The Instability Of Polar Ice Shelf Based On Remote Sensing-Observation And ISSM Numerical Modeling

The global climate warming intensified glacier melting,accelerated glacier velocity and rift propagation,which seriously affects the stability of the polar ice shelf.The ice shelf instability leads to frequent calving events,which increased the discharge from the ice-sheet interior into the ocean and accelerated the mass loss of ice sheet.Therefore,investigations on ice shelf instability have important scientific significance and application value for health assessment of the ice shelf,monitoring and prediction of terminal collapse,and prediction of future sea level change.Remote sensing has become macroscopic,rapid,dynamic and economical technology to study polar research.However,in the past it lacked dense observation limited by the low temporal and spatial resolution of satellite remote sensing.Therefore,it was difficult to record the detailed information of the ice shelf instability process.In addition,the decoupling of models affected the understanding of the ice shelf key process.In particular,the hydrological and ocean models need to be applied into glacier dynamics process to study of the key processes of the ice shelf.This paper takes advantage with the latest high-temporal resolution remote sensing observations and advanced ice flow models to study instability of the ice shelf.We selected the Petermann Glacier in the northwest of Greenland,the 79N Glacier in the northeast and the Brunt Ice Shelf in Antarctica as typical research areas to carry out research.The main research content and conclusions of the thesis are summarized as follows:(1)Based on high spatial-temporal resolution remote sensing observations,ice flow models and ocean models,this section acquired the hydrological and dynamic precursor of the Petermann Glacier before its collapse in 2017 and assessed the instability of the ice shelf.We derived ice velocity,melting pond,ice rifts,ice front and sea ice backscattering coefficients from the Sentinel series satellite data,in order to acquire the key parameters affecting ice shelf instability.The rigidity and sliding coefficient of the ice shelf was inverted using the coupled ice flow model to assimilate the ice velocity.And we forwarded calculated the spatial and temporal stress distribution and damage coefficient changes to quantify the ice shelf instability.The basal melt rate of the ice shelf was estimated based on the temperature and salt data coupled with the ocean model.The observation and modeling results of before calving event showed that the velocity of glacier terminal area increased sharply from 3 m/d to 30 m/d,the stress and the damage distribution is abnormal.And the basal melt rate increased and the landfast sea ice breakup in the fjord as the seawater temperature increased by 0.1℃.The area of melt ponds on the floating ice tongue began to increase in mid-May,quickly reached a peak at the end of June and lasted for nearly one month until the calving occurred.It is inferred that this calving event may relate to a weakening of the sea ice,shearing of the tributary glacier,and meltwater infiltrating crevasses according to the key parameters of Petermann instability.(2)The crack propagation and damage analysis of Brunt ice shelf in Antarctica.This paper analyzed the temporal and spatial characteristics of Brunt ice shelf flow velocity,ice temperature and crack propagation based remote sensing observations.And the forward calculation of the effective stress and damage was analyzed the evolution of the ice shelf instability using the ice shelf damage model.The results showed that the surface velocity increased during the period 2013-2018 and the crack propagation begin to increase rapidly from 2017.The annual and minimum temperature of the ice shelf gradually increased.At the same time,there were obvious stress distribution and increased damage in the ice shelf crack area and the shear area,which weakened the integrity of the ice shelf structure.We quantified the Brunt ice shelf instability and diagnosed and assessed the potential risk of Brunt ice shelf disintegration in the future to reveal the response relationship with crack growth and ice shelf instability.(3)The impact on surface melt and glacier velocity in Greenland 79N glacier.Based on the Google Earth Engine platform,this paper extracts the daily melt water extent(including surface melting ponds,glacial lakes and glacial rivers)of the ice shelf during the melt season of 2016-2020.The results showed that the obvious seasonal changes of melting water extent.The coverage of meltwater in 2019 and 2020 is significantly higher than other time periods.Combining with the climate model data ERA5,it is shown that the 79N ice shelf meltwater responds almost synchronously to the periodic changes of air temperature and the 79N glacial lake of grounded ice is highly correlated with the flow velocity in the grounding line area.Then we modeled the response process of meltwater production,glacial lake drainage,effective water pressure and flow velocity based on ice flow and hydrological model.The modeled results showed that the increased glacial lake drainage decreased the effective water pressure and increased glacier velocity.The surface melting intensified the ice shelf instability.