库布齐沙漠HDPE网和植物纤维网沙障防沙试验效应

在库布齐沙漠流动沙丘区建立HDPE网和植物纤维网工程沙障试验区,采用MetOne 014A/024A型8通道风速仪、8方位集沙仪、风蚀插钎,观测试验沙障影响下的风速、输沙量和地表侵蚀堆积,对比分析不同规格HDPE网、植物纤维网方格沙障和HDPE网前沿高立式阻沙沙障的防风固沙效应。结果表明：（1）一定孔隙度（50%）的方格沙障中心风速垂直变化幅度与变化规律,仅与沙障平面规格和高度（h）密切相关,与试验材料基本无关。相同平面规格的方格沙障,高度（h）大者降风效应显著;相同高度的方格沙障,小规格降风效应较为显著;（2）试验沙障及其防沙体系对风沙流输沙产生明显影响,相近地貌部位,5.0m×5.0m（h=100cm）植物纤维网方格中心输沙量远小于1.0m×1.0m（h=20cm）HDPE网方格和流动沙丘区,大规格高立式沙障固沙效应优于小规格低立式沙障;（3）试验沙障的地表侵蚀堆积状态仅与沙障规格有关,沙障材料的影响不明显。     

腾格里沙漠昂格尔图湖记录的988 AD以来的古气候变化

通过对腾格里沙漠东南部昂格尔图湖岩芯AGE15A的粒度、碳酸盐的百分含量和主要化学元素等多项沉积学气候代用指标及精确定年的综合分析,重建了该区域988 AD以来的古气候变化序列。结果表明：988 AD以来的研究区的气候环境的演化过程与我国西北西风区古气候变化基本一致,呈现"冷湿-暖干"交替变化的特征,但在时间上存在一定的延迟。具体表现为：988~1383 AD,昂格尔图湖由洼地发育成小型湖泊,化学风化作用弱,湖区气候环境整体偏冷湿,期间出现几次暖波动;1383~1560 AD,研究区处在中世纪暖期,为温暖、干旱的气候特征,此时湖泊扩张,湖中水生植物生长茂盛,呼吸作用增强,造成大量的碳酸盐沉淀,最高值达到8.16%;1560~1700 AD,致使气候在昂格尔图湖形成之后出现最寒冷的时期,降水增加,气候湿冷,此时段与小冰期最盛期相对应;1700 AD之后,温度开始上升,气候回暖,在1900 AD左右达到最甚,此时沉积物中碳酸盐的百分含量也达到最大值,为10.15%,此期间湖泊继续扩张,出现几次气候冷波动。基于我国古代文献重建的历史时期气候变化基本不包括沙漠地区,所以本文利用湖相沉积记录来反演腾格里沙漠昂格尔图湖历史时期的气候环境演变,对中国沙漠研究有着重要参考价值,同时也为中国西北历史时期的气候重建提供科学依据。     

巴丹吉林沙漠高大沙山近地层温湿廓线与能量交换特征

利用兰州大学冰川与沙漠研究中心科学观测实验站2015—2016年获得的高大沙山微气象数据,分析了巴丹吉林沙漠温湿廓线结构、土壤分层温度、辐射通量等特征,利用组合法和一维热传导方程分别计算了湍流通量及土壤热通量。结果表明：（1）近地层大气自下而上呈现近似等温或逆温分布,冬季逆温层厚度大于夏季。（2）初次观测到逆湿现象,比湿夏季最大,冬季最小,秋季和春季次之,全年平均约为4.2 g·kg^-1,高于塔克拉玛干沙漠。（3）土壤热通量在2月底至5月初振幅较大;感热通量具有显著的平均日变化特征,潜热通量平均日变化平稳,以0 W·m^-2为中心上下波动。能量交换以感热通量为主,陆-气温度差异是沙山感热通量变化的主要影响和控制因子。     

The Origin and Distribution of Salts on Alluvial Fans in The Atacama Desert,Northern Chile

The Atacama Desert has been predominantly hyperarid since the middle Miocene. Combined ionic and X-ray diffraction analysis shows that calcium sulphate is prevalent on three similar alluvial fans in salar basins across a transect of different environments in Antofagasta Province, northern Chile. Differences between the fans were largely due to the effect of local factors on salt input, secondary redistribution and deposit preservation. Thus carbonate was notable in the High Andes (fan C) and Pre-Cordillera (fan B), whereas in the Central Valley (fan A) greater qualities of the more soluble salts (chlorides and nitrates) probably reflect the higher level of aridity and an oceanic source (the camanchaca). Calcium sulphate distribution on the alluvial fans and on adjacent hilltops indicates an aeolian origin. Evidence from the Pre-Cordillera (fan B), however, suggests that salt input may have been episodic, related to changes in conditions within the general aridity and possibly to stone pavement and soil development. Calcium sulphate sources range from an input in Andean precipitation and the camanchaca to abundant regional evaporite deposits. It is probable, however, that products of Andean volcanism constitute the dominant primary source of calcium sulphate, and that the salt has subsequently been distributed widely within the endoreic basins of the region by a combination of groundwater, surface flow and the wind. © 1997 John Wiley & Sons, Ltd.     

早更新世以来腾格里沙漠形成与演化的风成沉积证据

对陇西盆地六盘山西侧山麓剥蚀面上厚约223 m的断岘黄土-古土壤剖面的古地磁、磁化率和粒度进行分析,该剖面具有1.8 Ma以来完整的风成沉积旋回。主要应用砂粒百分含量(>63μm)作为指示风成物质来源区沙漠范围和气候干旱的直接指标,初步发现腾格里沙漠自1.8 Ma以来至少有2次大的扩张与变化过程,分别发生在1.1和0.8 MaBP前后,表明腾格里沙漠的扩张与变化可能同全球性的冰量增加和冬季风增强以及区域性的青藏高原隆升有成因上的联系。     

古尔班通古特沙漠的辐射热量交换分析

位于新疆准噶尔盆地的古尔班通古特沙漠是我国第二大沙漠。根据古尔班通古特沙漠的自然条件,对不同下垫面区域的太阳短波辐射和大气长波辐射热量进行了测量。结果表明:在晴天状况下,流动沙丘和固定沙丘的热量交换差异主要是由地表状况、沙层性质和气温等因素决定的。流动沙丘区反射率与长波辐射大于固定沙丘区,并且日、季变化明显。长波最大辐射值出现在午后,近似于太阳总辐射,最小值出现在日出前;沙层热通量随着深度的增加而增大,而辐射热量传输则随其深度的增加而减小,无论是流动沙层还是固定沙层,其热通量的零界面深度却基本一致(9月份),均在30~35cm之间。根据上述结果,本文还讨论了沙漠区在热量交换过程中,辐射热量差异引起的沙漠小气候效应和沙漠对区域气候的反馈作用。     

Holocene Dune Activity in the Thar Desert,India

The Thar Desert dune system in north-west India and eastern Pakistan provides a rich archive of past environmental, geomorphological and climatic change. Much of the knowledge about the timing of dune accumulation in the Thar stems from scattered and sporadic records, based on older luminescence dating protocols. If the Thar dune record is to be incorporated within a growing multiproxy framework of past climate and environmental dynamics, it is necessary to generate a systematic record of the timing of dunefield accumulation. From this, relationships to climate and other drivers of dune activity may then be better established. To this end, an intensive programme of field sampling and optically stimulated luminescence (OSL) dating was carried out from a dunefield in the east-central Thar Desert. This study presents the first detailed Holocene dune accumulation history from the region, and sheds light on the development of the multi-generational parabolic dune systems. In contrast to previously published work, we identify the importance of the Holocene and the last millennium as periods with a number of preserved accumulation phases. OSL ages suggest that accumulation was persistent during the early and mid-Holocene (within 11.7-5.5 ka), late Holocene (2-1 ka), as well as two major phases in the last millennium (600 – 200 a and within the last 70 a). Potential drivers of dune mobility in the last century include a strong anthropogenic dimension. Rapid net accumulation is recorded in the last 70 years, with rates varying between 2 and 5 m/year, in an environment where agricultural pressures have increased dramatically with the advent of irrigation schemes expanding into dunefield areas. © 2019 John Wiley & Sons, Ltd.     

Dust provenance and its role as a potential fertilizing agent for the Okavango Delta,Botswana

Dust plays a globally important role in supplying biologically essential elements to landscapes underlain by nutrient-poor substrates. Here we show that dust may play a significant role in sustaining productivity in the vast wetlands of the Okavango Delta in southern Africa, one of the world's richest biodiversity hotspots. Dust accumulates preferentially on tree-covered islands in the seasonal swamps of the Delta, creating pockets of fine-grained, nutrient-rich material within the semi-arid landscape of the Kalahari Desert. Strontium and neodymium isotopes reveal that this dust likely originates predominantly from the Makgadikgadi salt pans, located 300 km away, and contributes 10–80% of the fine-grained material present in Okavango island soils. Surface material sourced from the Makgadikgadi Pans contains relatively high amounts of bioavailable phosphorus and iron, potentially influencing Okavango Delta biological productivity. We propose that long-term ecosystem productivity and nutrient availability in the Okavango may be strongly mediated by regional dust inputs. Understanding the influence of dust deposition on nutrient loads and biogeochemical cycling is thus critical for predicting the response of the Okavango Delta to future changes in climate. We suggest that dust inputs may play a significant role in the supply of nutrients to other large, global wetland systems located in dryland environments. © 2020 John Wiley & Sons, Ltd     

塔克拉玛干沙漠腹地秋季陆面过程特征

利用塔克拉玛干沙漠腹地塔中2014年10月的秋季涡动通量数据,分析了塔中秋季陆面过程通量变化特征。结果表明：（1）塔中秋季10月净辐射R_n、感热通量H、潜热通量LE、地表土壤热通量G₀峰值依次为273.0、141.6、5.0、105.0 W·m^-2,平均日总量依次为2.85、2.68、0.08、-0.57 MJ·m^-2,净辐射能量分配以感热能量输送为主。（2）不同典型天气下,净辐射日总量扬沙>晴天>阴天>降水;阴天、扬沙天气H随R_n不同程度削减而减少,降水天气潜热增多导致日变化特征有别于其他天气。（3）10月能量闭合率为79.0%,不同天气能量闭合率阴天>晴天>扬沙>降水,依次为86.8%、83.4%、79.4%、71.4%。（4）地表反照率晴天呈“U”型变化,阴天和扬沙天气地表反照率趋势变缓发生波动现象,降水天气波动较大,趋势先降低后回升。（5）月平均热通量日间为正值,夜间为负值。日间能量闭合率为73.9%,夜间为50.8%,存在较高的能量不闭合。     

塔克拉玛干沙漠北缘夏季典型晴天近地层湍流能谱特征

利用塔克拉玛干沙漠北缘肖塘地区涡动相关系统三维方向风速（u,v,w）、气温、CO₂、H₂O等观测数据,分析了夏季典型晴天不同大气稳定度条件下湍流功率谱和协谱。结果表明：大部分情况下湍流速度谱分布满足-2/3幂指数率,垂直方向高频段惯性副区符合程度更高,水平方向次之;CO₂和H₂O浓度则符合程度较低;温度谱与无因次频率总体上都具有很好的相关性。垂直风速与径向风速u的协谱斜率拟合值大多数情况下更接近-1,而在近中性层结条件下更符合-4/5斜线。稳定层结条件下的协谱峰值比不稳定层结时更大,且约大一个量级;不稳定层结条件下高频段协谱近直线型下降。u谱对应的谱峰波长随稳定度增加而减小,v谱和T谱对应的谱峰波长随稳定度的增加没有规律性增减;u、v、w、T谱谱峰波长约67~827、69~2417、4~54、12~661 m。