Saldanha Bay,South Africa II: estimating bay productivity

Saldanha Bay is a narrow-mouth bay on the west coast of South Africa linked to the southern Benguela upwelling system. Bay productivity was investigated by use of the conventional light-and-dark bottle oxygen method, and, for comparison, through assimilation of the stable isotope tracer ¹³C. Gross community production GCP and net community production NCP, as determined from the oxygen method, were respectively 2.6 and 2.4 times higher than estimates determined from the stable isotope method. Chlorophyll a (Chl a) concentrations increased with the onset of spring and well-defined subsurface maxima developed in association with increasingly stratified conditions (mean water column Chl a concentrations ranged from 5.4 to 31.5?mg m^?3 [mean 15.5?mg m^?3; SD 7.6]). A sharp decline in photosynthetic rates P* (GCP normalised to Chl a concentration) with depth was attributed to light limitation, as demonstrated by the high vertical attenuation coefficients for downward irradiance K_d, which varied from 0.29 to 0.70?m^?1 (mean 0.48?m^?1; SD 0.12). Productivity maxima were consequently near-surface despite the presence of deeper subsurface biomass maxima. The community compensation depth Z_cc, where gross community production balances respiratory carbon loss for the entire community, ranged from 2.9 to 9.2?m (mean 5.8?m; SD 2.2), and was typically shallower than the 1% light depth for PAR (photosynthetically available radiation), Z1%PAR, which is traditionally assumed to be the depth of the euphotic zone and which ranged from 6.6 to 15.9?m (mean 9?m; SD 2.6). Autotrophic communities, where organic matter is produced in excess of respiratory demand, were confined on average to the upper 5.8?m of the water column, and often excluded the bulk of the phytoplankton community, where light limitation is considered to lead to heterotrophic community metabolism. Estimates of integrated water column productivity ranged from 0.84 to 8.46?g C m–2 d^?1 (mean 3.35?g C m^?2 d^?1; SD 1.9).     

The last interglacial sea-level high stand on the southern Cape coastline of South Africa

The continental margin of southern South Africa exhibits an array of emergent marginal marine sediments permitting the reconstruction of long-term eustatic sea-level changes. We report a suite of optical luminescence ages and supplementary amino acid racemization data, which provide paleosea-level index points for three sites on this coastline. Deposits in the Swartvlei and Groot Brak estuaries display tidal inlet facies overlain by shoreface or eolian facies. Contemporary facies relations suggest a probable high stand 6.0-8.5 m above modern sea level (amsl). At Cape Agulhas, evidence of a past sea-level high stand comprises a gravel beach (ca. 3.8 m amsl) and an overlying sandy shoreface facies (up to 7.5 m amsl). OSL ages between 138 ± 7 ka and 118 ± 7 ka confirm a last interglacial age for all marginal marine facies. The high stand was followed by a sea-level regression that was associated with the accumulation of eolian dunes dating to between 122 ± 7 ka and 113 ± 6 ka. These data provide the first rigorous numerical age constraints for last interglacial sea-level fluctuations in this region, revealing the timing and elevation of the last interglacial high stand to broadly mirror a number of other far-field locations.     

Gold mineralisation throughout about 45 Ma of Archaean orogenesis: protracted flux of gold in the Golden Mile, Yilgarn craton, Western Australia

The Golden Mile deposit was discovered in 1893 and represents today the largest Archaean orogenic lode gold system in the world (50 M oz produced gold). The Golden Mile deposit comprises three major styles of gold mineralisation: Fimiston, Oroya and Charlotte styles. Fimiston-style lodes formed at 250 to 350 °C and 100 to 200 MPa and are controlled by brittle–ductile fault zones, their subsidiary fault zone and vein networks including breccias and open-cavity-infill textures and hydrothermally altered wall rock. Fimiston lodes were formed late D₁, prior to D₂ regional upright folding. Hydrothermal alteration haloes comprise a progression toward the lode of diminishing chlorite, an increase in sericite and in Fe content of carbonates. Lodes contain siderite, pyrite, native gold, 17 different telluride minerals (Au–Ag tellurides contain ~25% of total gold), tourmaline, haematite, sericite and V-rich muscovite. Oroya-style lodes formed at similar P–T conditions as the Fimiston lodes and are controlled by brittle–ductile shear zones, associated dilational jogs that are particularly well developed at the contact between Paringa Basalt and black shale interflow sedimentary rocks and altered wall rock. The orebodies are characterised by micro-breccias and zones of intense shear zone foliation, very high gold grades (up to 100,000 g/t Au) and the common association of tellurides and vanadian mica (green leader). Oroya lodes crosscut Fimiston lodes and are interpreted to have formed slightly later than Fimiston lodes as part of one evolving hydrothermal system spanning D₁ and D₂ deformation (ca. 2,675–2,660 Ma). Charlotte-style lodes, exemplified by the Mt Charlotte deposit, are controlled by a sheeted vein (stockwork) complex of north-dipping quartz veins and hydrothermally altered wall rock. The Mt Charlotte orebody formed at 120 to 440 °C and 150 to 250 MPa during movement along closely spaced D₄ (2,625 Ma) and reactivated D₂ faults with the quartz granophyre in the Golden Mile Dolerite exerting a strong lithological control on gold mineralisation. Veins consist of quartz–carbonate–minor scheelite, and wall-rock alteration comprises chlorite destruction and growth of ferroan carbonate–sericite–pyrite–native gold. Pyrite–pyrrhotite is zoned on the scale of vein haloes and of the entire mine, giving a vertical temperature gradient of 50–100 °C over 1,000 vertical metres. The structural–hydrothermal model proposed consists of four major stages: (1) D₁ thrusting and formation of Fimiston-style lodes, (2) D₂ reverse faulting and formation of Oroya-style lodes, (3) D₃ faulting and dissecting of Fimiston- and Oroya-style lodes, and (4) D₄ faulting and formation of Mt Charlotte-style sheeted quartz vein system. The giant accumulation of gold in the Golden Mile deposit was formed due to protracted gold mineralisation throughout episodes of an Archaean orogeny that spanned about 45 Ma. Fluid conduits formed early in the tectonic history and persisted throughout orogenesis with the plumbing system showing a rare high degree of focussing, efficiency and duration. In addition to the long-lasting fluid plumbing system, the wide variety of transient structural and geochemical traps, multiple fluid sources and precipitation mechanism contributed towards the richest golden mile in the world.Editorial handling: B. Lehmann     

Towards an integrated environmental assessment for wetland and catchment management

This paper develops a decision support system for evaluation of wetland ecosystem management strategy and examines its, so far partial, application in a case study of an important complex coastal wetland known as the Norfolk and Suffolk Broads, in the east of England, UK. Most managed ecosystems are complex and often poorly understood hierarchically organized systems. Capturing the range of relevant impacts on natural and human systems under different management options will be a formidable challenge. Biodiversity has a hierarchical structure which ranges from the ecosystem and landscape level, through the community level and down to the population and genetic level. There is a need to develop methodologies for the practicable detection of ecosystem change, as well as the evaluation of different ecological functions. What is also required is a set of indicators (environmental, social and economic) which facilitate the detection of change in ecosystems suffering stress and shock and highlight possible drivers of the change process. A hierarchical classification of ecological indicators of sustainability would need to take into account existing interactions between different organization levels, from species to ecosystems. Effects of environmental stress are expressed in different ways at different levels of biological organization and effects at one level can be expected to impact other levels, often in unpredictable ways. The management strategy, evaluation methodologies and indicators adopted should also assess on sustainability grounds whether any given management option is supporting, or reducing, the diversity of functions which are providing stakeholders with the welfare benefits they require.     

Mega-blowouts in Qinghai–Tibet Plateau: Morphology,distribution and initiation

Blowouts are wind-eroded landforms that are widely distributed in the north-eastern part in Qinghai–Tibet Plateau (QTP), China. These blowouts are thought to form in response to climate change and/or human activity but little is known about their morphodynamics. Using field surveys, remote sensing and geographic information system (GIS) spatial analysis, the distribution and morphology of blowouts are analysed and their initiation considered. Results show the QTP mega-blowouts are some of the largest in the world. The orientations of the trough shaped blowouts are parallel with the prevailing wind, but the saucer and bowl-shaped blowouts are influenced by bi-directional transport. Whilst regional patterns of blowout shape and size were observed to reflect the extent of aeolian sediments and wind regimes, the relationship between the different morphological parameters showed consistency. During initial stages of development, the length to width ratios of blowouts increase rapidly with area but after they reach a mega size this relationship stabilizes as blowouts widen. Initial luminescence dating shows that blowouts appear to have initiated ~100 to 500 years ago, coinciding with the Little Ice Age (LIA) climate event when northwest winds are known to have intensified. Further work is required to confirm this initiation period and establish the significance of mega blowouts for landscape degradation and human activities. © 2018 John Wiley & Sons, Ltd.     

重建地方：人文地理与GIS结合研究的路径

地方是很重要的地理学概念。中外学界对地方的研究有丰富积累。围绕地方的理论与现实问题,探索人文地理与GIS结合研究的路径和方法对中国地理学尤为重要。“重建地方”旨在打破学科界限,重新发现学术研究的“地方”,并将学术与生活、思想与技术紧密结合起来,反思和重建生活中的“地方”。人文地理与GIS结合研究主要聚焦于流动性的大尺度城市空间与稳定性的小尺度社区空间。通过运用开放的街景地图、3D-VQGIS等新GIS工具和方法,整合大数据与小数据,将定量与定性结合,丰富了地方性研究的方法与理论,使人文地理与GIS结合有新的方法论与可操作的手段。以地方为主题,人文地理与GIS的结合还将重塑这2个子学科,进而促进地理学发展。未来应该大力探索人文地理与GIS结合的思想、理论与方法,实现学科内的交融互动,并将其应用于解释尺度交错的现实问题,进而在理论和实践上重建地方。     

基于共享度的上海郊区社区居民活动空间隔离及其影响因素

在流动性不断增强与居民活动模式日益多样化的背景下,城市社会空间分异与隔离的内涵不断扩展,居民在日常生活中面临的空间隔离受到关注。以活动空间为基础的社会空间分异研究快速兴起,以期从更加动态的视角理解城市社会空间。基于上海市郊区问卷调查数据,构建活动空间共享度指标,建立个体尺度的活动空间分异指数和孤立指数,刻画社区内不同收入群体的活动空间隔离状况,并建立活动空间共享度的多层模型分析活动空间隔离的影响因素。研究发现居住在同一社区的不同收入居民之间存在活动空间隔离,居民更愿意与其社会经济属性相似的人共享活动空间。活动空间隔离程度受到个体社会经济属性、社区设施状况、社区周边环境、社区人口密度和社会混合程度等因素的影响,居住在人口密度高、社会混合度高、社区商业配置良好、公共空间充足的开放社区能提高居民的活动空间共享度,增加不同群体社会接触的可能性。     

Developing a 150 ka luminescence chronology for the barrier dunes of the southern Cape, South Africa

The southern coastline of South Africa exhibits extensive aeolianites and spectacular barrier dunes; the ages and palaeoenvironmental significance of which have, until recently, received limited attention. We present preliminary results for samples taken from a single 6.5 m section in the seaward barrier dune near to the town of Wilderness. The reliability of these ages has been investigated using a series of dose recovery and pulsed irradiation experiments, as well as through analyses of single aliquot and single grain D_e distributions. Results indicate that the SAR protocol is providing accurate and precise D_e determinations and that adequate sensitivity correction is being made. The application of pulsed irradiations does not result in significant changes in the dose–response curves or averaged D_e's. Single grain D_e distributions are broad, with significant levels of overdispersion, which may reflect beta dose heterogeneity effects.

Peaks in aeolian activity date to 157–154 and 140–125 ka, with a slower rate of deposition recorded from 115 to 85 ka. Brief phases at 40 and 21 ka are also identified. Some ages, notably those from OIS 3 and OIS 2, are surprising from a geomorphological perspective, given the likely distance of the dune from the shoreline at such times, although they are not inconsistent with evidence from the east coast of South Africa. The results reveal multiple phases of Late Quaternary barrier dune accumulation, and suggest that aeolian activity in this region has been episodic and potentially more complex than previously thought.     

Debris-flow susceptibility analysis using fluvio-morphological parameters and data mining: application to the Central-Eastern Pyrenees

Based on debris-flow inventories and using a geographical information system, the susceptibility models presented here take into account fluvio-morphologic parameters, gathered for every first-order catchment. Data mining techniques on the morphometric parameters are used, to work out and test three different models. The first model is a logistic regression analysis based on weighting the parameters. The other two are classification trees, which are rather novel susceptibility models. These techniques enable gathering the necessary data to evaluate the performance of the models tested, with and without optimization. The analysis was performed in the Catalan Pyrenees and covered an area of more than 4,000 km². Results related to the training dataset show that the optimized models performance lie within former reported range, in terms of AUC, although closer to the lowest end (near 70 %). When the models are applied to the test set, the quality of most results decreases. However, out of the three different models, logistic regression seems to offer the best prediction, as training and test sets results are very similar, in terms of performance. Trees are better at extracting laws from a training set, but validation through a test set gives results unacceptable for a prediction at regional scale. Although omitting parameters in geology or vegetation, fluvio-morphologic models based on data mining, can be used in the framework of a regional debris-flow susceptibility assessment in areas where only a digital elevation model is available.     

近地表速度结构的地脉动探测方法国际盲比检验

本文通过参加ESG2006组织的国际地脉动盲比测验,检验了利用地脉动方法探测近地表速度结构的精度和可信度.在对多个不同测试模型频散曲线的提取精度、速度结构平均速度相对偏差和场地放大效应估计等方面的比较中,本文方法在参加盲比测验的19个国际研究组中均处于前列.同时盲比测验结果表明,不论人工合成记录还是实际观测记录、速度还是加速度记录,地脉动空间自相关方法得到的场地瑞利波频散曲线,均能够为后续反演研究提供可靠的目标曲线;可以根据仪器实际情况自由选择观测加速度或速度.人工合成数据分析中,有两例频散曲线受到了高阶振型影响,在实际观测数据中影响不明显.结合盲比测验结果指出,空间自相关方法的最大可探测波长一般达不到通常认为的15.7倍的最大半径,大多情况小于10倍;而最小波长要小于2倍的最小半径,可以到1倍的最小半径.