Assessment of the impact of climate change on flow regime at multiple temporal scales and potential ecological implications in an alpine river

The source region of Yellow river is an alpine river sensitive to climate changes, but the potential effects of climate change on hydrological regime characteristics and ecological implications are less understood. This study aims to assess the response of the alterations in the flow regimes over the source region of Yellow river to climate change using Soil and Water Integrated Model driven by different Global Circulation Models (GFDL-ESM2M, IPSL-CM5A-LR and MIROC-ESM-CHEM) under three Representative Concentration Pathway emission scenarios (RCP2.6, RCP4.5 and RCP8.5). Indicators of hydrological alteration and River impact index are employed to evaluate streamflow regime alterations at multiple temporal scales. Results show that the magnitude of monthly and annual streamflow except May, the magnitude and duration of the annual extreme, and the number of reversals are projected to increase in the near future period (2020–2049) and far future period (2070–2099) compared to the baseline period (1971–2000). The timing of annual maximum flows is expected to shift backwards. The source region of Yellow river is expected to undergo low change degree as per the scenarios RCP2.6 for both two future periods and under the scenarios RCP4.5 for the near future period, whereas high change degree under RCP4.5 and RCP8.5 in the far period on the daily scale. On the monthly scale, climate changes mainly have effects on river flow magnitude and timing. The basin would suffer an incipient impact alteration in the far period under RCP4.5 and RCP8.5, while low impact in other scenarios. These changes in flow regimes could have several positive impacts on aquatic ecosystems in the near period but more detrimental effects in the far period.

     

When to conduct an isotopic survey for lake water balance evaluation in highly seasonal climates

One‐time or short‐term lake water isotopic surveys are often employed to evaluate regional lake water balance. However, it can be difficult to determine the optimal time‐window for sampling to obtain a representative long‐term perspective of lake water balance in settings influenced by seasonal variations in precipitation, evaporative loss, glacial/snow meltwater, and larger seasonal shifts in isotopic composition of precipitation. This is especially true for areas of the Tibetan Plateau that are influenced by the summer Indian monsoon. Although high‐frequency sampling is always preferred as the most rigorous approach to characterize the water budget of lakes or watersheds, this may be impractical in remote regions and over large spatial scales. To assess the potential sensitivity of isotope balance characterization to seasonal variability, we used a weekly lake water isotope data set acquired over a period of 3 years on the Tibetan Plateau to evaluate the potential inaccuracies that might have arisen from using isotopic data collected during narrower time‐windows. For this assessment, we use weekly isotopic data collected during the study and assume that these sampling events were stand‐alone one‐time surveys. We then demonstrate the sensitivity of the isotope balance method in this setting, particularly for the rainy season that significantly underestimated the evaporation/inflow. In contrast, isotopic composition of the lake water was found to be more representative of long‐term conditions when sampled in October on the Tibetan Plateau. To broaden our evaluation of seasonality effects over a range of climatic zones, published high‐frequency isotopic data were also compiled, and a similar assessment was carried out for selected regions of the world. The synthesized data and model outputs, which confirm pronounced variations in lake water isotopic composition and evaporation/inflow across a range of seasonal climates, were used to determine optimal sampling windows for these specific regions.     

基于平滑伪魏格纳-维勒分布的时频分析方法的震例回溯性研究

以四川及其邻区现有地磁台站数据为研究对象,基于平滑伪魏格纳-维勒分布的时频分析方法(SPWVD),对其进行时频计算,并对康定地震、九寨沟地震附近地磁台站及中强震活跃时段与平静时段的川滇地区部分地磁台站Z分量滤波后周期为4. 4h的振幅变化特征进行回溯性震例分析。研究发现:2014年康定地震之前,震中附近7个地磁台站4. 4h振幅存在同步高值异常现象,其中5个台的幅值为震前所研究时段的最高值;九寨沟地震前,震中附近6个台站存在同步相对高值的异常现象,其中3个台的幅值为震前所研究时段的最高值; 2014年川滇地震活跃时期,该区域地磁台站普遍存在4. 4h振幅同步异常,台站数量多、振幅大,与此时间段内中强地震发生强度呈正相关,在时间上呈现短临特征; 2018年川滇地区中强地震活动平静时期,4. 4h振幅变化较平稳,异常振幅相对较小,而后活跃期间同步异常的最大振幅增大且异常台站数量增加。综上所述,通过SPWVD时频方法对地磁数据进行处理和分析,以此得到的规律和认识,对未来川滇地区中强地震预测和研判区域地震活动性的强弱有积极意义。     

地震激励作用下锚固系统研究现状

地震激励作用下,柔性的锚杆支护体系与刚性的滑体合而为一,刚柔并济,协调系统位移与应力,主动抗震抗滑。基于以上优势,锚固边坡在高烈度地区广泛应用,其动力稳定性也成为近年来岩土工程领域研究的热点。通过分析锚固边坡的浅表动力效应、锚固体的动力响应、锚固体的破坏模式、锚固体的抗震机理及设计方法等4个方面发现,浅表动力效应研究和锚固体的动力响应分析研究成果相对较多、较成熟,但大都局限于位移、加速度、应力等单因素的分析,并没有具体到整个系统的动力响应过程;指出今后的研究方向更应趋向于整个锚固系统的动力响应过程、抗震机理及抗震设计理论,才能更好地为工程服务。     

The evolution of the Kuroshio Current over the last 5 million years since the Pliocene: Evidence from planktonic foraminiferal faunas

Meridional heat transport of the western Pacific boundary current (the Kuroshio Current) is one of the key factors in global climate change. This current is important because it controls the temperature gradient between low latitudes and the North Pacific and so significantly influences mid-latitude atmosphere-ocean interactions. Here we reconstruct changes in hydrological conditions within the mid-latitude mainstream of the Kuroshio Current based on faunal analysis of planktonic foraminifera in core DSDP 296 from the Northwest Pacific Ocean. This approach enabled us to deduce evolutionary processes within the Kuroshio Current since the Pliocene. A total of 57 species in the coarser section (>150 µim) were identified; results indicate that planktonic foraminiferal faunal evolution has mainly been characterized by three major stages, the first of which comprised mixed-layer warm-water species of Globigerinoides ruber which first appeared between 3.5 and 2.7 Ma and then gradually increased in content. Percentages of another warm-water species of G. conglobatus also gradually increased in number over this interval. Variations in warm-water species indicate a gradual rise in sea surface temperature (SST) and imply initiation of Kuroshio Current impact on the Northwest Pacific Ocean since at least 3.5 Ma. Secondly, over the period between 2.7 and 2.0 Ma, thermocline species of Globigerina calida, Neogloboquadrina humersa, Neogloboquadrina dutertrei, and Pulleniatina obliquiloculata started to appear in the section. This fauna was dominated by G. ruber as well as increasing G. conglobatus contents. These features imply a further rise in SST and its gradually enhanced influence on thermocline water, suggesting strengthening of the Kuroshio Current since 2.7 Ma. Thirdly, between 2.0 Ma and present, increasing contents of thermocline species (i.e., G. calida, N. dutertrei and P. obliquiloculata) indicate a gradual rise in seawater temperature at this depth and also imply more intensive Kuroshio Current during this period. On the basis of comparative records from cores ODP 806 and DSDP 292 from the low latitude Western Pacific, we propose that initiation of the impact of the Kuroshio Current in the Northwest Pacific and it subsequent stepwise intensifications since 3.5 Ma can be closely related to the closure and restriction of the Indonesian and Central American seaways as well as variations in the Western Pacific Warm Pool (WPWP) and equatorial Pacific region.

     

江宁地电台地表与井下地电阻率观测数据分析

地铁建设对江宁地电台地电阻率观测造成较大影响,通过分析观测数据,比较了地表、井下观测受地铁等因素的干扰情况,并探讨了用影响系数来研究地表、井下观测的地表浅层干扰抑制能力,得到以下初步结果:①地铁试运行期间的干扰影响大于正式运营;②井下观测对供电电流更加敏感;③井下观测能够减轻地铁等的干扰,其地表浅层干扰抑制能力优于地表观测,可作为地电观测的重点发展方向之一。     

2016年射阳M_S 4.4地震前后重力场变化

利用江苏重力测网2014—2017年重力场观测资料,采用绝对重力控制与相对重力联测相结合的平差方法,获取2016年射阳M_S 4.4地震前后重力场变化图。根据射阳M_S 4.4地震前后射阳地区各测线重力段差变化特点,绘制重力场等值线并进行对比分析,结合相关机理,探讨重力场变化与该地震的内在联系。同震观测数据显示:射阳M_S 4.4地震发生在重力异常值高梯度带附近,发震时震中地区位于NS挤压正异常、EW张拉负异常状态,震后区域重力梯度变化量开始减小,是一种典型的重力异常调整现象。     

孟中榴辉岩形成和演化和P-T轨迹

本文研究了江苏东海县孟中榴辉岩富铝单斜辉石中石榴子石出溶作用,利用温压计对榴辉岩中各阶段矿物组合进行了温压估算,由此建立了孟中榴辉岩形成和演化的P-T轨迹。结果表明,该榴辉岩经历了地幔条件下由于降温和可能的升压作用,富铝单斜辉石中出溶石榴子石并形成榴辉岩;榴辉岩构造侵位到高角闪岩相片麻岩基底中;退化变质这3个阶段的演化过程。      

洪泽湖出入河流及湖体氮、磷浓度时空变化(2010—2019年)

基于2010-2019年洪泽湖湖体水质逐月监测数据,筛选出影响湖体水质的主要污染物指标为总氮（TN）和总磷（TP）;选取洪泽湖周边25条主要入湖河流和2条出湖河流在2019年10月2020年9月的监测数据,探讨河流外源性输入对不同湖体区域氮磷的影响及其水期变化规律.结果发现：①湖体TN、TP浓度长期居高不下,年均浓度范围分别在1.39~1.86、0.080~0.171 mg/L波动.主要入湖河流TN、TP时空平均浓度（1.92~5.70和0.114~0.181 mg/L）,均高于同区域湖体（1.15~1.46和0.088~0.101 mg/L）,其中北部入湖河流肖河、马化河和五河与临近湖区TN、TP浓度呈现显著正相关,是影响北部湖体TN、TP浓度的主要河流;南部入湖河流维桥河和高桥河是临近湖区非极端降雨期TN、TP的主要来源.②调水工程对湖体及入湖河流TN、TP浓度分布影响显著,调水期湖体沿调水方向TP浓度逐渐上升,TN浓度则呈现先降后升的趋势,南部入湖河流维桥河和高桥河TN浓度达到水期峰值,分别为10.69和9.90 mg/L.③极端降雨期入湖河流的TN、TP浓度显著高于其它水期,由于湖体对TN、TP的富集作用不同,TP浓度呈现中间高,四周低,而TN浓度呈现沿洪水流向逐渐降低的规律.     

Reflection full-waveform inversion using a modified phase misfit function

Reflection full-waveform inversion (RFWI) updates the low- and highwavenumber components, and yields more accurate initial models compared with conventional full-waveform inversion (FWI). However, there is strong nonlinearity in conventional RFWI because of the lack of low-frequency data and the complexity of the amplitude. The separation of phase and amplitude information makes RFWI more linear. Traditional phase-calculation methods face severe phase wrapping. To solve this problem, we propose a modified phase-calculation method that uses the phase-envelope data to obtain the pseudo phase information. Then, we establish a pseudophase-information-based objective function for RFWI, with the corresponding source and gradient terms. Numerical tests verify that the proposed calculation method using the phase-envelope data guarantees the stability and accuracy of the phase information and the convergence of the objective function. The application on a portion of the Sigsbee2A model and comparison with inversion results of the improved RFWI and conventional FWI methods verify that the pseudophase-based RFWI produces a highly accurate and efficient velocity model. Moreover, the proposed method is robust to noise and high frequency.