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the Low Dome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.     

新疆罗北洼地湖相沉积物有机碳同位素的变化序列及其古环境意义

测定了新疆罗布泊地区湖相沉积物CK-2钻孔样品的总有机碳含量（TOC）及其同位素组成、碳酸盐含量和C/N比值等环境代用指标,以及石膏矿物的质谱-铀系年龄。测试结果表明,20～9kaB.P.期间沉积物δ¹³C_org.在-23.4‰～-16.1‰之间波动且阶段性明显,与TOC呈现良好的相关关系,整体变化趋势同南极Dome C冰芯中记录的全球大气CO₂浓度一致;C/N比值表明有机碳来源主要是陆生高等植物。因此大气CO₂浓度变化是影响20～9kaB.P.期间罗布泊湖相沉积物δ¹³C_org.值变化的主导因素,周围山体上C₃/C₄植物相对生物量的变化则是另一重要因素。依据δ¹³C_org.的变化序列将此时间段湖区古环境的演化分成6个阶段:20.0～14.1kaB.P.期间受到末次盛冰期的影响,气温偏低,湖水丰沛;14.1～13.3kaB.P.是一个气候不稳定期,冷暖波动较频繁,但以暖为趋势;13.3～12.8kaB.P.期间经历了一段冷期,于12.8kaB.P.结束了末次冰期,随后气候开始转暖至11.8kaB.P.;其后气温再次变冷并维持到10kaB.P.;最后从10kaB.P.进入全新世暖期。δ¹³C_org.序列明显向偏负方向变化,表明该地区变暖的趋势相当明显。罗布泊地区日益干旱化是全球气候变化的结果,尤其是受到全球CO₂浓度的不断升高所制约。     

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。     

负热电离质谱法测试硼同位素与大气pCO2的重建

海洋有孔虫的硼同位素能够反映海水酸碱度值的变化,为研究大气CO₂浓度在长时间尺度上的变化提供了一种新的手段,甚至可能超出冰芯所能企及的范围。天然样品中硼同位素的测定方法最为常用的是热电离质谱法,分为正热电离质谱法与负热电离质谱法。目前海洋有孔虫硼同位素分析主要应用负热电离质谱法,该方法最大的优点是所需要的样品量比较小（＜1ng B),实验精度却相对比较高(0.6‰～2.0‰;  2sd.)。近年来,基于常规负热电离质谱法发展的全蒸发负热电离质谱法通过分析完所有样品而有效降低分析过程中所发生的分馏效应所带来的影响,并使样品的信号最大化,该方法精度能够达到0.7‰(2s.d.)。本文详细介绍了常规负热电离质谱法和全蒸发负热电离质谱法的各个分析步骤,包括样品前处理、涂样、质谱分析、同质异位素干扰以及实验分析精度等方面。随着实验分析技术的进展,海洋有孔虫硼同位素已被用来重建长时间尺度(百万年和千万年)和短时间尺度(冰期-间冰期)的大气CO₂浓度变化。现有的研究证实利用海洋浮游有孔虫硼同位素重建的大气CO₂浓度变化与Vostok冰芯记录的大气CO₂浓度变化吻合地很好。     

深海沉积物10Be记录研究

DSDP519钻孔¹⁰Be测定结果表明，在B／M，M／G两地磁极性倒转期间，¹⁰Be产生率均约增加20％。DSDP519孔δ¹⁰Be曲线与DSDP502孔δ¹⁸O曲线具有明显的正相关关系。CT85－5钻孔¹⁰Be曲线在34000±3000aB．P存在明显的峰，峰值比正常值高出2．5倍，⁹Be，Zn变化曲线中均未观察到此峰，与Vostok冰芯¹⁰Be峰在时间上属于同期。这进一步说明了此时期内¹⁰Be浓度增加是全球性的，只能归因于¹⁰Be产生率的增加。Raisbeck峰讯号可以成为某些储存库精确时标。     

海南岛万泉河口沉积物有机碳、 氮同位素的特征及其环境意义*

对海南岛万泉河口沙美内海柱样K3和K4沉积物进行生物地球化学指标总有机碳(TOC)、总氮(TN)、有机碳同位素(δ¹³ C)、氮同位素(δ¹⁵ N)的分析,以及²¹⁰ Pb定年了解其近代变化特征,追踪沉积物有机质来源的变化,提取沉积环境演变及人类活动的信息。K3中TOC的变化介于0.51 ％ ~1.12 ％ ,K4变化介于0.43 ％ ~1.49 ％ ,而其随时间的变化反映了流域内人类活动的历史。17世纪TOC含量明显增加记录了明末清初开始流域内广泛种植农作物的活动,19世纪以来TOC含量逐渐增加,至现代达最高值,对应了工业革命以来人类活动的增强。K3和K4的δ¹³ C值变化分别在-24.38 ‰ ~-21.02 ‰ 之间和-24.74 ‰ ~-20.17 ‰ 之间,δ¹⁵ N值变化分别在2.20 ‰ ~4.62 ‰ 之间和2.39 ‰ ~5.02 ‰ 之间,映证了本区沉积物有机质是陆源物质和海洋物质混合的特点。明末清初开始流域内广泛种植玉米等农作物造成δ¹³ C值增加和δ¹⁵ N值减少; 自19世纪以来至现在,该区的经济活动增加,人口的持续增长,尤其是近50年来化肥农药的大量使用,造成陆源输入的有机碳含量大幅增加,使δ¹³ C值减少和δ¹⁵ N比值增加。 δ¹³ C值自19世纪以来就逐渐变轻,说明陆源和海洋有机碳的比例发生了变化,较轻的陆源有机碳比例相对增加,较重的海洋有机碳比例相对减少,反映了玉带滩沙坝的增长、沙美内海封闭、海水交换作用减少的状况。C/N比值分别从底部的16.19和17.36到顶部减小为11左右,自19世纪以来呈明显减小的趋势也反映了沙美内海泻湖自生的藻类有机质供应越来越多,也说明了其逐渐封闭、水动力条件越来越弱,与外海的交换作用逐渐减少的状况。     

云贵高原湖泊CO2的地球化学变化及其大气CO2源汇效应

湖泊是大气CO₂的源还是汇,长期以来一直都存有争议。云贵高原地区的湖泊由于受流域碳酸盐岩风化作用的影响,使这一问题就显得更特殊,也更复杂。本次研究通过化学平衡计算和气相色谱测定两种方法得到了比较一致的湖水CO₂浓度结果。研究发现,在夏季强烈的光合作用消耗了湖水CO₂,致使湖水中CO₂浓度降低。在贵州草海、百花湖以及云南的泸沽湖、杞麓湖,表层湖水CO₂分压(为便于与大气CO₂比较,文中湖水CO2用分压单位表示)小于200μatm,远低于大气CO₂分压,湖泊正不断地从大气中吸收CO₂,从而构成大气CO₂的汇。     

宇宙射线通量和气候变迁与地球磁场强度变化的关系

通过分析近30000年以来地球磁场强度和大气中¹⁴C 含量变化,讨论了¹⁴C年龄偏离实际值的原因,提出以地球磁场强度随时间的变化率校正¹⁴C 年龄T_c 偏离实际年龄T_t 的公式,即T_t=T_c-b(T_c-T_?|_F（1）ΔF/ΔT。用这一公式校正了¹⁴C 测年技术给出的新仙女木事件发生的时限,并获得了与树轮年龄和U-Th 年龄一致的结果。本文还对12000年以来地球磁场强度变化与气候变迁的相关性做了探讨。     

U37K与海水表层温度

Ｕ₃₇^Ｋ是指少数藻类生物所特有的一种分子化合物（长链不饱和酮）的不饱和指数。在现代海洋沉积物中，Ｕ₃₇^Ｋ与浮游有孔虫的¹⁸Ｏ值具有很好的相关性。在实验室培养的藻类生物体中、海洋悬浮颗粒物及海洋沉积柱样的表层样中均检测出长链不饱和酮，其Ｕ₃₇^Ｋ与生物生长环境的海水表层温度具有很好的线性关系。因此，在古气候研究中，Ｕ₃₇^Ｋ可作为一种有效的古温度指标，且在古气候研究中已得到应用。主要介绍了Ｕ₃₇^Ｋ作为海水表层温度指标的原理、定量公式及其研究现状和存在的问题。     

18.5kaB. P.以来东北四海龙湾玛珥湖全岩有机碳同位素记录及其古气候环境意义

结合含水量、TOC含量和TOC/TN比值变化曲线,18·5kaB·P·以来的四海龙湾玛珥湖沉积物全岩有机碳同位素组成（^δ13C_TOC）记录可划分为3个阶段:1)末次冰期晚期（18·5～14·7kaB·P·）,^δ13C_TOC值偏正,变化范围为-29·50‰～-26·18‰,平均值约为-28·10‰;2)末次冰消期（14·7～11·7kaB·P·）,^δ13C_TOC值显著偏负,变化范围为-33·92‰～-28·40‰,平均值约为-31·75‰,在^δ13C_TOC值变化曲线上表现为一个低谷,但在类似YoungerDryas的冷干事件期间（12·7～11·7kaB·P·）,^δ13C_TOC值再次显著偏正,最高可达-28·4‰;3)全新世以来（11·7kaB·P.至今）,^δ13C_TOC值变化幅度不大（-30·85‰～-27·37‰）,基本上都在平均值-29·1‰左右。研究表明,大气CO₂浓度变化是影响18·5kaB·P·以来四海龙湾玛珥湖^δ13C_TOC值变化的主导因素。     

The variations of stable-carbon isotope ratios in Qilian juniper in northwestern China

This is the first study of δ¹³C values that considers elevational influences of the Qilian mountains of China. The δ¹³C values of different parts of the Qilian juniper (Sabina przewalskii Kom.) at different elevations of the Qilian mountains, China, were measured. Relatively constant differences in δ¹³C values existed between the tree leaves and the trunk wood. No strong dependency of δ¹³C values on elevation was found. The temporal changes of wood δ¹³C values with directions, elevations and height in the tree showed general similarity. These results suggest that the isotopic effects of environmental factors expressed initially at the site of photosynthesis, i.e., the leaves could be contained in the trunks of a tree. Regardless of elevation, direction or height in the tree, wood δ¹³C values have been decreasing during the past 60 years. A composite 600-year δ¹³C chronology developed from four trees showed that δ¹³C values remain relatively constant before 1800. After 1800 AD, however, δ¹³C values became significantly more negative. The trend in wood δ¹³C values was consistent with that obtained for δ¹³C values in atmospheric CO₂. The results showed that for Qilian juniper, tree-ring δ¹³C chronology could be established to ascertain fluctuations of the atmospheric δ¹³C.     

青海湖冰后期以来古气候波动模式的研究

本文根据青海湖QH-16A近代沉积物岩芯中介形虫壳体的δ¹⁸O、δ¹³C、Mg/Ca和Sr/Ca值分析,讨论了青海湖区12,000年以来的气候特征。利用氧、碳同位素的相关性和相对温度、盐度变化曲线建立了青海湖区冰后期以来的气候波动模式,划分出5个气候期和23个气候阶。通过与布列特-谢尔南德冰后期气候方案对比,证实该气候波动模式具有世界性。     

The rise of trees and their effects on Paleozoic atmospheric CO2 and O2

The rise of large vascular plants during the mid-Paleozoic brought about a major increase in the rates of weathering of silicate minerals that induced a drop in the level of atmospheric CO₂ and contributed, via the atmospheric greenhouse effect, to global cooling and the initiation of the most long lived and a really extensive glaciation of the past 550 million years. Sedimentary burial of the microbiologically resistant remains of the plants resulted during the Permo-Carboniferous in both further lowering of CO₂ and in elevation of atmospheric O₂. Evidence of changes in CO₂ and O₂ are provided by mathematical models, studies of paleosols, fossil plants, fossil insects, and the effects of modern plants on silicate weathering, and by laboratory studies of the effects of changes in O₂ on plants and insects. To cite this article: R.A. Berner, C. R. Geoscience 335 (2003).     

A pedogenic goethite record of soil CO2 variations as a response to soil moisture content

The terrestrial carbon cycle and the role of atmospheric CO₂ concentrations in controlling global temperatures can be inferred from the study of ancient soils (paleosols). Soil-formed goethite and calcite have been the primary minerals used as a geochemical proxy for reconstructing atmospheric pCO₂ from ancient terrestrial records. In the case of goethite, optimum sampling strategies for reconstructing pCO₂ focus on the portion of the soil profile that displays steep gradients in both soil CO₂ concentration and δ¹³C values of soil CO₂ such that a keeling plot can be developed for a given soil and atmospheric pCO₂ can be calculated from it. We report data from a Carboniferous paleosol that depart from the expected linear trends. The results indicate that pedogenic goethite is sensitive to variations in the isotopic composition of soil CO₂, over a range of timescales, and can record these variations in the carbon isotope composition and mole fraction of Fe(CO₃)OH in solid solution with goethite. We explore possible environmental conditions that can drive these changes as a function of either moisture controlled variations in soil respired CO₂ or in the residence time of carbon in soils. The implications of this result are overestimation of paleoatmospheric pCO₂ from pedogenic goethite.     

汶川M_s 8.0地震破裂带CO_2、CH_4、Rn和Hg脱气强度

地震活动断裂带能够向大气释放大量的温室气体、放射性气体和有毒气体(CO_2、CH_4、Rn和Hg),并对大气环境的影响产生复杂的影响。利用静态暗箱法,对汶川M_s8.0地震破裂带CO_2、Rn和Hg脱气强度进行实地测量,并计算了CO_2和Hg脱气对大气的年贡献量。结果表明:(1)破裂带土壤气中CO_2、CH_4、Rn和Hg异常浓度最大值分别可以达到7.98%、2.38%、524.30k Bq/m~3和161.00ng/m~3;破裂带CO_2、Rn和Hg脱气平均通量是34.95g·m~(-2)d~(-1)、36.11m Bq·m~(-2)s~(-1)和26.56ng·m~(-2)h~(-1),最大值分别达到259.23g·m~(-2)d~(-1)、580.35m Bq·m~(-2)s~(-1)和387.67ng·m~(-2)h~(-1);(2)汶川Ms8.0地震破裂带向大气脱气的CO_2年贡献量是0.95Mt,Hg的年贡献量是15.94kg。汶川Ms8.0地震破裂带破裂CO_2、CH_4、Rn和Hg等的脱气强度,不仅与破裂带渗透率有关,还与断裂带浅部存在的气藏、煤层以及磷矿层等气体源有重要的联系。     

地下水中高锰酸盐指数和硝酸根铵根稳定性研究

高锰酸盐指数(CODMn)、硝酸根(NO-3)、铵根(NH+4)是判断水体是否受到三氮污染的重要指标。对于测定这三个指标的水样保存方式和时间,地质行业标准和国内外主要国家标准间存在明显差异。地质行业标准规定地下水样品原水室温保存,CODMn和NH+4在3天内测定;NO-3在20天内测定;国家标准和美国标准推荐样品硫酸酸化,避光或冷藏保存,在2~7天内完成CODMn和NO-3和1~7天内完成NH+4测试。为了分析各类标准在样品保存要求上的差异对检测结果的影响,确保检测数据能真实地反映水体污染状况,找寻简便的保存方式,本文在广州地区采集地下水,按照地质行业标准与国家标准进行处理和保存,并在不同时间段对三个指标进行测试。分析验证结果表明:地质行业标准与国家和美国标准关于水样的保存方法均非常可靠。地质行业标准主要针对静态地下水,保存方法相对宽松;国家标准和美国标准适用范围除了地下水,还包括动态的地表水和废水,采样对象成分更为复杂,更不稳定,更容易受外界影响发生变化,故保存条件高于地质标准。在广州地区,采用原水室温避光保存水样,CODMn、NH+4保存时间可为5天,NO-3保存时间可为30天;采用酸化水室温保存水样,CODMn、NO-3和NH+4保存时间可长达30天。这两种方式均比地质行业标准和国家标准推荐的有效时间长,且原水和酸化水室温保存方式相对于冷藏保存方式更为方便。本文提出,如果采集的水样能方便、快速送达实验室,可采用原水保存;如果不能在短时间内送达实验室检测,可采用硫酸酸化保存。     

Impact of climate and CO2 on a millennium-long tree-ring carbon isotope record

We present one millennium-long (1171-year), and three 100 year long annually resolved δ¹³C tree-ring chronologies from ecologically varying Juniperus stands in the Karakorum Mountains (northern Pakistan), and evaluate their response to climatic and atmospheric CO₂ changes. All δ¹³C records show a gradual decrease since the beginning of the 19th century, which is commonly associated with a depletion of atmospheric δ¹³C due to fossil fuel burning. Climate calibration of high-frequency δ¹³C variations indicates a pronounced summer temperature signal for all sites. The low-frequency component of the same records, however, deviates from long-term temperature trends, even after correction for changes in anthropogenic CO₂. We hypothesize that these high-elevation trees show a response to both climate and elevated atmospheric CO₂ concentration and the latter might explain the offset with target temperature data. We applied several corrections to tree-ring δ¹³C records, considering a range of potential CO₂ discrimination changes over the past 150 years and calculated the goodness of fit with the target via calibration/verification tests (R², residual trend, and Durbin-Watson statistics). These tests revealed that at our sites, carbon isotope fixation on longer timescales is affected by increasing atmospheric CO₂ concentrations at a discrimination rate of about 0.012‰/ppmv. Although this statistically derived value may be site related, our findings have implications for the interpretation of any long-term trends in climate reconstructions using tree-ring δ¹³C, as we demonstrate with our millennium-long δ¹³C Karakorum record. While we find indications for warmth during the Medieval Warm Period (higher than today’s mean summer temperature), we also show that the low-frequency temperature pattern critically depends on the correction applied. Patterns of long-term climate variation, including the Medieval Warm Period, the Little Ice Age, and 20th century warmth are most similar to existing evidence when a strong influence of increased atmospheric CO₂ on plant physiology is assumed.     

Air-sea exchange of CO2 in the Gulf of Kutch,northern Arabian Sea based on bomb-carbon in corals and tree rings

Radiocarbon analyses were carried out in the annual bands of a 40 year old coral collected from the Gulf of Kutch (22.6°N, 70°E) in the northern Arabian Sea and in the annual rings of a teak tree from Thane (19°14′N, 73°24′E) near Bombay. These measurements were made in order to obtain the rates of air-sea exchange of CO₂ and the advective mixing of water in the Gulf of Kutch. The Δ¹⁴C peak in the Thane tree occurs in the year 1964, with a value of ∼630‰, significantly lower than that of the mean atmospheric Δ¹⁴C of the northern hemisphere (∼ 1000‰). The radiocarbon time series of the coral was modelled considering the supply of carbon and radiocarbon to the gulf through air-sea exchange and advective water transport from the open Arabian Sea. A reasonable fit for the coral data was obtained with an air-sea CO₂ exchange rate of 11–12 mol m⁻² yr⁻¹, and an advective velocity of 28 m yr⁻¹ between the Arabian Sea and the Gulf of Kutch; this was based on a model generated time series for radiocarbon in the Arabian Sea. The deduced velocity (∼ 28 m yr⁻¹) of the advective transport of water between the gulf and the Arabian Sea is much lower than the surface tidal current velocity in this region, but can be understood in terms of net fluxes of carbon and radiocarbon to the gulf to match the observed coral Δ¹⁴C time series.