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121.
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
122.
V. S. N. Murty V. Ramesh Babu L. V. G. Rao Charuta V. Prabhu V. Tilvi 《Journal of Earth System Science》2000,109(2):267-277
Time-series data on upper-ocean temperature, Vessel-Mounted Acoustic Doppler Current Profiler (VM-ADCP) measured currents
and surface meteorological parameters have been obtained for the first time in the southern Bay of Bengal at 7‡N, 10‡N, and
13‡N locations along 87‡E during October–November, 1998 under BOBMEX-Pilot programme. These data have been analysed to examine
the diurnal variability of upper oceanic heat budget and to estimate the eddy diffusivity coefficient of heat in the upper
layer. Diurnal variation of near-surface temperature is typical at northern location (13‡N) with a range of 0.5‡C while the
diurnal range of temperature is enhanced to 0.8‡C at the central location (10‡N) due to intense solar radiation (1050 W/m2), clear skies and low wind speeds. At the southern location (7‡N), the diurnal variation of temperature is atypical with
the minimum temperature occurring at 2000 hrs instead of at early morning hours. In general, the diurnal curve of temperature
penetrated up to 15 to 20 m with decreasing diurnal range with depth. The VM-ADCP measured horizontal currents in the upper
ocean were predominantly easterly/northeasterly at southern location, north/northerly at central location and northwesterly
at northern location, thus describing a large-scale cyclonic gyre with the northward meridional flow along 87‡E. The magnitudes
of heat loss at the surface due to air-sea heat exchanges and in the upper 50 m layer due to vertical diffusion of heat are
highest at the southern location where intense convective activity followed by overcast skies and synoptic disturbance prevailed
in the lower atmosphere. This and the estimated higher value (0.0235 m2/s) of eddy diffusivity coefficient of heat in the upper ocean (0–50 m depth) suggest that 1-D processes controlled the upper
layer heat budget at the southern location. On the other hand, during the fair weather conditions, at the central and northern
locations, the upper layer gained heat energy, while the sea surface lost (gained) heat energy at northern (central) location.
This and lower values of eddy diffusivity coefficient of heat (0.0045 and 0.0150 m2/s) and the northward intensification of horizontal currents at these locations suggest the greater role of horizontal heat
advection over the 1-D processes in the upper ocean heat budget at these two locations. 相似文献
123.
Klaus Schäfer 《GeoJournal》2000,52(1):45-58
The article describes a new form of transnational environmental conflict that developed in the wake of globalisation. Activist in this new type of conflict still act as proxies of groups under pressure but in contrast to transnational environmental conflicts hitherto the target of their protests is rather their own society at home than the location of the pressured group. Despite these conditions it is claimed that this type of metaphorical conflict is going to become more frequent as alliances are built along the oppostion to a dominant discourse. According to the model, conflicts of values are easier to transfer on stages abroad or across the Atlantic than conflicts of interests and motivation for activists is higher as the return is affecting their home society. Dynamic and features of this type of conflict are explained with help of discourse theory. 相似文献
124.
Ar和H在矿物中的扩散补偿关系及其对扩散系数的预测 总被引:2,自引:0,他引:2
对现有实验扩散数据的检查发现 ,Ar和H两种元素在不同矿物中分别存在着扩散补偿关系。孔隙度作为矿物内部离子堆积密度的一种量度 ,它与Ar和H的扩散活化能之间存在负的线性相关性 ,因而可以用于预测元素在矿物中的扩散系数。文中采用离子孔隙度法预测了Ar和H在不同矿物中的扩散系数 ,得到的结果与已有的实验数据在实验误差范围内是一致的。由于扩散补偿效应 ,同一物质在不同矿物中的扩散速率在特定温度下趋于汇聚 ,Ar扩散的转折温度为 (86 0± 10 0 )℃ ,H扩散的转折温度为 (330± 50 )℃。这为地质过程中Ar和H扩散的封闭温度提供了一种借鉴 ,因此伴随Ar扩散的地质时钟在低于 86 0℃时才开始启动 ,共存矿物间的氢同位素地质温度计仅当温度低于 330℃时才是有效的。 相似文献
125.
126.
127.
The infrared spectrum of CaAl2Si2O7 · H2O-lawsonite, has been characterized to pressures of 20 GPa at 300 K. Our results constrain the response to compression of
the silicate tetrahedra, hydroxyl units, and water molecules in this material. The asymmetric and symmetric stretching and
bending vibrations of the Si2O7 groups (at zero pressure frequencies between 600 and 1000 cm−1) increase in frequency with pressure at rates between 3.6 and 5.9 cm−1/GPa. All silicate modes appear to shift continuously with pressure to 20 GPa, although the lowest frequency stretching vibration
becomes unresolvable above 18 GPa, and a splitting of the main bending vibration is observed near this pressure. The O-H stretches
of the hydroxyl units exhibit a discontinuity in their mode shifts at ∼8–9 GPa, which we interpret to be produced by a pressure-induced
change in hydrogen bonding. The stretching and bending vibrations of the water molecule are relatively unaffected by compression
to 20 GPa, thus demonstrating that the structural cavities in which water molecules reside are relatively rigid. Significant
changes in the amplitude of the O-H stretches of the hydroxyl and water units are observed at this pressure as well; nevertheless,
our results demonstrate that the dominant structural units in lawsonite persist metastably at 300 K with only modest structural
modifications well beyond the known stability field of this phase.
Received: 10 July 1998 / Revised, accepted: 23 October 1998 相似文献
128.
129.
湖泊沉积有机质的地球化学记录与古气候古环境重建 总被引:5,自引:1,他引:5
与深海沉积与冰芯记录相比,湖泊沉积主要反映区域气候变迁史,可以揭示百年、甚至十年尺度的古气候事件,是高分辨率古环境、古气候重建的理想场所.传统的地质地球化学方法主要侧重于宏观物理 /化学特性描述和孢粉学的研究,近 10年来,沉积有机质分子碳、氢同位素地球化学技术的渗入,使研究工作从传统的宏观、微观层次向分子级水平发展,对诸如古生产率估算、C3/C4植被演替史、古二氧化碳分压及古温度计算等深层次问题解决提供了强有力支持.本文评述了湖泊沉积有机质分子与碳、氢同位素地球化学记录及其在区域古环境、古气候研究中的应用前景. 相似文献
130.