Obduction triggered by regional heating during plate reorganization

The reason for obduction, or tectonic transport of oceanic lithosphere onto continents, is investigated by two‐dimensional thermo‐mechanical numerical modelling based on the geology of the Anatolia–Lesser Caucasus ophiolites. Heating of the oceanic domain and extension induced by far‐field plate kinematics appear to be essential for the obduction of ~80‐Ma‐old oceanic crust over distances exceeding 200 km. Heating of the oceanic lithosphere by mantle upwelling is evidenced by a thick alkaline volcanic series emplaced on top of the oceanic crust 10–20 Ma before obduction, at the onset of Africa–Eurasia convergence. Regional heating reduced the negative buoyancy and strength of the magmatically old lithosphere. Extension facilitated the propagation of obduction by reducing the mantle lithosphere thickness, which led to the exhumation of eclogite‐free continental crust previously underthrusted beneath the ophiolites. This extensional event is ascribed to far‐field plate kinematics resulting from renewed Neotethys oceanic subduction beneath Eurasia.     

How informative are stream level observations in different geographic regions?

Simple runoff models with a low number of model parameters are generally able to simulate catchment runoff reasonably well, but they rely on model calibration, which makes their use in ungauged basins challenging. In a previous study it has been shown that a limited number of streamflow measurements can be quite informative for constraining runoff models. In practice, however, instead of performing such repeated flow measurements, it might be easier to install a stream level logger. Here, a dataset of 600+ gauged basins in the USA was used to study how well models perform when only stream level data, rather than streamflow data, are available. A runoff model (the HBV model) was calibrated assuming that only stream level observations were available, and the simulations were evaluated on the full observed streamflow record. The results indicate that stream level data alone can already provide surprisingly good model simulation results in humid catchments, whereas in arid catchments some form of quantitative information (e.g. a streamflow observation or a regional average value) is needed to obtain good results. These results are encouraging for hydrological observations in data scarce regions as level observations are much easier to obtain than streamflow measurements. Based on runoff modelling, it might even be possible to derive streamflow time series from the level data obtained from loggers, satellites or community‐based approaches. Copyright © 2016 John Wiley & Sons, Ltd.     

Space-based aperture array for ultra-long wavelength radio astronomy

The past decade has seen the advent of various radio astronomy arrays, particularly for low-frequency observations below 100 MHz. These developments have been primarily driven by interesting and fundamental scientific questions, such as studying the dark ages and epoch of re-ionization, by detecting the highly red-shifted 21 cm line emission. However, Earth-based radio astronomy observations at frequencies below 30 MHz are severely restricted due to man-made interference, ionospheric distortion and almost complete non-transparency of the ionosphere below 10 MHz. Therefore, this narrow spectral band remains possibly the last unexplored frequency range in radio astronomy. A straightforward solution to study the universe at these frequencies is to deploy a space-based antenna array far away from Earths’ ionosphere. In the past, such space-based radio astronomy studies were principally limited by technology and computing resources, however current processing and communication trends indicate otherwise. Furthermore, successful space-based missions which mapped the sky in this frequency regime, such as the lunar orbiter RAE-2, were restricted by very poor spatial resolution. Recently concluded studies, such as DARIS (Disturbuted Aperture Array for Radio Astronomy In Space) have shown the ready feasibility of a 9 satellite constellation using off the shelf components. The aim of this article is to discuss the current trends and technologies towards the feasibility of a space-based aperture array for astronomical observations in the Ultra-Long Wavelength (ULW) regime of greater than 10 m i.e., below 30 MHz. We briefly present the achievable science cases, and discuss the system design for selected scenarios such as extra-galactic surveys. An extensive discussion is presented on various sub-systems of the potential satellite array, such as radio astronomical antenna design, the on-board signal processing, communication architectures and joint space-time estimation of the satellite network. In light of a scalable array and to avert single point of failure, we propose both centralized and distributed solutions for the ULW space-based array. We highlight the benefits of various deployment locations and summarize the technological challenges for future space-based radio arrays.     

Managing Bay and Estuarine Ecosystems for Multiple Services

Managers are moving from a model of managing individual sectors, human activities, or ecosystem services to an ecosystem-based management (EBM) approach which attempts to balance the range of services provided by ecosystems. Applying EBM is often difficult due to inherent tradeoffs in managing for different services. This challenge particularly holds for estuarine systems, which have been heavily altered in most regions and are often subject to intense management interventions. Estuarine managers can often choose among a range of management tactics to enhance a particular service; although some management actions will result in strong tradeoffs, others may enhance multiple services simultaneously. Management of estuarine ecosystems could be improved by distinguishing between optimal management actions for enhancing multiple services and those that have severe tradeoffs. This requires a framework that evaluates tradeoff scenarios and identifies management actions likely to benefit multiple services. We created a management action-services matrix as a first step towards assessing tradeoffs and providing managers with a decision support tool. We found that management actions that restored or enhanced natural vegetation (e.g., salt marsh and mangroves) and some shellfish (particularly oysters and oyster reef habitat) benefited multiple services. In contrast, management actions such as desalination, salt pond creation, sand mining, and large container shipping had large net negative effects on several of the other services considered in the matrix. Our framework provides resource managers a simple way to inform EBM decisions and can also be used as a first step in more sophisticated approaches that model service delivery.     

氮同位素研究城市湖泊沉积物有机质来源和迁移过程——以北京为例

城市湖泊是陆地水圈的重要组成部分,与人类活动关系极为密切。然而城市发展导致城市湖泊富营养化愈发严重,湖泊生态环境问题引起了广泛关注。本文研究了2012年至2013年间北京城区12个公园湖泊表层沉积物的有机氮同位素组成、碳氮比值、总有机氮和总有机碳含量的分布情况,探讨表层沉积物生产力状态、沉积物的有机质来源定性与定量分析、湖泊营养输入程度和过程等。研究表明,后海及群明湖等的有机碳、氮含量较其他公园湖泊的高,土壤和污水有机质等对湖泊沉积物的贡献突出,表明这些湖泊初级生产力及营养程度高,具有一定的富营养化风险;各个湖泊的分布位置、周围环境以及管理方式导致了其生产力、营养状况及有机质来源的差异,应该分别从控制水土流失、减少污水输入、及时清洁水面上的浮游植物与枯枝落叶等多方面着手进行,减少湖泊环境污染风险,保持湖泊环境生态平衡。本研究为了解城市湖泊环境有机质来源和过程、湖泊现代环境的管理和防治,提供可靠的研究方法和评价体系。