黄土微观参数指标与阻尼比关联度研究

对岷县地震台、庆阳黄土塬2~12m深度土层的粉土、粉质黏土样品,利用室内动三轴试验和扫描电镜试验,测定阻尼比和微观结构特征,研究了粉土、粉质黏土的阻尼比随深度的变化及应力应变关系,采用灰色关联度方法,分析了黄土竖向（沉积方向）和横向（垂直于沉积方向）的微观结构参数对阻尼比影响的主次关系及其权重。研究结果表明:小应变下,粉土和粉质黏土阻尼比随着深度的增加而减小;粉土和粉质黏土的微观参数与阻尼比有一定的关联性,粉土竖向的微观参数对阻尼比的影响较为敏感;粉质黏土横向的微观参数对阻尼比的影响更加敏感;影响权重方面,粉质黏土的平均形状系数影响权重最大,对阻尼比的影响最大;粉土的平均形状系数、分形维数和概率熵影响权重最大,对阻尼比影响最敏感。平均面积无论在关联度还是影响权重方面对阻尼比影响最小,该结论粉土与粉质黏土保持一致。     

Holocene paleoenvironmental changes inferred from diatom assemblages in sediments of Kusawa Lake, Yukon Territory, Canada

The southwest Yukon Territory, Canada, is an important region for recovering sensitive records of Holocene paleoclimatic change. More information is needed, however, to constrain the timing of the major Holocene climatic transitions, and to understand associated impacts on different ecosystems. For example, paleolimnological studies have focused on small lakes and ponds, but the history of large lakes has received little study. We analyzed diatom assemblages, species richness, valve concentrations, and biogenic silica, in the sediments of Kusawa Lake (60°16.5'N; 136°10.9'W; 671 m a.s.l.) to reconstruct the responses of this large (surface area = 142 km²), deep (Z_max = 135 m) freshwater ecosystem to Holocene climatic transitions. Diatoms colonized the lake soon after ice retreat, around 11,000 cal yr BP; assemblages throughout the record were dominated by planktonic types. Diatom concentrations and biogenic silica were high during the Holocene Thermal Maximum between 10,700 and 7300 cal yr BP, then began to decrease in response to cooling associated with orbitally driven reductions in insolation. Diatom assemblages shifted towards taxa with lower surface water temperature optima after 8300 cal yr BP, perhaps in response to abrupt and progressive cooling. Our study confirms that diatom assemblages in large lakes are sensitive to regional-scale paleoclimatic changes.     

南海北部金线鱼最大可持续产量和总可捕量的研究

限额捕捞试点工作逐步展开,预示着我国海洋渔业管理进入全面有序的管理时代。文章根据2008—2017年南海北部渔港渔业生产抽样调查数据,统计出南海北部金线鱼的产量主要来自刺网,占累计总产量的72.90%。剩余产量模型分析认为南海北部金线鱼的最大可持续产量在168 632.99~31 0518.85 t,平均为251 765.59 t。2017年实施最严格的休渔制度后,当年的捕捞努力量投入和渔业产量均未超过最适值,当前总可捕量可设为158 515 t。文章研究结果可为该鱼种限额捕捞政策实施提供参考。     

江苏省近百年汛期旱涝变化的诊断分析

本文应用历史气候资料和现代降水记录,对近百年来汛期江苏省各区域各年代进行旱涝诊断分析,采用滑动平均方法探讨其变化趋势,并用最大搞谱方法提取显著周期。得出以下三个比较有意义的结论：（1）近百年来,汛期全省较易发生旱的灾害,20－30年代为旱灾濒发期;（2）淮北地区近年有向早年发展的趋势,江淮之间及苏南地区进入90年代以来向旱年发展的趋势则愈来愈明显;（3）全省具有2－3年、5－6年的旱涝周期。     

末次冰期黄河解体事件初探

７０年代末，水文地质部门在华北平原上打下了大量第四系钻孔，１９９３年对其中近百个钻孔的沉积相和测年资料重新进行分析，发现在该区全新统之下、上更新统上部普遍发育了一层细砂层，埋深一般为２０－４０ｍ，厚度约为５－２０ｍ，平面分布连续而稳定。     

CO<Subscript>2</Subscript> Air–Sea Exchange due to Calcium Carbonate and Organic Matter Storage,and its Implications for the Global Carbon Cycle

Release of CO₂ from surface ocean water owing to precipitation of CaCO₃ and the imbalance between biological production of organic matter and its respiration, and their net removal from surface water to sedimentary storage was studied by means of a quotient θ = (CO₂ flux to the atmosphere)/(CaCO₃ precipitated). θ depends not only on water temperature and atmospheric CO₂ concentration but also on the CaCO₃ and organic carbon masses formed. In CO₂ generation by CaCO₃ precipitation, θ varies from a fraction of 0.44 to 0.79, increasing with decreasing temperature (25 to 5°C), increasing atmospheric CO₂ concentration (195–375 ppmv), and increasing CaCO₃ precipitated mass (up to 45% of the initial DIC concentration in surface water). Primary production and net storage of organic carbon counteracts the CO₂ production by carbonate precipitation and it results in lower CO₂ emissions from the surface layer. When atmospheric CO₂ increases due to the ocean-to-atmosphere flux rather than remaining constant, the amount of CO₂ transferred is a non-linear function of the surface layer thickness because of the back-pressure of the rising atmospheric CO₂. For a surface ocean layer approximated by a 50-m-thick euphotic zone that receives input of inorganic and organic carbon from land, the calculated CO₂ flux to the atmosphere is a function of the CaCO₃ and C_org net storage rates. In general, the carbonate storage rate has been greater than that of organic carbon. The CO₂ flux near the Last Glacial Maximum is 17 to 7×10¹² mol/yr (0.2–0.08 Gt C/yr), reflecting the range of organic carbon storage rates in sediments, and for pre-industrial time it is 38–42×10¹² mol/yr (0.46–0.50 Gt C/yr). Within the imbalanced global carbon cycle, our estimates indicate that prior to anthropogenic emissions of CO₂ to the atmosphere the land organic reservoir was gaining carbon and the surface ocean was losing carbon, calcium, and total alkalinity owing to the CaCO₃ storage and consequent emission of CO₂. These results are in agreement with the conclusions of a number of other investigators. As the CO₂ uptake in mineral weathering is a major flux in the global carbon cycle, the CO₂ weathering pathway that originates in the CO₂ produced by remineralization of soil humus rather than by direct uptake from the atmosphere may reduce the relatively large imbalances of the atmosphere and land organic reservoir at 10²–10⁴-year time scales.     

晚冰期以来大柴旦盐湖沉积记录的古气候演变及其尘暴事件

本文选择大柴旦盐湖DCD03沉积剖面柱硼镁石矿层下伏土黄色淤泥质粉砂层为研究对象,基于AMS ₁₄C年代学、岩性地层学、矿物学以及地球化学等研究方法,旨在探讨土黄色湖相淤泥质粉砂沉积记录的尘暴事件,以及重建晚冰期以来西风环流显著影响区的水文气候变化。研究结果表明,DCD03沉积剖面的淤泥质粉砂样品粒度频率曲线呈现为双峰态,主峰(均值10 μm)反映了河流作用携带入湖的细粒组分,次峰(﹥32 μm)则反映了风力作用以及河流作用等携带入湖的粗粉砂粒组分。大于64 μm的砂砾组分可能代表外源风尘物质的输入,由尘暴天气携带入湖。大柴旦地区晚冰期以来依次出现了博令和阿勒罗德暖期(12.94~12.17 cal. ka BP)、新仙女木冷期(12.17~11.37 cal. ka BP)、不稳定的早全新世气候(11.37~8.64 cal. ka BP)以及趋于偏冷干的中全新世早期(8.64~7.39 cal. ka BP)。     

Late Glacial fluvial response of the Niers‐Rhine (western Germany) to climate and vegetation change

The Niers valley was part of the Rhine system that came into existence during the maximum Saalian glaciation and was abandoned at the end of the Weichselian. The aim of the study was to explain the Late Pleniglacial and Late Glacial fluvial dynamics and to explore the external forcing factors: climate change, tectonics and sea level. The sedimentary units have been investigated by large‐scale coring transects and detailed cross‐sections over abandoned channels. The temporal fluvial development has been reconstructed by means of geomorphological relationships, pollen analysis and ¹⁴C dating. The Niers‐Rhine experienced a channel pattern change from braided, via a transformational phase, to meandering in the early Late Glacial. This change in fluvial style is explained by climate amelioration at the Late Pleniglacial to Late Glacial transition (at ca. 12.5 k ¹⁴C yr BP) and climate‐related hydrological, lithological and vegetation changes. A delayed fluvial response of ca. 400 ¹⁴C yr (transitional phase) was established. The channel transformations are not related to tectonic effects and sea‐level changes. Successive river systems have similar gradients of ca. 35–40 cm km^?1. A meandering river system dominated the Allerød and Younger Dryas periods. The threshold towards braiding was not crossed during the Younger Dryas, but increased aeolian activity has been observed on the Younger Dryas point bars. The final abandonment of the Niers‐Rhine was dated shortly after the Younger Dryas to Holocene transition. Traces of Laacher See pumice have been found in the Niers valley, indicating that the Niers‐Rhine was still in use during the Younger Dryas. Copyright © 2005 John Wiley & Sons, Ltd.     

Use of environmental magnetic measurements to validate the vertical extent of ice masses at the Last Glacial Maximum

Analysis of soil samples from above and below trimlines representing the upper limit of glacial erosion at the Last Glacial Maximum demonstrates that soils with prolonged weathering histories above such trimlines yield significantly different mineral magnetic signatures from soils below trimlines. The nature of the contrast is conditioned by lithology. Basalt soils above the trimline yield significantly higher values of concentration‐dependent magnetic parameters (χ, χ_arm, IRM_3T, soft IRM and hard IRM) than those below the trimline, due probably to transformation of non‐magnetic iron‐bearing minerals into magnetic forms. Conversely, for sandstone soils most magnetic parameters yield significantly lower values for above‐trimline samples, probably reflecting loss of ferrimagnetic minerals by dissolution and oxidation to aniferrimagnetic forms. These significant contrasts represent a new approach to validating high‐level weathering limits as periglacial trimlines cut at the Last Glacial Maximum. Copyright © 2002 John Wiley & Sons, Ltd.     

Glacial Lake Victoria,a high‐level Antarctic Lake inferred from lacustrine deposits in Victoria Valley

We present evidence of a large lake (Glacial Lake Victoria) that existed in Victoria Valley in the dry valleys region of Antarctica between at least 20 000 and 8600 ¹⁴C yr BP. At its highstands, Glacial Lake Victoria covered 100 km² and was ca. 200 m deep. The chronology for lake‐level changes comes from 87 AMS radiocarbon dates of lacustrine algae preserved in deltas and glaciolacustrine deposits that extend up to 185 m above present‐day lakes on the valley floor. The existence of Glacial Lake Victoria, as well as other large lakes in the dry valleys, indicates a climate regime significantly different from that of today at the last glacial maximum and in the early Holocene. Copyright © 2002 John Wiley & Sons, Ltd.