Study on the Instability of Two Large Glaciers in Northeast Greenland in Recent 60 Years

The Nioghalvfjerdsfjorden glacier (NG) and Zachariae Isstrøm (ZI) are major contributors to the mass balance of northeast Greenland, which drain 12% of the Greenland Ice Sheet. Accurate measurements of these two glaciers are crucial to the estimation of the mass balance in northeast Greenland. They also serve as an important parameter for reflecting climate change and predicting future sea level rise. In the past, early ice velocity data were scarce, primarily due to challenges in difficulties in image orthorectification caused by large distortions and low quality in historical remote sensing imagery. We proposed a systematic process for orthorectification of CORONA KH-4A imagery, which has proven to be both efficient and accurate in velocity mapping at a precision of 25m. By employing a hierarchical network densification approach based on ARGON KH-5 and CORONA KH-4A imagery, we have successfully reconstructed the ice flow velocity fields for NG and ZI from 1963 to 1967. Combining with other ice velocity products, we have obtained the ice velocity of NG and ZI spanning a period nearly 60 years. The results indicate that the average ice flow velocity near the grounding line has increased by 12.4% for NG and a substantial 81.4% for ZI from 1963 to 2020. While ZI is experiencing accelerated mass loss, the NG is still in a relatively stable state under the similar climate condition. The slight fluctuations in ice velocity for NG may be due to the unique topography and the hindering effect of ice rises, suggesting the climate change may have a comparatively less impact on it.