Identifying outliers and assessing the accuracy of amino acid racemization measurements for geochronology: I. Age calibration curves   总被引：1，自引：1，他引：0  

Matthew A. Kosnik  Darrell S. Kaufman  Quan Hua   《Quaternary Geochronology》2008,3(4):308-327

Numerical ages derived from amino acid racemization (AAR) geochronology are typically based on calibration curves that relate the extent of AAR to the age of independently dated specimens. Here, we compare options for developing calibration curves and quantifying age uncertainties using AAR data from 481 late Holocene shells, and AMS ¹⁴C analyses of 36 shells of four molluscan taxa (Ethalia, Natica, Tellina, and Turbo) collected from shallow sediment cores from a back-reef lagoon of the central Great Barrier Reef. The four taxa differed substantially in the quality of their geochronogical results. Explicitly including data from specimens alive at the time of collection improves calibration curves, but weighting numerical ages based on their uncertainty has no effect. Calibration curve statistics do not adequately assess calibration uncertainty. The relation between ages inferred from different amino acids is recommended for identifying aberrant specimens and quantifying the uncertainty of inferred ages. For this study, the AAR ages based on two amino acids (aspartic acid and glutamic acid) exceed 200 yr or 20% of their mean inferred age in 15% of the specimens. Once these were removed, the mean age error (1σ) for individual specimens based on two amino acids analyzed in duplicate subsamples ranged from 53 to 142 yr for Tellina and Turbo, respectively, or about a 30% age error for these relatively young shells. This compares favorably with analytical errors estimated at 50 yr or 5%. The presence of notable outliers undetectable using data from single amino acids emphasizes the importance of analyzing multiple amino acids.  相似文献   

Compound-specific radiocarbon dating of Ross Sea sediments: A prospect for constructing chronologies in high-latitude oceanic sediments   总被引：1，自引：0，他引：1  

Naohiko Ohkouchi  Timothy I. Eglinton 《Quaternary Geochronology》2008,3(3):235-243

We present an overview of the problems relating to the development of sedimentary chronologies for Antarctic margin sediments, and review the recent application of compound-specific radiocarbon dating methods for resolving them. Radiocarbon dating of solvent-extractable, short-chain (C₁₄, C₁₆, and C₁₈) fatty acids isolated from surface sediments of the Ross Sea, Antarctica, revealed their ages to be consistent with that of the modern dissolved inorganic carbon (DIC) reservoir age (pre-bomb, Δ¹⁴C≈−150‰; post-bomb, Δ¹⁴C≈−100‰) in this region. This contrasts sharply with the radiocarbon ages of bulk organic matter in the corresponding sediments are substantially older (Δ¹⁴C=−298‰ to −712‰). Furthermore, the radiocarbon ages of these fatty acids progressively increase with the core depth. These results clearly show a utility of the compound-specific radiocarbon dating for developing sediment chronologies in the Antarctic margin sediments. This approach is potentially applicable to Arctic Ocean, as well as other areas of Southern Ocean where similar interferences by fossil or pre-aged carbon inputs have hindered the progress in the development of late Quaternary paleoceanographic records.  相似文献   

Biogenic Volatile Organic Compounds (VOC): An Overview on Emission, Physiology and Ecology   总被引：50，自引：0，他引：50  

J. Kesselmeier  M. Staudt 《Journal of Atmospheric Chemistry》1999,33(1):23-88

This overview compiles the actual knowledge of the biogenic emissions of some volatile organic compounds (VOCs), i.e., isoprene, terpenes, alkanes, alkenes, alcohols, esters, carbonyls, and acids. We discuss VOC biosynthesis, emission inventories, relations between emission and plant physiology as well as temperature and radiation, and ecophysiological functions. For isoprene and monoterpenes, an extended summary of standard emission factors, with data related to the plant genus and species, is included. The data compilation shows that we have quite a substantial knowledge of the emission of isoprene and monoterpenes, including emission rates, emission regulation, and biosynthesis. The situation is worse in the case of numerous other compounds (other VOCs or OVOCs) being emitted by the biosphere. This is reflected in the insufficient knowledge of emission rates and biological functions. Except for the terpenoids, only a limited number of studies of OVOCs are available; data are summarized for alkanes, alkenes, carbonyls, alcohols, acids, and esters. In addition to closing these gaps of knowledge, one of the major objectives for future VOC research is improving our knowledge of the fate of organic carbon in the atmosphere, ending up in oxidation products and/or as aerosol particles.  相似文献   

Characterization of Chlorination By-products in Cooling Effluents of Coastal Nuclear Power Stations   总被引：3，自引：0，他引：3  

Anne-Sophie Allonier  Michel Khalanski  Valrie Camel  Alain Bermond 《Marine pollution bulletin》1999,38(12):214-1241

In power stations, the cooling effluents are chlorinated to avoid excessive biofouling. Yet, this disinfecting treatment leads to the formation of halogenated by-products. In spite of possible toxicity of such compounds towards aquatic organisms, there is an evident lack of information on the formation of halogenated compounds in chlorinated seawater samples. So, this study was undertaken to identify and quantify halogenated compounds (i.e. trihalomethanes, haloacetonitriles, halophenols and haloacetic acids) in effluents from three French nuclear power stations. In addition, experiments conducted in the laboratory allowed the determination of the kinetics of formation of the main compounds detected: bromoform, dihaloacetonitrile, 2,4,6-tribromophenol and dibromoacetic acid. Good agreement was obtained between the experiments conducted either on site or in the laboratory. In particular, evidence was given on the formation of brominated compounds (due to the high concentrations of bromide ions in seawater).  相似文献   

福建东山湾人工养殖池红树林浮岛养殖拟穴青蟹(Scylla paramamosain)的生长及肌肉营养成分分析     

李元跃  柏皓  陈融斌  陈政强  肖震  潘煌杰  李相威  陈凤淋  王秋荣 《海洋与湖沼》2023,54(6):1716-1727

为探究海水养殖池塘红树林浮岛养殖拟穴青蟹(Scylla paramamosain)的生长及其与野生拟穴青蟹营养成分的差异,选择福建省漳浦县东山湾北部的海水养殖池塘内设置四个拟穴青蟹养殖实验组,分别为红树林(秋茄)浮岛养殖组、海马齿浮岛养殖组、空白浮岛养殖组(水面无种植植物)和外围环沟养殖组,并以试验点附近海区捕获的拟穴青蟹(野生组)作为对照,对各组拟穴青蟹的肌肉营养成分进行分析。结果显示,空白浮岛组拟穴青蟹增重率、特定生长率、出肉率及存活率均高于红树林浮岛组、海马齿浮岛组和外围环沟组;红树林浮岛养殖拟穴青蟹肌肉粗蛋白含量(71.66%)最高,粗脂肪含量(2.52%)相对较低,各组拟穴青蟹肌肉中氨基酸总量在60.54%～68.68%之间,其中红树林浮岛组拟穴青蟹肌肉中氨基酸总量、必需氨基酸总量上均显著高于野生组(P<0.05);从氨基酸评分(AAS)和化学评分(CS)结果可以得出拟穴青蟹的第一限制性氨基酸是蛋氨酸+胱氨酸,各组拟穴青蟹肌肉中必需氨基酸指数(EAAI)均高于0.75;肌肉中均富含不饱和脂肪酸,尤其是多不饱和脂肪酸;红树林浮岛组拟穴青蟹肌肉中多不饱和脂肪酸总量(ΣPUF...  相似文献   

Seasonal variability in organic substances in surface and cave waters at Marengo Cave,Indiana     

Philip van Beynen  Derek Ford  Henry Schwarcz 《水文研究》2000,14(7):1177-1197

Water samples from forest soils and a shallow cave underlying them were collected for the hydrological year 1996–1997. The soil waters did not display much seasonal variability in concentrations of organic substances in them but the cave waters yielded distinct highest levels in the spring and autumn seasons. The important controls on the amount of organic substances reaching the cave are the seasonal fluctuation in volume of the percolation waters and the soil's ability to provide organic material for these waters. Fluorescence studies of the organic compounds isolated from these waters revealed shorter peak excitation and emission wavelengths for the cave waters than for the soil waters, a result of both differences in concentration and probably also of significant change in the proportional organic assemblages in the waters. Precipitation appears to affect the fluorescence in both waters, with the dry autumn producing the highest yields. Molecular size fractionation revealed how the larger hydrophobic compounds are preferentially removed from the water before it reaches the cave, with the consequence that the smaller hydrophilic compounds become the dominant fluorophore there. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Diet of Littoraria scabra, while vertically migrating on mangrove trees: Gut content, fatty acid, and stable isotope analyses   总被引：1，自引：1，他引：0  

Andrea C. Alfaro   《Estuarine, Coastal and Shelf Science》2008,79(4):718-726

The snail, Littoraria scabra, is a dominant grazer on tropical mangrove trees, and may play an important role in the food web dynamics of these ecosystems. Its daily vertical migration to avoid tidal submersion results in exposure to varying food types and abundances. A comprehensive diet analysis – gut contents, fatty acid profiles, and stable isotopes (δ¹⁵N and δ¹³C) – was conducted on snails migrating along mangrove trees and snails maintained in non-tidal mesocosms at Nananu-i-ra, Fiji Islands. In addition, fatty acid profiles and stable isotope signatures were obtained from surface scrapings of mangrove roots, trunks, branches, and leaves. Results from this multi-technique study indicate that L. scabra is mainly a generalist herbivore, which easily shifts diets depending on food availability, and which also has the ability to ingest and assimilate zooplankton. Ingestion of greater quantities of diverse foods (i.e., microalgae, foliose/corticated macrophytes, filamentous algae, mangrove tissues, zooplankton) takes place in the bottom areas of mangrove trees (roots and trunks) during low tides, while top areas (branches and leaves) provide limited food resources for snails feeding during high tides. However, snails preferentially assimilate microalgae and bacteria, regardless of their feeding habitat (different areas within mangrove trees and non-tidal mesocosms). The daily vertical movements of this snail result in variable feeding times, ingestion of different food types and amounts, and different assimilations. These findings also suggest that organic matter derived from mangrove tissues may not be readily transferred to higher trophic levels through this grazing pathway.  相似文献   

酸碱软硬度在成矿理论研究中的应用     

兰斌明  贾建业  谢娟  王建成 《地球科学与环境学报》1999,21(2):71

以Ｌｅｗｉｓ酸碱理论为基础发展起来的酸碱软硬度的理论广泛地应用于解释各类化学现象,包括类质同象置换,共生,应用于评价和预测化学反应极为简便和实用。然而,软硬酸碱度原理的理论基础尚在不断地充实之中。本文简要讨论了硫化物矿物的酸碱势标度,用酸碱软硬度理论解释了矿物的类质同象现象,是应用酸碱软硬度理论揭示和完善矿物成矿理论的一种偿试。  相似文献   

波纹巴非蛤肉的食品化学特性及其在鱼糜制品中的应用   总被引：5，自引：0，他引：5  

章超桦  洪鹏志  雷晓凌 《广东海洋大学学报》2000,20(1)

对波纹巴非蛤肉进行的食品化学特性研究表明 :其贝肉的粗蛋白含量为 70 .6 % (干基 ) ;蛋白质营养价高 ,氨基酸价为 85(第 1限制氨基酸为 Trp) ,并富含 Glu(10 0 g样品中 2 .2 g;以下单位同 )、Asp(1.4 7g)等呈味氨基酸及提取物成分 ,Ca、Fe等无机质含量丰富。波纹巴非蛤肉以 30 %的比例添加到蛇鲻鱼糜中 ,可制得具有贝类风味 ,色泽、弹性良好的“花甲螺丸”  相似文献   

硝酸银络合法浓缩金枪鱼鱼油多不饱和脂肪酸的研究   总被引：6，自引：2，他引：4  

刘卓华  刘书成  田树良  洪鹏志  章超桦 《广东海洋大学学报》2004,24(4):33-37

以金枪鱼鱼油混合脂肪酸为材料 ,利用硝酸银络合法浓缩其中的多不饱和脂肪酸 (PU FA) ,主要考察了搅拌时间和硝酸银浓度对产品得率和EPA和DHA含量的影响 ,并测定了产品的理化指标和脂肪酸组成。研究结果表明 :搅拌时间为 6 0min ,硝酸银浓度为 4mol/L时得到的产品得率为 18.0 3% ,浓缩产品中的EPA和DHA的质量分数分别为 9.78%和 86 .0 7% ,总质量分数达95 .85 % ,过氧化值为 7.35mmol/kg ,碘值 2 6 0 8.9g/kg。  相似文献