ALBERT

Description: We discuss two types of ice shelf firn aquifers present in coastal Antarctica: melt-derived and brine-infiltration. Mapping of melt-derived firn aquifers and regions of melt-saturated firn using both passive and active L-band microwave data has identified perennial melt-derived aquifers in the southwestern Antarctic Peninsula, and several seasonal melt-saturation regions there and in widely separated sites around the ice sheet fringe. Extensive melt aquifers are identified on the Wilkins Ice Shelf, the northern George VI Ice Shelf, and the Müller Ice shelf, and are suspected on the former Jones and Wordie ice shelves. Field work has confirmed the aquifer presence in at least two sites on both the Wilkins and Müller shelves. We also present an improved assessment of the extent of brine aquifers based on their characteristics in modern airborne ice-penetrating radar profiles. Brine aquifers are relatively widespread and are found in shelf areas with porous firn at the waterline, as was previously recognized by Cook et al.(2018). Our study also assesses the relative risk of hydrofracture for ice shelves bearing melt and brine aquifers under various scenarios of firn density, aquifer depth, and brine density. We find that ponded surface melt poses the greatest threat, but that the increased density of brine may also be an issue if the brine layer is relatively shallow in the shelf. We also discuss the likely future expansion of melt aquifers on ice shelves under warming conditions, and consider the process of transitioning from a brine aquifer to a melt aquifer.

Description: The Automated Meteorology - Ice - Geophysics - Ocean observing Systems are a series of multi-sensor stations that have been employed for in situ data gathering in support of polar research since 2009, with multiple installations on the Antarctic Peninsula, the Nansen Ice Shelf, and on Thwaites Glacier's eastern ice shelf. The station series have been optimized for weather data collection and near-surface glaciology (AMIGOS-I) and later augmented with sensors for measurements related to ice-ocean interaction and internal ice sheet temperature profiling (AMIGOS-II and -III). The stations are powered by a solar + battery system, and provide real-time data through an Iridium uplink. The stations include cameras, weather instruments, thermistors, and GPS sensors, with later versions including ocean instruments (CTDs and doppler current meters) and a Distributed Temperature Sensing (DTS) fiber optic system. We present an overview of the instrument, past data from earlier installations, and a summary of the data sets and results from the two AMIGOS-III units installed on the Thwaites Glacier ice shelf.

Description: When an ice shelf collapses, the removal of its backstress acting on the tributary glaciers results in increased flow speed, decreased surface elevation and decreasing ice thickness. Rises in surface slope gradients further drive an increase in flow speeds. Over February to March of 2002, the Larsen B Ice Shelf, in the northwestern Antarctic Peninsula, disintegrated, leading to its largest contributing glacier, Crane Glacier, to double in ice discharge and decrease in elevation by over 100 m from ~2003-2009. One parameter of Crane Glacier, its grounding line position, has never been documented and the effects of the external forces acting on grounding line dynamics have never been quantified. The exact position of the grounding line in 2002 is not well known, but by using multi-temporal geophysical datasets (e.g., digital elevation models, airborne radar; 1968-2022) the down-flow margin of the grounding zone—hydrostatic equilibrium boundary—can be estimated. The historical hydrostatic equilibrium boundaries are calculated using trimetrogon aerial imagery to produce orthometric elevations from 55 years ago using structure-from-motion photogrammetry. We assume that fluctuations in the location of the floatation limit directly reflects the migration of the grounding line. Analysis of Crane Glacier’s grounding line dynamics before and after the 2002 ice shelf break up offers a unique opportunity to better understand the stability of the Antarctic’s major ice-shelf-terminating outlet glaciers.