Adsorbed silica in stalagmite carbonate and its relationship to past rainfall

Despite considerable work on other trace elements, the incorporation of dissolved silicon from cave waters into speleothems has not been previously investigated. In this study, the controls on dissolved Si in cave waters and on adsorbed Si in resulting speleothems are therefore investigated. Bedrock (dolomite), soil water, dripping water, and cave carbonates were retrieved from Heshang Cave situated in the central Yangtze valley of China and were subjected to analysis of dissolved Si content (plus accompanying Ca and Fe analyses). Soil waters have Si/Ca of 45.5 mmol/mol, compared to only 3.2 mmol/mol in the dolomite bedrock, demonstrating that >80% of the dissolved Si must come from dissolution of silicate minerals in the soil. Drip waters have a dissolved Si concentration of ≈4.2 μg/mL, similar to that in the overlying soil water. Actively growing cave carbonates have a Si/Ca of 0.075 mmol/mol suggesting a partition coefficient for incorporation of dissolved silicon of 0.0014, in good agreement with previous laboratory studies. Extrapolating the results of these laboratory studies to the cave environment suggests that changes in Si/Ca in cave carbonates are likely to be primarily controlled by changes in drip-water Si/Ca. The drip-water Si/Ca will, in turn, be controlled by the rate of wind-blown silicate supply; by soil weathering rates; by rainfall dilution; and by precipitation of calcite. The general expectation is that these effects combine to produce high Si/Ca in speleothems during times of low rainfall. A δ¹⁸O record from a Heshang Cave stalagmite which grew between 20 and 11 thousand years ago allows these controls to be tested. Correlation of high Si/Ca with high δ¹⁸O demonstrates that regional rainfall exerts significant (but not complete) control on speleothem Si/Ca. With further understanding, speleothem Si/Ca may provide a proxy for past rainfall to complement existing proxies such as δ¹⁸O and Mg/Ca.     

北冰洋海冰和海水变异对海洋生态系统的潜在影响

最近30年来,北冰洋海冰和海水发生了急剧变化:海冰覆盖面积减少、冰层变薄、水温升高、淡水输入增加、污染加剧,正威胁着现有与海冰关系密切的生态系统。预期随着变化的持续,与海冰相关的食物链将在部分海域消失并被较低纬度的海洋物种所取代、总初级生产力有望增加并为人类带来更多的渔获量、而北极熊和海象等以海冰作为栖息和捕食场所的大型哺乳动物的生存前景堪忧。今后人类将更为重视对北冰洋生态环境变化规律的认识并加以运用、关注北冰洋特有物种的命运并加以力所能及的保护、评估北冰洋生态系统的变化对人类社会经济的影响以期及早采取应对措施。数据积累是目前制约北极研究的最大障碍,但随着 SEARCH 等大型国际研究计划的实施,对北冰洋生态系统的监测和研究将更为系统和全面。     

Distinguishing streamflow trends caused by changes in climate,forest cover,and permafrost in a large watershed in northeastern China

Understanding how rivers respond to changes in land cover, climate, and subsurface conditions is critical for sustainably managing water resources and ecosystems. In this study, long‐term hydrologic, climate, and satellite data (1973–2012) from the Upper Tahe River watershed (2359 km²) in the Da Hinggan Mountains of northeast China were analysed to quantify the relative hydrologic effects of climate variability (system input) and the combined influences of forest cover change and permafrost thaw (system characteristics) on average annual streamflow (system response) using 2 methods: the sensitivity‐based method and the Kendall–Theil robust line method. The study period was subdivided into a forest harvesting period (1973–1987), a forest stability period (1988–2001), and a forest recovery period (2002–2012). The results indicated that the combined effects of forest harvesting and permafrost thaw on streamflow (+ 47.0 mm) from the forest harvesting period to the forest stability period was approximately twice as large as the effect associated with climate variability (+20.2 mm). Similarly, from the forest stability period to the forest recovery period, the decrease in average annual streamflow attributed to the combined effects of forest recovery and permafrost thaw (?38.0 mm) was much greater than the decrease due to climate variability (?22.2 mm). A simple method was used to separate the distinct impacts of forest cover change and permafrost thaw, but distinguishing these influences is difficult due to changes in surface and subsurface hydrologic connectivity associated with permafrost thaw. The results highlight the need to consider multiple streamflow drivers in future watershed and aquatic ecosystem management. Due to the ecological and hydrological susceptibility to disturbances in the Da Hinggan Mountains, forest harvesting will likely negatively impact ecohydrological processes in this region, and the effects of forest species transition in the forest recovery process should be further investigated.     

Discharge‐sediment processes of the Zhadang glacier on the Tibetan Plateau measured with a high frequency data acquisition system

In high elevation cold regions of the Tibetan Plateau, suspended sediment transfer from glacier meltwater erosion is one of the important hydrological components. The Zhadang glacier is a typical valley‐type glacier in the Nyainqentanglha Mountains on the Tibetan Plateau. To make frequent and long period records of meltwater runoff and sediment processes in the very high elevation and isolated regions, an automatic system was installed near the glacier snout (5400 m a.s.l) in August 2013, to measure the transient discharge and sediment processes at 5‐min interval, which is shorter than the time span for the water flow to traverse the catchment from the farthest end to the watershed outlet. Diurnal variations of discharge, and suspended sediment concentration (SSC) were recorded at high frequency for the Zhadang glacier, before suspended sediment load (SSL) was computed. Hourly SSC varied from the range of 0.2 kg/m³ to 0.5 kg/m³ (at 8:00–9:00) to the range of 2.0 kg/m³ to 4.0 kg/m³ (at 17:00–18:00). The daily SSL was 32.24 t during the intense ablation period. Hourly SSC was linearly correlated with discharge (r = 0.885**, n = 18, p < 0.01). A digit‐eight hysteresis loop was observed for the sediment transport in the glacier area. Air temperature fluctuations influence discharge, and then result in the sediment variations. The results of this study provide insight into the responses of suspended sediment delivery processes with a high frequency data in the high elevation cold regions. Copyright © 2016 John Wiley & Sons, Ltd.     

三维古构造恢复技术在油气评价中的应用——以珠江口盆地番禺-流花地区为例

目前常用的古构造图的制作方法为"厚度图法"和"断层平移法",这两种方法对断控圈闭为主的古构造恢复具有一定的局限性,且不能定量化的研究古构造生长发育情况。本论文首次将三维古构造恢复技术应用于珠江口盆地番禺-流花地区。三维古构造恢复技术在应用时,避免了厚度异常现象,实现了去压实恢复,能够更真实的反映古构造情况。该技术在珠江口盆地番禺流花地区"A"构造的应用,达到了定量分析古构造发育的效果,并且认识到了A构造在关键时期T32时期古构造幅度较小,后期构造幅度增大是A构造充满度过低的重要原因之一。     

Identification of forcing mechanisms of convective initiation over mountains through high-resolution numerical simulations

正Convection and its ensuing severe weather,such as heavy rainfall,hail,tornado,and high wind,have significant impacts on our society and economy(e.g.,Cao et al.,2004;Fritsch and Carbone,2004;Verbout et al.,2006;Ashley and Black,2008;Cao,2008;Cao and Ma,2009;Zhang et al.,2014).Due to its localized and transient nature,the initiation of convection or convective initiation remains one of the least     

1960-2014年湖南省极端气温事件变化特征分析

利用1960-2014年湖南省88个地面气象站日最高和最低气温的均一化资料,运用百分位阈值法统计暖日、暖夜、冷日和冷夜数,采用线性回归、M-K突变检验、Morlet小波分析等方法,研究湖南省55a以来极端气温事件的时空变化特征。结果表明：(1)湖南省暖日和暖夜数呈上升趋势,其年际变化倾向率分别为0.68d.(10a)-1、2.73 d.(10a)-1,冷日和冷夜数呈下降趋势,其年际变化倾向率分别为-0.45d.(10a)-1、-2.46d.(10a)-1,夜间增暖幅度大于白天增暖幅度;(2)湖南省大部分地区的暖日、暖夜数呈上升趋势,冷日数、冷夜数呈下降趋势,其中湘北、湘南部分地区变化趋势明显;(3)暖日、暖夜、冷夜数有明显的阶段性变化,其突变检验特征较明显,暖日、暖夜分别在2008、2003年突变增加,冷夜在1986年突变减少;(4)湖南省极端气温日数在不同的时间段存在着长短不同的振荡周期。     

基于敏感源分析的动态大气污染排放方案模拟

选取2014年11月6—11日一次典型污染过程,以北京城区为重点关注的目标区域,基于印痕分析技术判别对该区域影响较大的敏感源区,设计重点区域减排试验和敏感源区逐日动态减排试验,利用区域化学传输模式WRF-Chem进行模拟对比。结果显示:上述两种方案对源强较高的减排当地PM_2.5浓度降低均有明显的改善作用,且在传输作用下会辐射影响到下游地区;但仅就目标区域而言,敏感源区减排方案的减排效率要远远高于重点区域减排方案。为了验证基于敏感源分析的动态减排方法的适用性,进一步开展了不同季节以及不同背景浓度的个例模拟。结果表明:基于敏感源区分析结果制定动态逐日减排措施,可降低削减成本、提高减排效率,以达到最具经济环境效益的减排效果。