Benjamin Joseph Davison

Although the Antarctic Peninsula has a similar climate to that of other regions hosting surge-type glaciers, only one glacier surge has been previously observed in this region. We examined ice surface velocity, elevation and terminus position changes of Antarctic Peninsula glaciers to identify glacier surges. This revealed only four surges from three glaciers, all on James Ross Island. Gourdon Glacier surged from 2005 to 2007 then again from 2013 to 2018, Kotick Glacier surged from 2013 to 2017 and Whisky Glacier surged from 2020 to 2024. All four surges were characterised by significant advances in glacier terminus position and, for the latter three surges where observations are more abundant, at least an order-of-magnitude speed-up accompanied by ice surface elevation gain in the terminal zone and drawdown of ice from above, as each surge progressed. The landform record and historical imagery suggest additional surges of Kotick Glacier and Gourdon Glacier may have occurred in the second half of the 20th century. Reanalyses, reconstructions and observations of air temperature suggest that atmospheric warming since 1940 has increasingly exposed these and neighbouring glaciers on the northern tip of the Antarctic Peninsula and its surrounding islands to conditions that are typical of surge-type glaciers globally. Climate projections indicate that future warming will expose more glaciers on the Peninsula to climatic conditions conducive to surging until the mid-20th century, after which the surge-conducive area remains steady under Shared Socioeconomic Pathway (SSP) 2-4.5 and declines under SSP5-8.5. This suggests that surges on the Antarctic Peninsula may become more common over the coming decades, motivating continued monitoring.

The seasonal evolution of subglacial hydrology exerts a primary control on ice sheet flow, yet the spatial structure and temporal evolution of subglacial drainage systems remains incompletely characterized. Here, we apply Sentinel-1 double-difference SAR interferometry across a land-terminating sector of the western Greenland Ice Sheet to resolve two distinct surface motion signals: (1) widespread late-summer flow deceleration followed by gradual recovery across an area extending ~110 km inland, and; (2) localized ice-surface subsidence, primarily aligned with bed troughs, persisting for several weeks after surface melt cessation. We interpret these signals as the dynamic response to coexisting subglacial drainage system components. The broad-scale flow speed recovery reflects progressive repressurization of the widespread weakly connected cavity system, driven by basal meltwater recharge. The trough-localized subsidence reflects a multi-week buffered release of stored water through well-connected corridors. Together, these signals provide a spatially-continuous view of the geometry and spatial extent of both the well- and weakly connected components of the late-season drainage system. Our findings highlight the disproportionate role of bed trough environments in late-season meltwater storage and drainage, demonstrate that the well-connected drainage system remains hydraulically active well beyond surface melt cessation, and emphasize the weakly connected system as the driver of large-scale seasonal ice flow changes.

Although the Antarctic Peninsula has a similar climate to that of other regions hosting surge-type glaciers, only one glacier surge has been previously observed in this region. We examined ice surface velocity, elevation and terminus position changes of Antarctic Peninsula glaciers to identify glacier surges. This revealed only four surges from three glaciers, all on James Ross Island. Gourdon Glacier surged from 2005 to 2007 then again from 2013 to 2018, Kotick Glacier surged during 2013 to 2017 and Whisky Glacier surged from 2020 to 2024. All four surges were characterised by significant advances in glacier terminus position and, for the latter three surges where observations are more abundant, at least an order-of-magnitude speed-up and mass transfer from upper to lower parts of each glacier. The landform record and historical imagery suggest additional surges of Kotick Glacier and Gourdon Glacier may have occurred in the second half of the 20^th century. Reanalyses, reconstructions and observations of air temperature suggest that atmospheric warming since 1940 has increasingly exposed these and neighbouring glaciers on the northern tip of the Antarctic Peninsula and its surrounding islands to conditions that are typical of surge-type glaciers globally. Climate projections indicate that future warming will expose more glaciers on the Peninsula to climatic conditions conducive to surging until the mid-20th century, after which the surge-conducive area remains steady under Shared Socioeconomic Pathway (SSP) 2-4.5 and declines under SSP5-8.5. This suggests that surges on the Antarctic Peninsula may become more common over the coming decades, motivating continued monitoring.

Although the Antarctic Peninsula has a similar climate to that of other regions hosting surge-type glaciers, only one glacier surge has been previously observed in this region. We examined ice surface velocity, elevation and terminus position changes of Antarctic Peninsula glaciers to identify glacier surges. This revealed only four surges from three glaciers, all on James Ross Island. Gourdon Glacier surged from 2005 to 2007 then again from 2013 to 2018, Kotick Glacier surged during 2013 to 2017 and Whisky Glacier surged from 2020 to 2024. All four surges were characterised by significant advances in glacier terminus position and, for the latter three surges where observations are more abundant, at least an order-of-magnitude speed-up and mass transfer from upper to lower parts of each glacier. The landform record and historical imagery suggest additional surges of Kotick Glacier and Gourdon Glacier may have occurred in the second half of the 20^th century. Reanalyses, reconstructions and observations of air temperature suggest that atmospheric warming since 1940 has increasingly exposed these and neighbouring glaciers on the northern tip of the Antarctic Peninsula and its surrounding islands to conditions that are typical of surge-type glaciers globally. Climate projections indicate that future warming will expose more glaciers on the Peninsula to climatic conditions conducive to surging until the mid-20th century, after which the surge-conducive area remains steady under Shared Socioeconomic Pathway (SSP) 2-4.5 and declines under SSP5-8.5. This suggests that surges on the Antarctic Peninsula may become more common over the coming decades, motivating continued monitoring.

Although the Antarctic Peninsula has a similar climate to that of other regions hosting surge-type glaciers, only one glacier surge has been previously observed in this region. We examined ice surface velocity, elevation and terminus position changes of Antarctic Peninsula glaciers to identify glacier surges. This revealed only four surges from three glaciers, all on James Ross Island. Gourdon Glacier surged from 2005 to 2007 then again from 2013 to 2018, Kotick Glacier surged during 2013 to 2017 and Whisky Glacier surged from 2020 to 2024. All four surges were characterised by significant advances in glacier terminus position and, for the latter three surges where observations are more abundant, at least an order-of-magnitude speed-up and mass transfer from upper to lower parts of each glacier. The landform record and historical imagery suggest additional surges of Kotick Glacier and Gourdon Glacier may have occurred in the second half of the 20^th century. Reanalyses, reconstructions and observations of air temperature suggest that atmospheric warming since 1940 has increasingly exposed these and neighbouring glaciers on the northern tip of the Antarctic Peninsula and its surrounding islands to conditions that are typical of surge-type glaciers globally. Climate projections indicate that future warming will expose more glaciers on the Peninsula to climatic conditions conducive to surging until the mid-20th century, after which the surge-conducive area remains steady under Shared Socioeconomic Pathway (SSP) 2-4.5 and declines under SSP5-8.5. This suggests that surges on the Antarctic Peninsula may become more common over the coming decades, motivating continued monitoring.

The subglacial drainage system of the Greenland Ice Sheet plays a central role in modulating basal sliding and ice flow dynamics. While the seasonal evolution of this system has been widely studied during the melt season onset, its late and post-melt season behavior remains poorly constrained due to limited spatial and temporal observational coverage. Here, we use Sentinel-1 double-difference interferometric SAR data to document spatially continuous patterns of vertical and horizontal ice sheet motion across the late melt season in a predominantly land-terminating region of western Greenland. Our observations reveal recurrent, localized vertical subsidence features, generally coinciding with subglacial troughs, that persist several weeks into the post-melt season (late August to October) after surface melt inputs have largely ceased. The localized subsidence signals are accompanied by ice flow deceleration at a regional scale, extending more than 100 km inland, to ice thicknesses above 1300 m. We interpret this pattern as a dynamic response to the gradual drainage of water stored in weakly-connected cavities or, alternatively, englacial or sedimentary components, which drives a large-scale water pressure decrease and hence widespread flow deceleration. Although prior studies have suggested that weakly-connected cavities are drained following de-pressurization of efficient channels, the multi-week time scale and far-inland extent of the observed dynamic response suggest that channels may not be the sole driving mechanism. The magnitude of both subsidence and slow-down scales with melt season intensity, suggesting a mechanistic link between meltwater drainage efficiency and late-season ice dynamics, in line with previous observations of ice flow self-regulation. Our findings offer new insights into the seasonal evolution of Greenland's basal hydrology with continuous spatial coverage, highlighting how localized corridors of meltwater evacuation affect ice motion over much larger scales.

Anomalous freshwater fluxes from the Greenland and Antarctic ice sheets and ice shelves are impacting the surrounding oceans, and we need to be able to account for these effects in climate model simulations over the historical period and in future projections. In previous phases of the Coupled Model Intercomparison Project (CMIP), models mostly either assumed that the ice sheets were in mass balance, or that discharge from the ice sheets was constant, but in neither case was the observed increasing discharge over the historical period properly represented. In this paper, we present data products of absolute and anomalous freshwater mass fluxes from both major ice sheets, and recommendations for their use in historical simulations. These fluxes can be implemented in climate simulations as a forcing for models that do not (yet) include interactive ice sheets, or used to evaluate models that do. We also make recommendations for how climatological and anomalous fluxes can be implemented in climate models that may have different approaches to interactions with the ice sheets. These forcings are available for CMIP7 simulations and should lead to more robust and coherent simulation of sea surface temperature, sea ice and regional sea level trends in the recent historical period and, as these data are extended, improve the credibility of projections.