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321.
322.
It has been suggested that part of the so-called “missing sink” of carbon dioxide introduced into the atmosphere by anthropogenic
activities, that is the imbalance between estimated anthropogenic carbon dioxide emissions and oceanic uptake, may be stored
in the vegetation in midlatitudes. Precise mechanisms of abstraction of additional carbon dioxide by vegetation, also known
as the “fertilization effect”, are poorly understood. Stable carbon and hydrogen isotope ratios of cellulose extracted from
annual growth rings (covering the time period 1980–1993) in an oak tree from Kalamazoo, SW Michigan provide a basis to investigate
at a physiological level how the fertilization effect may operate. The carbon isotope ratios show that the intercellular concentration
of carbon dioxide increased due to an increase in stomatal opening. Although increased intercellular concentration of carbon
dioxide translated to increased Water Use Efficiency and assimilation rates, it also resulted in increased transpiration rate
as shown by higher D/H of the fixed carbon. The two-fold significance of the isotope data are: first, they provide the first
field evidence based on isotope studies for excess CO2 induced biomass production and second, they suggest that this mechanism is likely to operate only in limited environments.
Vegetation in regions where moisture availability is not restricted so that there can be a gain in water use efficiency despite
increased leaf evaporation are best suited to sequester excess carbon from the atmosphere. 相似文献
323.
A simple model of the convective (thermal) internalboundary layer has been developed for climatologicalstudies of air-sea-ice interaction, where in situobservations are scarce and first-order estimates ofsurface heat fluxes are required. It is amixed-layer slab model, based on a steady-statesolution of the conservation of potentialtemperature equation, assuming a balance betweenadvection and turbulent heat-flux convergence. Boththe potential temperature and the surface heat fluxare allowed to vary with fetch, so the subsequentboundary-layer modification alters the fluxconvergence and thus the boundary-layer growth rate.For simplicity, microphysical and radiativeprocesses are neglected.The model is validated using several case studies.For a clear-sky cold-air outbreak over a coastalpolynya the observed boundary-layer heights,mixed-layer potential temperatures and surface heatfluxes are all well reproduced. In other cases,where clouds are present, the model still capturesmost of the observed boundary-layer modification,although there are increasing discrepancies withfetch, due to the neglected microphysical andradiative processes. The application of the model toclimatological studies of air-sea interaction withincoastal polynyas is discussed. 相似文献
324.
中国北方石墨矿床及赋矿孔达岩系碳同位素特征及有关问题讨论 总被引:24,自引:10,他引:14
本文综合了中国北方孔达岩系和石墨矿床的碳同位素数据 10 2件 ,发现片麻岩石墨 透辉岩石墨 <大理岩石墨 <石墨大理岩方解石 <大理岩方解石 ;混合岩化岩石中石墨δ1 3C总介于有机碳和无机碳之间 ;不同地体片麻岩石墨δ1 3C极为一致 ,变化于 - 2 2 .8‰~ - 2 1.48‰ ,略低于世界有机质平均值 - 2 6± 7‰ ;大理岩的原岩碳酸盐δ1 3C高于 2‰ ,与2 330~ 2 0 6 0 Ma期间全球性δ1 3Ccarb正向漂移事件一致。地质流体是碳同位素分馏、均一化的重要因素 ,是石墨矿床的 3种主要碳源之一 ,是碳的 5种存在形式之一 ,也是碳循环的重要媒介和方式 ;导致热液矿床δ1 3C=- 5‰左右的因素较多 ,依据δ1 3Ccalcite - 5‰得出成矿物质和流体来自地幔的结论值得怀疑 ;中国北方孔达岩系形成于古元古代 ,可能为 2 30 0~ 2 0 5 0 Ma。 相似文献
325.
A. Bechtel R. Gratzer W. Püttmann S. Oszczepalski 《International Journal of Earth Sciences》2000,89(1):72-89
max vs the present depth of the Kupferschiefer, soluble organic matter (SOM) yields, and relative proportions of saturated and
aromatic hydrocarbons of the SOM provide evidence for an oxidative alteration of organic matter in highly mineralized Kupferschiefer
samples near the Rote F?ule zones. This is confirmed by differences in the composition of the saturated and aromatic hydrocarbon
fractions of the soluble organic matter: Saturated hydrocarbons from Rote F?ule samples are dominated by short-chain n-alkanes
and higher abundances of pristane and phytane relative to heptadecane (n-C17) and octadecane (n-C18), respectively, compared
with samples more distant to the Rote F?ule zone. Compositional changes of the aromatic hydrocarbon fractions with decreasing
distance to that zone are characterized by the occurrence of polycyclic aromatic hydrocarbons and elevated ratios of phenanthrene
to methylphenanthrenes that are attributed to demethylation reactions and resulted in a decrease of the methylphenanthrene
index (MPI 1). Kupferschiefer samples from the barren zone of the Polish Basin do not show these alteration patterns. The
observed variations in organic matter composition with burial depth are consistent with changes due to increasing thermal
maturation. Maturity assessment is achieved from MPI 1 and the methyldibenzothiophene ratio (MDR). From the relationship between
the maturity of organic matter in terms of vitrinite reflectance values and depth of the Kupferschiefer strata, a continuous
increase in reflectance of vitrinite is obtained within the Polish Basin. The alteration pattern of organic matter related
to base metal mineralization of the Kupferschiefer corresponds to changes in the isotopic composition of organic carbon and
calcite. Kerogen within, or close to, Rote F?ule zone is enriched in 13C caused by the preferential release of isotopically light organic compounds through progressive degradation of organic matter.
The opposite tendency towards lower δ
13C and δ
18O values of calcite provides evidence for isotopic exchange between carbonate and the oxidizing, ore-bearing solutions and
for organic matter remineralization. In contrast, organic matter and calcite from the Kupferschiefer do not show regular trends
in δ
13C with increasing thermal maturation.
Received: 25 June 1999 / Accepted: 1 December 1999 相似文献
326.
The influences of boundary layer parameterization schemes on mesoscale heavy rain system 总被引:2,自引:0,他引:2
1.Introducti0nThemesoscaleoperationalmodel-whichisoftenused,isMM4orMM5'butMM4isusedfrequentlyonlO3kmscale.Thephysicalprocessesinthismodeldevelopconstantly.FororiginalMM4,thecomputationofsurfacefluxesisnotaccurate,andKmodelfortheturbu-lencefluxesbetweenany2levelsneedstobeimprovedbynewtreatment.Inordertostudytheinfluencesofboundarylayerparameterizationschemesonmesoscaleheavyrainsystem,sur-facefluxesandKmodelinoriginalMM4areimprovedbytherecentresearchinthispaPer.Theflux-profilerelationsforv… 相似文献
327.
Stable carbon isotope distribution of particulate organic matter in the ocean: a model study 总被引:4,自引:0,他引:4
Matthias Hofmann Dieter A. Wolf-Gladrow Taro Takahashi Steward C. Sutherland Katharina D. Six Ernst Maier-Reimer 《Marine Chemistry》2000,72(2-4)
The stable carbon isotopic composition of particulate organic matter in the ocean, δ13CPOC, shows characteristic spatial variations with high values in low latitudes and low values in high latitudes. The lowest δ13CPOC values (−32‰ to −35‰) have been reported in the Southern Ocean, whereas in arctic and subarctic regions δ13CPOC values do not drop below −27‰. This interhemispheric asymmetry is still unexplained. Global gradients in δ13CPOC are much greater than in δ13CDIC, suggesting that variations in isotopic fractionation during organic matter production are primarily responsible for the observed range in δ13CPOC. Understanding the factors that control isotope variability is a prerequisite when applying δ13CPOC to the study of marine carbon biogeochemistry. The present model study attempts to reproduce the δ13CPOC distribution pattern in the ocean. The three-dimensional (3D) Hamburg Model of the Oceanic Carbon Cycle version 3.1 (HAMOCC3.1) was combined with two different parametrizations of the biological fractionation of stable carbon isotopes. In the first parametrization, it is assumed that the isotopic fractionation between CO2 in seawater and the organic material produced by algae, P, is a function of the ambient CO2 concentration. The two parameters of this function are derived from observations and are not based on an assumption of any specific mechanism. Thus, this parametrization is purely empirical. The second parametrization is based on fractionation models for microalgae. It is supported by several laboratory experiments. Here the fractionation, P, depends on the CO2 concentration in seawater and on the (instantaneous) growth rates, μi, of the phytoplankton. In the Atlantic Ocean, where most field data are available, both parametrizations reproduce the latitudinal variability of the mean δ13CPOC distribution. The interhemispheric asymmetry of δ13CPOC can mostly be attributed to the interhemispheric asymmetry of CO2 concentration in the water. However, the strong seasonal variations of δ13CPOC as reported by several authors, can only be explained by a growth rate-dependent fractionation, which reflects variations in the cellular carbon demand. 相似文献
328.
洞庭湖区土壤实测碳量的分布规律及其对全球变化的响应 总被引:2,自引:1,他引:1
研究区域土壤碳库的分布特征对于全球变化研究、土壤肥力和生态系统的功能评价具有重要意义。在缺乏长期实测资料情况下,国内外多以模型、第二次土壤普查资料或较稀的实测数据进行研究。文中利用洞庭湖区生态地球化学调查实测数据,研究影响该区土壤碳分布的因素认为区域土壤碳量处于全国的中、高级水平;地质地貌条件是影响土壤无机碳量分布的最重要因素;土壤类型对土壤碳量有影响;本区水土流失强度对表层土壤总有机碳量影响不大;经济林、竹林的土地利用方式及防治土壤潜育化有利于土壤的碳储存;从TOC等沉积的时空演化规律说明,本区环境变化是对全球环境变化的响应,为区域土地利用、促进土壤碳固定及全球环境变化研究提供了依据。 相似文献
329.
330.
2023年5月17日,欧盟碳边境调节机制法规正式生效,年底就要进入试运行阶段。法规要求出口特定产品到欧盟的企业为产品生产过程中所产生的温室气体排放支付费用。根据各国学者的建模分析,这将增加所有销往欧盟市场的相关产品的温室气体排放成本,对欧盟以外国家的生产、贸易、就业和收入产生不利影响,而欧盟国家的企业则获得相对的竞争优势,这引发了诸多争议。对此,中国应在多边主义框架下积极与欧盟开展磋商,争取全球各国在公平的前提下提升减排雄心,同时加紧全国碳市场建设,促进国内的碳价提高到足以反映国内减排成本的水平,促进相关行业的碳排放核算能力建设,以求降低增加的管理成本,并推动低碳技术的发展,以降低欧盟碳边境调节机制带来的负面影响。 相似文献