Hard rock landforms generate 130 km ice shelf channels through water focusing in basal corrugations

This work is licensed under a Creative Commons Attribution 4.0 International License.Satellite imagery reveals flowstripes on Foundation Ice Stream parallel to ice flow, and meandering features on the ice-shelf that cross-cut ice flow and are thought to be formed by water exiting a well-organised subglacial system. Here, ice-penetrating radar data show flow-parallel hard-bed landforms beneath the grounded ice, and channels incised upwards into the ice shelf beneath meandering surface channels. As the ice transitions to flotation, the ice shelf incorporates a corrugation resulting from the landforms. Radar reveals the presence of subglacial water alongside the landforms, indicating a well-organised drainage system in which water exits the ice sheet as a point source, mixes with cavity water and incises upwards into a corrugation peak, accentuating the corrugation downstream. Hard-bedded landforms influence both subglacial hydrology and ice-shelf structure and, as they are known to be widespread on formerly glaciated terrain, their influence on the ice-sheet-shelf transition could be more widespread than thought previously.NASA grant # NNX10AT68GANT # NT-0424589University of KansasUK NERC AFI grant NE/G013071/

Facies analysis of the Late Eocene deep-marine middle- to outer-fan sequence of the Crocker Formation in Tenom District, Sabah, Malaysia

The Crocker Formation, Late Eocene to Middle Miocene in age, was deposited in a deep-marine environment by a turbidity current. Most of the facies identified in the field are related to the sedimentary bed-form structures belonging to Bouma sequences. These prominently include unit divisions such as Ta referring to grading sand, Tb for parallel laminae, Tc for cross laminae, Td for mud laminae, and Te referring to hemipelagic mud. Five facies have adequately been identified using Bouma sequence implications, namely Facies 1 (F1: Ta-Tb layers), Facies 2 (F2: Ta-Te layers), Facies 3 (F3: Tb-Te layers), Facies 4 (F4: Tb / Tc-Te layers), and Facies 5 (F5: Td-Te layers). Based on the Crocker Formation facies analysis, three distinct groups of facies associations were recognised: Deep-Marine Channel-Lobe Association (Type A1), Deep-Marine Channel-Levee Association (Type A2), and Distal Lobe Association. These facies associations precisely revealed that the Crocker Formation's depositional environments were likely deposited in the middle-fan with associated outer-fan settings

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)

Major ice‐sheet change in the Weddell Sector of West Antarctica over the last 5000 years

Until recently, little was known about the Weddell Sea sector of the West Antarctic Ice Sheet. In the last 10 years, a variety of expeditions and numerical modelling experiments have improved knowledge of its glaciology, glacial geology, and tectonic setting. Two of the sector's largest ice streams rest on a steep reverse‐sloping bed yet, despite being vulnerable to change, satellite observations show contemporary stability. There is clear evidence for major ice‐sheet reconfiguration in the last few thousand years, however. Knowing precisely how the ice sheet has changed in the past, and when, would allow us to better understand whether it is now at risk. Two competing hypotheses have been established for this glacial history. In one, the ice sheet retreated and thinned progressively from its Last Glacial Maximum position. Retreat stopped at, or very near, the present position in the Late Holocene. Alternatively, in the Late Holocene the ice sheet retreated significantly upstream of the present grounding line, and then advanced to the present location due to glacial isostatic adjustment, and ice‐shelf and ice rise buttressing. Both hypotheses point to data and theory in their support, yet neither has been unequivocally tested or falsified. Here, we review geophysical evidence to determine how each hypothesis has been formed, where there are inconsistencies in the respective glacial histories, how they may be tested or reconciled, and what new evidence is required to reach a common model for the Late Holocene ice sheet history of the Weddell Sea sector of West Antarctica

Numerical modelling on the performance of submerged breakwater using the SPH-based DualSPHysics model

Implementation of coastal structures are known to mitigate issues of coastal erosion and impacts of sea waves during storm events on coastal areas. Among the various coastal structures implemented in Malaysia, the submerged breakwater called as WABCORE is being studied. This structure was originally designed by the National Hydraulic Research Institute of Malaysia and has been implemented at the shores of Pulau Tinggi, Johor, Malaysia. The objective of this study is to identify the wave transmission coefficient of the improved WABCORE structure under a variety of wave conditions. The effect of wave steepness (Hi/L) parameter on the wave transmission coefficient would also be highlighted. The study also considers the arrangement of the WABCORE structures, whereby the structures are stacked in a 4:3:2 (broad) and 3:2:1 (narrow) manner. This study implements the use of an open-source code known as DualSPHysics to simulate the various conditions. The results signify that the WABCORE structure is capable of dissipating waves despite its various condition

Investigating antarctic ice-sheet vulnerability to internal ice-sheet processes

The Weddell Sea sector of West Antarctic Ice Sheet may be increasingly vulnerable to melting specifically close to the grounding line through atmospheric warming and modifications in ocean circulation. This project investigates the complexity of ice-sheet stability at and close to the grounding line in the Institute, Möller and Foundation Ice Streams using airborne radar data and satellite images. A new bed elevation model in the Weddell Sea sector is developed which updates the previous Bedmap2 bed product. While the gross form of the new bed elevation model is similar to Bedmap2, there are some notable differences. Ice-penetrating radar data show flow-parallel hard-bed landforms beneath the grounded ice, and channels incised upwards into the ice shelf, inherited from the landforms, beneath meandering surface features. Radar reveals the presence of subglacial water alongside the landforms, indicating a well-organised drainage system where water exits the ice-sheet as a point source. Both the Institute and Möller Ice Streams are also associated with the ice-shelf channels similar to Foundation Ice Stream. The location of the ice shelf channel coincides with the rough bed across the deep section of Robin Subglacial Basin upstream of Institute Ice Stream. Additionally, a deep subglacial embayment is discovered immediately inland of the Institute Ice Stream grounding line. For the Möller Ice Stream, subglacial water flows along the smooth basal trough. The trough moulds the ice-sheet base, such that at the point of flotation it is characterised by a notable downward-facing mound. The consistency between different grounding lines lineation is determined by the thickness of ice and the bed elevation. Results from model outputs is also compared with the geophysical data in the Weddell Sea sector. In general, the model is performing well in some areas, however, further improvement is needed for the model to accurately characterize the ice-sheet complexity.Open Acces

A deep subglacial embayment adjacent to the grounding line of Institute Ice Stream, West Antarctica

The Institute Ice Stream (IIS) in West Antarctica may be increasingly vulnerable to melting at the grounding line through modifications in ocean circulation. Understanding such change requires knowledge of grounding-line boundary conditions, including the topography on which it rests. Here, we discuss evidence from new radio-echo sounding (RES) data on the subglacial topography adjacent to the grounding line of the IIS. In doing so, we reveal a previously unknown subglacial embayment immediately inland of the IIS grounding zone which is not represented in the Bedmap2 compilation. We discuss whether there is an open-water connection between the embayment and the ice-shelf cavity. The exact location of the grounding line over the embayment has been the subject of considerable uncertainty, with several positions being proposed recently. From our compilation of data, we are able to explain which of these grounding lines is most likely and, in doing so, highlight the need for accurate bed topography in conjunction with satellite observations to fully comprehend ice-sheet processes in this region and other vulnerable locations at the grounded margin of Antarctica

1-km bed topography digital elevation model (DEM) of the Weddell Sea sector, West Antarctica

We present a new bed elevation digital elevation model (DEM) of the Weddell Sea sector, West Antarctica. The DEM consists a total area of ~125,000 km2 covering the Institute, Möller and Foundation ice streams and the Bungenstock Ice Rise with a 1 km spatial resolution. In order to produce the bed elevation DEM, ice thickness DEM was formed from the available radio-echo sounding (RES) data using the 'Topo to Raster' function in ArcGIS. The RES data used in this study were compiled from four main sources which are (1) Scott Polar Research Institute (SPRI) survey collected during several campaigns in the 1970s (Drewry, 1983), (2) British Antarctic Survey (BAS) airborne radar survey conducted during the austal summer 2006/07 (GRADES/IMAGE) (Ashmore et al., 2014). , (3) BAS airborne survey accomplished during the Institute and Möller Antarctic Funding Initiative (IMAFI) in 2010/2011 (Ross et al., 2012) and (4) Center for the Remote Sensing of Ice Sheet (CReSIS) data during the NASA Operation IceBridge (OIB) programme in 2012, 2014 and 2016 (Gogineni, 2012). The ice thickness picks were gridded at a uniform 1-km spacing using the Nearest Neighbour interpolation within the Topo to Raster. The ice thickness DEM was later subtracted from the 1-km ice-sheet surface elevation derived from the combined European Remote Sensing Satellite-1 (ERS-1) radar and Ice, Cloud and land Elevation Satellite (ICESat) laser satellite altimetry DEM (Bamber et al., 2009), to produce the bed topography referenced to the Polar Stereographic projection (Snyder, 1987)

Hard rock landforms generate 130 km ice shelf channels through water focusing in basal corrugations.

Satellite imagery reveals flowstripes on Foundation Ice Stream parallel to ice flow, and meandering features on the ice-shelf that cross-cut ice flow and are thought to be formed by water exiting a well-organised subglacial system. Here, ice-penetrating radar data show flow-parallel hard-bed landforms beneath the grounded ice, and channels incised upwards into the ice shelf beneath meandering surface channels. As the ice transitions to flotation, the ice shelf incorporates a corrugation resulting from the landforms. Radar reveals the presence of subglacial water alongside the landforms, indicating a well-organised drainage system in which water exits the ice sheet as a point source, mixes with cavity water and incises upwards into a corrugation peak, accentuating the corrugation downstream. Hard-bedded landforms influence both subglacial hydrology and ice-shelf structure and, as they are known to be widespread on formerly glaciated terrain, their influence on the ice-sheet-shelf transition could be more widespread than thought previously