| Summary: | The Siple Coast ice streams draining the West Antarctica Ice Sheet (WAIS) into the Ross Ice Shelf exhibit significant decadal to millennium-scale variability, including the complete shutdown of the Kamb Ice Stream, suggesting a complex response to a warming climate. Here we present a new elevation change record derived from laser altimetry observations using the Surface Elevation Reconstruction And Change detection (SERAC) method. The high temporal resolution ICESat (2003-2009) and ICESat-2 (2018-present) records were augmented with airborne laser altimetry observations and partitioned into changes due to surface processes - estimated by the GSFC and GEMB FDMs - and ice dynamics. Based on the dynamic thickness change time series, we distinguish local, rapid changes due to active hydrological systems, such as filling and draining subglacial lakes, and regional dynamic thickness changes associated with ice stream slow-down and speed up, which could signal impending stagnation or reactivation. The newly detected rapid local thickness changes indicate that the active subglacial hydrological network extends farther inland to the interior of WAIS than previously thought. Moreover, subglacial lake activity is detected along the Mercer Ice Stream across the Transantarctic Mountains, a pathway connecting the WAIS and EIAS. We further investigate dynamic thickness change patterns by examining ice velocity changes and inferring changes in basal conditions by reconstructing subglacial water routing from REMA DEMs fused with altimetry. Our results provide crucial insight into the processes controlling the Siple Coast ice streams, a vulnerable region with a considerable potential for future sea level rise.
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