中国湖泊柱样沉积物中239+240Pu的来源与分布特征

针对当前中国湖泊柱样沉积物中^239+240Pu的研究现状,对中国湖泊^239+240Pu的来源、^239+240Pu最大蓄积峰的年代以及^239+240Pu在湖泊沉积物中的迁移行为进行了研究总结。结果表明：中国湖泊^239+240Pu的主要来源于全球大气核试验沉降,湖泊沉积柱样中表层沉积物²⁴⁰Pu/²³⁹Pu均值为0.177±0.019;柱样²⁴⁰Pu/²³⁹Pu均值为0.177±0.008;柱样^239+240Pu的沉积通量范围在7.45~240.6 MBq/km²之间,因湖泊所处沉积环境及纬度的差异而变化。湖泊柱样剖面中的^239+240Pu的分布多呈单峰分布,湖泊沉积物中^239+240Pu的最大蓄积峰位置改变可以忽略不计,^239+240Pu最大蓄积峰具有时标价值。     

长江口水下三角洲239+240Pu和137Cs的分布特征及环境意义

在长江口水下三角洲采集沉积物柱状样SC07,通过测试沉积物柱样中^239+240Pu和¹³⁷Cs的活度,重点分析^239+240Pu活度的分布特征及其与¹³⁷Cs活度剖面的异同,以提取^239+240Pu活度剖面中的信息。结果表明：^239+240Pu活度剖面中存在与¹³⁷Cs一致的1963年蓄积峰和1958年次蓄积峰,且两者呈较显著的线性相关关系（R²=0.765）,表明在动力环境较强的河口地区,^239+240Pu与¹³⁷Cs仍可以反映相同的沉积过程。^239+240Pu活度起始层位对应于1948年,而¹³⁷Cs对应于1954年,表明^239+240Pu具有更高的测试灵敏度。SC07柱状样中¹³⁷Cs/^239+240Pu的同位素比值比全球均值低,说明^239+240Pu存在区域沉降来源。     

长江口放射性核素Pu的大气湿沉降初步研究

利用东京^239,240Pu的年沉降和年降水数据,对长江口地区1957~2005年^239,240Pu 的年大气湿沉降通量进行研究。结果表明：长江口地区1957~2005年间^239,240Pu的大气湿沉降量在0.001 2~5.531 Bq/m²之间,累计湿沉降通量为34.556 Bq/m²;该地区Pu的大气湿沉降主要集中在1960 s;1960 s初频繁的大气核试验是造成^239,240Pu在1960 s沉降量较大的主要原因。长江口地区与东京地区^239,240Pu大气沉降变化基本一致,两地的大气湿沉降均在1963 年出现明显峰值。     

土壤颗粒组成影响137Cs含量的初步实验结果

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。在¹³⁷Cs的再分配过程中,土壤颗粒组成是影响土壤¹³⁷Cs的重要因子。一般认为,土壤中的¹³⁷Cs活度主要与粘粘含量有关,但这要取决于原生沉积物的颗粒组成。通过选取共和盆地主要的三种土壤类型,采集0~30cm的混合样品,进行入工筛分,测定不同粒径成分的¹³⁷Cs含量。初步实验表明,砂质土的¹³⁷Cs活度与平均粒径之间呈负指数关系,0.01~0.1mm组分对¹³⁷Cs含量的影响最为显著;壤质土的¹³⁷Cs活度主要与粗粉砂(0.01~0.05mm)含量有关,与137Cs活度主要与原生沉积物的颗粒特性和粒度有关.¹³⁷Cs一旦被原生沉积物颗粒吸附,在以后的土壤颗粒再分配过程中,是很难被置换掉的。     

沼泽沉积剖面特征元素比值及其环境意义——盐碱化指标及气候干湿变化

沼泽发育过程中堆积的各类沉积物真实地记录下区域环境演变与沼泽发育过程的信息。以向海沼泽湿地为研究对象,由¹³⁷Cs、²¹⁰Pb法定年实现沉积层深度坐标向年代坐标的转换,对典型沉积剖面特征元素比值进行了综合剖析。结果表明: Sr/Ba、Rb/K、(CaO+K₂O+Na₂O)/Al₂O₃等比值具有盐碱化和气候干湿变化的指示意义。该区域的盐碱化并非只发生在近几十年,而是由来已久,只是近年来人类活动促进了盐碱化进程。霍林河流域近240年来气候存在冷干-暖湿-冷干的多次波动,1880年之前气候以冷干为主,并有小幅度波动;1880年后气候开始转暖,但仍以冷暖波动振荡为主。     

长江口外海域沉积物中有机物的来源及分布

通过分析长江口外海域不同区域有机碳和氮的分布特征及其影响因素,了解了底部沉 积物中有机碳和氮同位素的生物地球化学特征,探讨二者对长江口外海域底部沉积物中有机 物来源的指示意义。运用质量混合模型,计算了长江输入的陆源有机物的贡献及其空间变化。结果表明,长江口外海域沉积物中TOC 和TN 的分布和东海陆架的环流体系有着密切关系, 与环流的分布相对应,如果大致沿31^oN 和123^oE 作为分界线, 整个研究区的TOC 和TN 的分布可划分为4 个具有不同分布特征的区域。TOC、TN、δ¹³C 和δ¹⁵N 分别与沉积物的平均粒 径呈线性相关关系,因此,粒度效应是控制长江口外海域沉积物中有机物分布和稳定同位素 碳、氮的一个重要因素。研究区内的C/N 比值能够在一定程度上体现有机物的来源信息,但δ¹⁵N 表现出了与C/N 和δ¹³C 不同的区域分布和变化特征。陆源有机物来源比重较高的区域与 长江口外海域赤潮突发频率最高的地区相对应。长江口附近沉积物中的陆源有机物来源最高, 超过了50%,且等值线呈舌状向东北方向凸出,表明了长江冲淡水的影响。陆源颗粒态有机物沉海底后,要不断经历早期成岩作用和生物作用,因此在在相同地点,陆源有机物对沉积物中有机物的贡献,要明显小于对悬浮颗粒态有机物的贡献。     

新疆137Cs定年时标解析

¹³⁷Cs在年代测定和土壤流失等领域得到了广泛的应用。在认定¹³⁷Cs时标前,需要消除粘土和有机质（TOC）对¹³⁷Cs 的富集作用。通过对比新疆多个湖芯钻孔¹³⁷Cs 序列,发现它们异于北半球¹³⁷Cs 沉降模式,即出现了1954、1963、1975 和1986 这四种时标且1986 年的¹³⁷Cs 比活度可能异常的高。通过分析艾里克湖钻孔的¹³⁷Cs序列,并结合新疆其他地区多个钻孔的¹³⁷Cs序列,与北半球¹³⁷Cs沉降特征以及靠近北疆的Belukha冰芯²⁴⁰Pu²³⁹Pu沉降记录进行对比,分析了新疆¹³⁷Cs时标的可靠性以及1986年¹³⁷Cs比活度异常高的原因。在新疆¹³⁷Cs多个时标中,仅1963年的时标是高信度的（即北半球¹³⁷Cs最大沉积年）。1954年¹³⁷Cs蓄积峰代表其全球初始显著沉降,距今已有2个¹³⁷Cs半衰期,当年沉积通量低且可能发生¹³⁷Cs垂直迁移,仅能作为次要时标。1975年的时标反映了1960s- 1970s的中国核试验,但距离罗布泊～300 km的博斯腾湖对中国核试验有截然相反的记录,表明中国核试验不是稳定信号,其核沉降范围以及对湖芯的影响作用还需进一步评估,不能作为可信的时标。1986年蓄积峰对应切尔诺贝利核事故,因核尘埃未大量进入平流层且距离新疆较远（～4 000 km）,但同时考虑到新疆位于核事故的西风环流下风区,所以该事故对新疆有影响但影响不大。1986年的¹³⁷Cs时标可作为次要时标。新疆湖芯1986年的异常高蓄积峰可能是由新疆最近几十年的人类活动（如过牧、耕种等）加上1987/1988年的高降水导致的地表侵蚀增强引起的。增强的地表侵蚀导致含有高¹³⁷Cs含量的表层土壤颗粒被冲刷进入湖泊,叠加在切尔诺贝利核事故¹³⁷Cs沉降之上,进而导致了湖芯沉积物记录到显著的1986年¹³⁷Cs蓄积峰。     

中国海洋油气资源开发与国家石油安全战略对策

石油是中国能源安全的核心问题,随着我国石油供应对外依赖程度的增大,石油安全问题越来越突出,将会成为我国21世纪经济、社会可持续发展面临的一个重要问题。我国是海洋油气资源丰富的国家,广阔的海域中分布着近100×10⁴km²的含油沉积盆地,近海石油资源量为240×10⁸t,天然气资源量为140×10¹²m³。海洋油气资源的开发利用,将能部分解决我国油气资源进口数量。本文讨论了解决石油安全的四种模式,对我国油气安全的国际和国内条件进行了分析,提出了解决我国油气安全的战略对策。     

我国典型季风海洋性冰川区雪坑中 主要阴、阳离子的来源

运用海盐示踪法、相关分析、趋势分析等方法,对我国两处典型季风海洋性冰川(海 螺沟1 号冰川和白水1 号冰川) 积累区雪坑主要化学离子来源进行了综合分析,结果表明： 两冰川区除Na⁺ 是海洋源外,其他离子主要是非海洋源;Cl^-、NO₃ ^-、SO₄ ^2- 、K⁺、Ca²⁺、Mg²⁺ 非 海洋源所占的比重,在海螺沟1 号冰川依次为52%、99%、100%、98%、99.9%、83%,白水 1 号冰川依次为68%、99%、100%、98%、99%、59%;分析认为,海螺沟1 号冰川离子的非 海洋源主要是大气环流远源物质和高原面物质输入,而白水1 号冰川除上述来源外,冰川区 近源物质输入对离子浓度贡献很大。两冰川区各离子具体来源存在较大的差异性并且阴、阳 离子来源的共源性较低,其主要原因是：(1) 冰川区内局地环境的差异,比如岩性、山谷风系 统、地形地貌等;(2) 两冰川区离子淋溶作用强度的差异,分析认为,海螺沟1 号冰川离子淋 溶作用较强;(3) 不同离子的来源方式、沉降方式、自身化学特征以及沉积后过程不同所致。     

格陵兰海近海海域夏季海水水质特征分析

2010年7月,在北京青少年科技俱乐部组织的北极科学考察活动过程中,对斯瓦尔巴德群岛、格陵兰岛以及冰岛的近海海域进行表层海水水样、冰样及陆地径流的采集。对采集样品的9项指标分析结果表明,海水样品中未检到F^-和NO₃^-;其他离子含量的排序依次为:Cl^-,Na⁺,SO₄^2-,Mg²⁺,K⁺,Ca²⁺,与自然海水常规离子含量的排序基本一致;各离子含量与氯度的比值与恒比定律中给出的值基本一致,证明了北极海水主要受到陆地降水直接补给。近岸海水的离子含量远远低于远岸海水的原因是由于冰川融化,通过地表径流的方式补给表层海水有关。斯瓦尔巴德群岛的地表径流中存在有NO₃^-,但对所采海水样品的检验中,未检测到NO₃^-,说明地表径流中的NO₃^-在海水的对流等作用下得以充分稀释。     

The transport and mass balance of fallout radionuclides in Blelham Tarn, Cumbria (UK)

Although lake sediment archives are widely used for reconstructing historical records of atmospherically delivered pollutants, the quantitative relationship between fallout levels and their record in the sediments is complex and not well known. The original input signal from the atmosphere can be significantly distorted by mediating transport processes in the catchment, through the water column and within the sediments themselves. Since these processes also affect the fallout radionuclide ²¹⁰Pb commonly used to date sediments, a better understanding of their impact is also important to improving the accuracy and reliability of sediment dating. Blelham Tarn has been the subject of a number of palaeolimnological investigations using radiometric dating techniques since the early 1970s. More recently it was the site of a major study carried out within the EU Transuranics project concerning the long-term fate of fallout radionuclides in catchment/lake systems. This paper reviews the radiometric data from this study and uses the results to determine mass balances for fallout ²¹⁰Pb, ¹³⁷Cs and ^239+240Pu in Blelham Tarn, and their spatial distribution over the bed of the lake. Atmospheric fluxes were determined by measuring concentrations in rainwater and cumulative inventories in soil cores from non-eroding sites. Sediment records in a grid of 16 cores were used to determine the spatial distribution over the bed of the lake, and net inputs from the catchment. Mass balance calculations indicate that c. 47% of ²¹⁰Pb in the sediments derives from erosive inputs from the catchment. For ^239+240Pu the figure rises to 61%. Reduced amounts of ¹³⁷Cs in the sediments are attributed to greater losses of this radionuclide from the water column via the outflow due to its greater solubility. Inputs of radionuclides from the catchment are concentrated near one of the major input streams. Away from this part of the lake the sediment record is dominated by direct atmospheric fallout, though the detailed pattern is influenced by sediment focussing. A one parameter catchment/lake transport model is developed that incorporates the assumption that transport rates will decline with time as fallout on the catchment diffuses into the soil and becomes less available for removal. Values of the transport parameter were calculated for ²¹⁰Pb and ^239+240Pu and found to be comparable. The results suggest that it will take c. 11000 years to remove 50% of ^239+240Pu from the catchment to the lake.     

Anthropogenic radionuclides in the water column and a sediment core from the Alboran Sea: application to radiometric dating and reconstruction of historical water column radionuclide concentrations

Global fallout is the main source of anthropogenic radionuclides in the Mediterranean Sea. This work presents ¹³⁷Cs, ^239+240Pu and ²⁴¹Am concentrations in the water column in the southwest Alboran Sea, which was sampled in December 1999. A sediment core was taken at 800 m depth in the area (35°47′ N, 04°48′ W). ²¹⁰Pb, ²²⁶Ra, ¹³⁷Cs and ^239+240Pu specific activities were measured at multiple depths in the core for dating purposes. ¹³⁷Cs and ^239+240Pu profiles did not show defined peaks that could be used as time markers, and they extended up to depths for which the ²¹⁰Pb-based constant rate of supply (CRS) dating model provided inconsistent dates. These profiles can be useful to test dating models, understood as particular solutions of a general advection–diffusion problem, if the time series of radionuclide inputs into the sediment is provided. Thus, historical records of depth-averaged ¹³⁷Cs and ^239+240Pu concentrations in water, and their corresponding fluxes into the sediment, were reconstructed. A simple water-column model was used for this purpose, involving atmospheric fallout, measured distribution coefficient (k _d) values, and a first-estimate of sedimentation rates. A dating model of constant mixing with constant sedimentation rate was applied successfully to three independent records (unsupported ²¹⁰Pb, ¹³⁷Cs and ^239+240Pu), and provided the objective determination of mixing parameters and mass sedimentation rate. These results provide some insight into the fate of atmospheric inputs to this marine environment and, particularly, into the contribution from the Chernobyl accident.     

Sediment focusing in six small lakes inferred from radionuclide profiles

Sediment focusing in six small lake basins is inferred from sedimentary radionuclide profiles. The activities of¹³⁷Cs and⁹⁺²⁴⁰Pu do not decrease to zero above the sub-surface maximum but tail off gradually. Similar behavior is observed in the sediments of three lakes for¹³⁴Cs and⁶⁰Co, which were added only to the lake. This upward tailing is not caused by bioturbation or erosion from the watershed. Sediment focusing is the likely cause, further substantiated by inventories in deep sediments of⁹⁺²⁴⁰Pu and²¹⁰Pb that are twice as high as expected from atmospheric fallout. Inventories in deep sediments of¹³⁷Cs are in several cases lower than expected from atmospheric fallout, and cannot be explained by hydraulic flushing from the lakes, as this would require unreasonable flushing rates. The low¹³⁷Cs inventories and the sedimentary profiles of the¹³⁷Cs/⁹⁺²⁴⁰Pu ratio are consistent with¹³⁷Cs removal from the water column by boundary scavenging to shallow sediments. The profiles and inventories of all three nuclides could be reproduced with a simple three box model, assuming focusing of shallow sediments (50–60% of total sediment area) to deep sediments with a rate constant of 5–10% yr^–1.This is the seventh of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of lake sediment. Dr P. G. Appleby is guest editing this series.     

Evaluating the mobility of137Cs,239+240Pu and210Pb from their distributions in laminated lake sediments

Post-depositional mobility of¹³⁷Cs,^239+240Pu and²¹⁰Pb was assessed in six small lake basins by comparing sedimentary nuclide profiles with their known fallout history. Laminae couplets, when present, were determined to be varves because the¹³⁷Cs and^239+240Pu 1963 fallout peaks are present in laminae couplets corresponding to years 1962–1964. There is no evidence of mobility of²¹⁰Pb, because 1) mass accumulation rates based on²¹⁰Pb agree with those based on¹³⁷Cs and^239+240Pu peak depths and with those based on varve counts, and 2)²¹⁰Pb ages agree with varve ages. Significant mobility of¹³⁷Cs is evident from the penetration of¹³⁷Cs to depths 15–20 cm deeper than^239+240Pu. Deep penetration of¹³⁷Cs in spite of a sharp gradient below the peak is interpreted by a numerical model to suggest that¹³⁷Cs is present in two distinct forms in these sediments, 67–82% as an immobile form and 18–33% reversibly adsorbed with a K _d of approximately 5000. The profiles can be interpreted equally well assuming a small portionof the total¹³⁷Cs was present as an extremely mobile phase (K _d 5000) in the months to years following peak fallout, slowly becoming more strongly adsorbed. High NH ₄ ⁺ concentrations in porewaters may enhance diffusion of the mobile form of¹³⁷Cs, but not of the immobile form of¹³⁷Cs that defines the sharp gradient. Mobility of¹³⁷Cs is likely also enhanced by the low clay content and the high porosity of these sediments. Thus the first detection of¹³⁷Cs in the sediments cannot automatically be assumed to correspond to a date of 1952 (initial testing of thermonuclear weapons), although the depth of the peak can be assumed to correspond to 1963 (the year of maximum fallout from testing of thermonuclear weapons).^239+240Pu is a more reliable sediment chronometer than¹³⁷Cs because it is significantly less mobile.This is the sixth of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of lake sediments. Dr P.G. Appleby is guest editing this series.     

白令海和楚科奇海陆架区的生源物质埋藏通量研究

楚科奇海和白令海通过白令海峡相连,是气候变化研究的关键区域。利用210Pb过剩法开展两个海域沉积过程和生源物质的埋藏通量研究。研究发现,白令海陆架区沉积柱样(NB22)受到生物扰动影响,楚科奇海沉积物柱样(R17)所受生物扰动很小。通过建立模型,获得楚科奇海陆架区的沉积速率为0.6±0.1 mm·a~(-1),白令海陆架区的沉积速率为2.1±0.7 mm·a~(-1)。忽略沉积过程,白令海陆架区由生物扰动引起的混合因子为1.38±0.92 cm2·a~(-1);考虑沉积过程,则混合因子为0.65±0.95 cm2·a~(-1)。白令海的有机碳、生源硅、Ca CO3的埋藏通量分别为:6.85 mmol C·m-2·d-1、37.7 mmol Si·m-2·d-1、3.15 mmol C·m-2·d-1;楚科奇海的有机碳、生源硅、Ca CO3的埋藏通量分别为:5.71 mmol C·m-2·d-1、9.78 mmol Si·m-2·d-1、3.08 mmol C·m-2·d-1。楚科奇海陆架区具有高效的垂直输运的海洋生物泵,白令海陆架区海洋生物泵可能存在较强的水平输运过程。海洋沉积物中210Pb信号不仅可以定量沉积速率和埋藏通量,也在一定程度上反映海洋底栖生物的扰动强度。