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1.
Guo Jingxue Sun Bo Tian Gang 《应用地球物理》2007,4(3):214-220
As an important component of the cryosphere, sea ice is very sensitive to climate change. The study of sea ice physics needs accurate sea ice thickness. This paper presents an electromagnetic induction （EM） technique which can be used to measure the sea ice thickness distribution efficiently and its successful application in the Antarctic Neila Fjord. Based on the electrical properties of sea ice and seawater and the application of electromagnetic field theory, this technique can accurately detect the distance between the EM instrument and the ice/water interface to measure the sea ice thickness. Analyzing the apparent conductivity data obtained by the electromagnetic induction technique and drill-hole measurements at same location allows the construction of a transform equation for the apparent conductivity and sea ice thickness. The verification of the calculated sea ice thickness using this equation indicates that the electromagnetic induction technique is able to determine reliable sea ice thickness with an average relative error of only 5.5%. The ice thickness profiles show the sea ice distribution in Neila Fjord is basically level with a thickness of 0.8 - 1.4 m. 相似文献
2.
WU Guangjian YAO Tandong XU Baiqin LI Zheng TIAN Lide DUAN Keqin WEN Linke 《中国科学D辑(英文版)》2006,49(1):10-17
Dust grain size is a proxy for wind strength that en-trains it. Mineral aerosol blown from arid continent to remote sites has a broad diameter range, from less than 0.5 μm to larger than 75 μm[1]. For a long time, geolo-gists reveal the transport and sediment characteristics using grain size and size distribution. In loess research, grain size is widely used as the proxy for winter mon-soon strength[2,3]. Fractions entrained by the westerlies and winter monsoon can be discerned by grain size… 相似文献
3.
An implementation of the Ensemble Kalman filter (EnKF) with a coupled ice–ocean model is presented. The model system consists of a dynamic–thermodynamic ice model using the elastic-viscous-plastic (EVP) rheology coupled with the HYbrid Coordinate Ocean Model (HYCOM). The observed variable is ice concentration from passive microwave sensor data (SSM/I). The assimilation of ice concentration has the desired effect of reducing the difference between observations and model. Comparison of the assimilation experiment with a free-run experiment shows that there are large differences, especially in summer. In winter the differences are relatively small, partly because the atmospheric forcing used to run the model depends upon SSM/I data. The assimilation has the strongest impact close to the ice edge, where it ensures a correct location of the ice edge throughout the simulation. An inspection of the model ensemble statistics reveals that the error estimates of the model are too small in winter, partly a result of too low model ice-concentration variance in the central ice pack. It is found that the ensemble covariance between ice concentration and sea-surface temperature in the same grid cell is of the same sign (negative) throughout the year. The ensemble covariance between ice concentration and salinity is more dependent upon the physical mechanisms involved, with ice transport and freeze/melt giving different signs of the covariances. The ice-transport and ice-melt mechanisms also impact the ice-concentration variance and the covariance between ice concentration and ice thickness. The ensemble statistics show a high degree of complexity, which to some extent merits the use of computationally expensive assimilation methods, such as the Ensemble Kalman filter. The present study focuses on the assimilation of ice concentration, but it is understood that assimilation of other datasets, such as sea-surface temperature, would be beneficial.Responsible Editor: Jin-Song von Storch 相似文献
4.
Sensitivity study of the air–ice drag coefficient C Dai is presented with an ice–ocean coupled model for the Sea of Okhotsk. The C Dai?×?103 value is varied from 2 to 5 based on the direct measurements in the region. The maximum volume transport of the East Sakhalin Current and the mean sea ice velocity were intensified as C Dai increased. The sensitivity experiment with the ice–water drag coefficient C Diw showed that the East Sakhalin Current volume transport is hardly affected by C Diw but significantly intensified by C Dai. While the ice drift in the off-ice-edge direction was intensified by the increase in C Dai and the decrease in C Diw, the ice edge location was nearly unchanged. This was due to melting caused by the relatively warm water inflow from the North Pacific. That is, sea ice extent in the region is strongly influenced by melting caused by a large ice–ocean heat transfer. In the active melting regions, the ice–ocean heat transfer of more than 100 W/m2 occurred even in mid-winter. This is the same order as the cooling by air in winter, and a heat insulation capacity of sea ice is weakened in such regions. 相似文献
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Vertical quantitative and dominant population distribution of the bacteria isolated from the Muztagata ice core 总被引：6，自引：0，他引：6
XIANG Shurong YAO Tandong AN Lizhe WU Guangjian XU Baiqing MA Xiaojun LI Zhen WANG Junxia & YU Wusheng . Key Laboratory of Ice Core Cold Regions Environment Cold Arid Regions Environmental Engineering Research Institute Chinese Academy of Sciences Lanzhou China . Institute of Tibetan Plateau Research Chinese Academy of Sciences Beijing China . College of Life Science Lanzhou University Lanzhou China 《中国科学D辑(英文版)》2005,48(10)
With rapid development of microbiology on ex-treme environment, many microorganisms have been found on glacial surface and in deep glacier around the world. The extensive 16S rRNA sequence analysis of bacteria isolated from glacial samples indicates that the bacteria in ice are highly similar to those from ocean, lake, terrestrial sediment and agricultural soil on the earth[1,2]. This suggests a close relationship be-tween the microorganisms in glacial region and those in other environments s… 相似文献
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The glacial records of the inner-core regions of the Laurentide Ice Sheet (LIS) document complex yet coherent patterns reflecting ice-sheet change (e.g. ice-divide migration), providing unique insights into past glacial conditions. This study develops a conceptual model of subglacial dynamics evolution within a major ice-dispersal centre of the LIS in northeastern Quebec, Canada using a GIS-based analysis of the surficial geologic record. Multiple proxies of subglacial conditions (subglacial streamlined landforms, lake density and lake area over thin drift/bedrock) were analysed through grid-overlay techniques and then classified based on different proxy variables ranging from highly mobile warm-based to immobile cold-based conditions. An additional proxy (till blanket) was used to identify areas of thick till deposition, but with few proxies (few lake or landform metrics). Based on local ice-flow reconstructions, the most ‘relict’ glacial terrain zone (GTZ1) has warm-based conditions over 66% of its area and is remarkably well preserved, suggesting laterally extensive warm-based conditions during the oldest identified ice-flow phase. This relict glacial terrain is partially overprinted by two subsequent ice-flow phases in spatially restricted zones in the northeast (73% warm-based), east-central (41% warm-based), and northwest (33% warm-based) of the study area. A zone of more sluggish conditions (only 3% warm-based) was identified in the highlands at the centre of the study area, characterized by thin till cover, few landforms, yet with large patches of relatively abundant small lakes, indicative of areal scouring. No clear evidence of sustained cold-based conditions (i.e. high chemical index of alteration values or high 10Be abundances) was found in the study area. These results suggest that warm-based conditions (active erosion and/or deposition) were uniformly widespread during the earliest ice-flow phase, later becoming more spatially restricted with broader sluggish ice conditions. These spatially restricted regions of warm-based subglacial regimes were likely controlled by surrounding and down-flow ice streaming. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd 相似文献
9.
G. Durand A. Persson D. Samyn A. Svensson 《Earth and Planetary Science Letters》2008,265(3-4):666-671
We propose a new method to investigate the relationships between neighbouring crystals and apply it to the textures measured along the upper 900 m of the NorthGRIP ice core. This method shows unexpected correlations between neighbours in the so-called normal grain growth regime, questioning the classical view on the onset of rotation recrystallization in ice-sheets. Moreover, the fractionation rate associated to the rotation recrystallization appears constant through time. Finally, grains with low-angle boundaries do not present a special distribution pattern of their c-axes. This suggests that rotation recrystallization is an isotropic process not affected by the direction of the macroscopic strain. 相似文献
10.
Distribution of ice thickness and subglacial topography of the “Chinese Wall” around Kunlun Station,East Antarctica 总被引：1，自引：0，他引：1
As fundamental parameters of the Antarctic Ice Sheet, ice thickness and subglacial topography are critical factors for studying the basal conditions and mass balance in Antarctica. During CHINARE 24 (the 24th Chinese National Antarctic Research Expedition, 2007/08), the research team used a deep ice-penetrating radar system to measure the ice thickness and subglacial topography of the “Chinese Wall” around Kunlun Station, East Antarctica. Preliminary results show that the ice thickness varies mostly from 1600 m to 2800 m along the “Chinese Wall”, with the thickest ice being 3444 m, and the thinnest ice 1255 m. The average bedrock elevation is 1722 m, while the minimum is just 604 m. Compared with the northern side of the ice divide, the ice thickness is a little greater and the subglacial topography lower on the southern side, which is also characterized by four deep valleys. We found no basal freeze-on ice in the Gamburtsev Subglacial Mountains area, subglacial lakes, or water bodies along the “Chinese Wall”. Ice thickness and subglacial topography data extracted from the Bedmap 2 database along the “Chinese Wall” are consistent with our results, but their resolution and accuracy are very limited in areas where the bedrock fluctuates intensely. The distribution of ice thickness and subglacial topography detected by ice-penetrating radar clarifies the features of the ice sheet in this “inaccessible” region. These results will help to advance the study of ice sheet dynamics and the determination of future locations of the GSM’s geological and deep ice core drilling sites in the Dome A region. 相似文献
11.
This paper investigates the conditions under which a marine ice sheet may adopt a steady profile. The ice is treated as a linear viscous fluid caused to flow from a rigid base to and over water, treated as a denser but inviscid fluid. The solutions in the region around the point of flotation, or ‘transition’ zone, are calculated numerically. In-flow and out-flow conditions appropriate to ice sheet and ice shelf flow are applied at the ends of the transition zone and the rigid base is specified; the flow and steady free surfaces are determined as part of the solutions. The basal stress upstream, and the basal deflection downstream, of the flotation point are examined to determine which of these steady solutions satisfy ‘contact’ conditions that would prevent (i) the steady downstream basal deflection contacting the downstream base, and (ii) the upstream ice commencing to float in the event it was melted at the base. In the case that the upstream bed is allowed to slide, we find only one mass flux that satisfies the contact conditions. When no sliding is allowed at the bed, however, we find a range of mass fluxes satisfy the contact conditions. The effect of ‘backpressure’ on the solutions is investigated, and is found to have no affect on the qualitative behaviour of the junctions. To the extent that the numerical, linearly viscous treatment may be applied to the case of ice flowing out over the ocean, we conclude that when sliding is present, Weertman's ‘instability’ hypothesis holds. 相似文献
12.
The role of meteoric smoke as condensation nuclei for mesospheric ice has recently been challenged by model simulations on the global transport of meteoric material. At the same time a considerable fraction of smoke particles is charged in the mesosphere. This has significant effects on nucleation processes as it can remove the Kelvin barrier. We suggest that in particular nucleation on negatively charged smoke is likely to be a dominant mechanism for mesospheric ice formation. This is in contrast to nucleation on positive ion clusters as the latter is largely hampered by efficient ion/electron recombination. Surprisingly, the large potential of nucleation on charged smoke has so far not been considered in mesospheric ice models. A challenging question concerns the fraction of mesospheric smoke that is actually charged. An improved understanding of mesospheric charging and nucleation will require laboratory experiments on nuclei in the transition regime between molecular and particulate sizes. 相似文献
13.
Controversy exists over the extent of glaciation in Eastern Asia at the Last Glacial Maximum: complete ice sheet cover vs. restricted mountain icefields (an area discrepancy equivalent to 3.7 Greenland Ice Sheets). Current arguments favour the latter. However, significant last glacial ice-rafted debris (IRD) exists in NW Pacific ocean cores, which must have been sourced from a major ice sheet somewhere bordering the North Pacific. The origin of this IRD is addressed through a combination of marine core analysis, iceberg trajectory modelling and remote sensing of glacial geomorphology. We find compelling evidence for two stages of glaciation centred on the Kamchatka area of maritime southeast Russia during the last glacial, with ice extent intermediate in size between previous maximum and minimum reconstructions. Furthermore, a significant increase in iceberg flux precedes, and accompanies, a substantial marine core ash deposit at around 40 ka BP. We speculate that rapid decay of the first stage of the ice sheet may have triggered substantial volcanic activity. 相似文献
14.
It has been well known by oceanographers that the World Ocean Circulation originates inNorth Atlantic near the Greenland, where in wintertime the cooled surface water descends to form North Atlantic Deep Waters (NADW). The NADW, when passing the Antarctic… 相似文献
15.
Duanne White Réka-Hajnalka Fülöp Paul Bishop Andrew Mackintosh Gordon Cook 《Quaternary Geochronology》2011,6(3-4):289-294
Cosmogenic nuclide exposure dating of glacial clasts is becoming a common and robust method for reconstructing the history of glaciers and ice sheets. In Antarctica, however, many samples exhibit cosmogenic nuclide ‘inheritance’ as a result of sediment recycling and exposure to cosmic radiation during previous ice free periods. In-situ cosmogenic 14C, in combination with longer lived nuclides such as 10Be, can be used to detect inheritance because the relatively short half-life of 14C means that in-situ 14C acquired in exposure during previous interglacials decays away while the sample locality is covered by ice during the subsequent glacial. Measurements of in-situ 14C in clasts from the last deglaciation of the Framnes Mountains in East Antarctica provide deglaciation ages that are concordant with existing 26Al and 10Be ages, suggesting that in this area, the younger population of erratics contain limited inheritance. 相似文献
16.
Climatic and environmental changes over the last millennium recorded in the Malan ice core from the northern Tibetan Plateau 总被引：3，自引：0，他引：3
WANG Ninglian YAO Tandong PU Jianchen ZHANG Yongliang SUN Weizhen 《中国科学D辑(英文版)》2006,49(10):1079-1089
In this paper, climatic and environmental changes were reconstructed since 1129A.D. based on the Malan ice core from Hol Xil, the northern Tibetan Plateau. The record of δ 18O in the Malan ice core indicated that the warm-season air temperature variations displayed a general increase trend, the 20th-century warming was within the range of natural climate variability, and the warmest century was the 17th century while the warmest decade was the 1610s, over the entire study period. The “Medieval Warm Epoch” and “Little Ice Age” were also reflected by the ice core record. The dust ratio in the Malan ice core is a good proxy for dust event frequency. The 870-year record of the dust ratio showed that dust events occurred much frequently in the 19th century. Comparing the variations of δ 18O and the dust ratio, it is found that there was a strong negative correlation between them on the time scales of 101―102 years. By analyses of all the climatic records of ice cores and tree rings from the northern Tibetan Plateau, it was revealed that dust events were more frequent in the cold and dry periods than in the warm and wet periods. 相似文献
17.
Tenley J. Banik Paul J. Wallace Ármann Höskuldsson Calvin F. Miller Charles R. Bacon David J. Furbish 《Bulletin of Volcanology》2014,76(1):1-19
Products of subglacial volcanism can illuminate reconstructions of paleo-environmental conditions on both local and regional scales. Competing interpretations of Pleistocene conditions in south Iceland have been proposed based on an extensive sequence of repeating lava-and-hyaloclastite deposits in the Síða district. We propose here a new eruptive model and refine the glacial environment during eruption based on field research and analytical data for the Síða district lava/hyaloclastite units. Field observations from this and previous studies reveal a repeating sequence of cogenetic lava and hyaloclastite deposits extending many kilometers from their presumed eruptive source. Glasses from lava selvages and unaltered hyaloclastites have very low H2O, S, and CO2 concentrations, indicating significant degassing at or close to atmospheric pressure prior to quenching. We also present a scenario that demonstrates virtual co-emplacement of the two eruptive products. Our data and model results suggest repeated eruptions under thin ice or partially subaerial conditions, rather than eruption under a thick ice sheet or subglacial conditions as previously proposed. 相似文献
18.
L. P. Imaeva B. M. Koz’min V. S . Imaev N. N. Grib S. V. Ashurkov 《Journal of Seismology》2017,21(2):385-410
The paper presents the modern structural-tectonic pattern and a tectonodynamic model of the zone of interaction of the most seismically active northeastern side of the Baikal rift zone (BRZ) and the conjugate system of seismogenic structures of the Aldan-Stanovoy block, where disastrous events with M ≥ 6.0 have been reported. Regularities in the structural formation of active faults and their kinematics are discussed. The faults form block structures accumulating significant tectonic strain. Motions between large tectonic blocks cause sudden release of the strain, which results in catastrophic events (M ≥ 6.0) with focal mechanisms of definite kinematic type. 相似文献
19.
On the basis of distribution of active fault and regional rheological structure, a three-dimensional finite element model of Sichuan-Yunnan region, China, is constructed to simulate contemporary crustal motion and stress distri- bution and discuss the dynamic mechanism of crustal motion and deformation in the Sichuan-Yunnan region. Lin- ear Maxwell visco-elastic model is applied, which includes the active fault zones, the elastic upper crust and vis- cous lower crust and upper mantle. Four different models with different boundary conditions and deep structure are calculated. Some conclusions are drawn through comparison. Firstly, the crustal rotation about the eastern syntaxis of the Himalaya in the Sicuan-Yunnan region may be controlled by the special dynamic boundary condition. The drag force of the lower-crust on the upper crust is not negligible. At the same time, the main active fault zones play an important role in the contemporary crustal motion and deformation in Sichuan-Yunnan region. 相似文献