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B Replying to b Rott et al. I Nature Communications i 10.1038/s41467-020-16658-y (2020) In Tuckett et al.[1], we report short-term speed-up events of Antarctic Peninsula outlet glaciers. Here, we defend the meltwater hypothesis, present evidence against the sea-ice hypothesis, and examine potential bias in our glacier velocity measurements. Although sea-ice evacuation is coincident with the March 2018 speed-up event observed in Tuckett et al.[1], changes in sea-ice characteristics are not synchronous across all studied glaciers. Finally, the sea-ice hypothesis cannot explain how glaciers return to pre-event velocities[1], as the sea ice does not rapidly reform to its pre-breakup structure (Fig. [Extracted from the article]

Atmospheric warming is increasing surface melting across the Antarctic Peninsula, with unknown impacts upon glacier dynamics at the ice-bed interface. Using high-resolution satellite-derived ice velocity data, optical satellite imagery and regional climate modelling, we show that drainage of surface meltwater to the bed of outlet glaciers on the Antarctic Peninsula occurs and triggers rapid ice flow accelerations (up to 100% greater than the annual mean). This provides a mechanism for this sector of the Antarctic Ice Sheet to respond rapidly to atmospheric warming. We infer that delivery of water to the bed transiently increases basal water pressure, enhancing basal motion, but efficient evacuation subsequently reduces water pressure causing ice deceleration. Currently, melt events are sporadic, so efficient subglacial drainage cannot be maintained, resulting in multiple short-lived (<6 day) ice flow perturbations. Future increases in meltwater could induce a shift to a glacier dynamic regime characterised by seasonal-scale hydrologically-driven ice flow variations. Surface meltwater is known to influence the dynamics of some glaciers and the Greenland ice sheet. Here, the authors have identified the first examples of the drainage of surface meltwater to the bed of outlet glaciers on the Antarctic Peninsula that trigger large and rapid accelerations of ice flow. [ABSTRACT FROM AUTHOR]

Surface meltwater is widespread across the Antarctic Ice Sheet. While much recent research has focused on understanding the impact meltwater has on ice shelves, where its presence can act as a catalyst for rapid ice shelf break up, the effect of meltwater on grounded ice dynamics in Antarctica remains unknown. Using high-resolution ice velocity data derived from Sentinel 1 imagery we identify previously unobserved large (up to 100% greater than the annual mean), sudden, and synchronous accelerations in ice flow at 5 glaciers across the Antarctic Peninsula, which occur during modelled periods of surface melt. Coincident optical satellite imagery demonstrates that although much of the surface meltwater refreezes, some water appears to access the bed through crevasses and surface lake drainage. Several characteristics of the ice accelerations are consistent with the enhancement of basal motion by surface-derived meltwater reaching the ice bed. Firstly, speed-up events are often followed by short-lived reductions in ice velocity to pre-event values, and secondly, their relative magnitude is greater in regions of observed surface melt, immediately downstream of surface lake drainage events and after prolonged periods of no-or-little melt. Our data suggest that following arrival at the ice bed, meltwater is efficiently evacuated, limiting the duration of speed-up events to less than 6 days (the temporal resolution of our data). Although Antarctic Peninsula speed-up events are currently short-lived, we anticipate that predicted longer and more intense melt-seasons may lead to a shift in ice-dynamics in the region. [ABSTRACT FROM AUTHOR]