Soil organic carbon enrichment of dust emissions: magnitude,mechanisms and its implications for the carbon cycle

Soil erosion is an important component of the global carbon cycle. However, little attention has been given to the role of aeolian processes in influencing soil organic carbon (SOC) flux and the release of greenhouse gasses, such as carbon dioxide (CO₂), to the atmosphere. Understanding the magnitude and mechanisms of SOC enrichment in dust emissions is necessary to evaluate the impact of wind erosion on the carbon cycle. This research examines the SOC content and enrichment of dust emissions measured using Big Spring Number Eight (BSNE) wind‐vane samplers across five land types in the rangelands of western Queensland, Australia. Our results show that sandy soils and finer particulate quartz‐rich soils are more efficient at SOC emission and have larger SOC dust enrichment than clay‐rich aggregated soils. The SOC enrichment ratios of dusts originating from sites with sand‐rich soil ranged from 2·1–41·9, while the mean enrichment ratio for dusts originating from the clay soil was 2·1. We hypothesize that stronger inter‐particle bonds and the low grain density of the aggregated clay soil explain its reduced capacity to release SOC during saltation, relative to the particulate sandy soils. We also show that size‐selective sorting of SOC during transport may lead to further enrichment of SOC dust emissions. Two dust samples from regional transport events were found to contain 15–20% SOC. These preliminary results provide impetus for additional research into dust SOC enrichment processes to elucidate the impact of wind erosion on SOC flux and reduce uncertainty about the role of soil erosion in the global carbon cycle. Copyright © 2013 John Wiley & Sons, Ltd.     

Contemporary glacigenic inputs to the dust cycle

The importance of glacigenic dust in the Earth's system during glacial periods is widely acknowledged. Under contemporary conditions, the world's largest dust sources are in low‐lying, hot, arid regions and this is where most aeolian research is focused. However the processes of dust production and emissions are still operating in cold climate regions, particularly in proglacial areas. This paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle. It focuses on how elements in the glacial and aeolian geomorphic sub‐systems interact to determine the magnitude, frequency and timing of aeolian dust emissions, and on feedback mechanisms between the systems. Where they have been measured, dust emission intensity and deposition rates in glacierised catchments are very high, in some cases far exceeding those in lower latitudes, however, few studies span long time scales. The impact of future glacier retreat on the balance between sediment supply, availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered. This balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths, which promote dust emissions, and patterns and rates of soil development and vegetation succession on recently‐deglaciated terrain which protect sediments from deflation. Retreat of the Antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non‐glacigenic sources in the southern hemisphere. Copyright © 2012 John Wiley & Sons, Ltd.     

Response of the hydrological regime of the Yellow River to the changing monsoon intensity and human activity

Abstract

In the past 50 years, influenced by global climate change, the East Asian summer monsoon intensity (SMI) changed significantly, leading to a response by the water cycle of the Yellow River basin. The variation in SMI has three stages: (1) 1951–1963, SMI increased; (2) 1963–1965, SMI declined sharply, a feature that may be regarded as an abrupt change; and (3) 1965–2000, SMI remained at low levels and showed a tendency to decline slowly. The decreased SMI led to a reduction in water vapour transfer from the ocean to the Yellow River basin, and thus precipitation decreased and the natural river runoff of the Yellow River also decreased. Due to the increase in population and therefore in irrigated land area, the ratio of net water diversion to natural river runoff increased continuously. Comparison of the ratio of net water diversion to natural river runoff before and after the abrupt change in SMI indicates some discontinuity in the response of the man-induced lateral branch of the water cycle to the abrupt change in SMI. The frequently occurring flow desiccation in the lower Yellow River can be regarded as a response of the water cycle system to the decreasing summer monsoon intensity and increasing population. When the ratio of net water diversion exceeded the ratio of natural runoff of the low-flow season to the annual total natural runoff, flow desiccation in the lower Yellow River would occur. When the ratio of net water diversion is 0.3 larger than the ratio of the natural runoff of the low-flow season to the annual total natural runoff, an abrupt increase in the number of flow desiccation events is likely to occur.     

北半球环状模周期变化和突变研究

利用NOAA提供的1871-2008年月平均海平面气压场、雪盖、海冰等再分析资料、NASA提供的地表温度场资料、太平洋年代际振荡(PDO)指数,采用小波分析、带通滤波和凝聚谱分析等方法,研究了北半球环状模(NAM)周期变化及其影响因子.研究结果表明NAM在20世纪60年代前后发生了显著的年代际尺度周期突变,NAM在1895-1955年存在显著的准35年周期振荡,而在1971-2008年则主要以准15年周期振荡为主.NAM年代际尺度周期突变与外强迫源振荡周期变化有关,但突变前后与NAM周期振荡密切相关的外强迫因子并不尽相同.在1960年代之前,PDO、ATM、北美雪盖以及南极海冰涛动等外源强迫因子与NAM在准35年尺度上关系密切;而在1960年之后,NAM准15年振荡则与ATM和欧洲雪盖、南极海冰涛动等因素有关.     

Disintegration of Fan Sediments in Death Valley,California, by Salt Weathering

In Death Valley, California, an area of high aridity and great salinity, alluvial fans de scend into the zone of salt accumulation. When the rounded fan gravels come into contact with salt, some of which is sodium sulfate, they are rapidly shattered and reduced in size. Silt and clay are formed by this salt weathering process and this fine material may be subject to deflation processes.     

基于Parsivel天气现象仪资料的郑州“7·20”罕见特大暴雨微物理特征分析

基于2016-2018年ECMWF模式温度预报和浙江省72个国家基本站观测资料,根据温度日变化特征,采用K-近邻(KNN)回归算法进行误差订正,改进浙江省172 h精细化温度预报。在KNN回归算法中,将模式起报时刻的温度视作“背景”,由模式预报减去起报时刻温度消除“背景”影响,得到温度日变化曲线,通过温度日变化曲线构建差异指标,选取历史相似个例。根据历史相似个例的误差特征,对温度预报进行订正,得到改进的温度预报。检验结果表明,KNN方案的温度预报平均绝对误差较ECMWF和30 d滑动平均误差订正方案(OCF)的分别减小26.2%和5.2%;日最高和最低温度预报误差绝对值小于2℃,准确率较ECMWF的分别提高14.8%和4.3%,较OCF的分别提高3.0%和1.3%。KNN方案对地形复杂地区的温度预报改进效果更为明显,对冷空气活动和夏季高温等天气过程预报改善效果也较稳定。     

叶绿素荧光遥感在陆地生态系统碳循环和陆气相互作用中的应用研究进展

陆地生态系统通过植被光合作用可以吸收约30％的人为碳排放,在全球碳循环、减缓大气二氧化碳浓度上升等方面具有重要作用。最近10年发展起来的日光诱导叶绿素荧光遥感技术,可以监测植被实际光合作用,为全球陆地生态系统碳循环的研究提供了新的思路和方法。本文回顾了叶绿素荧光遥感产品发展及其在陆地生态系统碳循环和陆气相互作用中的应用研究进展,特别是在全球植被总初级生产力估算和陆地生态系统碳循环模型发展方面的进展,并进一步讨论了该领域研究面临的挑战和未来的发展方向。     

海水硝酸盐氮、氧同位素组成研究进展

海洋中氮的生物地球化学循环影响着海洋生态系统的结构和功能,并和全球气候变化有着密切的联系,一直是海洋科学研究的重点和热点。海水硝酸盐的15N/14N和18O/16O比值可以反映海洋中氮循环的主要过程,因而成为研究海洋氮循环的一个重要手段。综述海水硝酸盐氮、氧同位素组成的测定方法,同化吸收作用、硝化作用、反硝化作用、生物固氮作用等氮循环过程所导致的氮、氧同位素分馏及其在海洋学研究中的应用。海洋生态系中硝酸盐氮、氧同位素的分布可以提供支持生物生产力的氮来源信息,以及氮在不同储库迁移转化的路径与机制。未来的研究需要发展适用于低含量硝酸盐的同位素测量方法,构筑海洋氮的收支平衡,掌握影响上层海洋硝酸盐氮、氧同位素变化的过程,获取全球海域有关硝酸盐氮、氧同位素组成的更多数据。     

全球沉积盆地动态分类方法:从原型盆地及其叠加发展过程讨论

沉积盆地是油气生成和聚集的基本地质单元,其形成和发展为板块构造演化所控制,主要表现在两个方面,一是板块从分离到汇聚的不同阶段、板块的不同位置,产生不同的原型盆地,形成了特定的构造-沉积体系,决定了其生、储、盖等基本含油气条件;二是后期叠加的原型盆地不但本身具有新的油气地质特征,还能够改变早期原型盆地的成藏条件及油气分布规律。以板块构造演化历史为时间线索,通过对现今盆地早期原型及其后期叠加改造过程的系统解剖,用动态方法将全球处于一个威尔逊旋回的现今盆地划分为12种类型。在此基础上,总结了各类盆地的基本属性及含油气条件,为科学预测各类盆地的含油气远景奠定了基础。     

济阳坳陷惠民凹陷临盘地区始新统孔店组一段—沙河街组四段红层划分和对比

受气候控制的洪水事件沉积因其短暂性、广布性和周期性等特征,具有相对的等时效应,可以作为地层划分和对比的标志层。通过分析不同规模周期下的事件沉积和正常沉积特征,并结合基准面旋回理论,识别出济阳坳陷惠民凹陷临盘地区始新统孔店组一段—沙河街组四段下亚段红层短期、中期和长期三个级次的基准面旋回特征,短期旋回以洪水期和间洪水期内发育的不同类型沉积微相组合为特征,中期旋回以发育一套完整的洪水期—间洪水期沉积为标志,长期旋回则以多个中期旋回组成的地层叠加为特征;以此为依据将惠民凹陷临盘地区孔店组一段—沙河街组四段下亚段划分为5个长期旋回、16个中期旋回及若干个短期旋回层序,并对第一个长期旋回进行了精细层序地层对比,在此基础上建立了干旱气候控制下的红层层序的划分和对比模式。