Comparison of stable carbon and oxygen isotopes in Picea glauca tree rings and Sphagnum fuscum moss remains from subarctic Canada

Stable isotope ratios from tree rings and peatland mosses have become important proxies of past climate variations. We here compare recent stable carbon and oxygen isotope ratios in cellulose of tree rings from white spruce (Picea glauca), growing near the arctic tree line; and cellulose of Sphagnum fuscum stems, growing in a hummock of a subarctic peatland, in west-central Canada. Results show that carbon isotopes in S. fuscum correlate significantly with July temperatures over the past ~20 yr. The oxygen isotopes correlate with both summer temperature and precipitation. Analyses of the tree-ring isotopes revealed summer temperatures to be the main controlling factor for carbon isotope variations, whereas tree-ring oxygen isotope ratios are controlled by a combination of spring temperatures and precipitation totals. We also explore the potential of combining high-frequency (annual) climate signals derived from long tree-ring series with low-frequency (decadal to centennial) climate signals derived from the moss remains in peat deposits. This cross-archive comparison revealed no association between the oxygen isotopes, which likely results from the varying sensitivity of the archives to different seasons. For the carbon isotopes, common variance could be achieved through adjustments of the Sphagnum age model within dating error.     

新疆阿勒泰地区小冰期特征的树轮δ13C记录

建立了新疆阿勒泰地区一个长约450a的落叶松树轮碳同位素年表.该年表一个最为明显的特点是1850年后年轮δ¹³C显著降低,这是化石燃料燃烧和土地利用方式改变的缘故.在1550—1850年期间,该年表经历了明显的距平“正负”(即暖冷)变化:17世纪年轮δ¹³C值相对偏负,气温较低,18世纪年轮δ¹³C值相对偏正,温度较高.根据已有的树轮δ¹³C温度系数,17世纪的温度相对偏低约0.67～2.46℃.广泛的区域性对比表明,该年表所揭示的小冰期温度变化具有较高的可信度。     

稳定碳同位素在第四纪古环境研究中的应用

文章对陆相沉积物、湖沼相沉积物以及脊椎动物牙齿中的δ¹³C研究作了系统的综述,特别对存在的问题提出了一些看法,认为黄土-古土壤序列中有机质δ¹³C与碳酸盐δ¹³C变化趋势相反的原因是CO₂与碳酸盐交换平衡时的分馏系数在古土壤堆积时和黄土发育时不一致造成的;陆相沉积物的有机质δ¹³C较碳酸盐δ¹³C能更加直接地反映沉积时地表植被状况,陆相沉积物的碳酸盐δ¹³C在古生态中的应用还有待于对它的形成机制和形成过程进行进一步的研究;我国黄土高原末次冰期的气候不利于C4的生长.文章强调古环境、古生态研究应该从现代过程入手,了解现代植物δ13C与气候参数的关系以及现代C4植物的分布规律.同时还认为分子化石的稳定同位素研究这一新研究手段将会给第四纪研究带来更新的活力.     

从树轮纤维素δ13C序列看树木生长对大气CO2浓度变化的响应

在新疆昭苏树轮碳同位素组成研究的基础上，初步分析了近280a以来云杉内外CO2浓度比（Ci/Ca)，云杉内部CO2浓度（Ci)和水分利用效率（A／g)的变化，结果表明，在整个分析时段内Ci/Ca相对恒定在0．52左右，暗示树木生长对大气CO2浓度升高的基本响应策略；Ci和A/g都有较明显的升高趋势，说明可能有更多的碳被固定在树木之中，进一步分析表明，它们的这种趋势与大气CO2浓度变化有关，从另一个侧面证明了人类活动释放的碳有一部分被树木吸收。     

利用稳定同位素技术研究广西桂江流域水体中碳的来源

本文对岩溶区不同类型样品中的有机碳同位素样品前处理的分离提纯技术进行了研究,并对广西桂江流域水体进行了稳定有机碳同位素分析.结果表明,C3植物对桂江水体可溶性有机碳(DOC)有很大比例的贡献,而水生生物对水体有机碳影响较小.抚河流域比漓江流域有较高的(DOC)含量,可能与非岩溶区土壤微生物活动强,土壤活性有机碳含量高有...     

Stable isotope coherence in the earlywood and latewood of tree-line conifers

Annually resolved and replicated tree-ring stable isotope series have the potential to reconstruct growing season environmental parameters over multi-millennial timescales. As this archive may require only minimal statistical detrending, it has the potential to preserve a large portion of low frequency climate signals. To date, many studies have utilised only the latewood portion of the tree ring, in an attempt to minimize carry-over effects from previous year reserves and maximise the annual nature of the climate signal preserved. However, the old trees from tree-line locations, necessary to build long chronologies, often display narrow ring-widths (< 0.5 mm), making accurate earlywood–latewood separation difficult and particular time consuming. The resulting samples may also be too small for efficient cellulose purification or multiple isotopic determinations. As photosynthates from the current year are predominantly used in conifer ring formation at marginal sites with short growing seasons, latewood separation may not be especially advantageous in determining a useful climate signal and therefore unnecessary where resources are limited. To test this hypothesis, Scots pine from Northern Norway and European larch from the Swiss Alps are used. Both sites are tree-line locations where growth is predominantly temperature limited. Tree rings were cut and extracted to cellulose for both the earlywood and latewood of each annual growth ring and stable carbon isotope ratios were measured. Our results demonstrate a very high common carbon isotope signal between earlywood and latewood in both species (r_larch = 0.68 and r_pine = 0.79), which also show high correlations with summer temperature over the investigated period (AD 1980–2004 for larch and AD 1929–1978 for pine). High turnover rates and small reserve pools at these tree-line locations may account for these high common signals. These results suggest that for European tree-line conifers, the separation of earlywood from latewood is unnecessary to resolve an annual isotopic signal and make a reliable climate calibration. Using the whole ring may provide additional analytical advantages and consequently even improve climate calibrations.     

Climate variability in central China over the last 1270 years revealed by high-resolution stalagmite records

Oxygen and carbon isotopic variations in the upper section of a stalagmite (SF-1) from Buddha Cave (33°40′N 109°05′E) dated by ²³⁰Th/²³⁴U ²¹⁰Pb and lamination counting to a time resolution as fine as 1–3 years have recorded climate changes in central China for the last 1270 years. The changes include those corresponding to the Medieval Warm Period Little Ice Age and 20th-century warming lending support to the global extent of these events. The isotopic records also show cycles of 33, 22, 11, 9.6, and 7.2 years. The 33-year cycle could well represent the ∼35-year periodicity of climate fluctuations previously recognized in China and Europe. Cycles of 22, 11, and 9.6 years have often been associated with the Sunspot or lunar-orbit variations. The 7.2-year cycle was recently identified also in tree-ring records from an area close to Buddha Cave. These cycles suggest that external forcing (e.g. solar irradiance) may affect the summer monsoon over eastern China. The general consistency between the climate characteristics inferred from the stable isotope records of SF-1 and those from other proxy records underscores the value of stalagmites as recorders of paleoclimate.     

Weakening climatic signal since mid-20th century in European larch tree-ring chronologies at different altitudes from the Adamello-Presanella Massif (Italian Alps)

Tree rings from temperature-limited environments are highly sensitive climate proxies, widely used to reconstruct past climate parameters for periods prior to the availability of instrumental data and to analyse the effect of recent global warming on tree growth. An analysis of the climatic signal in five high-elevation tree-ring width chronologies of European larch (Larix decidua Mill.) from the tops of five different glacial valleys in the Italian Central Alps revealed that they contain a strong summer-temperature signal and that tree-ring growth is especially influenced by June temperatures. However, a moving correlation function analysis revealed a recent loss of the June temperature signal in the tree-ring chronologies. This signal reduction primarily involves the two lowest-altitude chronologies. It is probable that the observed increasing importance of late-summer temperature for tree-ring growth over the past 50 yr is an effect of the lengthening growing season and of the variations in the climate/tree-ring relationship over time. All the chronologies considered, especially those at the highest altitudes, show an increasing negative influence of June precipitation on tree-ring growth. The climatic signal recorded in tree-ring chronologies from the Italian Central Alps varies over time and is also differentially influenced by climatic parameters according to site elevation.     

末次间冰期以来渭南黄土地区土壤有机碳碳库的演变

冰期-间冰期的陆地碳库变化成为最近十几年来碳循环研究的热点之一,以深海氧同位素、模型模拟和古环境证据等手段展开对不同时间尺度上不同碳库之间碳通量变化研究.土壤碳库的巨大储量导致了土壤碳库的任何微小波动都比陆地生态系统其他碳库更容易影响陆地生态系统碳循环以及大气CO₂浓度,并最终影响到全球气候变化.通过对过去4万年来黄土高原地区土壤有机碳碳库的演变研究发现,深海氧同位素第3阶段期间,土壤有机碳碳密度相对于磁化率在细节上更能够表现出气候的小波动,这一期间的土壤有机碳碳密度快速上升,在较高的水平上多次波动,可能是因为这一时期的气候环境整体上更适宜碳在黄土古土壤中的累积和保存.在末次盛冰期(LGM)时,土壤有机碳碳密度急剧下降,伴随气候的快速波动,其间有一次较大规模的反弹,持续约2 ka,最低值出现在14 ka BP和19 ka BP.对比深海氧同位素曲线,土壤有机碳碳库与其在末次盛冰期和全新世都表现出良好的一致性.而磁化率在大约15 ka BP以后就开始增加,似乎超前于土壤有机碳碳密度和深海氧同位素的增加.并且,在全新世早期到晚期土壤有机碳碳密度经历了逐渐上升继而下降的变化过程,该时段的最高值出现在大约7~5 ka BP.      

Carbon isotope effects associated with autotrophic acetogenesis

The carbon kinetic isotope effects associated with synthesis of acetate from CO2 and H2 during autotrophic growth of Acetobacterium woodii at 30 degrees C have been measured by isotopic analyses of CO2, methyl-carbon, and total acetate. Closed systems allowing construction of complete mass balances at varying stages of growth were utilized, and the effects of the partitioning of carbon between CO2 and HCO3- were taken account. For the overall reaction, total carbonate --> total acetate, isotope effects measured in replicate experiments ranged from -59.0 +/- 0.9% to -57.2 +/- 2.3%. Taking into account all measurements, the weighted mean and standard deviation are -58.6 +/- 0.7%. There is no evidence for intramolecular ordering in the acetate. The carbon isotopic composition of sedimentary acetate, otherwise expected to be near that of sedimentary organic carbon, is likely to be depleted in environments in which autotrophic acetogenesis is occurring.     

Oxygen isotope ratios of cellulose-derived phenylglucosazone: An improved paleoclimate indicator of environmental water and relative humidity

Oxygen atoms within fossil wood provide high-resolution records of climate change, particularly for the Quaternary. However, current analysis methods of fossil cellulose do not differentiate between different positions of the oxygen atoms. Here, we propose a refinement to tree-cellulose paleoclimatology modeling, using the cellulose-derived compound phenylglucosazone as the isotopic substrate. Stem samples from trees were collected at northern latitudes as low as 24°37′N and as high as 69°00′N. We extracted stem water and cellulose from each stem sample and analyzed them for their ¹⁸O content. In addition, we derived the cellulose to phenylglucosazone, a compound which lacks the oxygen attached to the second carbon of the cellulose-glucose moieties. Oxygen isotope analysis of phenylglucosazone allowed us to calculate the ¹⁸O content of the oxygen attached to the second carbon of the cellulose-glucose moieties. By way of these analyses, we tested two hypotheses: first, that the ¹⁸O content of the oxygen attached to second carbon will more closely reflect the ¹⁸O content of the stem water, and will not resemble the ¹⁸O content of either cellulose or its derivative phenylglucosazone. Second, tree-ring models that incorporate the variable oxygen isotope fractionation shown here and elsewhere are more accurate than those that do not. Our first hypothesis was rejected on the basis that the oxygen isotope ratios of the oxygen attached to the second carbon of the glucose moieties had a noisy isotopic signal with a large standard deviation and gave the poorest correlation with the oxygen isotope ratios of stem water. Related to this isotopic noise, we observed that the correlation between oxygen isotope ratios of phenylglucosazone with both stem water and relative humidity were higher than those observed for cellulose. Our hypothesis about tree-ring models which account for changes in the oxygen isotopic fractionation during cellulose synthesis was consistent only for the ¹⁸O content of phenylglucosazone. We showed that the tree-ring model based on the ¹⁸O content of phenylglucosazone was an improvement over existing models that are based on whole cellulose. Additionally, this approach may be used in other cellulose based archives such as peat deposits and lacustrine sediments.     

Research Progress in Responses of Modern Terrestrial Plant Carbon Isotope Composition to Climate Change

Global climate change has been one of the most concerned environmental problems in the world since the 1980s. Since stable carbon composition (¹³C) in plant tissues can record abundant information on climate changes, it has been widely used as an important climate proxy in global change studies and becomes a powerful tool for obtaining paleoclimate information, understanding paleoenvironment reconstruction and modern climate change, and predicting future climate trends. However, a lot of potential uncertainties have always involved in the reconstruction of paleoclimate and paleoenvironment by carbon isotope of the past period sediment or fossils. Among them, the most dominant uncertainty is due to our poor understanding of the relations between carbon isotope ratios of plants and climatic factors and the climatic and environmental significance indicated by modern plant ¹³C. This may limit the application of plant ¹³C in the study of climatic and environmental changes. Based on the Summary of plant ¹³C fractionation and carbon isotope distribution of different photosynthetic plants, the effects of environmental factors, e.g., temperature, precipitation, atmospheric CO₂ concentration, and altitude on terrestrial plant ¹³C and their relationships were reviewed in this paper, and the response mechanism of plant ¹³C to climate changes were also analyzed. Furthermore, the current existing problems and the future prospects in carbon isotope study were discussed. It is pointed out that strengthening some studies such as the response of C₄ plants ¹³C to climate environmental parameters, the transformation relation of different scale plant ¹³C, intersection and permeation of related disciplines, and various proxies and scientific method, will undoubtedly make us have a more accurate understanding of the climate history and eventually broaden the development of the field during the process of global change study by plant carbon isotope techniques.     

树轮稳定碳同位素研究的应用现状与发展趋势

获取历史时期环境气候变迁资料是研究环境气候变迁的基础，在各种获取资料的方法中，树轮同位素方法是较为新颖，准确，定量的一种高分辨率方法。本文较为系统，深入地评述了树轮稳定碳同位素方法的原理及其在环境气候变迁研究的应用现状，并简要归纳了研究工作中的发展趋势。     

秦岭东部牛背梁自然保护区巴山冷杉树轮宽度与气候因子的关系

基于树木年代学方法,通过响应分析与回归分析对秦岭东段主脊牛背梁自然保护区巴山冷杉（Abies fargesii）树轮宽度所蕴涵的气候意义进行探讨。结果表明：巴山冷杉年轮宽度标准化年表和差值年表的各项特征值较高,反映树轮资料包含较强的环境信息;归纳相关分析结果,发现春夏季气温是树木径向生长的主导因子,当年1-8月不同时段的平均气温普遍对巴山冷杉生长有促进作用,其中1-2月平均气温对树木生长的影响最为显著,而前一年10-11月平均气温的“滞后作用”不可忽略。降水不是该区巴山冷杉生长的主要限制因子,但当年1-2月的降水过多会导致组织生长减缓;回归模型能较好模拟年轮宽度与气候因子之间的关系,据此结合极宽、极窄轮出现年份的气候状况印证了巴山冷杉树轮宽度年际变化是生长季初期气温、降水相互制衡、共同作用的结果,并推测巴山冷杉林带位置有向高海拔迁移的可能。为秦岭植被生长在气候变化过程中的生态模式演变研究提供一定的依据。     

An Overview of the Applications of Lipid Carbon Isotope Compositions in the Paleoenvironmental and Paleoecological Reconstructions in Lacustrine and Peat Deposits

Lipids preserved in geological materials mainly originate from cell membrane and leaf waxes, and have the potential to infer biological sources, metabolic pathways, and environmental information. Thus,lipid-based proxies have been widely applied to reconstruct paleoenvironment and paleoecology in the Quaternary. Except the concentration and molecular composition, the carbon isotope compositions of lipids are also a type of important signal sources. For photoautotrophs, the carbon isotope compositions of lipids are mainly mediated by the carbon isotope discrimination during the photosynthesis and lipid biosynthesis processes. In contrast, the carbon isotope compositions of heterotroph derived lipids are controlled by substrates and the carbon isotope fractionation during biosynthesis. In this review, we overview the advances of applications of lipid carbon isotope ratios in lacustrine and peat deposits. In the near future, more attention is suggested to pay to instrumental techniques, such as reduce the sample amount, direct analysis the carbon isotope compositions of molecules with relatively large molecular weight (e.g. BHPs, GDGTs), and widely application of compound-specific radiocarbon isotope analysis. In addition, combination of carbon isotope ratios from multi lipids, or the application of dual carbon and hydrogen isotope ratios of lipids, will shed more information on the response of ecological processes to climate changes. Furthermore, more works are worthy to investigate the relation between biogeochemical processes and paleoclimate changes in the Quaternary.     

始新世—渐新世气候转变研究进展

始新世—渐新世（E—O）气候转变（34 Ma前后）是新生代气候演化过程中最显著的变冷事件之一,标志着地球气候由“温室”进入“冰室”。这一转变伴随着地球环境的一系列重大变化,对于研究新生代气候变冷的驱动机制、区域气候对全球重大气候事件的响应方式、重大气候事件对生态环境及生物演替的影响等具有重要意义。近年来地质记录和气候模拟在E—O转变研究上取得了一系列重要进展：①不同纬度区的地质记录揭示出这一转变伴随着全球性的显著降温,指示其触发因素是全球性的;②气候模拟研究揭示出大气CO2浓度降低及与之联系的全球碳循环变化是导致这一转变的主因,否定了传统认为的环南极流形成导致E—O气候变冷的假说;③深海沉积记录揭示出这一转变过程持续400～500 ka,表现为全球降温和南极冰盖形成先后两阶段变化;④海—陆气候记录的对比初步揭示出陆地区域的干旱化可能主要与全球降温（对应于E—O转变的第一阶段）相关。当前对E—O气候转变的研究还存在地质记录分辨率不够高、模拟结果与地质记录不完全吻合、陆地记录相对较少等方面的不足。更精确的大气CO2浓度和温度的重建、更多高分辨率海—陆气候记录的研究以及古气候数值模拟的改进有望进一步揭示出E—O转变过程中气候系统各要素的变化特征和相互关系,为更深入认识这一转变的驱动机制提供依据。     

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.     

表层岩溶系统碳迁移路径及其土被效应探讨

为了弄清楚表层岩溶系统碳汇机理,有必要对该系统中气、液和固三相不平衡体系中碳的迁移途径进行研究。2010年,在板寨地下河流域布置了8个碳稳定同位素分析测试点。通过碳稳定同位素示踪剂及空气CO2分压对比,发现森林区岩溶水和自由大气中大部分碳是来自土壤空气。在表层岩溶系统碳汇过程中整个碳迁移路径可分为4个环节,依次为(1)植被光合作用吸收空气CO2;(2)土壤根系的呼吸作用及腐殖质分解向土壤释放CO2;(3)地下水循环岩溶作用将气态CO2转换成液态HCO3-离子;(4)地下水中的碳随水流向河流及海洋。在整个碳汇过程中,森林和土壤起到了“加压泵”的作用,大大提高了大气CO2向土壤空气CO2转换过程中的CO2分压,从而显著地提高了岩溶的作用速率。      

古大气CO2浓度重建方法技术研究现状

温室气候引起的全球气候变暖越来越引起人们的关注,大气中不断上升的CO2浓度被认为是导致气候变暖的主要因素.地史时期大气CO2浓度变化与温室气候可能存在类似的关系,可提供参考,因而古大气CO2浓度重建是首要任务.总结近年来古大气CO2浓度重建的进展,重点介绍GEOCARB模型模拟、植物叶片气孔参数和同位素指针的方法和技术.GEOCARB模型是反映全球古大气CO2浓度长期变化的碳相关模型;气孔参数方法是使用气孔比例来估计古大气CO2浓度;同位素指针包括成壤碳酸盐、浮游植物有机质生物标记物、钙质浮游有孔虫、古苔藓植物等,其中成壤碳酸盐碳同位素方法使用最为广泛.国内只是在叶片参数研究方面有一些进展,古大气CO2浓度重建工作任重而道远.     

利用多年冻土区湖相沉积物中埋藏植物稳定碳同位素组成重建大气CO2浓度

沉水植物碳同位素分馏同水中溶解无机碳浓度有一定的关系，因而可以通过青藏高原多年冻土区的湖相沉积物中埋藏沉水植物－－龙须眼子菜（Potamogeton pectinatus)植物屑的碳同位素组成重建该地大气CO2浓度的变化情形，研究结果表明，该地在9．17－6．77ka BP间，大气CO2浓度是整个研究时间段中最低的，其后在6．77－4．56ka BP时期大气CO2浓度增加，在4．56－2．17ka BP之间，大气CO2浓度是整个研究时间内CO2浓度最高的阶段，植物屑的碳同位素组成反映了溶解无机碳浓度的变化，从而可用以重建大气CO2浓度的变化情况。