| The Antarctic ice sheet is an important part in the earth system, and plays a prominent status in reconstructing the history of climate evolution, investigating the variability of ocean circulation and sea level change.But the Antarctic contitent is least accessible , extremely complicated and poorest known. Dome A(Kunlun Station), the summit of the Antarctic ice sheet,is considered a likely place for finding an ice core record reaching back to one million years. During the 21st and 24th Chinese National Antarctic Research Expedition (CHINARE 21, 2004/05;CHINARE 21, 2007/08), two datasets of Ice radio-echo sounding based ground in Dome A,the central region of East Antarctica, were made. And the other datasets from airborne radar systems was collected by AGAP(Antarctica’s Gamburstev Province project)and Alfred Wagner Institute(DOCO plans,Dome Connection East Antarctica)。Using the radar datasets and numerical modelling,some results are shown here. The aim of the thesis is to understand the flow and form of the ice sheet around the Dome A region of central East Antarctica. The thesis has the following objectives:first,dealing with and analyzing the radar datasets of linking Dome A and Vostok,where exsists the location of ice core;second,to determine the depth-age relationship of ice around Dome A and to reconstruct the accumulation of the past hundred thousand years by numerical model;third, to establish the ice thickness and the bed topography of Dome A,and to reveal the long-term glacial history of Dome A.Putting the results together would maximise our knowledge of Dome A,even of the Antarctic ice sheet and the global change.The internal isochronous layering of the Antarctic Ice Sheet, revealed by ice radar, is a prerequisite for selecting sites for deep ice core drilling that can be used for studying the paleoclimatic record. In 2004/2005, during the 21st Chinese National Antarctic Research Expedition (CHINARE 21), a 200 km long, continuous radar profile was obtained across Dome A. The internal layers along the profile were derived from the stratigraphy detected by the radar. The morphology of the isochronous layers shows that: (1) The internal layers in the shallow ice sheet (0–500 m) are generally flat, with no more than 50 m of layer intervals, and have typical synclines and anticlines in some localized regions; (2) At 500–2000 m below the surface of the ice sheet, the layers appear as“bright layers”, and the width of the layer intervals expands to 50–100 m; (3) When the basal topographic wavelengths are approximate to the thickness of the ice (3 km), the traced internal layers, with localized bumps or concave folds, are asymptotic parallel to the subglacial topography. For the longer topographic wavelengths (-20 km) wider than the thickness of the ice, the layers do not rise and fall with the basal topography. The internal layers surrounding some mountain peaks representing the most extreme variation in the terrain are sharply disturbed by the subglacial topography; (4) Layer discontinuity and fracture were detected in the basal ice sheet. Finally, by combining this new information with that derived from existing data regarding ice thickness , we were able to select three potential sites for reconstructing the age-depth relationship of the ice core.The radar profiles were done providing a full information of centre of the Dome A region. The RES data were acquired using a high-frequency monopulse ice-penetrating radar with multi-frequency of 60MHz and 179MHz . The datasets show arches and troughs in isochronous ice layers. In some sites the inclined layers and distortion of isochronous layers in ice revealed by ice-penetrating radar. We also find there is no radar signal in some sites and some sections exhibit instable sedimentation and discontinuation of the internal reflections. At Dome A, the changes of surface elevation is not obvious, the highest is 4092m. The data of ice-penetrating radar revealed flat isochronous layers. In addition, bed topography appears to be the result of a saddle-backed basin. Also,we find a north-east deep channel according to 3D RES exploration result in Dome A, its ice thickness exceeds 3000m.By the disscusions, the identification of the depth-age relationship of ice shows that there is the best site to drill the deep ice core around the Dome A. The datasets also show some arches and troughs in isochronous ice layers. There exist some typical synclines and anticlines in ice revealed by ice-penetrating radar in some local regions.A 1-D model is used to calculate the past rates of ice accumulation by internal layering. An approximate mean accumulation from 0.018 to 0.027m/yr over the past 34.6k years, along the RES profiles, was estimated. Also, we have taken the accumulation was 0.02-0.045m/yr in the past 34.6-44.6kyr , and 0.01-0.023m/yr in the past 44.6-84.6kyr along the profile. The variability of accumulation in time -space around the ice divide also was given.We also introduce the 3-dimensional coupled model for Antarctic ice sheet– GLIMMER model, and make an idealized ice sheet simulation test under EISMINT-1 benchmark,gets various evolution curves expressing conservation of mass, momentum and energy of ice sheet, and indicates that under fixed boundary condition and moving condition, the physical characteristic curves when ice sheet is in a steady state are in accordance with our current knowledge on Antarctic ice sheet on the whole. In order to consider further simulation of the relation of‘‘depth-age-accumulation’’at Dome A region, we simplify the GLIMMER model into a 2-dimensional ice flow model with coupled temperature field and test it under some brief assumptions. The change of elevation,temperature field and velocity field of ice flow profile in evolution steady state of ice sheet are obtained quantitatively.The results are similar to the calculation results of GLIMMER model. |
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