雷州半岛造礁珊瑚Porites lutea月分辨率的δ18O温度计研究

对雷州半岛西南部珊瑚岸礁区1995～1997年生长的造礁珊瑚Poriteslutea的骨骼密度、生长速度和δ¹⁸O分析表明：1)造礁珊瑚骨骼的密度、生长速度和δ¹⁸O与其生存环境的表层海水温度之间存在很好的相关性,高密度、低生长速率和高δ¹⁸O值对应于冬季;2)δ¹⁸O具有明显的年际和季节性变化。根据δ¹⁸O估计的表层海水温度变化范围与实测基本一致,进一步揭示了珊瑚骨骼δ¹⁸O可作为定量研究高分辨率表层海水温度变化的温度计。     

用树轮δ13C重建1685年以来的大气CO2浓度变化趋势

对采自浙江西天目山地区的3株柳杉树盘,交叉定年后,测定了3株树轮^δ13C的年序列,分析了3株树轮^δ13C序列中所含的共同环境变化信息。用二项式拟合法去除气候因素引起的3个^δ13C序列的高频变化,得到3个低频变化序列。分析了theLowDome冰芯记录的大气CO₂浓度与树轮^δ13C序列低频变化趋势的关系,建立了相应的转移函数,重建了天目山地区1685年以来大气CO₂浓度变化。结果表明:用3株树轮^δ13C序列重建的结果有较好的一致性,并与南极冰芯的记录及前人研究结果有很好的吻合。这一结果表明用同一地区不同树木个体的树轮^δ13C序列的低频变化序列可以重建出基本一致的大气CO₂浓度变化历史。     

现代沉积的210Pb计年

²¹⁰Pb具有百年时间尺度沉积计年的重要价值。²¹⁰Pb_ex计年假设：沉积物是封闭系统；进入水体的²¹⁰Pb能有效地转移到沉积物中并不发生沉积后迁移；非过剩²¹⁰Pb与其母体²²⁶Ra保持平衡。²¹⁰Pb_ex计年可用稳定输入通量-稳定沉积物堆积速率模式、常量初始浓度模式或恒定补给速率模式。沉积物柱芯必须保持原态并以0．5～1cm间隔分截；用相应层节²²⁶Ra校正。沉积物表层混合作用及²²²Rn的丢失可能导致顶部²¹⁰Pb_ex异常。季节性缺氧湖泊沉积物顶部可能存在²¹⁰Pb及²¹⁰Po的再迁移。²¹⁰Pb与¹³⁷Cs两种计年方法原理上具有根本差别。²¹⁰Pb，¹³⁷Cs与沉积纹理方法对比是准确计年的重要保证。     

南海北部4MaB.P.以来古海洋变迁的长链烯酮记录

通过对ODP184航次1147/1148站位约4MaB.P.以来沉积物中来源于定鞭金藻的生物标志化合物的研究,对南海北部晚上新世以来的古海洋生产力、表层海水温度及CO₂分压的变化情况进行了探讨.定鞭金藻生产力与硅藻生产力一样在0.9MaB.P.以前比较稳定地保持在较低水平,而0.9MaB.P.后定鞭金藻生产力较高,且呈现冰期低间冰期高的波动,硅藻生产力则呈现持续升高的趋势.由C37烯酮不饱和度指标获得的南海北部4MaB.P.以来表层海水的UK′37温度与浮游有孔虫壳体δ18O具有较好的相关性,且能显示出0.9MaB.P.来的19个氧同位素期,表明将U37K′37温标应用到晚第四纪以前基本上是可行的.由δ13C37:2计算的表层海水pCO₂显示,晚上新世的pCO₂要高于300μL/L,而第四纪的pCO₂尽管存在波动,却基本上在300μL/L以下.计算出的晚第四纪的pCO2十分稳定,与同期的大气pCO₂历史变化不一致.这可能与计算中简单地假定某些参数(如生长速率)为常数有关,这些参数在第四纪冰期间冰期旋回中可能有较大变化.     

BrF5法氧同位素实验系统中CO2转换器的改进及意义

硅酸盐、氧化物的氧同位素测定分析,是成岩成矿物质 源区鉴定、矿物岩石形成温度确定、成岩成矿地球化学机理 推测的重要手段之一^[1]。在固体地球科学的诸多学科^{[2]以 及环境科学、水文、古气候、天体化学等其他学科均有着广泛 的应用。因此,随着样品量的增加,提高实验室的BrF5法氧 同位素实验系统的工作效率颇有意义。 图1为BrF₅法氧同位素实验系统装置。当系统真空抽 至3×10-3Pa时,充入氩气。分别将已称好的200目干燥样 品12mg加入各反应器,经2小时200℃去气抽真空后,将化 学计算量}     

东北四海龙湾玛珥湖沉积物纹层计年与137Cs、210Pb测年

对东北四海龙湾玛珥湖SHLF6孔纹层沉积物的¹³⁷Cs放射性测量表明:¹³⁷Cs比活度的最大值出现在55cm处,对应于1963年世界原子弹试爆高峰期。纹层计年表明0～6cm共有35个纹层层偶。从75cm到65cm,¹³⁷Cs比活度从256±009dpm/g急剧增加到1868±017dpm/g,可能65cm对应于1954年。通过测量²²⁶Ra子核²¹⁴Pb和²¹⁴Bi（能量为295keV,352keV和609keV）放射的光子数获得²²⁶Ra比活度数据,然后求得过剩²¹⁰Pb_{比活度（²¹⁰Pbuns）。²¹⁰Pbuns比活度随深度增加而呈指数衰减,其异常波动可能与人类活动以及沉积速率变化有关,例如55cm处²¹⁰Pb比活度较高,与¹³⁷Cs的峰值对应,这可能与1963年前后人工核实验的高峰有关,因为核试验不仅产生¹³⁷Cs,而且可以产生208Pb和²¹⁰Pb;45cm处²¹⁰Pb比活度较低,而²²⁶Ra较高,可能与人类活动加剧,导致沉积速率增加有关。根据²¹⁰PbunsCRS模式,SHLF6孔0～19cm的平均沉积速率为20mg/cm²·a,或约为011cm/a。²¹⁰Pb测年数据与¹³⁷Cs时标及纹层计年均有很好的一致性。四海龙湾玛珥湖发育的纹层为年纹层,可以建立高分辨率时间序列。}     

中东亚干旱半干旱区C3植物δ13 C值的分布 及其对气候的响应*

植物化石和土壤中的有机质碳同位素指标常用来反映古气候的变化,然而碳同位素这个指标在特定地区反映气候的定量关系缺乏检验。研究剖面选择自中国的秦岭(34°14'24″N,106°55'30″E)到蒙古人民共和国北部,接近贝加尔湖地区(51°35'08″N, 100°45'49″E)的研究剖面线,选择了3种C₃植物(Artemisia scoparia, Ajania achilleides 和 Artemisia frigida),在剖面线上沿南北方向上每隔4'到5'采取一个样点,共选取161个C₃植物茎叶样品进行了δ¹³ C值测定。同时收集了剖面线附近气象站的降水、气温等资料,用插值方法得到每个采样点的气温、降水数据。分析表明:C₃植物的δ¹³ C值分布范围为-30 ‰ ~-22 ‰ ,其平均值为-26.81 ‰ ,该平均值较全球C₃植物δ¹³ C平均值偏正。通过对比C₃植物δ¹³ C与年均温、年均降水量、生长季节的干燥度等随纬度的变化规律,发现C₃植物δ¹³ C、年均降水量、生长季节的干燥度有非常一致的变化趋势,而C₃植物δ¹³ C和年均温不具有一致性。通过一元回归分析也同样发现C₃植物δ¹³ C与年均降水量呈线性负相关关系(y=-0.0077x-24.838,n=161,R²=0.4418,p=0.01),与生长季节的干燥度呈线性正相关关系(y=0.7328x-28.806,n=161,R²=0.3685,p=0.01),而与年均温度没有明显的相关关系(y=-0.0461x-26.756,n=161,R²=0.0232,p=0.01)。在本研究区C₃植物δ¹³ C对年均降水量和生长季节的干燥度响应十分显著,而对温度的响应不明显。研究区具有明显的降水和温度的梯度分布特征,是验证植物碳同位素与气候关系的理想场所,而土壤中的有机质碳同位素与其地面上的植物碳同位素息息相关。研究也说明,在本研究区或其他气候植物组合相似的地区可以利用古土壤中的有机质碳同位素来定量或半定量地反映古气候的变化。     

沉积岩中无机CO2热模拟实验研究

结合三水盆地的地质特点，分析了无机CO₂热模拟实验研究的可能性，进行了不同条件下的模拟试验和相关的分析测试，提出了无机CO₂生成量和转化率的概念和计算方法。从实验结果来看：含有一定量碳酸盐矿物的沉积岩，在一定温度下可转化形成相当数量的无机CO₂，无机CO₂转化率越高，岩石中碳酸盐矿物越容易转化生成无机CO₂；相同热成熟度条件下，Ⅱ型干酪根生成有机CO₂的量较Ⅲ型的少；CO₂中碳同位素与CO₂的成因密切相关，随有机质热成熟度的增加，同种类型有机质生成的有机CO₂相对富集¹³C；无机CO₂较有机CO₂的碳同位素明显富集¹³C，随水介质的pH值降低，无机CO₂气含量、模拟温度及时间的增加，无机CO₂相对富集¹³C。实验研究结果为CO₂成因研究及其资源评价提供了实验依据。     

CaCO3生物矿化的研究进展——有机质的控制作用

生物CaCO₃是自然界分布最广泛的一类生物矿物,其组成除了无机相的CaCO₃外,还含有少量的有机质,包括水可溶(SM)和水不可溶有机质(IM),SM富含阴离子基团,是控制CaCO₃结晶的重要因素之一。通过有机—无机界面分子识别,有机质选择性地与CaCO₃晶体特定方向的面网相互作用,从而对CaCO₃的生长、形貌、多型及结晶学定向等产生明显的控制作用。有机—无机界面的分子识别机制包括静电、晶格几何匹配和立体化学互补等。仿生矿化的研究为进一步深入了解生物矿化的机理及制造高级复合材料提供了新的方法。     

长江河口水下三角洲137Cs地球化学分布特征

文章通过对长江口水下三角洲采集的10个柱状样放射性核素¹³⁷Cs的分析可以得知,长江口水下三角洲¹³⁷Cs剖面中均存在清晰的最大蓄积峰,其峰值比活度介于5.68±1.03～21.74±1.39Bq/kg之间,平均值为14.11±1.10Bq/kg,最大蓄积峰所处的深度为55～117cm。剖面中¹³⁷Cs最大蓄积峰应该与1963年的¹³⁷Cs散落沉降相对应。长江口水下三角洲的表层沉积物中的¹³⁷Cs比活度范围介于0～9.19±1.12Bq/kg之间,并且与长江流域其他地区的表层¹³⁷Cs比活度相一致。长江口水下三角洲可探测到的¹³⁷Cs比活度的最大深度范围在88～160cm的范围内变化,¹³⁷Cs蓄积总量为2361.30±174.38～17714.94±262.14Bq/m²,平均值为9664.97±100.05Bq/m²,¹³⁷Cs比活度的最大深度及¹³⁷Cs蓄积总量均表现出从岸向海逐渐增加的趋势。实测的¹³⁷Cs总量均大于长江流域的¹³⁷Cs背景值,说明了长江口水下三角洲的¹³⁷Cs蓄积既有大气散落直接沉降的来源,又有流域侵蚀带来的¹³⁷Cs输入,并且主要以后者为主。通过放射性核素示踪模型分析长江口水下三角洲¹³⁷Cs散落蓄积特征可以得知,长江口水下三角洲¹³⁷Cs的蓄积以长江流域来源为主,说明了放射性核素¹³⁷Cs在长江口水下三角洲沉积物中的蓄积主要受流域侵蚀因素的影响。     

古海洋、古气候研究的新工具

“分子温度计”是通过有机地球化学方法获得的沉积物中烯酮化合物的相对丰度来估算古海水表面温度的。烯酮化合物的不饱和度（Ｕｋ３７）与其生物母源Ｅｍｉｌｉａｎｉａｈｕｘｌｅｙｉ的生长温度密切相关，同时这种信息不受有机质溶解与成岩作用影响，而能较完整地保存于海洋沉积物中，因而通过它能很好地反映古海洋与古气候的演变。这种方法不受盐度、上升流与极地冰盖变化等因素影响，尤其适用于碳酸盐贫乏海区的古海洋与古气候研究     

Application of the long chain diol index (LDI) paleothermometer to the early Pleistocene (MIS 96)

Recently, a new organic geochemical paleothermometer based on the relative abundance of long chain alkyl 1,13- and 1,15-diols, the so-called long chain diol index (LDI), was proposed. Because of its novelty, the proxy has not been reported for sediments older than 43 ka. We therefore determined the LDI for 14 sediment samples from the early Pleistocene between 2.49 and 2.41 Ma, comprising Marine Isotope Stage (MIS) 98 to 95, and converted the values to sea surface temperature (SST) estimates to test whether the LDI could be applied or not to the early Quaternary. We show that the long chain diols can be preserved in marine sediments from the early Pleistocene, although at our study site this is limited to periods of increased biomarker accumulation (glacials). Although the results are based on a limited time interval and number of samples, the similarity between LDI-based SST and alkenone-based SST from the same samples suggests that the LDI proxy may have potential for studies covering the entire Quaternary.     

南海长链烯酮化合物的检测及U37^k值的应用

首次系统地在南海大面积站位中检测出长链烯酮化合物。通过长链烯酮指标Ｕ３７ｋ与实测表层海水温度（ＳＳＴ）的对比研究,发现海洋沉积物样品在室温下长期（１７ａ）密封保存,长链烯酮指标Ｕ３７ｋ值无明显变化。Ｕ３７ｋ值在南海海区指示的表层海水温度与季节有关,主要反映秋、冬两季,即１０月至次年３月间的ＳＳＴ。     

六盘山群沉积物磁化率记录的早白垩世气候变化

白垩纪气候环境研究对认识现今全球环境格局的形成具有重要意义,现有的白垩纪环境变化记录均来自海洋沉积物,本文通过对我国中部六盘山地区六盘山群地层沉积与岩石磁化率测量分析,获得了128.15～115.82Ma期间陆相沉积物记录的气候变化信息。结果显示磁化率值总体较低,以125Ma为界大致可以分为前低后高两个阶段;结合岩石磁学测量及沉积相、岩石中铁含量与磁化率变化关系分析,认为岩石磁化率主要与源区磁性矿物的种类及含量有关,据此揭示六盘山地区在该时间段气候总体为干热环境,并可分为128.15～125Ma间气候相对湿热和125～115.82Ma间气候相对温湿两个阶段。磁化率记录的这种气候转变与海洋沉积物记录的全球海平面温度变化趋势一致,但相对海平面温度由升高到降低的转折时间提前约1.7Ma。     

Flandrian sea-level changes in the Fenland. I: The geographical setting and evidence of relative sea-level changes

The Flandrian sediments of the Fenland record the infilling of the Wash embayment on the east coast of England, UK. Since at least 6500 BP changes in sea level have been a major control on the rate and pattern of sediment accumulation. New data are presented from the area which together with published information allow the reconstruction of palaeoenvironments from 6500 to 2500 BP. The major environmental changes involved alternations between freshwater fen and intertidal marine sedimentation. Each episode was characterised by transitional changes as vegetation and sediment zones shifted over large areas. Marine/brackish sediments are found up to 45 km inland of the present coast. Radiocarbon dated sea-level index points, with relevant stratigraphic and micropalaeontological data, ranging from 6415 BP at ?8.17m OD to 2595 BP at +1.45m OD, are described.     

Temperature and Salinity Effects on Alkenone Ratios Measured in Surface Sediments from the Indian Ocean

We compare alkenone unsaturation ratios measured on recent sediments from the Indian Ocean (20°N–45°S) with modern sea oceanographic parameters. For each of the core sites we estimated average seasonal cycles of sea surface temperature (SST) and salinity, which we then weighted with the seasonal productivity cycle derived from chlorophyll satellite imagery. The unsaturation index (U₃₇^K′) ranges from 0.2 to 1 and correlates with water temperature but not with salinity. TheU₃₇^K′versus SST relationship for Indian Ocean sediments (U₃₇^K′= 0.033 SST + 0.05) is similar to what has been observed for core tops from the Pacific and Atlantic oceans and the Black Sea. A global compilation for core tops givesU₃₇^K′= 0.031 T + 0.084 (R= 0.98), which is close to a previously reported calibration based on particulate organic matter from the water column. For temperatures between 24° and 29°C, however, the slope seems to decrease to about 0.02U₃₇^K′unit/°C. For Indian Ocean core tops, the ratios of total C₃₇alkenones/total C₃₈alkenones and the slope of theU₃₇^K′-SST relationship are similar to those previously observed for cultures ofEmiliania huxleyibut different from those previously published forGephyrocapsa oceanica.EitherE. huxleyiis a major producer of alkenones in the Indian Ocean or strains ofG. oceanicaliving in the northern Indian Ocean behave differently from the one cultured. In contrast with coccolithophorid assemblages, the ratios of C₃₇alkenones to total C₃₈alkenones lack clear geographic pattern in the Indian Ocean.     

Fluvial deposits within the Pleistocene Crag at Thorpe St Andrew,Norwich, England

This paper records the findings at a temporary exposure at Thorpe St Andrew near Norwich, Norfolk, UK in Early and early Middle Pleistocene Crag deposits. The British Geological Survey (BGS) describes the particular formation exposed as Norwich Crag consisting of Early Pleistocene shallow marine sediments. The section shows a succession of sorted sands and gravels overlain by a sandy diamicton. Based on field evidence and clast analysis, the sands and gravels are interpreted as the product of point bar and overbank sedimentation and represent the product of a river cutting into and aggrading within the more widespread shallow marine deposits. Composition of the sediments indicates derivation, primarily from Wroxham Crag Formation, with a contribution from Norwich Crag. The sandy diamicton is interpreted as late Middle Pleistocene Corton Till that is recorded in the area. A distinct pattern of colour changes at the top of the sands and gravels is interpreted as a soil that developed on the fluvial sediments before being overridden by the glacier that deposited the Corton Till. The existence of the fluvial sediments within the regional shallow marine deposits suggests that a fall of sea-level, possibly due to climate cooling, while the elevation of the sediments and the adjacent Crag implies that the site has been uplifted since sedimentation. This is the first observation of terrestrial sediments within the shallow marine Crag. The paper also makes a contribution to understanding the diagenetic processes that give deposits within this region some distinctive colour and sediment patterns.     

白令海与西北冰洋表层沉积物中四醚膜类脂物研究及其生态和环境指示意义

通过对中国第3次和第4次北极考察在白令海和西北冰洋采集的65个表层样沉积物中生物标记物四醚膜类脂物(GDGTs)的研究,发现西北冰洋表层沉积物中类异戊二烯和支链GDGTs的浓度分布大致以楚科奇海和波弗特海的陆坡为界线,呈现南高北低的特征,这一特征主要与水体生产力和陆源有机质的输入量有关.基于GDGTs的陆源输入指数BIT显示,从楚科奇海北部到高纬度区的阿尔法脊,陆源有机质的相对比例明显增加,与有机碳稳定同位素等结果一致,表明BIT可以用来指示北极陆源有机质输入量的变化.应用前人TEXL86-SST方程估算的研究区表面海水温度SST与现代年均SST和夏季平均SST的相关性较差,原因可能与陆源输入的类异戊二烯GDGTs干扰以及低的古菌生产力有关.从季节性海冰覆盖区到永久性海冰覆盖区,基于支链GDGTs的环化指数CBT明显升高,可能反映了CBT对海冰覆盖状况的响应,但其响应机制还不清楚.基于支链GDGTs的环化指数CBT和甲基化指数MBT估算的北极陆地年均大气温度和土壤pH差异较大,可能是由表层沉积物的来源复杂以及混合作用造成的.     

海洋沉积物可溶铁测定条件的探讨

海洋沉积物可溶铁Fe~(3+)/Fe~(2+)比值,已被海洋地质工作者作为海洋油气化探的一项间接指标应用于东海油气化探中。这种铁的含量受提取酸的种类、浓度、样品微沸时间、放置时间等条件的影响。必须采用统一的可溶铁测定方法,只有在同一标准条件下测定的海洋沉积物可溶铁结果才有对比意义。     

Exploration of empirical relationship between surface soil temperature and surface soil moisture over two catchments of contrasting climates and land covers

Soil moisture plays a very important role in hydrological processes. It has been found in many studies that the surface soil moisture (SSM) is highly related to the diurnal change of the surface soil temperature (?SST) at the same soil depth. However, some studies contradict this common belief with findings of a much stronger correlation between the SSM and the SST. In order to investigate this further, we have carried out for the first time a comparative assessment of the in-situ measured SST and ΔSST for SSM estimations, over two catchments with contrasting climate types and land uses (i.e. one in the UK and the other in Australia). In both catchments, the time point for the highest relationship between the SST and the SSM is explored. As a result, it is found the SST is more suitable to monitor the variability of the SSM than the ΔSST in both catchments. Moreover the proposed seasonal-based classification method further improves the SSM simulation results in both catchments, with a superior performance observed in the UK catchment (NSE = 0.900 and RMSE = 0.030). In the Australian catchment, a relatively weaker correlation is observed and some potential reasons are explained. The potential applications of the findings for remote sensing soil moisture retrievals are also discussed.