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1.
High-resolution mean sea surface computed with altimeter data of Ers-1 (geodetic mission) and topex-poseidon 总被引：1，自引：0，他引：1
A. Cazenave P. Schaeffer M. Berge C. Brossier K. Dominh M. C. Gennero 《Geophysical Journal International》1996,125(3):696-704
The remote-sensing satellite ERS-1, launched in 1991 to study the Earth's environment, was placed on a geodetic (168-day repeat) orbit between 1994 April and 1995 March to map, through altimetric measurements, the gravity field over the whole oceanic domain with a resolution of 8 km at the equator in both along-track and cross-track directions. We have analysed the precise altimeter data of the geodetic mission, and, by also using one year of Topex-Poseidon altimeter data, we have computed a global high-resolution mean sea surface. The various steps involved in pre-processing the ERS-1 data consisted of correcting the data for environmental factors, editing, and reducing, through crossover analyses, the radial orbit error, which directly affects sea-surface height measurements. For this purpose, we adjusted sinusoids at 1 and 2 cycle rev−1 along the ERS-1 profiles in order to minimize crossover differences between ERS-1 and yearly averaged Topex-Poseidon profiles. In effect, the orbit of Topex-Poseidon is very accurately determined (within 2–3 cm for the radial component), so Topex-Poseidon altimeter profiles can serve as a reference to reduce the ERS-1 radial orbit error. The ERS-1 residual orbit error was further reduced through a second crossover analysis between all ascending and descending profiles of the geodetic mission. The along-track ERS-1 and Topex-Poseidon data were then interpolated over the whole oceanic domain on a regular grid of 1/16°× 1/16° size. The mapping of the gridded sea-surface heights reveals the very fine structure of the marine geoid, up until now unknown at a global scale. This new data set will be most useful for marine geophysical and tectonic investigations. 相似文献
2.
Reconstruction of the Ross Ice Drainage System, Antarctica, at the Last Glacial Maximum 总被引：2，自引：0，他引：2
George H. Denton & Terence J. Hughes 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):143-166
We present here a revised reconstruction of the Ross ice drainage system of Antarctica at the last glacial maximum (LGM) based on a recent convergence of terrestrial and marine data. The Ross drainage system includes all ice flowlines that enter the marine Ross Embayment. Today, it encompasses one-fourth of the ice-sheet surface, extending far inland into both East and West Antarctica. Grounding lines now situated in the inner Ross Embayment advanced seaward at the LGM (radiocarbon chronology in Denton and Marchant 2000 and in Hall and Denton 2000a, b), resulting in a thick grounded ice sheet across the Ross continental shelf. In response to this grounding in the Ross (and Weddell) Embayment, ice-surface elevations of the marine-based West Antarctic Ice Sheet were somewhat higher at the LGM than at present (Steig and White 1997; Borns et al. 1998; Ackert et al. 1999). At the same time, surface elevations of the East Antarctic Ice Sheet inland of the Transantarctic Mountains were slightly lower than now, except near outlet glaciers that were dammed by grounded ice in the Ross Embayment. The probable reason for this contrasting behavior is that lowered global sea level at the LGM, from growth of Northern Hemisphere ice sheets, caused widespread grounding of the marine portion of the Antarctic Ice Sheet, whereas decreased LGM accumulation led to slight surface lowering of the interior terrestrial ice sheet in East Antarctica. Rising sea level after the LGM tripped grounding-line recession in the Ross Embayment, which has probably continued to the present day (Conway et al. 1999). Hence, gravitational collapse of the grounded ice sheet from the Ross Embayment, accompanied by lowering of the interior West Antarctic ice surface and of outlet glaciers in the Transantarctic Mountains, occurred largely during the Holocene. At the same time, increased Holocene accumulation caused a slight rise of the inland East Antarctic ice surface. 相似文献
3.
Palaeomagnetic investigations and Rb–Sr dating were carried out on samples from two plutons from the Granite Harbour Intrusives of the Transantarctic Mountains inland of Terra Nova Bay. The Rb–Sr whole rock–biotite ages from Teall Nunatak (475±4, 483±4 Ma), a quartz-diorite pluton cropping out to the south of Priestley Glacier, are older than that from the Mount Keinath monzogranite (450±4 Ma), which is located to the north of the glacier. These results are consistent with the literature data, which suggest that during the last phases of the Ross Orogeny the cooling rate of the basement was significantly lower to the north than to the south of Priestley Glacier. The Teall Nunatak quartz-diorite is characterized by a stable magnetization, whose blocking-temperature spectrum ranges from 530 to 570 °C. At one site, the stable magnetization is screened by a large secondary component of opposite polarity, removed by thermal demagnetization below 300 °C. The characteristic directions after thermal demagnetization yielded a southern pole located at lat. 11°S, long. 21°E. The magnetization of Mount Keinath monzogranite consists of several components with overlapping stability spectra. A characteristic direction was isolated at one site only, obtained by demagnetizing the specimens in the temperature range from 380 to 460 °C.
Comparison with the other East Antarctica poles shows that those from Victoria Land are very well grouped and give a reliable early Ordovician palaeopole (lat. 5°S, long. 23°E, with K =196 and A95 =3.7°), whereas the poles from Wilkes, Enderby and Dronning Maud Land are dispersed. We tentatively advance the hypothesis that the dispersion reflects different magnetization ages due to the slow cooling of these regions during the last stages of the Ross Orogeny. 相似文献
Comparison with the other East Antarctica poles shows that those from Victoria Land are very well grouped and give a reliable early Ordovician palaeopole (lat. 5°S, long. 23°E, with K =196 and A
4.
Evidence for warmer event from quartz grains in the soil of Grove Mountains,East Antarctica 
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下载免费PDF全文 <正> The cold desert soil has been discovered at first time in southern ridge ofMount Harding,Grove Mountains of interior East Antarctica Ice Sheet.Based on themicro structural observation,dominant characteristics of quartz grains include:dis-tinct surface stria and fractures,and clean features of frost action at both of crystalmargins and micro crannies of quartz grains.These features show a pedogenesis envi-ronment of few water,short transportation and frost action,revealing a warmer climat-ic event existed in this region. 相似文献
5.
DENSIFICATION PROCESS WITHIN THE NEAR-SURFACE LAYER OF THE ANTARCTIC ICE SHEET 总被引：1，自引：0，他引：1 下载免费PDF全文
下载免费PDF全文 The densification process within the near-surface layer of Antarctic Ice Sheet is dominated by the environment and exhibits geographic zonality, In this article, the processes are found to be of three types: warm, cold and alternate, on the basis of the studies on a lot of shallow snow/firm cores from Wilkes Land, Antarctica, and the available data. Warm type densification takes place mainly on the periphery of the Antarctic Ice Sheet, where the mean annual temperature is about --10----15℃. High temperature in summer and consequent melting and infiltration are the main factors influencing the densification process. Cold type densification occurs in the huge central region of the Antarctica, where the mean annual temperature is below --25℃, with the maximum below 0℃ in summer. In this region, ice sintering is a main cause for the densification. The alternate type densification occurs in the transition zone between the above two regions, where the mean annual temperature is --15----25℃ and the highest 相似文献
6.
南极冰盖物质平衡最新的研究进展表明,西南极洲表现出两种变化模式,西部在增厚,而北面在更快地减薄。西南极冰盖总体可能正在减薄,其物质损失的速率可能足以使海平面每年上升近0.2mm。东南极冰盖物质不平衡可能很小,甚至其符号还不能被确定。南极半岛正在经历着快速变化。目前还不能可靠地估算南极冰盖的物质平衡状态。同时,大型冰川的停滞,一些冰川流速加快,冰盖大范围加速减薄,冰架大面积的快速崩解和支流冰川的加速,以及着地线强烈的底部融化等显示出南极冰盖存在快速变化。南极冰盖物质平衡未来的重点研究领域是开展冰盖表面高程变化的监测与模拟,确定表面物质平衡及其在各冰流盆地的分布,着地线的冰流通量,冰架底部的融化,了解冰后期冰盖退缩的动力过程,以及开发、对比和改进与冰盖物质平衡模拟和预测相关的各种模型。 相似文献
7.
南极冰盖自形成以来就一直是全球环境体系最重要的组成部分 ,其扩展和消融的动态演化过程不仅是南极大陆最重要的地质过程 ,而且也是全球气候和环境变化最直接的反映和体现。因此 ,有关这一课题的研究一直是国际地质学界所关注的热点。本文回顾了南极冰川和气候演化研究的历史 ,总结了当前这方面研究的成果以及所存在的问题 ,探讨了其未来的发展趋势 ,在此基础上 ,对我国南极考察队发现格罗夫山 (GroveMountains)地区新生代沉积岩的意义进行了阐述 相似文献
8.
New seismological constraints on differential rotation of the inner core from Novaya Zemlya events recorded at DRV, Antarctica 总被引：1，自引：0，他引：1
Annie Souriau 《Geophysical Journal International》1998,134(2):F1-F5
Novaya Zemlya nuclear test records at the seismic station DRV, Antarctica, are analysed in order to obtain further constraints on a possible differential rotation of the inner core with respect to the mantle. These data allow the sampling of the inner core along a nearly polar path in very stable conditions over more than two decades, from 1966 to 1990. The PKP (BC)– PKP (DF) traveltime residuals, which reflect the inner-core anisotropy and/or heterogeneities sampled along the path, exhibit a great stability through time. A computation of the residuals that are expected for various differential rotation rates and the same rotation axis as the mantle has been performed using the worldwide residual catalogue of Engdahl et al . (1997) for summary rays that include the time as an additional parameter in data stacking. Comparison of data and predictions shows that an eastward differential rotation with a rate as large as 3° yr−1 , as suggested by some authors, is not possible, but an eastward rotation at 1° yr−1 or lower cannot be rejected. 相似文献
9.
WESLEY E. LEMASURIER SERGIO ROCCHI 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):51-66
ABSTRACT. Hydrovolcanic deposits, interbedded tills and recycled microfossils, together with erosion anomalies in the Marie Byrd Land (MBL) landscape, each provide a portion of the record of glaciation and deglaciation events from late Oligocene to the present. We have attempted to synthesize these data sources to provide a more complete record, and to reconcile them with climatic events recorded elsewhere in Antarctica and the deep sea. The MBL data suggest that the late Oligocene was marked by the development of an ice cap at Mount Petras, where the MBL dome was beginning to rise from a near-sea-level position. Furthermore, unusually advanced cirque development in the dome crest area is difficult to explain unless there was a period of effective cirque erosion in that area between c. 25 and 15 Ma BP. These inferences are consistent with evidence from the Ross Sea for an expansion of the West Antarctic Ice Sheet (WAIS) in mid-Miocene (15–17 Ma BP) time.
The deep sea oxygen isotope proxy record has been interpreted to show the inception of West Antarctic glaciation around 6 Ma BP. This can perhaps be reconciled with the terrestrial record if one considers (1) the observation that large volume changes in the WAIS cannot produce a ω18 O signal that is significantly outside limits of error, and (2) that the landscape in West Antarctica has evolved from very low regional relief in the Oligocene, to more than 2 km of local relief in the present day, as a result of dome uplift since c. 27 Ma BP, and the growth of large volcanoes since c. 19 Ma BP. 相似文献
The deep sea oxygen isotope proxy record has been interpreted to show the inception of West Antarctic glaciation around 6 Ma BP. This can perhaps be reconciled with the terrestrial record if one considers (1) the observation that large volume changes in the WAIS cannot produce a ω
10.
本文根据作者随中国第１１次南极考察队（１９９４－１９９６年）赴中山站夏考期间，使用ＴＭＴ（系留式气象塔）观测系统，在中山站、冰盖和海冰等三个点上观测到的气温、湿度、风速、风向和气压等大气要素的廓线资料，利用相似理论的通量－廓线关系，给出这三个观测点上的动量通量、曳力系数和感热通量，在近中性条件下，中山站粗糙度高度为２．９ｃｍ，冰盖与海冰点二者粗糙度高度差不多，分别为２．８×１０－２ｃｍ和３．６×１０－２ｃｍ，曳力系数则分别为５．０６×１０－３、１．３４×１０－３和１．４１×１０－３。结果表明，即使在中山站地区这样一个尺度范围内，由于下垫面的热力学特性、地形、地貌、地势和地理位置等的差异，无论是大气边界层结构还是湍流通量等的输送特性都有明显的差别，因此南极地区的大气边界层结构和冰（雪）－气交换特征都是比较复杂的，具有很强的局地性 相似文献
11.
We present new palaeomagnetic and isotopic data from the southern Victoria Land region of the Transantarctic Mountains in East Antarctica that constrain the palaeogeographic position of this region during the Late Cambrian and Early Ordovician. A new pole has been determined from a dioritic intrusion at Killer Ridge (40 Ar/39 Ar biotite age of 499 ± 3 Ma) and hornblende diorite dykes at Mt. Loke (21°E, 7°S, A 95 = 8°, N = 6 VGPs). The new Killer Ridge/Mt. Loke pole is indistinguishable from Gondwana Late Cambrian and Early Ordovician poles. Previously reported palaeomagnetic poles from southern Victoria Land have new isotopic age constraints that place them in the Late Cambrian rather than the Early Ordovician. Based upon the new palaeomagnetic and isotopic data, new Gondwana Late Cambrian and Early Ordovician mean poles have been calculated. 相似文献
12.
目前,位于东南极冰盖分冰岭中心的冰穹-Dome A已成为深入理解南极冰盖演化、稳定性和找寻地球气候久远记录的研究热点。通过整理总结在Dome A获得的冰川学研究进展,结合国际冰芯科学研究计划(International Partnerships in Ice Core Sciences,简称IPICS)有关寻找最古老冰芯的相关资料,对Dome A的气象要素、地貌、冰厚、冰下地形、冰体流速、冰盖内部结构等环境特征进行归纳分析,讨论Dome A冰川学的最新发展及其对深冰芯钻探计划的影响,并分析概述Dome A深冰芯钻探需考虑的问题和未来发展动向。 相似文献
13.
Predicted present-day evolution patterns of ice thickness and bedrock elevation over Greenland and Antarctica 总被引：4，自引：0，他引：4
This paper discusses predicted evolution patterns of present-day changes of ice thickness, surface elevation, and bedrock elevation over the Greenland and Antarctic continents. These were obtained from calculations with dynamic 3-D ice sheet models which were coupled to a visco-elastic solid Earth model. The experiments were initialized over the last two glacial cycles and subsequently averaged over the last 200 years to obtain the current evolution. The calculations indicate that the Antarctic Ice Sheet is still adjusting to the last glacial-interglacial transition yielding a decreasing ice volume and a rising bedrock elevation of the order of several centimetres per year. The Greenland Ice Sheet was found to be close to a stationary state with a mean thickness change of only a few millimetres per year, but the calculations revealed large spatial differences. Predicted patterns over Greenland are characterized by a small thickening over the ice sheet interior and a general thinning of the ablation area. In Antarctica, almost all of the predicted changes are concentrated in the West Antarctic Ice Sheet, which is still retreating at both the Weddell and Ross Sea margins. Over most of both ice sheets, the model indicates that the surface elevation trend is dominated by ice thickness changes rather than by bedrock elevation changes. 相似文献
14.
Hydrographic (CTD), current and water level measurements obtained in the vicinity of the floating Ronne and Filchner Ice Shelves are presented. The distribution of Western Shelf Water (S > 34.7) and Ice Shelf Water (T<−1.9°C) are discussed. The general circulation in the area seems to consist of two large cyclonic gyres, one in the Filchner Depression and one north of the Ronne Ice Shelf. Each gyre shows a'warm'(T 1°C) southgoing flow of Modified Weddell Deep Water and a cold northward flow of Ice Shelf Water. The mean surface current was found to be 8cm/s towards the north-west along the barrier. The mean flow below the ice shelf shows significant components normal to the barrier, and mixing seems to be very efficient here. Well mixed layers down to more than 150 m were observed. North of Berkner Island the water level shows a typical mixed tide with tidal range ∼3m. In the tidal currents the semidiurnal constituents dominate (∼30cm/s) and with the largest current components normal to the barrier. 相似文献
15.
陨石是来自地球之外的岩石样品,是研究太阳系的起源与演化的重要窗口。半个多世纪以来,国际上在南极冰盖上发现了大量陨石样品,证实了南极是地球上最重要的陨石富集区。1998年中国首次在格罗夫山地区发现南极陨石,经过4次南极考察,共收集陨石样品9834块。这不但填补了中国在该领域的空白,也为中国积累了大量珍贵的科学样品。目前,中国先后6年开展了陨石分类研究工作,并取得了显著进展:(1)完成了684块陨石的分类命名,其中发现了许多特殊类型陨石,如火星陨石、橄辉无球粒陨石、碳质球粒陨石等;(2)初步建立了陨石库和资源共享网络平台;(3)通过南极系统分类研究,建立了南极陨石分类程序、样品管理和申请程序;(4)通过国内陨石分类合作研究,培养了一批年轻专业人才。 相似文献
16.
We applied an image correlation method to Japanese Earth Resources Satellite-1 (JERS-1) synthetic aperture radar (SAR) data obtained from 1996 to 1998 to examine flow velocity within Shirase Glacier, Antarctica. From the grounding line to the downstream region of the glacier, the obtained ice-flow velocity was systematically higher on the western streamline than the eastern. The differences between the two streamlines were 0.31 km/a in 1996 and 0.37 km/a in 1998, significantly larger than the error estimate of 0.03 km/a. The direction of ice flow was about 312° at the grounding line and changed to 327° at 10 km, 346° at 20 km and 2° at 30 km downstream from the grounding line. The total accumulated deflection is 50° to the east. Under the assumption of the conservation of ice mass across the glacier, the observed eastward change in flow direction can be explained by an asymmetric deepening of bedrock topography, that is, across the 8 km width of the glacier, the eastern side is 50 m (10%) deeper than the western side. This eastward turning of flow direction appears to be accelerated by tributary inlets, that flow to the north and northeast at 60–75% of the velocity of inlets on the western streamline. 相似文献
17.
The Holocene glacial and climatic development in Antarctica differed considerably from that in the Northern Hemisphere. Initial deglaciation of inner shelf and adjacent land areas in Antarctica dates back to between 10-8 Kya, when most Northern Hemisphere ice sheets had already disappeared or diminished considerably. The continued deglaciation of currently ice-free land in Antarctica occurred gradually between ca. 8-5 Kya. A large southern portion of the marine-based Ross Ice Sheet disintegrated during this late deglaciation phase. Some currently ice-free areas were deglaciated as late as 3 Kya. Between 8-5 Kya, global glacio-eustatically driven sea level rose by 10-17m, with 4-8 m of this increase occurring after 7 Kya. Since the Northern Hemisphere ice sheets had practically disappeared by 8-7 Kya, we suggest that Antarctic deglaciation caused a considerable part of the global sea level rise between 8-7 Kya, and most of it between 7-5 Kya. The global mid-Holocene sea level high stand, broadly dated to between 8-4 Kya, and the Littorina-Tapes transgressions in Scandinavia and simultaneous transgressions recorded from sites e.g. in Svalbard and Greenland, dated to 7-5 Kya, probably reflect input of meltwater from the Antarctic deglaciation. 相似文献
18.
Relative sea level curves from glaciated North America reveal coherent spatial patterns of response times. In the Laurentide Ice Sheet area, curve half-lives range from 1.2–1.4 ka at the uplift centre to 1.7–2 ka in a ridge of high values inboard of the glacial limit. Half-lives decline from this ridge to less than 1 ka along the margin. In the Innuitian Ice Sheet area, half-lives are about 2 ka at the uplift centre and decline to less than 1 ka at the margin. The central Laurentide response times are about half those of central Fennoscandia. This accords with the theoretical expectation that central response times are inversely proportional to ice sheet radius for ice loads large enough that rebound at the centre is insensitive to lithospheric thickness. The Innuitian central response time indicates that rebound at the centre of this ice sheet, which is much smaller than the Fennoscandian Ice Sheet, remains sensitive to lithospheric thickness. Radial gradients in response times reflect the increasing influence of the lithosphere at sites increasingly closer to the margin. Along this gradient, rebound progresses as though at the centres of smaller and smaller ice sheets. That is, the effective spatial scale of the ice load decreases toward the margin. Near the glacial limit, postglacial isostatic adjustment is complicated by forebulge migration and collapse. This is seen most strongly in the relative sea level record of Atlantic Canada, which has subsided during the Holocene more than 20 m more than the adjacent American seaboard. The relative sea level history of some areas, notably the St. Lawrence Estuary, is complicated by tectonic processes. 相似文献
19.
A. G. Iosifidi S. Bogdanova A. N. Khramov & G. Bylund 《Geophysical Journal International》1999,137(3):723-731
A palaeomagnetic investigation has been carried out of rocks from the eastern part of the Voronezh Massif, which constitutes, together with the Ukrainian Shield, the Sarmatian segment in the southern part of the East European Craton. The samples were collected in a quarry close to the town of Pavlovsk (50.4°N, 40.1°E), where a syenitic-granitic body intrudes Archaean units. U–Pb (zircon) dating has yielded an age of 2080 Ma for the intrusion.
Two characteristic magnetic components, A and B, were isolated by thermal and alternating-field demagnetization. Component A was obtained from granites and quartz syenites (11 samples) and has a mean direction of D = 229°, I = 28°, and a pole position at 12°N, 172°E. This pole is close to a contemporary mean pole (9°N, 187°E) for the Ukrainian Shield, which implies that the Voronezh Massif and the Shield constituted a single entity at 2.06 Ga. These poles differ from contemporaneous poles of the Fennoscandian Shield, indicating that the relative positions of the two shields were different from their present configuration about 2100 Myr ago.
A component B, isolated only in quartz monzonites (five samples), has a mean direction D = 144°, I = 49°, and a pole position at 4°N, 251°E, which is close to late Sveconorwegian (approximately 900 Ma) poles for Baltica. This suggests that the East European Craton was consolidated some time between 2080 and 900 Ma. Comparison with other palaeomagnetic data permit us to narrow this time span to 1770–1340 Ma. 相似文献
Two characteristic magnetic components, A and B, were isolated by thermal and alternating-field demagnetization. Component A was obtained from granites and quartz syenites (11 samples) and has a mean direction of D = 229°, I = 28°, and a pole position at 12°N, 172°E. This pole is close to a contemporary mean pole (9°N, 187°E) for the Ukrainian Shield, which implies that the Voronezh Massif and the Shield constituted a single entity at 2.06 Ga. These poles differ from contemporaneous poles of the Fennoscandian Shield, indicating that the relative positions of the two shields were different from their present configuration about 2100 Myr ago.
A component B, isolated only in quartz monzonites (five samples), has a mean direction D = 144°, I = 49°, and a pole position at 4°N, 251°E, which is close to late Sveconorwegian (approximately 900 Ma) poles for Baltica. This suggests that the East European Craton was consolidated some time between 2080 and 900 Ma. Comparison with other palaeomagnetic data permit us to narrow this time span to 1770–1340 Ma. 相似文献