Ice Thickness And Subglacial Topography Detection By Ice Radar In Antarctic Ice Sheet And Its Evolution Research

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.