Comparing numerical ice-sheet model output with radio-echo sounding measurements in the Weddell Sea sector of West Antarctica

Numerical ice-sheet models are commonly matched to surface ice velocities from InSAR measurements by modifying basal drag, allowing the flow and form of the ice sheet to be simulated. Geophysical measurements of the bed are rarely used to examine if this modification is realistic, however. Here, we examine radio-echo sounding (RES) data from the Weddell Sea (WS) sector of West Antarctica to investigate how output from a well-established ice-sheet model compares with measurements of the basal environment. We know the WS sector contains the Institute, Möller and Foundation ice streams, each with distinct basal characteristics: Institute Ice Stream lies partly over wet unconsolidated sediments, where basal drag is very low; Möller Ice Stream lies on relatively rough bed, where basal drag is likely larger; and Foundation Ice Stream is controlled by a deep subglacial trough with flow-aligned bedrock landforms and smooth unconsolidated sediments. In general, the ice-sheet model represents each ice-stream system well. We also find that ice velocities do not match perfectly in some locations, and that adjustment of the boundaries of low basal drag, to reflect RES evidence, should improve model performance. Our work showcases the usefulness of RES in calibrating ice-sheet model results with observations of the bed

A new bed elevation model for the Weddell Sea sector of the West Antarctic Ice Sheet

We present a new bed elevation digital elevation model (DEM), with a 1 km spatial resolution, for the Weddell Sea sector of the West Antarctic Ice Sheet. The DEM has a total area of ~125,000 km2 covering the Institute, Möller and Foundation ice streams and the Bungenstock ice rise. In comparison with the Bedmap2 product, our DEM includes several new aerogeophysical datasets acquired by the Center for Remote Sensing of Ice Sheets (CReSIS) through the NASA Operation IceBridge (OIB) program in 2012, 2014 and 2016. We also update bed elevation information from the single largest existing dataset in the region, collected by the British Antarctic Survey (BAS) Polarimetric Airborne Survey Instrument (PASIN) in 2010-11, as BEDMAP2 included only relatively crude ice thickness measurements determined in the field for quality control purposes. This have resulted in the deep parts of the topography not being visible in the fieldwork non-SAR processed radargrams. While the gross form of the new DEM is similar to Bedmap2, there are some notable differences. For example, the position and size of a deep trough (~ 2 km below sea level) between the ice sheet interior and the grounding line of Foundation ice stream has been redefined. From the revised DEM, we are able to better derive the expected routing of basal water at the ice-bed interface, and by comparison with that calculated using Bedmap2 we are able to assess regions where hydraulic flow is sensitive to change. Given the sensitivity of this sector of the ice sheet to ocean-induced melting at the grounding line, especially in light of improved definition of the Foundation ice stream trough, our revised DEM will be of value to ice-sheet modelling in efforts to quantify future glaciological changes in the region, and therefore the potential impact on global sea level. The new 1 km bed elevation product of the Weddell Sea sector, West Antarctica can be found in the http://doi.org/10.5281/zenodo.1035488

Numerical modelling of coastal structure using SPH-based DualSPHysics model

Coastal structures are implemented along the coasts as measures to counter coastal erosion and the detrimental effects caused by sea waves. In order to maximize the efficiency of these structures, sea conditions during extreme events should be taken into consideration as to avoid the occurrence of wave overtopping, erosion and thus leading to structure failure. This study with the objective to identify the force exerted on several coastal structures and overtopping occurrence under a variety of wave conditions will be compared with the numerical results done by Dang et al., (2021). This study, however, focuses on three different structures; the vertical wall, the trapezoidal wall and the stepped wall, and is simulated using DesignSPHysics, a new addition to the open-source code named DualSPHysics. A simulation with no coastal structure is also presented in this study. The cases take damping systems into account, particularly active wave absorption system. Furthermore, overtopping simulations were conducted as to assess the various structures under the chosen wave conditions. Results signifies that, the stepped wall has the least overtopping occurrence in comparison to the other structures. The simulation presented in this study well replicates that of the study done by Dang et al., (2021)

A new bed elevation model for the Weddell Sea sector of the West Antarctic Ice Sheet

We present a new digital elevation model (DEM) of the bed, with a 1 km gridding, of the Weddell Sea (WS) sector of the West Antarctic Ice Sheet (WAIS). The DEM has a total area of ∼ 125 000 km2 covering the Institute, Möller and Foundation ice streams, as well as the Bungenstock ice rise. In comparison with the Bedmap2 product, our DEM includes new aerogeophysical datasets acquired by the Center for Remote Sensing of Ice Sheets (CReSIS) through the NASA Operation IceBridge (OIB) program in 2012, 2014 and 2016. We also improve bed elevation information from the single largest existing dataset in the region, collected by the British Antarctic Survey (BAS) Polarimetric radar Airborne Science Instrument (PASIN) in 2010–2011, from the relatively crude measurements determined in the field for quality control purposes used in Bedmap2. While the gross form of the new DEM is similar to Bedmap2, there are some notable differences. For example, the position and size of a deep subglacial trough (∼ 2 km below sea level) between the ice-sheet interior and the grounding line of the Foundation Ice Stream have been redefined. From the revised DEM, we are able to better derive the expected routing of basal water and, by comparison with that calculated using Bedmap2, we are able to assess regions where hydraulic flow is sensitive to change. Given the potential vulnerability of this sector to ocean-induced melting at the grounding line, especially in light of the improved definition of the Foundation Ice Stream trough, our revised DEM will be of value to ice-sheet modelling in efforts to quantify future glaciological changes in the region and, from this, the potential impact on global sea level. The new 1 km bed elevation product of the WS sector can be found at https://doi.org/10.5281/zenodo.1035488.</p

Antarctic basal environment shaped by high-pressure flow through a subglacial river system

The stability of ice sheets and their contributions to sea level are modulated by high-pressure water that lubricates the base of the ice, facilitating rapid flow into the ocean. In Antarctica, subglacial processes are poorly characterized, limiting understanding of ice-sheet flow and its sensitivity to climate forcing. Here, using numerical modelling and geophysical data, we provide evidence of extensive, up to 460 km long, dendritically organized subglacial hydrological systems that stretch from the ice-sheet interior to the grounded margin. We show that these channels transport large fluxes (~24 m3 s−1) of freshwater at high pressure, potentially facilitating enhanced ice flow above. The water exits the ice sheet at specific locations, appearing to drive ice-shelf melting in these areas critical for ice-sheet stability. Changes in subglacial channel size can affect the water depth and pressure of the surrounding drainage system up to 100 km either side of the primary channel. Our results demonstrate the importance of incorporating catchment-scale basal hydrology in calculations of ice-sheet flow and in assessments of ice-shelf melt at grounding zones. Thus, understanding how marginal regions of Antarctica operate, and may change in the future, requires knowledge of processes acting within, and initiating from, the ice-sheet interior

ICECAP-2 consortium processed airborne ice thickness data from the Princess Elizabeth Land, East Antarctica

Airborne ice thickness data from the Princess Elizabeth Land (PEL), East Antarctica was collected in four separate seasons. During the first ICECAP2 season (2015/16), a survey acquiring exploratory ‘fan-shaped’ radial profiles to maximize range and data return on each flight was completed across the broadly unknown region of PEL. These flight lines extend from the coastal Progress Station to the interior ice-sheet divide at Ridge B. In the second and third seasons (2016/17 and 2017/18), a survey ‘grid’ was completed, targeting enhanced resolution over a proposed subglacial lake and a series of basal canyons (Jamieson et al., 2016). In the fourth season (2018/19), a few additional transects were completed to fill the largest data gaps within aircraft range. Field data acquisition was achieved using the “Snow Eagle 601” aero geophysical platform; a BT-67 airplane operated by the Polar Research Institute of China for the Chinese National Antarctic Research Expedition (CHINARE) program. The suite of instruments configured on the airplane include a phase-coherent radio-echo sounder system, operating at a central frequency of 60 MHz and a peak power of 8 kW, making it capable of penetrating deep (>3 km) ice in Antarctica. After applying coherent integration and pulse compression at a bandwidth of 15 MHz, which gave an along-track spatial sampling rate and a vertical resolution of ~10 m and ~5.6 m, respectively.Airborne ice thickness data from the Princess Elizabeth Land (PEL), East Antarctica was collected in four separate seasons. During the first ICECAP2 season (2015/16), a survey acquiring exploratory ‘fan-shaped’ radial profiles to maximize range and data return on each flight was completed across the broadly unknown region of PEL. These flight lines extend from the coastal Progress Station to the interior ice-sheet divide at Ridge B. In the second and third seasons (2016/17 and 2017/18), a survey ‘grid’ was completed, targeting enhanced resolution over a proposed subglacial lake and a series of basal canyons (Jamieson et al., 2016). In the fourth season (2018/19), a few additional transects were completed to fill the largest data gaps within aircraft range. Field data acquisition was achieved using the “Snow Eagle 601” aero geophysical platform; a BT-67 airplane operated by the Polar Research Institute of China for the Chinese National Antarctic Research Expedition (CHINARE) program. The suite of instruments configured on the airplane include a phase-coherent radio-echo sounder system, operating at a central frequency of 60 MHz and a peak power of 8 kW, making it capable of penetrating deep (>3 km) ice in Antarctica. After applying coherent integration and pulse compression at a bandwidth of 15 MHz, which gave an along-track spatial sampling rate and a vertical resolution of ~10 m and ~5.6 m, respectively.