLC), Spectral Angle Mapper (SAM), Maximum Likelihood combined with an Expert System (MaxExpert) and Spectral Angle Mapper combined with an Expert System (SAMExpert). The combination of conventional classifiers with an Expert System proved to be an effective approach for forest mapping. This was also the first time that the SAMExpert had been used in the mapping of tropical forests. SAMExpert not only maps with high accuracy, but is also fast and easy to use, making it attractive for use in less developed countries. Another advantage is that it can be executed on a standard PC set up for image processing.Combining the conventional classifiers (MLC and SAM) with the Expert System significantly improved the classification accuracy. The highest overall accuracy (94.6%) was obtained with SAMExpert. The MaxExpert approach yielded a map with an accuracy of 85.2%, which was also significantly higher than that obtained using the conventional MLC approach.The SAMExpert classifier accurately mapped individual classes. Of the four classes of woodland mapped, the Open Woodland (with Terminalia) and Wooded Grassland classes were more accurately mapped using SAMExpert. The Open Woodland had been previously identified by ecologists, but had never been mapped.  相似文献   

Are water tables a subdued replica of the topography?   总被引：3，自引：0，他引：3  

Haitjema HM  Mitchell-Bruker S 《Ground water》2005,43(6):781-786

The water table in unconfined aquifers is often believed to be a subdued replica of the topography or land surface. However, this assumption has not been widely tested and in some cases has been found to be in error. An analysis of ground water rise in regional unconfined aquifers, using both a two-dimensional boundary element model and a one-dimensional Dupuit-Forchheimer model, reveals the conditions under which the water table does or does not closely follow the topography. A simple decision criterion is presented to estimate in advance under which conditions the water table is expected to be largely unrelated to the topography and under which conditions the topography controls the position of the water table.  相似文献   

Byssal detachment underestimates tolerance of mussels to toxic compounds     

Rajagopal S  van der Velde G  van der Gaag M  Jenner HA 《Marine pollution bulletin》2005,50(1):20-29

Mussels are sedentary organisms attached to solid substrata by means of byssus threads. Mussels detached from their substratum tend to reattach by producing new byssus threads. Therefore, in bioassays using mussels, if the test animals are in an unattached status, increased byssogenic activity would expose their soft body parts to the toxic compound used. We test the tolerance of two mussel species (Mytilopsis leucophaeata and Mytilus edulis) to an oxidizing biocide (chlorine) and show that detached mussels are 24-28% less tolerant than byssally attached ones. Detached mussels also showed higher oxygen consumption, filtration rate, foot activity, byssus thread production and byssogenesis index, parameters which are associated with valve opening. A review of literature showed that most of the published data on toxicity against heavy metals and biocides are generated using unattached mussels. The data, therefore, represent an underestimation of the toxicity of the tested compound. Correction data are presented for chlorine tolerance of Dreissena polymorpha, Mytilopsis leucophaeata and Mytilus edulis. The present study suggests the importance of maintaining mussels in their attached status, while undertaking toxicity bioassays.  相似文献   

Modelling grain-size distributions. A comparison of two models and their numerical solution     

Taco den Bezemer  Henk Kooi  Jurjen Kranenborg  Sierd Cloetingh 《Tectonophysics》2000,320(3-4):347-373

Three main diffusion-based models are currently used to study grain-size distributions. In this paper, two of these approaches — perfect sorting and imperfect sorting — are compared in a parameter study. First, the numerical solution of the imperfect-sorting model is extensively discussed, and numerical tests are performed. Then, the two sedimentation models are compared for a basin under varying conditions. For some of the imposed variations, predictions of both models differ markedly due to the different approach. The position of the gravel front in the perfect sorting model depends on gravel input and proximal accommodation space. The position of grain-size boundaries in the imperfect-sorting model is strongly controlled by gravel input, the position of the basin axis and the difference in diffusivities. As a result, those two models may predict gravel progradation for different situations. Both models suggest that gravel progradation should always be coupled with sedimentation rates in order to suggest an explanation of gravel progradation observed in the geological record. Simulations with the imperfect sorting model show that this criterion may also fail, showing that a unique interpretation of gravel progradation may be impossible.  相似文献