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Surface meltwater is widespread around the Antarctic Ice Sheet margin and has the potential to influence ice shelf stability, ice flow and ice–albedo feedbacks. Our understanding of the seasonal and multi-year evolution of Antarctic surface meltwater is limited. Attempts to generate robust meltwater cover time series have largely been constrained by computational expense or limited ice surface visibility associated with mapping from optical satellite imagery. Here, we add a novel method for calculating visibility metrics to an existing meltwater detection method within Google Earth Engine. This enables us to quantify uncertainty induced by cloud cover and variable image data coverage, allowing time series of surface meltwater area to be automatically generated over large spatial and temporal scales. We demonstrate our method on the Amery Ice Shelf region of East Antarctica, analysing 4164 Landsat 7 and 8 optical images between 2005 and 2020. Results show high interannual variability in surface meltwater cover, with mapped cumulative lake area totals ranging from 384 to 3898 km 2 per melt season. By incorporating image visibility assessments, however, we estimate that cumulative total lake areas are on average 42 % higher than minimum mapped values. We show that modelled melt predictions from a regional climate model provide a good indication of lake cover in the Amery region and that annual lake coverage is typically highest in years with a negative austral summer SAM index. Our results demonstrate that our method could be scaled up to generate a multi-year time series record of surface water extent from optical imagery at a continent-wide scale. [ABSTRACT FROM AUTHOR]

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]