Study On The Ice Sheet Charactristics Of Transect And The Spatio-temporal Variability Of Past Accumulation Rates At Dome A,East Antarctica

The study of ice sheet structures and dynamics is an important content of future sea level forecasting.Increasingly,however,research is showing that East Antarctica is also going through rapid changes the same as West Antarctica.Recognizing the characteristics and evolution history of ice sheet will provides the precondition and base for the study of ice sheet dynamics,therefore,understanding the mechanism of mass balance and the history characteristics of East Antarctic ice sheet is essential for the study of Antarctic ice sheet dynamic.Many characteristics and structures of the ice sheet,such as surface topography,surface mass balance(SMB),ice velocity,ice thickness and bedrock topography,have been observed along the transect from Zhonshan station to Dome A,East Antarctica.By contrast,the internal structures of the transect from Zhongshan station to Dome A remain largely unkown.Radio-echo sounding(RES)surveys over Antarctic ice sheet revealed internal layers visible between the surface and bed radar echoes.These layers are isochrones and their stratigraphy results from such comprehensive factors as basal topography,strain rate variations,changes to the surface accumulation rate,ice sheet convergence or divergence,basal sliding and basal melting.How these processes distort the internal layers within ice sheet,which requires improved understanding and representation in next generation ice sheet models as they aim toward better forecasts of ice sheet response to climatic forcing such as global warming.In this study,We present the 29th and 32nd Chinese National Antarctic Research Expedition(CHIN ARE 29,2012/13;CHIN ARE 32,2015/16)ground-based and airborne RES data along a transect from Zhongshan station to Dome A,East Antarctica,which indicate the internal structure of isochrones.Four sectors of radargram were imaged after being processed by the Sobel filter:Slope area,Plateau area,Lambert ice upstream area and Dome area,to provide information on spatial variability in isochronic architectures.We investigated the patterns of internal reflection layers and related surface and sub-glacial characteristics from Zhongshan station to Dome A.The result shows that the pattern of near surface isochronic layers,in general,is controlled by accumulation,which appears to be controlled mainly by surface topography and local climate.A series of reflection anomaly,however,can be seen in Dome area.These unconformities are result from persistent wind scour on surface and located over steep bedrock topography(associated with the Gamburtsev mountains).The length(a distant of about 160 km)and depth(less than 1000 m)of infill feature indicates that wind scour process has persisted for many years and there is a periodic nature to the infill phases.At depth,isochronic layers showing significant relationships to the basal topography.They are typically track or drape the long topographic wavelength(more than the ice thickness).However,discontinuous and even absent internal layering lies above a wide depression that located in the onset region of Lambert ice stream.Isochronic layers override the long topographic wavelength in radar lines is likely determined by the presence of short-wavelength topography orthogonal to the section.In general,basal topography with mountains will disturb internal layers around them,but these layers are still traceable.While mountains that located at a special area,such as the area of the ice stream margins with complex ice-flow and strain,will cause isochronic layers untraceable.In addition,Dome A is the highest plateau of the Antarctic ice sheet,and it has been identified as an important location to drill a deep ice core.There are several publications about recent accumulation rates at Dome A,but studies of palaeo-accumulation rates are entirely absent.Sun et al.modeled the age of the ice beneath Dome A,and we use these age-depth scales as part of the basis for the dating here of six layers(spanning 30-161 ka BP)that are linked to the Vostok ice core along the continuous RES profile between Dome A and Vostok.Then,spatio-temporal variations in ice accumulation rates for the past?161 ka are calculated from isochronous internal layering and traced from RES data collected by the Polar Research Institute of China(PRIC)during the 21st CHINARE.The layers are dated by linking them to the site of Vostok ice core along an RES profile,which was flown by the Alfred-Wegener-Institut(AWI)in the Dome Connection East Antarctica(DoCo)project.The Dansgaard-Johnsen model,using the depth-age measurements as input,is used to determine the spatial and temporal pattern of ice accumualtion in Dome A region.The results show that there is a slight increasing pattern of ice accumulation from south to north along the 216 km radar profile at Dome A.The relatively consistent spatial patterns at Dome A suggest that the geometry of the ice-sheet surface has not changed in gross form over the last?161 ka.The lowest ice accumulaiton rates were calculated around the Dome A zone(smoothed over 40 km),which are 2.09,2.30,2.41,1.79,2.21 and 1.88 cm/a for TP1(0-34.3± 1.3 ka),TP2(0-39.6±0.1 ka),TP3(0-47.5± 1.7 ka),TP4(0-93.3±0.4 ka),TP5(0-123.5?1.5 ka)and TP6(0-161.4± 1.0 ka),respectively.In the past-90 ka,there were relatively high accumulation rates during the time period 34-47 ka(Marine Isotope Stage 3,29-59 ka ago)at Dome A.While temperature might play a role in accumulation rates,it might not be the only story since the most recent warm interval does not appear to have high accumulation rates.