CPP-14. Expanding the temporal scale of Antarctic outlet glacier hypsometry using historical aerial photography

Abstract
Detailed hypsometric studies of Antarctic glaciers have been restricted to the 1990s and later due to altimetry data availability and spatial coverage. Prior to 1990, large expanses of the continent had only approximate elevation observations, forcing mass balance studies to rely on modeling to estimate ice sheet response to warming climate conditions. Without observations to corroborate modeling projections (or initial states), our knowledge of outlet glacier behavior is left with gaps. To better understand how Antarctic outlet glaciers reacted to the early stages of a transforming climate prior to 1990, we use trimetrogon aerial photography collected over Antarctica during the 1960s. These images were collected at all latitudes and at high enough spatial resolution to provide a reliable estimate for the amount of elevation change these glaciers have been undergoing in Antarctica for the past 55—60 years. In this study, we specifically look at glaciers along the eastern edge of the Ross Ice Shelf and those located on the Walgreen Coast (aka Amundsen Sea Embayment). We generate surface elevations for these regions using structure-from-motion photogrammetry in conjunction with manually extracted ground control from high resolution present-day digital elevation models. We find for the Transantarctic Ross Ice Shelf glaciers (e.g. Nimrod and Scott Glaciers) elevation changes ranging ± ~6 m whereas the average change for the Walgreen Coast is significantly larger and spans a range of -60 to +10 m. Both sets of glaciers terminate at ice shelves, so we explore the difference in circumstances driving these changes (e.g. dynamics v. basal melt). In doing so, we gain an improved insight into the feedback of Antarctic outlet glaciers to changing external forces over a far longer timespan, and into what to expect in the future should the current climate trend continues.