青海共和盆地土壤风蚀的^137Cs法研究（I）——^137Cs分布特征

土壤风蚀作为土地沙漠化的首要环节,对其准确测定和评估是十分迫切和必要的。放射性核素137Cs作为人类核试验的产物,以其独特的理化性质而成为研究土壤侵蚀和泥沙沉积一种良好的示踪源。137Cs法在水蚀研究领域已取得了显著的进展,而在风蚀研究中的应用却相对不足,目前尚处于探索阶段。作者选择青海共和盆地作为研究区,探讨137Cs法在土壤风蚀研究中应用的可行性。通过对共和盆地不同类型土壤剖面的137Cs取样分析,基本查清了区域137Cs分布的若干特性,测定出不同类型土地137Cs活度的排序为:林地>干湖盆>高寒草原>旱作农田≈干草原>固定沙丘>荒漠草原>流动沙丘>风蚀地,137Cs总量的排序为:干湖盆>林地>流动沙丘>高寒草原>旱作农田≈干草原>固定沙丘>荒漠草原>风蚀地。并分析了一些典型剖面的137Cs深度分布及其机制,将137Cs深度剖面划分为正常剖面、沉积剖面、侵蚀剖面和人为扰动剖面4种型式。沙丘砂由于遭受反复吹失和沉积,其137Cs含量逐渐减小,趋于微量的均匀化;而高寒草原的137Cs含量在区域上也较为均匀,在深度分布上,接近负指数分布曲线保存了相对完好的137Cs初始沉积剖面,是理想的137Cs背景值样点。     

The potential of site-specific and local chironomid-based inference models for reconstructing past lake levels

We examined the relationship between three key environmental variables (water depth, loss-on-ignition, and bottom-water temperature) and fossil chironomid distributions sampled from within-lake gradients in three small, moderately deep (18–35 m), maar lakes on St Michael Island, western Alaska. Site-specific (one lake, 29 samples) and local (three lakes, 87 samples) inference models for reconstructing water depth were developed using partial least squares regression and calibration. These models and a previously published regional model (136 lakes, one central-lake sample from each) are used to infer water depths from 78 fossil samples spanning the last ~30,000 ¹⁴C years B.P. at Zagoskin Lake. Although the site-specific [r ² _boot = 0.90, root mean square error of prediction (RMSEP) = 1.76] and local (r _boot² = 0.68, RMSEP = 4.36) inference models have better performance statistics than the regional model, few clear trends among all three models exist in the lake-level reconstruction. We propose that multiple, within-lake sampling of gradients can be used to improve the performance statistics of water-depth transfer functions and ultimately reconstruct paleohydrology in regions known to exhibit large fluctuations in moisture balance through time given that: (1) adequate analogs are established and (2) taphonomic processes important to benthic invertebrate remains are more fully understood.     

Modelling the dynamics of snow cover, soil frost and surface ice in Norwegian grasslands

Studying the winter survival of forage grasses under a changing climate requires models that can simulate the dynamics of soil conditions at low temperatures. We developed a simple model that simulates depth of snow cover, the lower frost boundary of the soil and the freezing of surface puddles. We calibrated the model against independent data from four locations in Norway, capturing climatic variation from south to north (Arctic) and from coastal to inland areas. We parameterized the model by means of Bayesian calibration, and identified the least important model parameters using the sensitivity analysis method of Morris. Verification of the model suggests that the results are reasonable. Because of the simple model structure, some overestimation occurs in snow and frost depth. Both the calibration and the sensitivity analysis suggested that the snow cover module could be simplified with respect to snowmelt and liquid water content. The soil frost module should be kept unchanged, whereas the surface ice module should be changed when more detailed topographical data become available, such as better estimates of the fraction of the land area where puddles may form.     

基于210Pb、137Cs分布和粒度特征的海床液化深度判定研究以埕岛海域为例

黄河水下三角洲海床液化现象分布广泛,对海底工程设施造成了极大威胁,确定液化深度可为海上工程建设提供参考,具有很大的理论意义和应用价值。在黄河水下三角洲北部埕岛海域液化扰动区钻探取得柱状沉积物对其进行剖面图像扫描、放射性核素和粒度成分测试,获得图像分层特征、²¹⁰Pb、¹³⁷Cs活度及粒度剖面,在此基础上计算得到沉积速率。结果表明：埕岛海域受黄河1976年由刁口流路改道清水沟流路事件影响显著,这一时期沉积速率大幅减小并呈现阶段性特征;快速沉积时期表层沉积物频繁液化产生的砂层不断累积,从而形成密集砂层;通过分析²¹⁰Pb_ex、¹³⁷Cs活度剖面获得研究区液化历史的沉积记录,判定历史液化深度至少为5 m,这一结论与前人研究相近。以²¹⁰Pb、¹³⁷Cs的活度为工具来判断沉积物液化历史及深度存在一定的可行性,具有很大的发展潜力。     

巴丹吉林沙漠腹地地温变化特征

以巴丹吉林沙漠苏木巴润吉林观测站地温与气象数据为基础,分析巴丹吉林沙漠腹地地温变化特征。结果表明：（1）巴丹吉林沙漠地温、气温日变化特征明显,最高值出现时刻为17：00左右,相对东部地区滞后3 h;不同季节地温与气温变化趋势基本保持一致,地温变化相对气温、太阳辐射明显滞后;（2）地温在11月末至2月降至0 ℃以下,深度60 cm下全年高于0 ℃,地温变化幅度随深度增加逐渐减小;（3）地温变化幅度直接由太阳辐射强度决定,但影响地温的环境因子存在季节性特征,春、秋、冬季主要影响因子为气温、太阳辐射及降水,气温和太阳辐射的影响具有连续性,降水则导致地温骤减,风速仅在夏季影响地温。     

High-frequency rock temperature data from hyper-arid desert environments in the Atacama and the Antarctic Dry Valleys and implications for rock weathering

In desert environments with low water and salt contents, rapid thermal variations may be an important source of rock weathering. We have obtained temperature measurements of the surface of rocks in hyper-arid hot and cold desert environments at a rate of 1/s over several days. The values of temperature change over 1-second intervals were similar in hot and cold deserts despite a 30 °C difference in absolute rock surface temperature. The average percentage of the time dT/dt > 2 °C/min was ~ 8 ± 3%, > 4 °C/min was 1 ± 0.9%, and > 8 °C/min was 0.02 ± 0.03%. The maximum change over a 1-second interval was ~ 10 °C/min. When sampled to simulate data taken over intervals longer than 1 s, we found a reduction in time spent above the 2 °C/min temperature gradient threshold. For 1-minute samples, the time spent above any given threshold was about two orders of magnitude lower than the corresponding value for 1-second sampling. We suggest that a rough measure of efficacy of weathering as a function of frequency is the product of the percentage of time spent above a given threshold value multiplied by the damping depth for the corresponding frequency. This product has a broad maximum for periods between 3 and 10 s.     

The Arequipa (Peru) earthquake of June 23, 2001

The Arequipa earthquake of 23 June 2001 hasbeen the largest earthquake (Mw = 8.3)occurredin the last century in southern Peru with amaximum intensity of VIII (MM scale). Focalmechanisms of main shock and three largeraftershocks have been studied, showingthrusting solutions for main shock and twoaftershocks and normal motion for the eventof July, 5. The rupture area has beenobtained from distribution of aftershocks.The occurrence of the Arequipa earthquakeis related with the convergence processbetween the Nazca and South Americaplates.     

河流水情要素遥感研究进展

河流是促进地貌形成和演化的重要因素,也是地球上最重要的淡水资源之一。河流的水体范围、水位/水深、流量、水质和冰情等水情要素在水资源动态监测和水文生态环境保护等研究中具有至关重要的作用。通过水文站观测河流可获得站点上的水情信息,但该方式在财力、物力方面均耗费巨大。同时,对于日益增长的河流水情信息需求,迫切需要一种能够快捷、准确补充河流实测数据的方法。遥感凭借全方位、多时相的对地观测能力极大地提升了河流水情信息获取的效率,已广泛应用于多尺度水情监测、无资料流域水文模拟等多个方面,取得了丰硕的研究成果。因此,有必要对近年来遥感应用于河流水情要素反演所取得的进展进行归纳、总结和展望,以期进一步促进遥感数据和方法在该领域的应用。论文以“河流水情要素遥感”为主题,系统归纳了河流水体遥感提取的常用传感器及方法、水位/水深遥感反演方法、河道流量遥感估算、河流水质及河冰遥感监测的研究进展,详细归纳了利用光学/微波遥感等不同类型的遥感手段获取河流水体范围、水位、水深的优势与不足,总结得出了河流水情要素遥感研究的数据、方法及应用方面的主要结论：① 新型遥感数据在河流水情要素监测中的应用愈加广泛,在空间分辨率、时间分辨率或光谱分辨率等方面不断突破,进一步丰富了河流水情要素研究的数据来源;② 多数中低空间分辨率光学影像依旧面临混合像元影响水体提取精度的问题,合成孔径雷达影像也存在数据处理算法开发难度大的问题,细小河流及非开阔水体的提取方法仍需探索;③ 大数据和云计算技术的发展为实现大尺度、长时序的河流水情要素高时空分辨率遥感监测提供了高效手段。     

冰川槽谷横剖面沿程变化及其对冰川动力的反映

冰川槽谷梯级宽深比定义为槽谷槽剖面上相同等高线间距离与对应深度的比值。它可以描述槽谷横剖面形态的总体特征,便于不同槽谷横剖面形态的对比。统计分析表明槽谷梯级宽深比随槽谷深度的变化幂函数模型。使用这一模型描述冰川槽谷横剖面的总体形态并据此探讨冰川槽谷横剖面形态的沿程变化。主要结论如下：简单槽谷从上源到雪线附近,模型参数显示为槽谷展宽,谷壁变陡,从雪线向下游,槽谷变窄,谷壁变缓;从简单槽谷段向槽谷段,     

冻土对沙尘暴的影响研究

利用1951-2000年中国大陆685个沙尘暴站、412个冻土深度及706个气温站的观测资料,分析了近50a来沙尘暴与冻土深度的时空分布特征。结果表明:沙尘暴多发中心总与当月的冻深极小值或相对低值区对应,且冻深越小(大),沙尘暴日数越大(小);气温是冻深与沙尘暴反相关关系的纽带。