Profile response of a lacustrine multiple barred nearshore to a sequence of storm events

Profile change in a lacustrine multiple-barred nearshore was investigated over the ice-free season of 2001/2002 at Burley Beach on the southeastern shore of Lake Huron in order to identify the feedback mechanisms between the pre-existing morphology and the wave forcing and the consequence of those feedbacks to the behaviour of the nearshore environment. The characteristics of the offshore wave field were monitored using a Falmouth Scientific combined 3D-ACM wave recorder and pressure transducer. Supplemental wave data were downloaded from a 3-m discus buoy operated by the National Data Buoy Center, 75 km to the NW of the study site. The three nearshore bars were in a quasi-equilibrium state through a large part of the ice-free season, with dramatic changes occurring during relatively moderate storm events that followed much larger storms in late October. A comparison of the incident wave field with changes in the nearshore profile through canonical correlation analysis indicates that the morphology responds to the distribution of the significant, root-mean-square (rms) and average wave heights between surveys. The threshold between bar decay and onshore bar migration and growth is associated with the onset of breaking of the rms wave at the bar crest (H_rms h_cr⁻¹ ≈0.3–0.4). The threshold between onshore and offshore migration is associated with the onset of breaking of the average wave at the bar crest (H_avg h_cr⁻¹ ≈0.3–0.4), coincident with complete dissipation of the significant wave over the lakeward slope of the bar (H_s h_cr⁻¹ >0.6). Inshore wave data collected during an instrumented study at the same site revealed that the middle and inner bars remained at the threshold of onshore and offshore migration over a wide range of offshore significant wave heights (0.8 to 2.4 m) prior to the October storms. This self-organised equilibrium is a result of changes to the incident wave distribution through breaking on the outer bar. It is concluded that the prediction of bar response requires an understanding of the feedback between the bar and the local wave distribution in addition to an understanding of the feedback associated with the profile as a whole.     

Inference of past climate from borehole temperature data using Bayesian Reversible Jump Markov chain Monte Carlo

Estimates of past climate derived from borehole temperatures are assuming a greater importance in context of the millennial temperature variation debate. However, recovery of these signals is usually performed with regularization which can potentially lead to underestimation of past variation when noise is present. In this work Bayesian inference is applied to this problem with no explicit regularization. To achieve this Reversible Jump Markov chain Monte Carlo is employed, and this allows models of varying complexity (i.e. variable dimensions) to be sampled so that it is possible to infer the level of ground surface temperature (GST) history resolution appropriate to the data. Using synthetic examples, we show that the inference of the GST signal back to more than 500 yr is robust given boreholes of 500 m depth and moderate noise levels and discuss the associated uncertainties. We compare the prior information we have used with the inferred posterior distribution to show which parts of the GST reconstructions are independent of this prior information. We demonstrate the application of the method to real data using five boreholes from southern England. These are modelled both individually and jointly, and appear to indicate a spatial trend of warming over 500 yr across the south of the country.     

Realizing the Literate Traveller

A current research project is addressing the problem of finding appropriate geographical information by developing a (geo)information realization resource based upon the concepts of the Literate Traveller. It has as its main goal to provide tools for geographical knowledge building and exploration, by providing conventional spatial information plus geographical interpretation and appreciation artifacts. These artifacts are delivered in an interactive multimedia environment. This research examines the formulation of an initial prototype component to assist in providing geographical knowledge. The prototype is based on a study site in Townsville, Australia, and is being used as a vehicle to explore enhanced spatial information provision through the use of rich media. The research examines new ways to prospect for, discover and disseminate spatial knowledge within an intelligence‐briefing context. The paper reports on the concepts behind the design of the application developed for the test site, and presents initial findings from the early evaluation of the prototype.     

On 50th Anniversary of the Global Carbon Dioxide Record

The 50-year global CO₂ record led the way in establishing a scientific fact: modern civilization is changing important properties of the global atmosphere, oceans and biosphere. The evidence on which this scientific fact is based will be refined further, but the next challenge for scientists is broader. In addition to its traditional role in providing discovery, diagnosis, and prediction of the changes that are taking place on our planet, science has now also a role in helping society mitigate emissions by objectively quantifying them, and in helping adaptation by providing environmental forecasts on regional scales. Science is also expected to provide new options for society to tackle the transition to a new energy system, and to provide thorough environmental evaluation of all such options. This is what the meeting recognized as planetary responsibilities for scientists in the next 50 years.     

紫硫镍矿交代镍黄铁矿的水热反应机理及动力学

本工作首次在实验室条件下对浅生区紫硫镍矿(Ni,Fe)3S4交代镍黄铁矿(Ni,Fe)9S8水热反应的机理及动力学进行了研究。起始反应矿物采用高纯自然镍黄铁矿,合成纯镍黄铁矿或合成镍黄铁矿-磁黄铁矿集合体。反应pH值采用0.2M醋酸-醋酸纳缓冲溶液控制在3～5的范围内。反应进程由X-射线衍射物相定量分析及扫描电镜观察进行跟踪。结果表明,当反应温度恒定在80℃时,交代20(4)%的镍黄铁矿需792h。相同条件下加入少量H2S可将反应速率提高一倍。当反应在125℃饱和蒸汽压水热环境下进行时,完全交代纯镍黄铁矿需约168h。此过程由于磁黄铁矿的存在而被催化,交代集合体中的镍黄铁矿仅需68h,进一步反应磁黄铁矿被交代成白铁矿。磁黄铁矿的催化作用可能源于溶解产生的微裂纹加速了流体的传质过程。当反应温度升高至145℃时,速率反而下降,不遵循Arrhenius经验规律。动力学分析得80℃速率常数介于5.8×10-8～3.0×10-7/s之间,125℃及145℃速率常数分别介于2.8×10-6～2.08×10-5/s及1×10-6～5.1×10-6/s之间,远高于同温度下固相扩散反应的速率常数,表明该反应在地质时标上为一快速反应。此外,用背散射电子显微技术对矿物表面形貌进行了分析,发现交代产物紫硫镍矿具有颗粒细小及存在微裂纹等特征,与自然界浅生矿床中的紫硫镍矿非常相似;电镜实验还表明该交代作用是一个典型的耦合溶解-再沉淀反应。其耦合机制的驱动力可能与反应界面处微空隙对流体饱和度的控制有关。     

Assessing the vulnerability of food crop systems in Africa to climate change

Africa is thought to be the region most vulnerable to the impacts of climate variability and change. Agriculture plays a dominant role in supporting rural livelihoods and economic growth over most of Africa. Three aspects of the vulnerability of food crop systems to climate change in Africa are discussed: the assessment of the sensitivity of crops to variability in climate, the adaptive capacity of farmers, and the role of institutions in adapting to climate change. The magnitude of projected impacts of climate change on food crops in Africa varies widely among different studies. These differences arise from the variety of climate and crop models used, and the different techniques used to match the scale of climate model output to that needed by crop models. Most studies show a negative impact of climate change on crop productivity in Africa. Farmers have proved highly adaptable in the past to short- and long-term variations in climate and in their environment. Key to the ability of farmers to adapt to climate variability and change will be access to relevant knowledge and information. It is important that governments put in place institutional and macro-economic conditions that support and facilitate adaptation and resilience to climate change at local, national and transnational level.     

Full-scale structural monitoring using an integrated GPS and accelerometer system

Accurate in situ measurement of the full-scale structural responses, especially tall buildings, under severe loading conditions is an important requirement for validating their design, evaluating their construction as well as facilitating their maintenance. Traditionally such response has been measured using accelerometers. However, it is impossible to measure the static and quasi-static components of motion with acceleration sensors. An integrated system comprising of RTK-GPS and accelerometers has been developed with the objective of assessing full-scale structural responses by exploiting the complementary characteristics of GPS and accelerometer sensors. The data used in this paper were obtained from GPS and accelerometer sensors installed on a 108-m-high steel tower in Tokyo, together with other sensors such as anemometer and strain gauge. The seismic and wind-induced responses of the tower were analyzed using the Fast Fourier Transformation (FFT) and compared to results from finite element modeling (FEM). In order to study the system reliability, the correlated signals were extracted by applying a digital filtering technique. Then the filtered data sets were converted to displacement (in the case of accelerometer data) and acceleration (in the case of GPS data) through double integration and double differentiation, respectively, for the purpose of direct comparison and to further fuse data from the two different sensors. The results agree with each other very well, although the static and quasi-static components are missing from the accelerometer-derived results. The redundancy of the monitoring system therefore has been achieved.