Erosion at extended continental margins: Insights from new aerogeophysical data in eastern Dronning Maud Land

Modelling-, rock cooling-, sedimentation- and exposure-based interpretations of the mechanisms by which topography evolves at extended continental margins vary widely. Observations from the margin of Dronning Maud Land, Antarctica, have until now not strongly contributed to these interpretations. Here, we present new airborne gravity and radar data describing the eastern part of this margin. Inland of a tall (2.5 km) great escarpment, a plateau topped by a branching network of valleys suggests preservation of a fluvial landscape with SW-directed drainage beneath a cold-based ice sheet. The valley floor slopes show that this landscape was modified during a period of alpine-style glaciation prior to the onset of the current cold-based phase around 34 Ma. The volume of sediments in basins offshore in the Riiser-Larsen Sea balances with the volume of rock estimated to have been eroded and transported by north-directed drainage from between the escarpment and the continental shelf break. The stratigraphy of these basins shows that most of the erosion occurred during the ~40 Myr following late Jurassic continental breakup. This erosion is unlikely to have been dominated by backwearing because the required rate of escarpment retreat to its present location is faster than numerical models of landscape evolution suggest to be possible. We suggest an additional component of erosion by downwearing seawards of a pre-existing inland drainage divide. The eastern termination of the great escarpment and inland plateau is at the West Ragnhild trough, a 300 km long, 15–20 km wide and up to 1.6 km deep subglacial valley hosting the West Ragnhild glacier. Numerous overdeepened (by >300 m) segments of the valley floor testify to its experience of significant glacial erosion. Thick late Jurassic and early Cretaceous sediments fanning out from the trough's mouth into the eastern Riiser-Larsen Sea betray an earlier history as a river valley. The lack of late Jurassic relief-forming processes in this river's catchment in the interior of East Antarctica suggests this erosion was related to regional climatic change

Surface accumulation in Northern Central Greenland during the last 300 years

The internal stratigraphy of snow and ice as imaged by ground-penetrating radar may serve as a source of information on past accumulation. This study presents results from two ground-based radar surveys conducted in Greenland in 2007 and 2015, respectively. The first survey was conducted during the traverse from the ice-core station NGRIP (North Greenland Ice Core Project) to the ice-core station NEEM (North Greenland Eemian Ice Drilling). The second survey was carried out during the traverse from NEEM to the ice-core station EGRIP (East Greenland Ice Core Project) and then onwards to Summit Station. The total length of the radar profiles is 1427 km. From the radar data, we retrieve the large-scale spatial variation of the accumulation rates in the interior of the ice sheet. The accumulation rates range from 0.11 to 0.26 m a−1 ice equivalent with the lowest values found in the northeastern sector towards EGRIP. We find no evidence of temporal or spatial changes in accumulation rates when comparing the 150-year average accumulation rates with the 321-year average accumulation rates. Comparisons with regional climate models reveal that the models underestimate accumulation rates by up to 35% in northeastern Greenland. Our results serve as a robust baseline to detect present changes in either surface accumulation rates or patterns

The internal layering of Pine Island Glacier, West Antarctica, from airborne radar-sounding data

This paper presents an overview of internal layering across Pine Island Glacier, West Antarctica, as measured from airborne-radar data acquired during a survey conducted by the British Antarctic Survey and the University of Texas in the 2004/05 season. Internal layering is classified according to type (continuous/discontinuous/missing) and the results compared with InSAR velocities. Several areas exhibit disruption of internal layers that is most likely caused by large basal shear stresses. Signs of changes in flow were identified in a few inter-tributary areas, but overall the layering classification and distribution of layers indicate that only minor changes in ice-flow regime have taken place. This is supported by bed-topography data that show the main trunk of the glacier, as well as some of the tributaries, are topographically controlled and located in deep basins

Oldest Ice in Antarctica – the 3d continental ice sheet modelling perspective.

The ongoing quest to find the oldest continuous ice core in Antarctica draws on the expertise of multiple disciplines. Here we present our efforts to inform on the location of potential future drilling sites by 3d continental ice sheet modelling. We present the results of an ensemble of ice sheet model simulations spanning the last 2 million years utilizing a variety of different model setups and boundary conditions including new radar derived bedrock elevation. In our analysis we focus on the physical properties and ice dynamics around the major drill sites such as Dome Fuji and Dome C and discuss the effects of the ice sheets history on the present day flow regime. By using a continental setup and applying a transient forcing created from paleo climate modelling studies and ice core data we are able to take a holistic view of Antarctic Ice Sheet dynamics and its impact on the vertical stratigraphy around the East Antarctic ice domes

Cryoegg: development and field trials of a wireless subglacial probe for deep, fast-moving ice

nnovative technological solutions are required to access and observe subglacial hydrological systems beneath glaciers and ice sheets. Wireless sensing systems can be used to collect and return data without the risk of losing data from cable breakage, which is a major obstacle when studying fast flowing glaciers and other high-strain environments. However, the performance of wireless sensors in deep and fast-moving ice has yet to be evaluated formally. We report experimental results from Cryoegg: a spherical probe that can be deployed along an ice borehole and either remain fixed in place or potentially travel through the subglacial hydrological system. The probe makes measurements in-situ and sends them back to the surface via a wireless link. Cryoegg uses very high frequency (VHF) radio to transmit data through up to 1.3 km of cold ice to a surface receiving array. It measures temperature, pressure and electrical conductivity, returning all data in real time. This transmission uses Wireless M-Bus on 169 MHz; we present a simple “radio link budget” model for its performance in cold ice and confirm its validity experimentally. Power is supplied by an internal battery with sufficient capacity for two measurements per day for up to a year, although higher reporting rates are available at the expense of battery life. Field trials were conducted in 2019 at two locations in Greenland (the EastGRIP borehole and the RESPONDER project site on Sermeq Kujalleq/Store Glacier) and on the Rhone Glacier in Switzerland. Our results from the field demonstrate Cryoegg’s utility in studying englacial channels and moulins, including estimating moulin discharge through salt dilution gauging with the instrument deployed deep within the moulin. Future iterations of the radio system will allow Cryoegg to transmit through up to 2.5 km of ice

Ice-penetrating radar survey of the subsurface debris field at Camp Century, Greenland

The warming climate is changing the surface dynamics of the Greenland Ice Sheet, including the balance between snowfall and melt. Increasing surface melt impacts the structure of the relatively porous near-surface layer known as firn. Camp Century, a base abandoned in 1967, now comprises a subsurface debris field within the firn in Northwest Greenland. We collected 80 km of 100 or 250 MHz radar data in nested grids over this subsurface debris field. Here, we present a comprehensive analysis and interpretation of this ice-penetrating radar survey. The vast majority (95%) of subsurface reflectors are located at depths of greater than 32 m. The tunnel network, as well as an overlying layer associated with historical surface activities, is readily visible in the radar data. This subsurface debris field is approximately circular with a radius of less than 1 km. Local downwarping of clear internal layers – likely annual accumulation layers - identifies now-collapsed liquid sumps. Analysis of radar signal polarity suggests that liquid hydrocarbons are likely present in one of these sumps. The radar data and a geo-referenced site map of Camp Century are freely accessible at http://www.campcenturyclimate.d

Five decades of radioglaciology

Radar sounding is a powerful geophysical approach for characterizing the subsurface conditions of terrestrial and planetary ice masses at local to global scales. As a result, a wide array of orbital, airborne, ground-based, and in situ instruments, platforms and data analysis approaches for radioglaciology have been developed, applied or proposed. Terrestrially, airborne radar sounding has been used in glaciology to observe ice thickness, basal topography and englacial layers for five decades. More recently, radar sounding data have also been exploited to estimate the extent and configuration of subglacial water, the geometry of subglacial bedforms and the subglacial and englacial thermal states of ice sheets. Planetary radar sounders have observed, or are planned to observe, the subsurfaces and near-surfaces of Mars, Earth's Moon, comets and the icy moons of Jupiter. In this review paper, and the thematic issue of the Annals of Glaciology on ‘Five decades of radioglaciology’ to which it belongs, we present recent advances in the fields of radar systems, missions, signal processing, data analysis, modeling and scientific interpretation. Our review presents progress in these fields since the last radio-glaciological Annals of Glaciology issue of 2014, the context of their history and future prospects

Design and Performance of the Hotrod Melt-Tip Ice-Drilling System

We introduce the design and performance of a melt-tip ice-drilling system designed to insert a temperature sensor cable into ice. The melt tip is relatively simple and low cost, designed for a one-way trip to the ice-bed interface. The drilling system consists of a melt tip, umbilical cable, winch, interface, power supply, and support items. The melt tip and the winch are the most novel elements of the drilling system, and we make the hardware and electrical designs of these components available open access. Tests conducted in a laboratory ice well indicate that the melt tip has an electrical energy to forward melting heat transfer efficiency of ~35 % with a theoretical maximum penetration rate of ~12 m/hr at maximum 6.0 kW power. In contrast, ice-sheet testing suggests the melt tip has an analogous heat transfer efficiency of ~15 % with a theoretical maximum penetration rate of ~6 m/hr. We expect the efficiency gap between laboratory and field performance to decrease with increasing operator experience. Umbilical freeze-in due to borehole refreezing is the primary depth-limiting factor of the drilling system. Enthalpy-based borehole refreezing assessments predict refreezing below critical umbilical diameter in ~4 hours at -20 ˚C ice temperatures and ~20 hours at -2 ˚C. This corresponds to a theoretical depth limit of up to ~200 m, depending on firn thickness, ice temperature and operator experience.</p