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921.
The concentrations of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) are determined in atmospheric aerosol samples collected at a rural sampling site in Hungary. For the n-alkanes the chromatographic profiles are established and the average carbon number and carbon preference index (CPI) are calculated. An attempt is made to obtain the origin of n-alkanes found in atmospheric aerosol samples. Based on the results of the measurements the probable importance of a round-the-year biogenic source for the n-alkanes with CPIs close to unity is emphasized. 相似文献
922.
海洋生物过程在海洋吸收大气二氧化碳中的作用 总被引:5,自引:0,他引:5
使用一个包括浮游生物(植物、动物和细菌)和无生命氮(有机碎片、溶解有机氮、硝酸盐和铵)的食物网来描述发生在海洋上层的生物过程。并将该生物模式分别用在佛罗里达海峡的一个固定位置和从佛罗里达海峡(24°N,80°W)流经挪威海(68°N,10°E)(扩展湾流体系,EGSS)的一个水块中,研究了海洋中上述的生物过程对水块吸收大气二氧化碳的影响。水块模式的结果十分明显地表明了海洋中的水华季,比包括浮游植物-浮游动物-硝酸盐体系得到的峰陡,结果更合理。扩展湾流体系中平均净初级生产力为43gCm-2a-1,小于观测值。模拟的总碱度,总二氧化碳和二氧化碳分压落在观测值的范围内,在水块吸收大气CO2的总量中生物泵的作用约占16%。 相似文献
923.
Compound-specific stable carbon isotope (δ
) measurements on the aliphatic hydrocarbons released from an immature Tertiary oil shale (Göynük, Turkey) via hydropyrolysis, following solvent extraction and a milder hydrogenation treatment, have further highlighted that significant compositional differences may exist between the principal aliphatic constituents of the solvent extractable (bitumen) phase and the insoluble macromolecular network (kerogen) comprising the bulk of sedimentary organic matter. Whilst inputs from diverse sources; including algae, bacteria and terrestrial higher plants, were implied from analysis of solvent-extractable alkanes, the much larger quantities of kerogen-bound n-alkyl constituents released by hydropyrolysis had a uniform isotopic signature which could be assigned to (freshwater) algae. Remarkably, the aliphatics bound to the kerogen by relatively weak covalent bonds, liberated via catalytic hydrogenation, appeared to comprise mainly allochthonous higher plant-derived n-alkanes. These results provide further compelling evidence that the molecular constituents of bitumen and, indeed, of low-yield kerogen degradation products, are not necessarily reliable indicators of kerogen biogenicity, particularly for immature Type I source rocks. The isotopic uniformity of aliphatic n-hydrocarbons released by the high-conversion hydropyrolysis step for the ultralaminae-rich Göynük oil shale, lends further support to the theory that selective preservation of highly resistant aliphatic biomacromolecules is an important mechanism in kerogen formation, at least for alginite. 相似文献
924.
Since 1978, a measuring station has been operated at Cape Point (34°21 S, 18°29 E). In this article, results of measurements of CO, CFCl3, CCl4, O3, N2O and CH4 are presented as monthly means and analyzed with respect to long-term trends and seasonal variations. For CO and CH4, very similar seasonal variations have been observed, indicating strong interrelations between these two gases. For CO and O3, no significant changes of the mean annual concentrations can be established for the observation periods of 10 and 5 years, respectively. The measurements yield a growth rate of 9.1 pptv yr-1 for CFCl3 (1980–1987) and 0.6 ppbv yr-1 for N2O (1983–1987). The concentration increases of CH4 (10.3 ppbv yr-1 for 1983–1987) and of CCl4 (2.1 pptv yr-1 for 1980–1988) are analyzed for temporal changes during the last years.Presented at the Second Conference on Baseline Observations in Atmospheric Chemistry (SABOAC II) in Melbourne, Australia, November 1988. 相似文献
925.
Christopher L. Sabine Richard A. Feely Yutaka W. Watanabe Marilyn Lamb 《Journal of Oceanography》2004,60(1):5-15
The recent changes in the North Pacific uptake rate of carbon have been estimated using a number of different techniques over
the past decade. Recently, there has been a marked increase in the number of estimates being submitted for publication. Most
of these estimates can be grouped into one of five basic techniques: carbon time-series, non-carbon tracers, carbon tracers,
empirical relationships, and inverse calculations. Examples of each of these techniques as they have been applied in the North
Pacific are given and the estimates summarized. The results are divided into three categories: integrated water column uptake
rate estimates, mixed layer increases, and surface pCO2 increases. Most of the published values fall under the water column integrated uptake rate category. All of the estimates
varied by region and depth range of integration, but generally showed consistent patterns of increased uptake from the tropics
to the subtropics. The most disagreement between the methods was in the sub-arctic Pacific. Column integrated uptake rates
ranged from 0.25 to 1.3 mol m−2yr−1. The mixed layer uptake estimates were much more consistent, with values of 1.0–1.3 μmol kg−1yr−1 based on direct observations and multiple linear regression approaches. Surface pCO2 changes showed the most obvious regional variability (0.5–2.5 μatm yr−1) reflecting the sensitivity of these measurements to differences in the physical and biological forcing. The different techniques
used to evaluate the changes in North Pacific carbon distributions do not completely agree on the exact magnitude or spatial
and temporal patterns of carbon uptake rate. Additional research is necessary to resolve these issues and better constrain
the role of the North Pacific in the global carbon cycle.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
926.
Measurements of nitrogen fixation (acetylene reduction) showed greatest rates in the saltmarsh pans with a benthic layer of cyanobacteria present. The smallest amount of nitrogen fixation occurred on the marsh surface where a Puccinellia maritima/Halimione portulacoides plant association shaded the underlying sediment. Phototrophic nitrogen fixation was always greater than dark, chemotrophic, bacterial fixation.Only a small proportion of the total amount of ammonium, which was formed during detrital breakdown, was nitrified to nitrate. Although there is a high capacity for bacterial nitrate reduction in these sediments, the process is limited by low nitrate availability and most nitrate upon reduction is converted to ammonium rather than being denitrified to gaseous products. Denitrification does not, therefore, result in any great loss of nitrogen from the saltmarsh.There was little net import or export of nitrogen on an annual basis, although nitrate and organic-N in small particulate material was removed from tidal water by the marsh, and there was net annual export of ammonium, dissolved organic-N and organic-N in large particulate material. Losses of nitrogen by the small net tidal export and by denitrification were approximately balanced by nitrogen fixation. It was concluded that the nitrogen cycle of the Colne Point saltmarsh was balanced on an annual basis, with most nitrogen being recycled within the marsh. The saltmarsh did not apparently act as a net source of nitrogen for the adjacent estuary, although it may act as an important processor of nitrogen, removing some forms of nitrogen such as nitrate from tidal water while exporting other forms of nitrogen such as dissolved organic-N. 相似文献
927.
928.
The effect of different fixation and storage protocols on the flow cytometric (FCM) simultaneous analysis of bacterioplankton and phytoplankton in coastal seawater samples (Mediterranean coastal lagoons) was investigated. FCM measurements (cell number, fluorescence and scatter characteristics) were obtained through DAPI staining. Three fixatives [glutaraldehyde (GA), formaldehyde (FA) and paraformaldehyde (PFA)] and two storage (3 months duration) methods (5 °C and −196 °C) were tested. Two dominant populations were detected in studied samples: bacteria and eukaryotic picophytoplankton. Adding fixatives (2% final concentration) appears necessary to obtain FCM exhaustive counts of all the bacteria and phytoplanktonic cells. This was related to the permeation effect of fixatives which allowed a better DAPI staining of the cells. Maximum fluorescence, i.e. optimal staining of the cells was obtained with FA or PFA, and significant lower fluorescences with GA. Fixed samples stored at 5 °C induced rapid cell loss. Only storage in liquid nitrogen of samples fixed with FA or PFA, allows mid-term (≥4 months) preservation of bacteria or picophytoplankton cell numbers, and limited evolution of DAPI-induced fluorescence and scatter characteristics. 相似文献
929.
930.
取自东太平洋的CC48柱状样的底栖有孔虫δ^13C研究结果表明,该柱状样下,中新统地层至少存在3个碳移位事件,这些事件完全能与Louit等(1983)剖面相比较,它们为该孔的地层划分提供了依据,为区域对比提供了标准,为古地磁地层学和古生物地层学研究结果的正确与否提供良好判别标志。通过这一对比研究,可以推定δ^13C地层是未来高分辨地层的主要研究方向之一。 相似文献