1 INTRODUCTION

Black carbon (BC) is a chemically heterogeneous class of carbon compounds produced during the incomplete combustion of biomass and fossil fuels(Masiello and Druff el, 1998), as well as from ancient graphitic carbon derived from weathered metamorphic rocks (Dickens et al., 2004). BC is broadly distributed in diverse environmental media such as the atmosphere, soils, sediments, water, and ice, and it might well be preserved in soils and sediments for long durations (Dickens et al., 2004; Elmquist et al.,2007; McConnell et al., 2007; Flores-Cervantes et al.,2009; Agarwal and Bucheli, 2011; Yang et al., 2015).BC in various environments has caused increasing concern within the scientific community in recent years for a number of reasons. For example, BC is the second most important greenhouse substance with the sunlight-absorbing ability in aerosols; it provides an excellent record of fire history in sediments, ice cores,loess, and soils; BC is an important marker of the biogeochemical cycle of carbon and global changes;and it is a good absorbent for diverse toxic organic pollutants in soils and sediments (Smith, 2005;Elmquist et al., 2007; Han et al., 2011; Ni et al., 2014).Additionally, BC in soils and sediments plays an important role in carbon sequestration and it might represent a significant sink in the global carbon cycle(Crombie et al., 2015; Wang et al., 2015).

There is consensus that BC, as an important constituent of total organic carbon (TOC) in soils/sediments, might generally be employed as a robust indicator of environmental change because of its chemically and biologically inert characteristics (Jia et al., 2003; Elmquist et al., 2007; Sun et al., 2008;Han et al., 2011; Liu et al., 2011). For example, BC has already been used to study the history of regional terrestrial biomass burning, photosynthetic pathway evolution in terrestrial ecosystems, terrestrial environmental changes, shifts in the historical energy structure, global carbon cycling, and human activities(Jia et al., 2003; Elmquist et al., 2007; Wang and Li,2007; Marlon et al., 2008; Sun et al., 2008; Lin et al.,2012; Wang et al., 2013). However, previous studies have focused primarily on BC records in terrestrial environments (Elmquist et al., 2007; Agarwal and Bucheli, 2011; Han et al., 2011; Wang et al., 2013;Crombie et al., 2015). In the most recent 20 years,records of marine-deposited BC have attracted increasing interest because of their excellent continuity and stability relative to terrestrial BC records (Verardo and Ruddiman, 1996; Masiello and Druff el, 1998; Middelburg et al., 1999; Jia et al.,2003; Dickens et al., 2004; Sun et al., 2008; Flores-Cervantes et al., 2009; Liu et al., 2011; Masiello and Louchouarn, 2013; Coppola et al., 2014). For example, Jia et al. (2003) provided a 30-Ma sedimentary record of BC from the northern South China Sea, revealing the photosynthetic pathway evolution of terrestrial ecosystems in the late Cenozoic. Sun et al. (2008) presented a sedimentary record of BC in the Pearl River estuary and adjacent northern South China Sea. Lohmann et al. (2009)suggested that attempts to construct a global BC mass balance should include estimates of atmospheric deposition based on BC data from deep-sea sediments.

“敬礼！”夏国忠带领幸存下来的三十几名战士，向留在阵地上的这朵小黄花进行告别。从此，这朵顽强的小黄花将继续坚守在高家岭的阵地上。

设锚杆与锚固剂共同组成锚固复合体，锚固复合体直径D大小等同钻孔直径。复合弹性模量为Ea，其中锚固剂弹性模量为Em，锚杆弹性模量为Es，锚杆杆体直径为d，锚固长度为Lb，假定锚杆与锚固剂共同发生变形，孔壁上的剪应力为τ(u)，为剪切位移u的函数。假定弹性变形阶段锚固体材料符合胡克定律，在锚固段任意深度z处取锚固体微元段，其长度为dz，如图2所示。

The Yellow Sea (YS) is of specific interest with regard to anthropogenic eff ects on the carbon cycle because it is located downwind of large population centers in China. The rapidly increasing emissions of BC and other air pollutants present a serious environmental problem for the regions of the YS and Bohai Sea. The YS is an epicontinental shelf surrounded by mainland China and the Korean Peninsula. The circumambient land of the YS and large rivers in China, including the Yellow and Yangtze rivers, supply large amounts of terrestrial material to the YS (Fig.1) (Xin et al., 2015).Consequently, several areas of fine-grained sediments have formed on the YS shelf under the combined eff ects of tides, waves/storms, and currents (Li et al.,2014). Furthermore, the important hydrological phenomenon of the Yellow Sea Cold Water Mass(YSCWM) has received considerable attention from oceanographers (Hu, 1984; Qu and Hu, 1993; Pang and Hu, 2002). Recent studies have demonstrated that the fine-grained depositional areas in the YS constitute important sinks of TOC and anthropogenic organic pollutants, and that they might play important roles in the transport, burial, and fate of TOC (Hu et al., 2013).BC represents an important constituent of TOC in the sediments of the Bohai Sea, East China Sea (ECS)shelf, and YS, and its distribution, concentration, 14 C age, and relation to persistent organic pollutants(mainly in surface sediments) have been studied widely (Wang and Li, 2007; Kang et al., 2009; Jiang et al., 2010; Hung et al., 2011; Wang et al., 2011;Huang et al., 2012; Lin et al., 2012; Zhang et al.,2013; Fang et al., 2014; Cui et al., 2015). Although some researches on the sedimentary records of BC and/or polycyclic aromatic hydrocarbons in the Bohai Sea and northern YS has been reported, to the best of our knowledge, no century-scale high-resolution records of BC have been compiled for the fine-grained sediment cores in the YSCWM. In this paper, the continuous century-scale high-resolution BC records in sediment cores H43 and H44 from the YSCWM area are presented to constrain the temporal changes and cycling of BC. Then, the origins of exceptional BC sequences with three distinct BC peaks are discussed. The results are considered to deepen the understanding of the source-sink BC history in the YS.

2 MATERIAL AND METHOD

2.1 Study area and sample collection

The YS is located within the region 31°40′–39°50′ N, 119°10′–126°50′ E between mainland China and the Korean Peninsula. It forms a semi-enclosed flat basin to the north and a wide continental shelf to the south, covering an area of 380 000 km 2 with a central water depth of 50- 80 m (Fig.1). The YS is connected to the Bohai Sea via the Bohai Strait to the north and to the ECS to the south. It can be considered as divided into the North Yellow Sea and South Yellow Sea (SYS) by the Shandong Peninsula (Li et al., 2015).

The typical circulation pattern of the SYS in winter is characterized by the northward-flowing Yellow Sea Warm Current (YSWC) along the western side of the Yellow Sea Trough and southward-flowing currents along the coasts of China and Korea, including the Yellow Sea Coastal Current (YSCC), Korean Coastal Current (KCC), and Liaodong Coastal Current(LDCC) (Fig.1). The YSWC transports the warm and salty water of the open ocean into the YS in winter(Fig.1). The prominent oceanographic YSCWM is a winter water mass that appears in the northern and southern regions of the YS (Tang et al., 2006), where the central bottom water might include remnant winter water with low temperature and high salinity(Hu, 1984; Yao et al., 2012; Xin et al., 2015). The YSWC almost disappears in summer, partially because of the presence of the YSCWM in the central SYS (Zhang et al., 2008; Moon et al., 2009; Oh et al.,2013). Under these combined hydrodynamic systems,several areas of fine-grained sediments have formed on the YS shelf (Li et al., 2014). Of these sedimentary areas, the Central Yellow Sea Mud (CYSM) has attracted greatest attention because of its sediment provenance and deposition processes (Xin et al.,2015).

Fig.1 Map illustrating the location of the Yellow Sea-East China Sea area, modified according to Yuan et al. (2008) and Li et al. (2014)

Shaded areas with diff erent blue colors show the distributions of fine-grained sediments with diff erent grain sizes at the sea bottom (darker colors indicate finer grains). Red stars indicate the locations of cores H43 and H44. Surface circulation in winter is also illustrated. Arrows represent the Yellow Sea Warm Current (YSWC), Yellow Sea Coastal Current (YSCC), Korean Coastal Current (KCC), Liaodong Coastal Current (LDCC), Taiwan Warm Current (TWC), Shandong Coastal Current (SDCC), East China Sea Coastal Current (ECSCC), Kuroshio Current (KC), and Changjiang(Yangtze) Dilute Water (CDW).

The carbon isotope ratios of BC ( δ 13 C BC) in sediment core H44 were measured using an elemental analyzer-isotope ratio mass spectrometer (EA-IRMS)at the Laboratory of Bioorganic Geochemistry, School of Marine Sciences, Sun Yat-Sen University. Briefly,approximately 15 mg of each sample treated sequentially by the acidification and WXY methods was weighed and loaded into a clean tin capsule. The capsules containing the samples were placed on an automatic feeder of solid samples for the vario ISOTOPE cube elemental analyzer (Elementar,Hanau, Germany) and burned in an ultrapure O 2 atmosphere in a combustion CuO tube at 950°C.Combustion gases were eluted through a reduction column by a stream of He gas and passed into the gas chromatograph where the CO 2 in the He stream was separated from the other gases. The gas stream then entered an IsoPrime 100 isotope ratio mass spectrometer (Elementar, Manchester, UK), in which the CO 2 gas was analyzed by comparison with a reference CO 2 gas with a known δ 13 C value (-33.21‰,calibrated against the IAEA-NBS-22 reference material with a δ 13 C value of -30.03‰± 0.04‰).During every batch of analyses, an empty tin capsule was analyzed as the blank to check the background,and a reference material (sulfanilamide) with a known δ 13 C value (-28.13‰± 0.02‰) was used to assess the reproducibility and accuracy. Low background, i.e., a peak height ＜0.01 V, which was much lower than the peak height of the sample (1.50 V), and excellent reproducibility and accuracy were achieved. The corresponding standard deviation of the analysis and the deviation between the measured and predetermined data were within ± 0.2‰. Stable carbon isotope ratios of BC were expressed using the conventional delta ( δ)notation:

where R sample and R std are the 13 C/ 12 C isotope ratios corresponding to the sample and international internal standard (V-PDB), respectively (Craig, 1957; Coplen et al., 2006).

2.2 Dating of sediment core H44

In light of the published 210 Pb dating and sedimentation rate data from the study area (Li et al.,2002), 12 sediment samples from core H44 were sectioned in a cold room (4° C) at average depths of 0.5, 2.0, 4.0, 6.0, 10.0, 14.0, 18.0, 22.0, 26.0, 30.0,34.0, and 37.8 cm with the nearly identical error of 0.3 cm (Table S1). All samples were freeze-dried for 48 h and then ground into powders with the grain size of ＜200 mesh. The 210 Pb activity in each sample was detected at the Guangzhou Institute of Geochemistry,Chinese Academy of Sciences, via analysis of the α radioactivity of its decay product 210 Po, with the presumption that the two are in equilibrium. Polonium isotopes were extracted, purified, and self-plated onto silver disks containing 0.5 mol/L analytical grade HCl (the same as below) at 75- 80° C for 2 h, using 209 Po as the yield monitor and tracer in the quantification. Counting was performed using computerized multichannel α spectrometry with Au-Si surface barrier detectors and an average error of＜3%. Supported 210 Po was gained by indirect measurement of the α activity of the supporting parent 226 Ra, which was carried by coprecipitated BaSO 4.The average sedimentation rate of core H44 was determined using a constant initial 210 Pb concentration model (McCall et al., 1984).

通过搭建各种测试场景进行牵引供电系统供电能力测试。测试前，对车辆负载特征进行分析，并联合设计单位对牵引供电系统和车辆的负荷特性进行分析，包括对牵引供电系统的各种运行模式所对应的负荷运行进行编排；重点对接触网在不同运行方式(双边供电、单边供电、大双边供电)下的供电能力进行检验，并记录AW0(空载)、AW3(超载)等不同载荷列车的起动电流波形；同时观察牵引供电设备(DC 1 500 V开关柜及保护、钢轨电位限制装置等)是否发生误动作，以确保牵引供电系统的供电能力满足标准及设计要求；复核设计单位关于运营过程中的负载状态，以确保线路安全运营。

2.3 Grain size analysis

Grain sizes of the sediments were analyzed using a Mastersizer 2000 laser particle analyzer (Malvern,Worcestershire, UK) with a measurement range of 0.02–2 000.00 μm, size resolution of 0.01 μm, and measurement error of ＜2%. Before measuring the grain sizes, the samples were homogenized by ultrasonic vibration, oxidized using 10% H 2 O 2 to remove organic matters, and dispersed in a 0.05%solution of sodium hexametaphosphate to separate discrete particles. The sorting coeffi cient ( σ),skewness ( Sk), and kurtosis ( Kg) were calculated as follows (Folk and Ward, 1957):

where μ 5, μ 16, μ 25, μ 50, μ 75, μ 84, and μ 95 are the particle sizes (in μ) at diff erent frequencies. Grain sizes were classified into three fractions: sand (＞63 μ m), silt (4–63 μ m), and mud (＜4 μ m).

可见，生产力、生产方式、经济基础的决定作用是“归根到底”意义上的，在实际的历史行程中，上层建筑包括政治体制、法律制度、意识形态，当然也包括领袖人物的活动，都会对经济基础产生这样那样的反作用，而且往往决定着历史运动的“斗争形式”。历史上的成功的变法、革命、改革，都是例证。这些变法、革命、改革，推动了国家经济、政治、文化、教育、交通、军事、财政等领域的迅速进步，都会对时代产生重要影响，其中成果卓著者则会开创新时代。

2.4 Detection of TOC

Approximately 100 mg of each dry and thoroughly ground sediment sample was transferred into a disposable ceramic crucible with the microporecontrolled ability (LECO, Michigan, USA). Then, the crucibles were labeled and placed accordingly into a self-made Teflon ® holder, which was held in a whiteenameled salver. Three mol/L HCl was added into the salver and each crucible, and the HCl level inside the crucible was kept the same as that outside. After 12 h,the crucibles, holder, and salver were heated in a thermostatic water bath at 80° C for 1 h. After complete exclusion of the HCl from the crucibles, ultrapure water was added to the crucibles in sextuplicate to remove the resultants of inorganic carbon and residual HCl. Then, the crucibles were freeze-dried for 48 h.The TOC contents were measured quantitatively with a CS230 C/S analyzer (LECO, Michigan, USA). The limit of quantification (defined as the mean blank value plus 10 times the standard deviation) in this study was (2.3± 0.3) μ g/g.

2.5 Quantification of BC

BC in the sediments was analyzed using an improved chemothermal oxidation (WXY) method(Gustafsson et al., 2001; Xu et al., 2018). Briefly,approximately 150 mg of each dry and fully ground sediment sample was transferred to a disposable ceramic crucible with the micropore-controlled ability for removal of carbonates. The acidification procedure used was the same as for TOC detection. After acidification, the crucibles were blow dried at 60° C and held in an SG-GL1100 tube furnace (made by Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences, Shanghai, China) at 375° C for 24 h under an active airflow. Quantification of BC was performed using a CS230 C/S analyzer.The limit of quantification in this study was(2.3± 0.3) μ g/g.

Nemati A, Wang Q, Hong M H, Teng J H. Tunable and reconfigurable metasurfaces and metadevices. Opto-Electronic Advances1, 180009 (2018).

Fig.2 Results of 210 Pb dating for sediment core H44 in the South Yellow Sea

2.6 Analysis of stable carbon isotope ratio of BC( δ 13 C BC)

In this study, two sediment cores (50-cm length× 10-cm diameter) were collected from the southwestern CYSM in May 2012 using a box corer. The sampling locations of cores H43 and H44 are 35° 29.382′ N,122° 58.371′ E and 35° 30.017′ N, 22° 39.739′ E,respectively (Fig.1). The sediment cores were sealed in clean PVC pipes and frozen immediately in situ.Then, the cores were delivered to a laboratory and stored at -20° C until further analysis.

从资产保护的角度看，要依照相关的法律法规保护农村集体经济组织成员的合法权利。就目前的发展现状来看，集体经济组织成员各项权益所受到的侵害主要出现在公共权利方面。各个成员之间的财产纠纷能够通过内部协调、行政机构仲裁以及民事诉讼来进行解决，一旦出现组织成员权利与政府公共权力不一致的情况，组织成员的利益极易受到侵害。故此，必须出台相应的法律法规，切实保护组织成员的财产安全。

所有的社会组织都需要到政府规定的相应部门或机构进行注册在案，方可取得正式合法身份，这也就是通常所讲的“登记注册”。这一程序是否运行适当，关系到千千万万的社会组织能否合法地开展活动和履行其功能，因此具有相当深刻的意义。对于民办非企业单位，特别是大量的草根组织而言，这一环节就显得尤为重要。

2.7 Analysis of precipitation data

The mean monthly precipitation data in the reaches of the Huanghe (Yellow) River during 1900- 2010 AD were downloaded from the China Meteorological Data Sharing Service System. To analyze the relationship between the precipitation and BC variation, the data were processed using a three-year moving average and they were reset to zero in cases where precipitation was ＜150 mm/month.

3 RESULT

3.1 210 Pb chronology and average sedimentation rate

The 210 Pb dating results of core H44 are presented in Table S1 and Fig.2. It can be seen from Fig.2 that the relationship between excess 210 Pb activity and ln(depth) for 10 samples can be described using the following equation:

where X, Y, and r represent the average depth (cm),excess 210 Pb activity (dpm/g), and correlation coeffi cient, respectively. The linear trend demonstrates that the excess 210 Pb activity decreased exponentially downcore, suggesting a continuous deposition and yielding an average sedimentation rate of (3.1 ±0.2) mm/a over the period of approximately 1891- 2010 AD for core H44.

目前各种计算机网络安全问题层出不穷，特别是信息的泄露给用户带来了非常大的负面影响。信息的泄露指的就是用户的一些保密信息被不法分子非法的窃取。随着时代的不断进步和电子技术与各种高端信息技术的快速的发展，随之而来的是人们的各种信息安全无法得到有效的保障。出现这种现象有很多种可能性，比如说内部的资料被偷窃、存储设备意外丢失等。因此现代人的信息安全已经成为不可忽视的一个问题，信息泄露已经直接损害到用户的利益。

3.2 Sedimentary sequences of cores H43 and H44

The data of grain size analysis for cores H43 and H44 are listed in Tables S2 and S3. Figure 3 illustrates their top-to-bottom grain size compositions, as well as the related parameters of mean grain size ( Mz),median grain size ( Md), sorting coeffi cients ( σ),skewness ( Sk), and kurtosis ( Kg).

It appears that the contents of sand and mud for core H43 vary significantly with depth, whereas there is no evident change in the contents of silt (Fig.3a).The sand and mud contents range from 2.03% to 22.09% with a mean value of 8.69% and from 8.42%to 17.42% with a mean value of 12.23%, respectively.The values of Md and Mz range from 4.90 (in μ, the same below) to 6.27 with an average value of 5.49 and from 5.28 to 6.44 with an average value of 5.78,respectively. The parameters σ , Sk, and Kg for core H43 fluctuate markedly within the intervals of 1.51–1.82 (mean: 1.67), 0.20–0.36 (mean: 0.30), and 0.94–1.27 (mean: 1.07), respectively (Fig.3a).

It is well known that BC is originated from the incomplete combustion of biomass and fossil fuels as well as graphitic carbon from weathered rocks(Dickens et al., 2004; Elmquist et al., 2004). BC derived from burning might be transported into marine sediments via aerosols and/or surface runoff ,whereas surface runoff is the sole input pathway of BC derived from graphitic carbon into the sea. Thus,the BC sequence of one marine sediment core could reflect the combination of various factors, principally including the sediment sources, transportation,composition, and depositional environments.

The contents of sand and mud for core H44 also change notably with depth, while the change in the silt contents remains within a relatively narrow range(Fig.3b). The sand and mud contents vary within the intervals of 0.43%- 22.76% with a mean value of 5.50% and 9.24%- 44.79% with a mean value of 24.56%, respectively. The values of Md and Mz vary within the ranges of 4.93- 7.80 with a mean value of 6.57 and 5.25- 7.84 with a mean value of 6.68,respectively. The parameters σ, Sk, and Kg for core H44 fluctuate significantly within the intervals of 1.52- 2.20 (mean: 1.74), 0.00- 0.34 (mean: 0.11), and 0.92- 1.32 (mean: 0.99), respectively.

To match the vertical variation of BC for further analysis of its cycling, the sediment sequences of cores H43 and H44 were divided artificially into five stages to evaluate their diff erences in grain composition, grain size distribution, and other related parameters. The curves of grain size distribution for cores H43 and H44 at diff erent stages are illustrated in Fig.4a and 4b, respectively. Details of the comparison of the two sequences are given below.

Fig.3 Grain size parameters for (a) core H43 and (b) core H44 in the South Yellow Sea

Mz, Md, σ, Sk, and Kg represent mean grain size, median grain size, sorting coeffi cient, skewness, and kurtosis, respectively.

Stage 1 (37.8- 36.3 cm, corresponding to the period 1891- 1895) in core H43 is characterized by relatively high sand content (9.41%), low mud content (11.34%),and small Md (5.39) and Mz (5.69) values, together with a relatively lower σ value (1.65) and higher Kg value (1.09). Stage 1 in core H44 is characterized by relatively low contents of sand (5.84%) and mud(22.95%), and small Md (6.55) and Mz (6.61) values,together with a relatively higher σ value (1.80) and lower Sk value (0.98).

Stage 2 (36.0- 29.7 cm, corresponding to the period 1896–1916) in core H43 is characterized by sediments with reduced silt (77.32%) and increased mud(12.70%) contents, with an increased σ value of 1.72 and a reduced Kg value of 1.05. As a result, the values of Md and Mz at this stage are relatively higher at 5.45 and 5.77, respectively. Stage 2 in core H44 is characterized by reduced silt (70.51%) and increased sand (6.61%) contents, with a decreased σ value of 1.74 and an increased Sk value of 0.13.

Stage 3 (29.4–25.8 cm, corresponding to the period 1917–1929) in core H43 is characterized by sediments with an evident reduction in sand content to 7.36%and increased silt content (79.86%), with σ reduced to a mean value of 1.67. Stage 3 in core H44 is characterized by an evident reduction in silt content to 68.14% and increased mud content (25.31%), with an increased σ value of 1.81 and a reduced mean value of Sk of 0.09.

Stage 4 (25.5–2.1 cm, corresponding to the period 1930–2004) in core H43 is characterized by increased sand content (8.50%) and slightly decreased mud content (12.13%). All grain size parameters are similar to Stage 3. Stage 4 in core H44 is characterized by an evident reduction in sand content to 5.05% and increased silt content (70.29%), with a decreased σ value of 1.73 and an increased mean value of Sk of 0.12.

Stage 5 (1.8- 0.0 cm, corresponding to the period 2005–2010) in H43 is characterized by fractions of sand, silt, and mud, as well as grain size parameters,similar to Stage 4. Stage 5 in core H44 is characterized by increased mud content (29.53%) and reduced silt content (65.82%), with a reduced Sk value of 0.09.Hence, the values of Md and Mz at this stage are increased to 6.86 and 6.95, respectively.

The contents of TOC in core H44 are presented in Table S4, and the content-versus-depth sequence is illustrated in Fig.5. It can be seen from Table S4 and Fig.5 that the TOC contents in core H44 ranges from 0.643- 1.283 wt.% with a mean value of 0.786 wt.%( n=126). At depths of 25.8- 37.8 cm, corresponding to sedimentation Stages 1- 3, the TOC contents fluctuate within a narrow interval of 0.694- 0.847 wt.% with nearly identical averages of 0.753- 0.782 wt.%. From 2.1 to 25.5 cm, equivalent to Stage 4, the TOC contents vary dramatically and they exhibit a U-shaped valley with basal values of 0.643- 0.685 wt.%in 1975- 1978 (Fig.5). From the top to a depth of 1.8 cm (Stage 5), i.e., since 1979, the TOC content exhibits a rapidly increasing trend with the highest mean of 1.090 wt.% (Fig.5).

Fig.4 Mean grain size distribution curves of the samples from (a) core H43 and (b) core H44

The sediment sequences of cores H43 and H44 are divided artificially into five stages.

3.3 Vertical distributions of TOC

The grain sizes in core H43 clearly vary smoothly from Stages 1–5, whereas those in core H44 change sharply, especially in Stage 5 with the diff erent Md,Mz, and Sk values. Additionally, the sediments at the diff erent stages of core H43 always maintain a unimodal distribution with the maximum volume content at the grain size of 32 μ m (Fig.4a), while the grain size distribution curves of core H44 change with each stage (Fig.4b). The grain size distribution curves for Stages 1- 4 in core H44 exhibit the same flattopped unimodal pattern with the maximum volume content at the grain size of 4- 16 μ m, whereas the curve at Stage 5 appears as a sharp unimodal pattern with the maximum volume content at the grain size of 4 μ m (Fig.4b).

Fig.5 Sequence of the total organic carbon (TOC) contents for core H44 in the South Yellow Sea

Fig.6 Sequences of BC contents in (a) core H43 and (b) core H44 in the South Yellow Sea

3.4 Vertical variations of BC in cores H43 and H44

The data of BC contents in sediment cores H43 and H44 are presented in Tables S2 and S4, respectively,and the content-versus-depth sequences are plotted in Fig.6a and 6b, respectively. The BC content in core H43 ranges from 0.086 8 to 0.228 0 wt.% with a mean value of 0.108 0 wt.% ( n=126, Table S2), while the BC contents in core H44 vary within the interval 0.037 6 -0.213 0 wt.%, with an average of 0.063 6 wt.% ( n=126,Table S4). Except for the segments with three peaks,the BC contents fluctuate within narrow intervals throughout the sequences of cores H43 and H44. As indicated in Fig.6a and 6b, three BC peaks occur simultaneously within the two sequences. These peaks are characterized by a rapid increase in BC from the background level, followed by a slower gentle attenuation down to the background level.

3.5 Vertical change in stable carbon isotope ratio of BC ( δ 13 C BC)

The stable carbon isotope ratios of BC ( δ 13 C BC) in core H44 are presented in Table S4, and its vertical distribution is presented in Fig.7. Table S4 and Fig.7 show that the δ 13 C BC values vary from -22.66‰ to-20.07‰ with a mean value of -21.67‰ ( n=126). At depths of 36.3- 37.8 cm, corresponding to Stage 1, the δ 13 C BC values fluctuate smoothly within a narrow interval of -21.79‰ to -21.42‰ with a mean value of-21.63‰. From 29.7 to 36.0 cm, equivalent to Stage 2, the δ 13 C BC values change markedly within a relatively wide gap of -22.37‰ to -21.28‰. At depths of 25.8- 29.4 cm, corresponding to Stage 3, the δ 13 C BC values fluctuate dramatically within an even wider interval (-22.66‰ to -21.57‰). From Stages 1 through 3, the δ 13 C BC values show a slightly decreasing trend. Stage 2 could be divided into two periods: an early period (10.8- 25.5 cm) when the δ 13 C BC values seesaw within a very narrow gap of -22.17‰ to-21.50‰, and a late period (2.1- 10.5 cm) when the δ 13 C BC values range from -21.95‰ to -20.17‰,exhibiting a gradual increasing trend. The BC in the sediments from the top to a depth of 1.8 cm, i.e., in Stage 5, possesses higher δ 13 C BC values of -20.07‰ to-20.88‰, with no evident variation.

高校创新创业教育课程建设质量监测与评价体系建设既需要政府的政策支持，也需要高校的具体落实和组织实施，需要高校在政策、人员、场地、经费、保障机制等多方面的支持下，才能有效组织开展实施。只有高校领导真正重视此项工作，这项工作才能取得实效。

3.6 Century-scale storm records for the reaches of the Huanghe River

The tiny light BC particles in the YSCWM area primarily are originated from surface runoff in the reaches of the Huanghe River and atmospheric deposition. When the reaches of the Huanghe River were aff ected by long-term drought, BC from incomplete combustion could have accumulated in terrestrial surface soils/sediments, where longer periods of drought would result in greater deposition of BC. The subsequent occurrence of a heavy storm could have eroded the previously accumulated BC from the terrestrial surface soils/sediments, which was then transported into the YS via surface runoff ,particularly from the Huanghe River. Thus, flood events evidently could have introduced greater quantities of previously accumulated BC into the YS,enhancing BC deposition in the YSCWM area. Thus,it is suggested that the peaks in the two sequences might have been originated from BC sedimentation strengthened markedly by surface runoff , particularly from the Huanghe River, which augmented the atmospheric deposition. The facts that the periods 1919- 1921 and 2000- 2001 AD reflect times of reduced precipitation and there were no heavy storms during the last 110 years (Fig.8), together with the occurrence of severe droughts, support the above inference. It must be noted that considerable hydrodynamic changes have occurred in the Huanghe River because of impoundment by large reservoirs,e.g., the Sanmenxia, Liujiaxia, Longyangxia,Wanjiazhai, and Xiaolangdi reservoirs in 1958, 1968,1986, 1995, and 1997, respectively. These hydrodynamic changes could have restricted the occurrence of BC peaks in the sequences of cores H43 and H44 in other periods (Yu et al., 2013).

4 DISCUSSION

4.1 Improvements in the BC quantification method and occurrence of exceptional BC sequences in the sediment cores from the YSCWM area

In this study, based on the 210 Pb dating (Fig.2) and systematic measurement of BC in core H44 from the YSCWM area, an exceptional BC sequence with annual resolution has been determined (Fig.6b). This sequence is characterized by three peaks of BC contents of 0.115 0 wt.%, 0.136 0 wt.%, and 0.213 0 wt.%, enhanced considerably from the unusually low background mean BC level of 0.051 6 wt.%, which correspond approximately to 1891, 1921, and 2007 AD, respectively (Table S4;Fig.6b). Core H43 is not dated, but because it was obtained from a location close to core H44 (Fig.1),their sequences might be correlated based on their sediment properties. Grain size analysis suggests that they possess similar silt-mud-dominated compositions and grain size parameters (Tables S2 and S3; Fig.3),also implying a continuous sedimentation for core H43 similar to Core H44. Therefore, the 210 Pb-based sedimentation rate for core H44 was extrapolated to core H43. It can be seen from Fig.6a and 6b that the BC sequences for cores H43 and H44 are similar,suggesting their sequences were regionally controlled by the same BC deposition. Thus, the three peaks might be indicative of important natural and/or anthropogenic events.

A few earlier studies have investigated centuryscale BC records in the Sishili Bay (Wang et al., 2011)and the northern YS (Cui et al., 2015); however, BC sequences similar to those revealed in this study have not been reported previously in or near the current study area. It is considered that the most important factor regarding exceptional BC sequences is relatively low BC recovery. This is particularly relevant in areas containing low background levels of BC, where tiny BC particles might be lost during sample treatment,either because they are suffi ciently fine to remain in suspension or because of sorption onto the surfaces of centrifuge tubes. Dickens et al. (2004) demonstrated that the BC recovery rate was only 46% for Washington Lake sediments. To augment the level of BC recovery in this study, an improved CTO-375 method, i.e.Wang-Xu-Yuan method (Xu et al., 2018) was employed to treat the samples, i.e., the adoption of disposable ceramic crucibles with the microporecontrolled ability to remove carbonates in the sediments for avoiding BC loss. The revelation of exceptional BC sequences in this work might be attributable to the enhancement of BC recovery.

“从民族起源的研究视角来看，共同的社会记忆对于一个民族或族群的孕育与形成，具有突出的凝聚作用，而这种共同记忆主要体现在对祖先及族源的构想上。”[注]江帆：《满族生态与民俗文化》，中国社会科学出版社，2006年，第192页。以满族祖先及族源追溯的正史记录和底层记忆为例，无论是史料记载还是民间传说都与“三仙女吞红果”的神话密不可分。在满族社会，“三仙女佛库仑吞朱果”的叙事一直被视为是族群起源的权威版本，得到满族民众的高度认可。这种历史记忆和社会解释不仅在民间流传广泛，在上层社会的正史典籍中也有记录。其最早记录见于《旧满洲档》的《天聪九年档》中的一段文字：

Fig.7 Sequence of carbon isotope ratio of δ 13 C BC in core H44 in the South Yellow Sea

Fig.8 Century-scale storm records in the reaches of the Huanghe River

4.2 BC deposition for sediment cores in the YSCWM area

提供增值服务的范围可以很广。简单一点的服务，比如提供整合每个员工某年度的所有相关信息的检索界面；提供所有员工某年度或某区间的科研项目与成果信息的检索界面；提供各个人奖、惩信息的检索界面；提供某级别职称的员工姓名；等等。

The Huanghe River is the second largest river in terms of sediment load in the world. Previous studies have indicated that the fine-grained sediments in the SYS are originated from various material sources(Lim et al., 2007; Milliman and Farnsworth, 2011).However, there is consensus that sediments from the modern Huanghe River (i.e., since 1855 AD) could be transferred southeastward through the southern Bohai Strait (Shi et al., 2003; Bi et al., 2011). This is especially possible given the conditions of strong resuspension and enhanced coastal currents due to winter monsoon activities (Yuan et al., 2008; Bi et al.,2011), and the relict Older Huanghe River subaqueous delta (1128–1855 AD) (Li et al., 2014). Additionally,after the course of the Huanghe River shifted northward into the Bohai Sea in 1855, the Older Huanghe River Delta (1128–1855 AD) underwent strong erosion, which provided a plentiful supply of sediments to the SYS (Li et al., 2014).

In principle, small amounts of BC from surface runoff , together with other particles, especially finegrained silt and mud, might be transferred into the YSCWM area. However, because of the existence of cyclonic eddies that form in the complicated hydrodynamic system of the YS (Hu, 1984; Shi et al.,2003), it remains open to debate whether BC from surface runoff could be deposited in the YSCWM region. The BC/TOC ratio is a robust and widely accepted marker for identifying BC sources, i.e., the incomplete burning of biomass will generate an average BC/TOC value of ＜0.11, while the mean ratio produced by fossil fuels is approximately 0.50 (He and Zhang, 2009). It was established in this study that the mean BC/TOC ratios in core H44 were lower than 0.11 for Stages 2 and 4 (Table S4; Fig.6b), suggesting that the BC in these two stages could largely be attributed to the incomplete combustion of biomass.Meanwhile, the mean BC/TOC ratios were 0.116,0.129, and 0.155 (i.e., ＞0.11) for Stages 1, 3, and 5(Table S4; Fig.6b), respectively, implying that BC derived from the burning of fossil fuels and/or graphitic carbon from weathered rocks was probably transferred into the sediments during these three stages (Dickens et al., 2004; He and Zhang, 2009). In fact, the BC contents in core H44, except for the segments with the three peaks, were within the interval of 0.037 6- 0.089 9 wt.% with a mean value of 0.051 6 wt.%, evidently lower than those of the Bohai Bay (0.218 0 wt.%) (Kang et al., 2009), Sishili Bay (0.118 0 wt.%) (Wang et al., 2011), Bohai Sea(0.084 wt.%) (Jiang et al., 2010), and northern YS(0.056 0- 0.132 0 wt.%) (Cui et al., 2015).

4.3 Origin of BC peaks in the sequences of sediment cores in the YSCWM area

Three peaks with high BC contents corresponding to 1891, 1921, and 2007 AD were found in cores H43 and H44 from the YSCWM area (Fig.6). Two of the peaks are coeval with the two time points of 1921 and 2007 AD, when the first heavy storms occurred just after the termination of long-term (4- 5-year) droughts(Fig.8). Because of the lack of longer time series of precipitation data for the reaches of the Huanghe River, it cannot be confirmed whether a corresponding relationship exists between the BC peak in 1891 AD and the occurrence of a heavy storm. It might be reasonable to interpret the occurrence of the BC peaks in the sediment cores from the YSCWM area as follows.

The mean monthly precipitation data after data processing in the reaches of the Huanghe River in the period 1900- 2010 AD are presented in Table S5 and Fig.8. It can be seen from Fig.8 that the mean monthly rainfall was ＜40 mm/month in two periods:1919- 1921 and 2000- 2001. These periods reflect times of lowest precipitation and the occurrence of severe droughts. In particular, no heavy storms aff ected the reaches of the Huanghe River during 1917- 1921 and 1998- 2004 AD.

Evident diff erences were noted between the BC peaks in Stages 1, 3, and 5 (Fig.6). Grain size analysis indicated that the grain size parameters of Md, Mz,and Sk in Stage 5 in core H44 diff ered from those in Stages 1 and 3 (Table S3). The curve of grain size distribution in Stage 5 exhibits a sharp unimodal pattern with the maximum volume content at the grain size of 4 μ m, which is diff erent from Stages 1 and 3 (Fig.4b). Stable carbon isotope analysis indicated that the δ 13 C BC values in Stages 1 and 3 range from -21.79‰ to- 21.42‰ with a mean value of-21.63‰ and from -22.66‰ to -21.57‰ with a mean value of -22.11‰, respectively. These are notably diff erent from Stage 5 (from -20.07‰ to -20.88‰with a mean value of -20.49‰) (Table S4). Therefore,it is considered that the increase in δ 13 C BC values in Stage 5 might result from the input of weathered rock-derived graphitic carbon caused by artificial annual water-sediment modulation in the Huanghe River since 2005 (Bi et al., 2014).

4.4 Fractions of rock-derived graphitic carbon in BC peaks in core H44 in the YSCWM area

To determine the proportions of weathered rockderived graphitic carbon in the stages with BC peaks in core H44 in the YSCWM area, proper δ 13 C endmember values of BC from the incomplete burning of oil ( δ 13 C oil) and coal ( δ 13 C coal) were chosen.Chen et al. (2012) reported mean δ 13 C oil and δ 13 C coal values of -25.17‰ ( δ 13 C oil) and -23.46‰ ( δ 13 C coal),respectively. Ni et al. (2014) provided the recent fractions of total energy consumption in China, i.e.,46% coal ( F coal), 37% biomass ( F biom), and 17% oil( F oil). If the above energy fractions ( F coal, F oil, and F biom) are used as the BC contributions in atmospheric deposition, then the mean δ 13 C values of BC from fossil fuels ( δ 13 C ff ) can be calculated as follows:

where F oil, F coal, δ 13 C oil, and δ 13 C coal are 17%, 46%,-25.17‰, and -23.46‰, respectively.

Assuming a mean δ 13 C BC value of -21.68‰ (Table S4) for the sediment segments with no BC peaks is the normal background level ( δ 13 C nbl), the mean δ 13 C BC value for biomass ( δ 13 C biom) can be calculated as follows:

where F oil, F coal, F biom, δ 13 C nbl, and δ 13 C ff are 17%, 46%,37%, -21.68‰, and -23.92‰, respectively.

Adopting the normal background level of BC/TOC(0.067, Table S4) as that of the biomass, the variations in BC/TOC for Stages 1, 3, and 5 can be calculated as 0.049, 0.062, and 0.088, respectively. Furthermore,supposing that the residue, other than the BC derived from biomass, comes from fossil fuels, the mean fractions of fossil fuels ( F ff ) for Stages 1, 3, and 5 can be determined as 42.24%, 48.06%, and 56.77%,respectively. Based on the above mean fractions of fossil fuels, the mean δ 13 C values in the sediments with peaks (for stages 1, 3, and 5) can be estimated.

水源热泵项目取用地下水水资源论证技术要点分析……………………………………………… 江 剑，董殿伟(3.50)

Because no δ 13 C data of ancient graphite ( δ 13 C gc) in the reaches of the Yellow River are available, the average δ 13 C value of ancient graphite (-20.0‰,δ 13 C gc) in metamorphic rocks in the Qinling orogenic belt can be used as the δ 13 C endmember value (Chen et al., 2000). Thus, the fraction of graphitic carbon( F gc) can be calculated as follows:

甲洛洛感觉丁主任说了这话后，嘎绒的眼神马上不对劲了，而且收工回家时，嘎绒的嘴角很明显地挂着一个让人无法释怀的冷笑，甲洛洛隐隐感到危险正一步步逼近自己。

where δ 13 C sample, δ 13 C biom, δ 13 C ff , and F ff are -20.49‰,-17.86‰, -23.92‰, and 56.77%, respectively.

The above result shows that the proportion of weathered rock-derived graphitic carbon in core H44 is 22.97% in Stage 5. Similarly, estimates of the proportions of graphitic carbon in Stages 1 and 3 indicate that no weathered rock-derived graphitic carbon is present in Stages 1 or 3. Despite the lack of direct evidence, the low fraction of graphitic carbon in core H44 might be attributable to diffi culties associated with resuspension, because a similar phenomenon was observed along the Washington Coast (Dickens et al., 2004).

5 CONCLUSION

In summary, the remarkable sequences with three BC peaks were revealed in two sediment cores in the YSCWM area using an new WXY method. The three BC peaks corresponded approximately with 1891,1921, and 2007 AD, coeval with the occurrence of the first heavy storms following long-term droughts.Stable carbon isotope analysis of BC and numerical simulations indicated that the input of weathered rock-derived graphitic carbon only occurred in Stage 5, which was induced by the annual artificial watersediment modulation in the Huanghe River since 2005 AD.

6 ACKNOWLEDGEMENT

We would like to thank the National Meteorological Information Center of the People’s Republic of China for providing the precipitation data for the reaches of the Huanghe River. We are also grateful to Mr. LI Kechang at the Guangzhou Institute of Geochemistry,Chinese Academy of Sciences, for kindly assisting with the 210 Pb dating experiment.

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