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991.
992.
Vincent Le Fouest Clare PostlethwaiteMiguel Angel Morales Maqueda Simon BélangerMarcel Babin 《Continental Shelf Research》2011,31(17):1869-1879
Tides and wind-driven mixing play a major role in promoting post-bloom productivity in subarctic shelf seas. Whether this is also true in the high Arctic remains unknown. This question is particularly relevant in a context of increasing Arctic Ocean stratification in response to global climatic change. We have used a three-dimensional ocean-sea ice-plankton ecosystem model to assess the contribution of tides and strong wind events to summer (June-August 2001) primary production in the Barents Sea. Tides are responsible for 20% (60% locally) of the post-bloom primary production above Svalbard Bank and east of the Kola Peninsula. By contrast, more than 9% of the primary production is due to winds faster than 8 m s−1 in the central Barents Sea. Locally, this contribution reaches 25%. In the marginal ice zone, both tides and wind events have only a limited effect on primary production (<2%). Removing tides or winds faster than 8 m s−1 promotes a regime more sustained by regenerated production with a f-ratio (i.e. the proportion of nitrate-based “new” primary production in the total primary production) that decreases by up to 26% (east of the Kola Peninsula) or 35% (central Barents Sea), respectively. When integrated over all Barents Sea sub-regions, tides and strong wind events account, respectively, for 6.8% (1.55 Tg C; 1 Tg C=1012 g C) and 4.1% (0.93 Tg C) of the post-bloom primary production (22.6 Tg C). To put this in context, this contribution to summer primary production is equivalent to the spring bloom integrated over the Svalbard area. Tides and winds are significant drivers of summer plankton productivity in the Barents Sea. 相似文献
993.
在地震灾害发生后,地震应急卫星通信网为地震救援提供高效可靠的音视频以及数据传输信道。由于地震灾害的突发性和不可预见性,地震应急卫星通信网在满足业务传输需求的同时需要实现灵活组网。OSPF(Open Shortest Path First,优先开放最短路由协议)较小的网络开销以及兼具灵活的组网方式,对于带宽资源有限的卫星通信系统来说无疑是相当具有优势的。本文着重研究了OSPF在地震应急卫星通信网中的具体应用。 相似文献
994.
The effect of sea-ice on various aspects of the Southern Hemisphere (SH) extratropical climate is examined. Two simulations using the LMD GCM are performed: a control run with the observed sea-ice distribution and an anomaly run in which all SH sea-ice is replaced by open ocean. When sea-ice is removed, the mean sea level pressure displays anomalies predominantly negatives near the Antarctic coast. In general, the meridional temperature gradient is reduced over most of the Southern Ocean, the polar jet is weaker and the sea level pressure rises equatorward of the control ice edge. The high frequency filtered standard deviation of both the sea level pressure and the 300-hPa geopotential height decreases over the southern Pacific and southwestern Atlantic oceans, especially to the north of the ice edge (as prescribed in the control). In contrast, over the Indian Ocean the perturbed simulation exhibits less variability equatorward of about 50°S and increased variability to the south. The zonal averages of the zonal and eddy potential and kinetic energies were evaluated. The effect of removing sea-ice is to diminish the available potential energy of the mean zonal flow, the available potential energy of the perturbations, the kinetic energy of the growing disturbances and the kinetic energy of the mean zonal flow over most of the Southern Ocean. The zonally averaged intensity of the subpolar trough and the rate of the baroclinic energy conversions are also weaker. 相似文献
995.
Radionuclide activities (210Pb, 210Bi, 210Po) were investigated in Mount Etna plume from 1983 to 1995. At SE crater the long-term observation (12 years) of the 210Po/210Pb ratio shows that it can behave as a degassing vent not directly related to the main magma reservoir depending on the magma level inside the volcano. Since 1992, the simultaneous determination of radionuclides and sulfur in the main plume results in new constraints on the degassing model of Lambert et al. (Earth Planet. Sci. Lett., 76 (1986) 185). The 210Po/SO2 and 210Pb/SO2 ratios enable us to identify two sources of 210Po in the plume: one is magmatic, correlated with SO2, the other one is an additional component issued from the decay of 210Pb in the shallow degassing cell, and depends directly on the residence time of the gases before their emission. Estimations of the volume of degassing magma, the residence time of the gases and the proportion of undegassed magma renewing the shallow degassing cell are given for the period 1992–1995. During the 1992 eruption, the rate of degassing magma volume is estimated to have been as high as 5×106 m3/day, and the volume of the shallow degassing magma reservoir about 0.5 km3. In 1994 and 1995 the rate of non-erupted degassing magma volume was estimated to have been about 0.18 km3/year. During the entire 1983–1995 period, only 15–20% of the degassed magma was erupted. 相似文献
996.
F. Le Guern P. Morel H. Tazieff C. Vavasseur 《Journal of Volcanology and Geothermal Research》1982,12(1-2)
Using an infrared radiometer, the authors measured the infrared radiation emitted by the plume during the 1972 Piton de la Fournaise (Réunion Island) eruption in the 9.1- to 11.9-μm range.Eight histograms summarize twenty hours of continuous measurements and show a flux between 0.557 and 1.279 W/cm2 with an average of 0.88 W/cm2. The greatest number of events correspond to the flux emitted by lava fountains, while the high and rare flux values (4–6 W/cm2) correspond to detonations of chemical explosions, probably of H2 and O2.After calibration in the laboratory on a reference black body and in the field by correlation with field observations, such a technique can be used to follow changes of volcanic activity in remote and dangerous spots. Information on the number of explosions, their magnitude, and the presence and relative significance of hot magma can be transmitted continuously to a safe place. 相似文献
997.
Bouvet Island, situated near the southernmost end of the Mid-Atlantic Ridge, is characterized by lavas ranging in composition from hawaiite through mugearite and benmoreite to rhyolite. Major and trace elements vary systematically throughout the sequence, as do mineral compositions, and geochemical modelling indicates that the compositional variations observed in the differentiated lavas can be ascribed to extensive fractional crystallization of a parental hawaiite magma. Following this scheme the hawaiite parent magma experienced approximately 44% fractional crystallization of plagioclase + clinopyroxene + olivine + opaque oxides and minor apatite to give rise to the mugearite magma, which in turn experienced a further 69% fractional crystallization of the same phase assemblage (though with more evolved compositions) to give rise to the Bouvet Island rhyolite. Extensive fractional crystallization (64%), possibly separated in time, of the parental hawaiite gave rise to the benmoreite magma. In the latter scheme the fractionating phases are similar both in composition and proportion to those crystallizing in the passage from hawaiite to mugearite, suggesting that the Bouvet Island hawaiites correspond in composition to a six phase (plag + of + cpx + Fe-Ti oxide + ap+ lq) saturation surface and that the more differentiated lavas resulted from differing degrees of crystallization on this surface. 相似文献
998.
海平面变化是全球气候系统变化的一个组成部分,是环境变化的重要指标,也会影响沿海区域及岛屿的生态环境甚至存亡.全球海平面变化由海水质量变化和比容海平面变化构成.海水质量变化主要是由于两极冰盖和高山区的冰川融化流入海洋所致;比容海平面变化是由海水的温度和盐度变化所引起的,其中温度变化是最主要的因素.本文介绍了海平面变化各种监测技术的发展过程,并对海平面变化的研究现状进行了总结.所有研究成果均表明,近100多年以来,全球海平面一直处于上升态势;近几十年以来,海平面呈现加快上升并且越来越快的趋势.目前仍然存在一些问题:人们还没有完全掌握海平面变化规律,对未来海平面变化预测有较大不确定性;深海缺乏实测数据;厄尔尼诺—南方涛动(ENSO)的变化规律以及对海平面的影响;GRACE陆地与海洋信号无法完全分离以及GRACE与GRACE-FO之间的一致性分析等.这些问题都需要进一步开展研究. 相似文献
999.
地震应急卫星通信网一直存在路由异常的问题,时常造成卫星站点通信不畅。通过对网络拓扑结构进行分析,总结造成路由异常的原因。通过列举实例,提出以通过设置静态路由的方式,来解决目前网络中存在的路由异常问题。 相似文献
1000.