Study On Characteristics And Significance Of The Internal Layering And Subglacial Topography Of The Ice Sheet In Princess Elizabeth Land,east Antarctica Based On Ice-Penetrating Radar Data

The Antarctic ice sheet(AIS)is an important component of the global climate system,which not only controls the earth’s energy balance and regulates the hydrological cycle,but also influences the atmospheric and oceanic circulations in the Southern Hemisphere.However,the greatest challenge is the very limited knowledge of the change mechanisms of the AIS,which creates great uncertainty for predicting future climate change.Aerogeophysical survey technology can overcome the limitations of the harsh environmental conditions in Antarctica and efficiently acquire large-scale aerogeophysical data.This technology provides scientists with datasets such as gravity,magnetic and ice radar and provides important data support for studying the past,present and future evolution of the AIS.In recent years,Chinese National Antarctic Research Expedition(CHINARE)deployed the airborne geophysical survey from 2015 to 2020 of Princess Elizabeth Land(PEL)in the East Antarctic,where is one of the largest data gaps in the Antarctic.Now aerogeophysical surveys carried out by countries around the world have basically covered the entire AIS.The high-resolution ice-penetrating radar(IPR)technology can comprehensively and accurately portray ice thickness and basal topography revealing the geometric features of AIS,so as to achieve the research objectives of efficient and precise digital elevation model(DEM);can reveal the internal structure of the ice sheet to provide the internal layering information and provide a basis for the establishment of isochronous models of AIS;can help us to understand the relationship with ice dynamics and climate dynamics to assess the mass balance of the ice sheet and the mechanism of changes in ice sheet stability;can provide scientific basis for ice core drilling site selection,ice sheet formation and evolution.However,although the three-dimensional subglacial topography of PEL has been preliminarily characterized,the understanding of the characteristics of the subglacial topography and the internal structure of the ice sheet is still very limited.Therefore,this thesis studies the characteristics and significance of the internal structure of the ice sheet and the subglacial topography of the Princess Elizabeth land in East Antarctica based on the vehicle-based IPR surveys during the CHINARE 21(2004/2005)and CHINARE 29(2012/2013)and the airborne radar data from the 32 nd CHINARE(2015/2016)to 36 th CHINARE(2019/2020).This study will focus on the englacial layer structure and the subglacial topography of the ice sheet,develop and optimize the noise reduction and preprocessing technology of ice radar data,quantitatively calculate the continuity of the internal reflector and the basal roughness of the subglacial topography,analyze and explain the key physical process and the temporal and spatial variation of the ice layer geometry of the East Antarctic ice sheet and its ice flow effect,and combine with the ancient wind erosion layering structure and ice flow model to infer the age of paleoclimate wind erosion activity.Firstly,in this thesis,conventional ground-penetrating radar(GPR)methods are applied to IPR data,and three different ice radar system datasets are processed separately in a targeted manner.It is found that the prediction deconvolution and instantaneous amplitude methods are effective for improving the data signal-to-noise ratio of the vehicle-mounted dual-frequency radar system of CHINARE 21.F-K filtering can effectively remove the oblique stripe diffraction interference noise in the airborne ice radar data.F-K migration can focus the bedrock diffraction wave to a certain extent and improve the interface resolution.The non-consecutive data obtained by the vehicle high-resolution ice radar system during CHINARE 29 have the highest resolution,and are suitable to research structural characteristics and applications of deep ice layers below 500 m.Combined with the manual interactive semi-automatic interface extraction method,the ice surface,the ice-rock interface and the internal layer are picked up,and the reliability and uncertainty of the manual picking results are analyzed.Secondly,this thesis analyzes the results of aircraft flight elevation,ice surface elevation,ice thickness and bed elevation over PEL.The basal roughness is calculated using the two-parameter roughness method.Combining ice velocity data reveals spatial variability of the roughness parameters.The relationship between four different types of basal roughness feature combinations and ice flow,basal temperature,and subglacial hydrology is analyzed and discussed,and their representative basal environmental processes are deduced.Then,The ILCI results for the internal layers of ice sheet obtained for the middle 3/5 ice column of PEL and different ILCI change with depth of different depth ranges are calculated.Factors affecting the results of ILCI are discussed.In the case of excluding the obvious influence of environmental conditions,the relationship between four types of the depth-dependent ILCI and ice flow and subglacial topography is analyzed.Finally,the paleoclimate environment on the Dome A to the southern of Lambert glaciers is analyzed.The geometric characterization of englacial structures,such as unconformity and dune structure formed by the persistent katabatic winds,is observed and analyzed.Combined with the age-depth information of continuously trace six age-restricted isochronous IRHs between 35.6 ka and 169.4ka,wind-scoured activities are discussed.The temporal and spatial variability of the ancient wind erosion layering and the paleoclimate abrupt event revealed at the tenthousand-year scale are analyzed.A one-dimensional ice flow model is used to estimate the earliest unconformity structure formed by the paleoclimate wind erosion activity as early as ～105.6 ka B.P.The paleoclimate changes that may have occurred during the last interglacial-glacial period in the southern hemisphere are revealed.Based on the ice radar survey data,this thesis uses interpretation tools to reveal the complex characteristics of basal roughness,internal continuity and buried aeolian terranes in PEL,East Antarctica.They reveal the little-known regional subglacial environment and englacial processes,provide constraints for more direct geophysical exploration in the future,and provide important support for practically promoting scientific research of CHINARE.The data processing flow and processed ice radar data products designed in this study also directly lay a foundation for subsequent application research.