【作者】 崔祥斌；

【导师】 田钢； 孙波；

【作者基本信息】 浙江大学 ， 地球探测与信息技术， 2010， 博士

【摘要】 南极冰盖是地球上最大的陆缘冰体,其物质收支和稳定性对全球气候变化和海平面升高有重要的影响。冰雷达(Ice radar),又称无线电回波探测(Radio-echosounding,RES)或探冰雷达(Ice-penetrating radar),主要用于极地冰盖冰厚、内部结构和冰下地貌调查,是冰川学家调查南极冰盖冰下特征的主要方法。这些参数是计算冰盖体积和物质平衡、重建过去冰雪积累和消融率以及冰盖动力和沉积过程的基础。现在,冰雷达测量覆盖了南极绝大部分区域,极大地提升了人们对南极冰盖和全球系统间相互作用的理解。本文首先重点评述了冰雷达在探测研究南极冰盖厚度和冰下地形、内部反射层、冰下湖和冰下水系、冰床粗糙度以及冰晶组构等主要领域的进展,并且对未来冰雷达探测研究南极冰盖的前景进行了展望,给出了我国的现状。冰雷达的性能,如探测深度、分辨率和精度等,直接决定了观测结果的有效性和准确性,进而影响冰盖的物质平衡和稳定性研究。自上世纪60年代被引入极地冰盖调查和研究以来,冰雷达性能、探测方法和研究内容得到了不断的提高和发展,成为冰盖研究不可获取的手段。本文分三个时间段(1960s～1980s,1980s～2000年和2000年之后)综述了冰雷达的发展,并展望了其未来的发展趋势。Dome A(冰穹A)位于东南极冰盖中央,是南极冰盖最高点。冰盖演化模式显示,Dome A区域很可能保存了过去超过百万年的地球古气候和古环境记录,被认为是深冰芯钻孔的理想位置。冰厚和冰下地形是模式评估冰芯年代尺度和深冰芯钻孔选址的重要依据。中国第21次和24次南极科学考察(CHINARE 21,2004/05;CHINARE 24,2007/08)期间,车载冰雷达系统被用于Dome A区域中心30km×30km范围内冰盖的三维调查,成功获得高分辨率、高精度冰厚和冰下地形数据,得出140.5m×140.5m网格分辨率冰厚分布和冰下地形DEM。调查结果显示,Dome A中心方形区域内的冰厚平均值为2233m,冰厚最小值1618m,昆仑站位置冰厚最大,为3139m;冰下地形起伏相对剧烈,海拔范围949-2445m,呈现典型、清晰的山地冰川作用地貌格局,很可能反映了南极冰盖的早期演化。依据冰厚分布和冰下地形特征,认为昆仑站位置适合开展首支分辨率高、年代久远深冰芯的钻探。不过,冰盖内部层序结构和冰底消融情况仍需进一步研究确定。南极冰盖的形成始于～3400万年前,当时的地球气候出现显著而快速的变化。冰盖和气候模式研究的结果显示,大气二氧化碳浓度的降低(不到工业化前280ppm的3倍),以及南极绕极流的形成,导致了地球的大幅度降温,并出现与地球轨道变化相关的冰川作用。基于现有的南极冰盖冰下地形,数值模拟得出的南极冰盖发源地在南极的山脉区域,包括位于东南极冰盖中央Dome A区域的Gamburtsev山脉。尽管如此,由于缺少对Gamburtsev山脉现在地形特征的了解,使得现在关于南极大陆型冰盖的早期冰川作和后续发展仍然很不确定。根据我们通过冰雷达获得的Dome A区域的冰下地形,冰下地貌呈现了经典的阿尔卑斯山脉地形特征,发育有经过山地冰川剥蚀的早期河流谷底,而这样的地形特征的形成需要平均约3℃的夏季表明温度。Dome A区域的冰下地形很可能形成于南极冰盖冰川作用的初期。根据南极的气候历史(来自深海沉积记录),认为Gamburtsev山脉的形成可能早于3400万年前,并且该区域是南极冰盖起源的核心区域。此外,1400万年以来,Dome A区域的冰下地形很可能得到了很好的保存。东南极冰盖中山站至Dome A断面是国际横穿南极科学考察计划的核心断面之一,途经过伊丽莎白公主地,沿Lambert冰川东侧上游至Dome A下覆的Gamburtsev冰下山脉区域。东南极冰盖中山站至Dome A断面的冰厚和冰下地形源于CHINARE 24期间的车载冰雷达探测,测线总长1170km,其中在82%的测线上成功探测到冰岩界面,实测数据的水平分辨率＜5.6m。测量结果显示:断面上的平均冰厚为2037m,730km处冰厚最大,冰盖边缘位置冰厚最小(891m),内陆1020km位置冰厚略大于冰厚最小值,为1078m;冰下地形平均海拔728m,远高于东南极冰下地形高程平均值,其中1034km处海拔最高,达到2650m,765km处海拔最低。内陆深处900-1170km范围内冰下地形海拔较高,与该段位于Gamburtsev冰下山脉区域有关。除900km位置冰下地形的剧烈升高在冰面造成明显的地形抬升外,总体上,冰下地形对冰面地形的影响不大。在冰雷达探测到冰岩界面的部分,小尺度的冰厚和冰下地形变化相对密集且剧烈,表明沿断面的冰床粗糙度较大,认为是冰流运动、冰下环境和冰下地质构造共同作用的结果。冰雷达未能探测冰岩界面的部分,冰厚明显较大。此外,由于该段冰流运动较强,增加了冰盖内部结构的复杂性,导致冰雷达信号在冰体内传播的衰减严重。更多还原

【Abstract】 The Antarctic ice sheet is the largest continental ice on the earth, its mass budget and stability has an important influence on global climate change and sea level rise. Ice radar, also called radio-echo sounding(RES) or ice-penetrating radar, mainly used to investigate ice thickness, internal structure and subglacial morphology of the polar ice sheets, constitutes the principal means by which glaciologists investigate the subsurface properties of the Antarctic ice sheet. These parameters are fundamental to calculate ice volume and mass balance and reconstruct past snow accumulation and melting rates, ice dynamics and deposition process. Now, RES has covered most regions in Antarctica and provided significant understanding of the interactions between ice sheet and global system. In the paper, we firstly reviewed the progress of ice radar in investigating and researching Antarctic ice sheet thickness and subglacial topography, internal reflecting horizons, subglacial lakes and water systems, subglacial bedrock roughness and crystal orientation fabrics(COF), and even the prospect of ice radar in investigating and researching Antarctic ice sheet in the future and our present situation was proposed.The performances of ice radar, such as the maximal penetrating depth, vertical resolution and precision, determine directly the validity and accuracy of the measurements, and influence the imports and boundary conditions of the models finally. Since ice radar was introduced into the investigation and research of the polar ice sheets from 1960s, the instrument performance, surveying methods and research contents have been improved and developed incessantly. has become an indispensable means of ice sheet study. The development of ice radar in three periods (1960s～1980s, 1980s～2000 and after 2000) was reviewed and its future development was prospectedDome A, located in the central East Antarctic ice sheet (EAIS), is the highest summit of the Antarctic ice sheet. From ice-sheet evolution modeling results, Dome A is likely to preserve over one million years of the Earth’s paleo-climatic and -environmental records, and considered an ideal deep ice core drilling site. Ice thickness and subglacial topography are critical factors for ice-sheet models to determine the timescale and location of a deep ice core. During the 21st and 24th Chinese National Antarctic Research Expedition (CHINARE 21, 2004/05; CHINARE 24, 2007/08), ground-based ice radar systems were used to a three-dimensional investigation in the central 30 km×30 km region at Dome A. The successfully obtained high resolution and accuracy data of ice thickness and subglacial topography were then interpolated into the ice thickness distribution and subglacial topography digital elevation model (DEM) with a regular grid resolution of 140.5 m×140.5 m. The results of the ice radar investigation indicate that the average ice thickness in the Dome A central 30 km×30 km region is 2233 m, with a minimal ice thickness of 1618 m and a maximal ice thickness of 3139 m at Kunlun Station. The subglacial topography is relatively sharp, with an elevation range of 949—2445 m. The typical, clear mountain glaciation morphology is likely to reflect the early evolution of the Antarctic ice sheet. Based on the ice thickness distribution and subglacial topography characteristics, the location of Kunlun Station was suggested to carry out the first high-resolution, long time-scale deep ice core drilling. However, the internal structure and basal environments at Kunlun Station still need further research to determineIce-sheet development in Antarctica was a result of significant and rapid global climate change about 34 million years ago. Ice-sheet and climate modelling suggest reductions in atmospheric carbon dioxide (less than three times the pre-industrial level of 280 parts per million by volume) that, in conjunction with the development of the Antarctic Circumpolar Current, led to cooling and glaciations paced by changes in Earth’s orbit. Based on the present subglacial topography in Antarctic ice sheet, numerical models point to ice-sheet genesis on mountain massifs of Antarctica, including the Gamburtsev mountains at Dome A, the centre of the present ice sheet. Our lack of knowledge of the present-day topography of the Gamburtsev mountains means, however, that the nature of early glaciation and subsequent development of a continental-sized ice sheet are uncertain. According to our radar information about the base of the ice at Dome A, revealing classic Alpine topography with pre-existing river valleys overdeepened by valley glaciers formed when the mean summer surface temperature was around 3.6℃. This landscape is likely to have developed during the initial phases of Antarctic glaciation. According to Antarctic climate history (estimated from offshore sediment records), the Gamburtsev mountains are probably older than 34 million years and were the main centre for ice-sheet growth. Moreover, the landscape has most probably been preserved beneath the present ice sheet for around 14 million years.The traverse between Zhongshan Station and Dome A in East Antarctic ice sheet, via Elizabeth Princess Land, along eastern upstreams of Lambert Glacier to Gamburtsev Subglacial Mountains at Dome A region, is a critical transect in ITASE (International Trans-Antarctic Scientific Expedition) project. The ice thickness and subglaical topography of the traverse between Zhongshan Station and Dome A in the paper were detected by ice radar during CHINARE 24. The total radar survey line is 1170 km, of which about 82% ice-bedrock interface is detected successfully, and the horizontal resolution along the traverse is less than 5.6 m. The preliminary results show that, the averaged ice thickness along the traverse is 2037 m, the thickest ice is at 730 km, the thinnest ice (891 m) is at the edge of the ice sheet, but the minimal ice thickness in inland appears at 1020 km(1078 m). The averaged subglacial topography elevation is 728 m, greatly larger than the average subglacial topography elevation in East Antarctic ice sheet. The largest elevation is at 1034 km, reaches up to 2650 m, and the lowest terrain locates at 765 km. In the further inland of 900 - 1170 km, the subglacial topography is relatively high due to the existing of Gamburtsev Subglacial Moutains in the region. Generally, the influence of subglacial topography to ice surface is not significant, in addition to the location of 900 km where ice surface uplifts evidently caused by rising of subglacial topography. Where ice-bed interface was detected, the frequent and strong change of ice thickness and subglacial topography in small-scale means the large bedrock roughness along the traverse, and is consider as the result of the integrated action of ice flow, basal environments and geology. The segment where bedrock was not detected has very large ice thickness. The strong ice flow there probably makes internal structure more complicated and induces serious attenuation of radar signals.更多还原