The major outlet glaciers that drain the eastern sector of the Amundsen Sea Embayment (Smith, Haynes, Thwaites and Pine Island) are among the largest, fastest-flowing and fastest-thinning glaciers in West Antarctica. Their recent ice-flow acceleration is linked to ocean-induced ice-shelf thinning, but may also arise from additional losses of ice-shelf buttressing that are not well understood. Here we present a comprehensive history of coastal change in the eastern Amundsen Sea Embayment between 1972 and 2011 derived mostly from Landsat imagery. The termini of all four major outlet glaciers have retreated, but retreat is most rapid along the ice-shelf margins, where progressive rifting has occurred. This pattern of retreat coincides with the recent acceleration of grounded ice and contributed to loss of ice-shelf buttressing. The observed pattern of margin-led gradual ice-shelf disintegration appears to be common in accelerating ocean-terminating outlet glaciers. We hypothesize that this pattern is part of a positive feedback between glacier acceleration and rift growth that could drive further buttressing loss in the eastern Amundsen Sea Embayment.

Hyporheic mixing and surface water-groundwater interactions are critical processes in aquatic environments. Yet, there is a lack of methods for assessing the spatial extent and distribution of these mixing zones. This study applied time-lapse electrical resistivity (ER) imaging in a 60-m wide and 0.7-m deep alluvial river whose stage periodically varied by 0.7 m due to dam operations to assess dynamic hyporheic mixing and surface water-groundwater interactions. Sixteen channel-spanning repeat ER tomograms (2D sections) over one flood cycle captured the dynamic ER distribution. We mapped a laterally discontinuous hyporheic zone, which had mainly river water circulating through it, several meters into the bed. Underneath the hyporheic zone was a transitional mixing zone intermittently flushed by mixing river water and deep groundwater. Minimally mixed groundwater dominated the deepest areas. ER imaging allows for unraveling hyporheic and deep mixing zone dynamics in large regulated rivers.