| Global climate and environmental changes are one of the important factors affecting the Antarctic ice sheet changes.The current global warming continues to intensify,which poses a serious threat to the stability of the Antarctic ice sheet.It also affects the future survival and development of human-being.Therefore,research on the quantitative changes of the Antarctic ice sheet is of great practical significance,which can deepen global climate change understanding and predict future global sea level changes.This paper summarizes and analyzes the previous researches,and proposes an NPF(Novel plain Fitting)solution model which can deal with the problems and deficiencies in satellite altimetry missions deviations and ascending-descending orbit deviations.And this study combined with Envisat and Cryo Sat-2 data to investigate the Antarctic ice sheet elevation changes in the past 20 years based on the NPF model.We also utilized the GRACE gravity satellite data to analyze the Antarctic ice sheet mass changes over the same period.Finally,ICA(Independent component analysis)was carried out to obtain the components of each independent climate factor(ENSO,IPO,IOD,SAM).The separation of the influence of climate factor and the direct impact of human activities was achieved for the first time.And mass change of Antarctic ice sheet caused by human direct or indirect activities was estimated.The main research results and contents of this paper are as follows:(1)To deal with the problems and deficiencies in satellite altimetry missions deviations and ascending-descending orbit deviations,this paper proposes a Novel model(NPF model)based on the traditional plane fitting method when studying the elevation change of the Antarctic ice sheet.This model effectively eliminates the effects of the two deviations on the elevation change results by introducing the inter-mission deviation and ascending-descending orbit deviations.The model has the simultaneous solution ability under a unified mathematical model,which can obtain a high-precision,continuous and consistent time series of the Antarctic ice sheet elevation change,and the spatial distribution of satellite altimetry missions deviations and ascending-descending orbit deviations.(2)Based on the NPF model proposed in this paper,we combined with the Envisat and Cryo Sat-2 data.And the monthly average ice sheet surface elevation grid time series of Antarctic with 5×5 km spatial resolution from 2002.05 to 2019.04was constructed.With ICEBridge elevation data from 2009 to 2017 and the ICESat elevation change rate from 2003 to 2009 were validated on the extracted elevation grid time series.The results show that the extracted time series of elevation based on the NPF model in this paper is reliable,and the results at the junction of the two satellite missions are more consistent.(3)Based on the grid time series of the elevation change extracted from the combined Envisat and Cryo Sat-2 data,the least-squares nonlinear fitting analysis was used to suggest that the volume of the Antarctic ice sheet was constantly melting during 2002.05-2019.04.The average change rate of volume is-80±8.6 km~3/yr.In addition,the volume of the east Antarctic ice sheet is in an increasing situation and its average volume change rate is 62.2±7.4 km~3/yr.At the Queen Maud Land and Enderby Land in the east Antarctic,the volume of ice sheet is also thickening with volume average change rates of 24.1±3.6 km~3/yr and 23.5±2.0 km~3/yr respectively.At the Toten Glacier Basin in the east Antarctic,its volume changes also show a trend of continuous melting,with an average change rate of 12.2±2.9 km~3/yr.The volume of the west Antarctic ice sheet melts fast,with change rate of-142±4.31 km~3/yr.Especially on the coast of the Amundsen Sea in the west Antarctica,the volume of the ice sheet melts extremely quickly,with the average change rate of-119±2.04 km~3/yr.The spatial and temporal analysis by EMD(Empirical Mode Decomposition)method suggest that the ice sheet elevation showed a downward trend on the whole Antarctic.Meanwhile,the west Antarctic ice sheet elevation showed an accelerated downward trend.The east Antarctic ice sheet elevation showed a slow upward trend.The volume change of ice sheet has the characteristics of annual cycle change.There are also interannual cycle changes longer than one year cycle.These interannual changes are likely related to the climate factors which is included in the volume change of ice sheet.(4)Based on the grid time series of the ice sheet surface elevation extracted by Envisat and Cryo Sat-2 data,and combined with the surface mass balance(SMB)from RACMO 2.3,the grain snow densification model(IMAU-FDM)and the ICE＿6G-C glacier equilibrium adjustment(GIA),the Antarctic ice sheet elevation change grid time series was converted into the Antarctic ice sheet mass change grid time series in this paper.In addition,the spatial and temporal analysis of the Antarctic ice sheet mass change is also carried out with EMD and least squares fitting.The results show that the mass of the Antarctic ice sheet is decreasing continuously,and the mass change rate during the period from May 2002 to December 2016 is-113.1±13.2Gt/yr.And the mass of the whole east Antarctic ice sheet increased slightly,with an average mass change rate of 34.9±11.1 Gt/yr.But the mass of the west Antarctic ice sheet is in accelerated melting situation,with an average mass change rate of-148±7.2 Gt/yr.And its acceleration of mass loss was also in a increasing situation.Antarctic ice sheet mass change time series has strong annual cycle variation characteristics,and there are also interannual changes longer than 1 year cycle.Similar to the time and space analysis of ice sheet elevation change time series,this interannual variability characteristics in the mass change may be related the influence of climate factors.(5)With the GRACE satellite gravity data and combined filtering method of P7M11 decorrelation filtering and 400km radius Fan filtering,the mass change of the Antarctic ice sheet from 2002.05-2016.12 was estimated,which is compared with the mass change estimated by the altimetry satellite.The results show that the mass change trends of GRACE and altimetry are more similar in spatial distribution.But in terms of the amount of mass change,there is a certain difference between the estimated results based on the GRACE and altimetry satellite data.There are two main reasons for the difference in the mass results estimated from two kind of data.For one thing,the GRACE quality change results will still have leakage errors that cannot be completely eliminated.For another thing,when the height change estimated by altimetry is converted into mass change,the current observation data used to determine FDM is still relatively scarce which reduced the accuracy of the FDM.These influence factors also limit the accuracy of ice sheet mass change estimated from altimetry satellite data.(6)In order to investigate the influence of human activities on the Antarctic ice sheet changes,this paper analyzes the correlation between the climate factors and the Antarctic ice sheet changes.And then with ICA method,we obtained independent climate factor components from climate factors.The the least squares multivariate linear fitting method was carried out to achieve separation between impact of the climate factors and the direct impact of human activities in the Antarctic ice sheet changes for the first time in this paper.It also found that the climate factors and the Antarctic ice sheet changes have strong correlation.By comparing the results of the ice sheet changes between result including the influence of climate factors and result without the influence of climate factors,it suggests that the climate factors(the impact of human indirect activities)is the main reason for the accelerated melting mass of the Antarctic ice sheet.And the direct impact of human activities contributes less to the acceleration of Antarctic ice sheet mass loss. |
