11:30 〜 11:45
[MIS15-10] Directly observed basal sliding of Langhovde Glacier in East Antarctica during speed-up events caused by surface runoff
キーワード：氷河、氷床、南極、氷河流動
The Antarctic ice sheet is losing mass due to increased ice discharge through fast-flowing outlet glaciers. Since the fast glacier flow is caused by basal motion, understanding its mechanisms is critical for predicting the future evolution of the ice sheet (e.g. Ritz et al., 2015). However, the processes controlling basal motion are poorly understood because subglacial observations are difficult. Here, we present data obtained by direct observations of glacier basal sliding using a device called “ploughmeter”, equipped with an accelerometer and a water-pressure sensor (Kondo et al., 2024). The accelerometer measures three-axis acceleration with a sampling rate of 100 Hz; this allows us to observe signals associated with basal motion simultaneously with subglacial water-pressure variations. We installed the device at the base of Langhovde Glacier, East Antarctica, using a 550-m long borehole drilled approximately 1 km upstream of the grounding line during a hot-water drilling campaign in the austral summer 2021/22. On the glacier surface, GNSS receivers and an automatic weather station were operated to measure glacier flow speed and weather conditions.
As a result of the observations, flow acceleration of up to 20% was measured when the subglacial water pressure rapidly increased by 215 kPa. During the same period, impulsive and strong horizontal vibration events were observed by the subglacial accelerometer. The occurrence of the events was twice greater than the background rate, suggesting active basal sliding during the speedup. Horizontal displacement rate of the ploughmeter calculated by the device posture suggested two fold increase in the basal sliding rate during the acceleration period. The increase in the subglacial water pressure occurred a day after the rainfall of 30 mm d−1 over the glacier. The correspondence of the speed up with rain strongly suggests the drainage of surface water into the glacier bed and enhanced basal sliding. Our study results provide the first evidence of glacier acceleration induced by surface water in East Antarctica. These findings suggest that the glacier dynamics are more sensitive to climate than previously assumed in the region.
References
Kondo K., S. Sugiyama, M. Minowa and E. A. Podolskiy (2024): Ploughmeter for subglacial observations with an accelerometer and a water pressure sensor. Bulletin of Glaciological Research, 42, 113–121.
Ritz C., T. L. Edwards, G. Durand, A. J. Payne, V. Peyaud and R. C. A. Hindmarsh (2015): Potential sea-level rise from Antarctic ice-sheet instability constrained by observations. Nature, 528, 115–118.
As a result of the observations, flow acceleration of up to 20% was measured when the subglacial water pressure rapidly increased by 215 kPa. During the same period, impulsive and strong horizontal vibration events were observed by the subglacial accelerometer. The occurrence of the events was twice greater than the background rate, suggesting active basal sliding during the speedup. Horizontal displacement rate of the ploughmeter calculated by the device posture suggested two fold increase in the basal sliding rate during the acceleration period. The increase in the subglacial water pressure occurred a day after the rainfall of 30 mm d−1 over the glacier. The correspondence of the speed up with rain strongly suggests the drainage of surface water into the glacier bed and enhanced basal sliding. Our study results provide the first evidence of glacier acceleration induced by surface water in East Antarctica. These findings suggest that the glacier dynamics are more sensitive to climate than previously assumed in the region.
References
Kondo K., S. Sugiyama, M. Minowa and E. A. Podolskiy (2024): Ploughmeter for subglacial observations with an accelerometer and a water pressure sensor. Bulletin of Glaciological Research, 42, 113–121.
Ritz C., T. L. Edwards, G. Durand, A. J. Payne, V. Peyaud and R. C. A. Hindmarsh (2015): Potential sea-level rise from Antarctic ice-sheet instability constrained by observations. Nature, 528, 115–118.