High-frequency Earth rotation variations deduced from altimetry-based ocean tides     

Matthias Madzak  Michael Schindelegger  Johannes Böhm  Wolfgang Bosch  Jan Hagedoorn 《Journal of Geodesy》2016,90(11):1237-1253

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Disaster risk profiling in southern Africa: inventories,impacts and implications     

Jan de Waal  Coleen Vogel 《Natural Hazards》2016,84(3):1921-1942

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Identification of Greigite in the Pliocene Sediments of Qinghai Lake and Its Geological Significance     

FU Chaofeng  Jan BLOEMENDAL  QIANG Xiaoke  Mimi J. HILL  AN Zhisheng 《《地质学报》英文版》2016,90(6):2261-2262

正Objective The Qinghai Lake in North China is the largest interior plateau lake in Central Asia,and is sensitive to climate change and the environmental effects of Tibetan Plateau uplift.An almost continuous 626 m long sediment core was drilled in an in-filled part of the southern lake basin in the Scientific Drilling at Qinghai Lake.Previous  相似文献   

Ocean currents determine functional connectivity in an Antarctic deep‐sea shrimp          下载免费PDF全文

Johannes Dambach  Michael J. Raupach  Florian Leese  Julia Schwarzer  Jan O. Engler 《Marine Ecology》2016,37(6):1336-1344

The coherency among larval stages of marine taxa, ocean currents and population connectivity is still subject to discussion. A common view is that organisms with pelagic larval stages have higher dispersal abilities and therefore show a relatively homogeneous population genetic structure. Contrary to this, local genetic differentiation is assumed for many benthic direct developers. Specific larval or adult migratory behavior and hydrographic effects may significantly influence distribution patterns, rather than passive drifting abilities alone. The Southern Ocean is an ideal environment to test for the effects of ocean currents on population connectivity as it is characterized by several well‐defined and strong isolating current systems. In this study we studied the genetic structure of the decapod deep‐sea shrimp Nematocarcinus lanceopes, which has planktotrophic larval stages. We analysed 194 individuals from different sample localities around the Antarctic continent using nine microsatellite markers. Consistent with a previous study based on mitochondrial DNA markers, primarily weak genetic patterns among N. lanceopes populations around the continent were found. Using ocean resistance modeling approaches we were able to show that subtle genetic differences among populations are more likely explained by ocean currents rather than by geographic distance for the Atlantic Sector of the Southern Ocean.  相似文献   

Seasonal variations in the nitrogen isotopic composition of settling particles at station K2 in the western subarctic North Pacific     

Yoshihisa?MinoEmail author  Chiho?Sukigara  Makio?C.?Honda  Hajime?Kawakami  Kazuhiko?Matsumoto  Masahide?Wakita  Minoru?Kitamura  Tetsuichi?Fujiki  Kosei?Sasaoka  Osamu?Abe  Jan?Kaiser  Toshiro?Saino 《Journal of Oceanography》2016,72(6):819-836

Intensive observations using hydrographical cruises and moored sediment trap deployments during 2010 and 2012 at station K2 in the North Pacific Western Subarctic Gyre (WSG) revealed seasonal changes in δ ¹⁵N of both suspended and settling particles. Suspended particles (SUS) were collected from depths between the surface and 200 m; settling particles by drifting sediment traps (DST; 100–200 m) and moored sediment traps (MST; 200 and 500 m). All particles showed higher δ ¹⁵N values in winter and lower in summer, contrary to the expected by isotopic fractionation during phytoplankton nitrate consumption. We suggest that these observed isotopic patterns are due to ammonium consumption via light-controlled nitrification, which could induce variations in δ ¹⁵N(SUS) of 0.4–3.1 ‰ in the euphotic zone (EZ). The δ ¹⁵N(SUS) signature was reflected by δ ¹⁵N(DST) despite modifications during biogenic transformation from suspended particles in the EZ. δ ¹⁵N enrichment (average: 3.6 ‰) and the increase in C:N ratio (by 1.6) in settling particles suggests year-round contributions of metabolites from herbivorous zooplankton as well as TEPs produced by diatoms. Accordingly, seasonal δ ¹⁵N(DST) variations of 2.4–7.0 ‰ showed a significant correlation with primary productivity (PP) at K2. By applying the observed δ ¹⁵N(DST) vs. PP regression to δ ¹⁵N(MST) of 1.9–8.0 ‰, we constructed the first annual time-series of PP changes in the WSG. This new approach to estimate productivity can be a powerful tool for further understanding of the biological pump in the WSG, even though its validity needs to be examined carefully.  相似文献   

Cutting of Phragmites australis as a lake restoration technique: Productivity calculation and nutrient removal in Wuliangsuhai Lake, northern China     

Jan Felix K&#;bbing  Niels Thevs  Stefan Zerbe 《寒旱区科学》2016,8(5):400-410

Reed is one of the most frequent and dominant species in wetlands all over the world, with common reed (Phragmites australis (Cav.) Trin. ex Steud.) as the most widely distributed species. In many wetlands, P. australis plays a highly ambivalent role. On the one hand, in many wetlands it purifies wastewater, provides habitat for numerous species, and is a potentially valuable raw material, while on the other hand it is an invasive species which expands aggressively, prevents fishing, blocks ditches and waterways, and builds monospecies stands. This paper uses the eutrophic reed-swamp of Wuliangsuhai Lake in Inner Mongolia, northern China, as a case to present the multiple benefits of regular reed cutting. The reed area and aboveground biomass production are calculated based on field data. Combined with data about water and reed nutrient content, the impact of reed cutting on the lake nutrient budget (N and P) is investigated. Currently, at this lake around 100,000 tons of reed are harvested in winter annually, removing 16% and 8% of the total nitrogen and phosphorus influx, respectively. Harvesting all available winter reed could increase the nutrient removal rates to 48% and 24%, respectively. We also consider the effects of summer harvesting, in which reed biomass removal could overcompensate for the nutrient influx but could potentially reduce reed regrowth.  相似文献   

Allocation of degraded hillsides to landless farmers and improved livelihoods in Tigray,Ethiopia     

Hailemariam Meaza  Diress Tsegaye  Jan Nyssen 《Norsk geografisk tidsskrift. Norwegian journal of geography》2016,70(1):1-12

In the northern highlands of Ethiopia degraded hillsides have been allocated to landless farmers for tree planting since the mid-1990s. The authors assessed the effect of hillside plantations on the livelihoods of landless farmers in the eastern part of the Tigray Region by using transect walks, focus group discussions, and pretested questionnaires. A matched-pairs design was used to compare crop yields, livestock holdings per household, and household incomes to test the differences before and eight years after the intervention. In addition, regression analysis was used to capture variables influencing hillside management. The findings revealed that the plantations significantly increased crop yields, livestock holdings, and the household incomes of all beneficiaries. In addition, tree planting on degraded hillsides had a positive impact on the livelihoods of formerly landless farmers. However, moisture stress and free-ranging livestock were crucial problems. The findings are highly relevant in a conservation context because many existing or planned hillside allocations to landless farmers are located on degraded steep slopes that are unsuitable for crop production. Thus, replicating the practice to other areas with similar environment and problems would be worthwhile, although the management should focus on careful planning to avoid conflicts of interest between beneficiaries and non-beneficiaries.  相似文献   

Investigation about rainfall-induced shallow landslides in CYL and TWR watersheds,Taiwan     

Chyan-Deng Jan  Ssu-Yao Yang  Yu-Wen Su  Wen-Shun Haung 《Environmental Earth Sciences》2016,75(10):898

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Comparison between cell-centered and nodal-based discretization schemes for linear elasticity     

Halvor M. Nilsen  Jan Nordbotten  Xavier Raynaud 《Computational Geosciences》2018,22(1):233-260

In this paper, we study newly developed methods for linear elasticity on polyhedral meshes. Our emphasis is on applications of the methods to geological models. Models of subsurface, and in particular sedimentary rocks, naturally lead to general polyhedral meshes. Numerical methods which can directly handle such representation are highly desirable. Many of the numerical challenges in simulation of subsurface applications come from the lack of robustness and accuracy of numerical methods in the case of highly distorted grids. In this paper, we investigate and compare the Multi-Point Stress Approximation (MPSA) and the Virtual Element Method (VEM) with regard to grid features that are frequently seen in geological models and likely to lead to a lack of accuracy of the methods. In particular, we look at how the methods perform near the incompressible limit. This work shows that both methods are promising for flexible modeling of subsurface mechanics.  相似文献   

Computing derivative information of sequentially coupled subsurface models     

Rafael J. de Moraes  José R. P. Rodrigues  Hadi Hajibeygi  Jan Dirk Jansen 《Computational Geosciences》2018,22(6):1527-1541

A generic framework for the computation of derivative information required for gradient-based optimization using sequentially coupled subsurface simulation models is presented. The proposed approach allows for the computation of any derivative information with no modification of the mathematical framework. It only requires the forward model Jacobians and the objective function to be appropriately defined. The flexibility of the framework is demonstrated by its application in different reservoir management studies. The performance of the gradient computation strategy is demonstrated in a synthetic water-flooding model, where the forward model is constructed based on a sequentially coupled flow-transport system. The methodology is illustrated for a synthetic model, with different types of applications of data assimilation and life-cycle optimization. Results are compared with the classical fully coupled (FIM) forward simulation. Based on the presented numerical examples, it is demonstrated how, without any modifications of the basic framework, the solution of gradient-based optimization models can be obtained for any given set of coupled equations. The sequential derivative computation methods deliver similar results compared to FIM methods, while being computationally more efficient.  相似文献