ALBERT

Description: Ice shelves play a crucial role in helping controlling the current rate of mass loss from the Antarctic ice sheet through their buttressing potential. This control is modulated by variations in ice shelf mass balance, which cause changes in the thickness of the ice shelf, and therefore in its ability to restrain flow from the grounded ice sheet. We present results showing temporal variability in sub-shelf melting using autonomous phase-sensitive radio-echo sounders (ApRES) near the grounding line of the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica. When combined with additional oceanographic evidence of seasonal variation in stratification and the amplification of the diurnal tides around the Gunnerus Bank, the results suggest an intricate mechanism in which topographic waves control the seasonal melt rate variability near the grounding line of the Roi Baudouin Ice Shelf.

Description: Ice shelves play a crucial role in helping controlling the current rate of mass loss from the Antarctic ice sheet through their buttressing potential. This control is modulated by variations in ice shelf mass balance, which cause changes in the thickness of the ice shelf, and therefore in its ability to restrain flow from the grounded ice sheet. We present results showing temporal variability in sub-shelf melting using autonomous phase-sensitive radio-echo sounders (ApRES) near the grounding line of the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica. When combined with additional oceanographic evidence of seasonal variation in stratification and the amplification of the diurnal tides around the Gunnerus Bank, the results suggest an intricate mechanism in which topographic waves control the seasonal melt rate variability near the grounding line of the Roi Baudouin Ice Shelf.

Description: A 120 m-long ice core was drilled in 2012 on the Derwael Ice Rise, coastal Dronning Maud Land, East Antarctica. Water stable isotopes (d18O and dD) stratigraphy is supplemented by discontinuous major ion profiles and continuous electrical conductivity measurements. The base of the ice core is dated to AD 1759 ± 16, providing a climate proxy for the past ~250 years. This data set presents the core's annual layer thickness history in meters water equivalent for the oldest age-depth estimate before correction for the influence of ice deformation.

Description: Ice shelves play a crucial role in helping controlling the current rate of mass loss from the Antarctic ice sheet through their buttressing potential. This control is modulated by variations in ice shelf mass balance, which cause changes in the thickness of the ice shelf, and therefore in its ability to restrain flow from the grounded ice sheet. We present results showing temporal variability in sub-shelf melting using autonomous phase-sensitive radio-echo sounders (ApRES) near the grounding line of the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica. When combined with additional oceanographic evidence of seasonal variation in stratification and the amplification of the diurnal tides around the Gunnerus Bank, the results suggest an intricate mechanism in which topographic waves control the seasonal melt rate variability near the grounding line of the Roi Baudouin Ice Shelf.

Description: Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB) i.e., the difference between refreezing and melting. Here, we present an improved technique - based on satellite observations - to capture the small-scale variability in the BMB of ice shelves. As a case study, we apply the methodology to the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica, and derive its yearly averaged BMB at 10 m horizontal gridding. We use mass conservation in a Lagrangian framework based on high-resolution surface velocities, atmospheric-model surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which preserves abrupt changes in flow velocities and their spatial gradients. Such changes may reflect a dynamic response to localized basal melting and should be included in the mass budget. Our BMB field exhibits much spatial detail and ranges from -14.7 to 8.6 m/a ice equivalent. Highest melt rates are found close to the grounding line where the pressure melting point is high, and the ice-shelf slope is steep. The BMB field agrees well with on-site measurements from phase-sensitive radar, although independent radar profiling indicates unresolved spatial variations in firn density. We show that an elliptical surface depression (10 m deep and with an extent of 0.7 km ×1.3 km) lowers by 0.5 to 1.4 m/a , which we tentatively attribute to a transient adaptation to hydrostatic equilibrium. We find evidence for elevated melting beneath ice shelf channels (with melting being concentrated on the channel's flanks). However, farther downstream from the grounding line, the majority of ice shelf channels advect passively (i.e. no melting nor refreezing) toward the ice shelf front. Although the absolute, satellite-based BMB values remain uncertain, we have high confidence in the spatial variability on sub-kilometre scales. This study highlights expected challenges for a full coupling between ice and ocean models.

Description: Antarctic ice shelves are buttressed by numerous pinning points attaching to the otherwise freely-floating ice from below. Some of these kilometric-scale grounded features are unresolved in Antarctic-wide datasets of ice thickness and bathymetry, hampering ice flow models to fully capture dynamics at the grounding line and upstream. We investigate the role of an 8.7 km² pinning point at the front of the Roi Baudouin Ice Shelf, East Antarctica. Using ERS interferometry and ALOS-PALSAR speckle tracking, we derive, on a 125 m grid spacing, surface velocities deviating by -5.2 ± 4.5 m/a from 37 on-site global navigation satellite systems-derived velocities. We find no evidence for ice flow changes on decadal time scales and we show that ice on the pinning point virtually stagnates, deviating the ice stream and causing enhanced horizontal shearing upstream. Using the BISICLES ice-flow model, we invert for basal friction and ice rigidity with three input scenarios of ice velocity and geometry. We show that inversion results are the most sensitive to the presence/absence of the pinning point in the bathymetry; surface velocities at the pinning point are of secondary importance. Undersampling of pinning points results in erroneous ice-shelf properties in models initialised by control methods. This may impact prognostic modelling for ice-sheet evolution in the case of unpinning.

Description: This dataset describes ice thickness, surface elevation and bed elevation of a small pinning point located at the ice-shelf front of the Roi Baudouin Ice Shelf, Dronning Maud Land, Antarctica. The scientific context is as follows: Antarctic ice shelves are buttressed by numerous pinning points attaching to the otherwise freely-floating ice from below. Some of these kilometric-scale grounded features are unresolved in Antarctic-wide datasets of ice thickness and bathymetry, hampering ice flow models to fully capture dynamics at the grounding line and upstream. We investigate the role of an 8.7 km2 pinning point at the front of the Roi Baudouin Ice Shelf, East Antarctica. Using ERS interferometry and ALOS-PALSAR speckle tracking, we derive, on a 125 m grid spacing, surface velocities deviating by −5.2 ± 4.5 m a−1 from 37 on-site global navigation satellite systems-derived velocities. We find no evidence for ice flow changes on decadal time scales and we show that ice on the pinning point virtually stagnates, deviating the ice stream and causing enhanced horizontal shearing upstream. Using the BISICLES ice-flow model, we invert for basal friction and ice rigidity with three input scenarios of ice velocity and geometry. We show that inversion results are the most sensitive to the presence/absence of the pinning point in the bathymetry; surface velocities at the pinning point are of secondary importance. Undersampling of pinning points results in erroneous ice-shelf properties in models initialised by control methods. This may impact prognostic modelling for ice-sheet evolution in the case of unpinning.

Description: A gridded bathymetry of the sea floor under Ekström Ice Shelf, Antarctica. The seismic data used to map the bathymetry were collected between 2010 and 2018, using two different seismic vibroseis sources. The same snow streamer was used for all data acquisition - a 1500 m long, 60 channel snow streamer, with 25 m group spacing. Each group contains eight gimballed P-wave SM-4, 14 Hz geo-phones. For each seismic profile, the reflection time of the sea floor horizon was identified. The data across all profiles was gridded and depth converted, using an ice velocity of 3601 m/s a sea-water velocity of 1451 m/s.

Description: This ASCII file contains ice thickness, surface- and bed elevation derived from radar surveys on Derwael Ice Rise in 2012 and 2013. Radar thickness/bed measurements use wave speed of 1.68e8 m/s; Firn correction applied; Surface elevation measured by differential, kinematic GPS with dual phase receivers.

Description: Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves causing grounded glaciers to accelerate and sea level to rise. In the Antarctic Peninsula (AP), foehn winds enhance melting near the grounding line, which in the recent past has led to the disintegration of the most northerly ice shelves. Here, we provide observational and model evidence that this process also occurs over an East Antarctic (EA) ice shelf, where meltwater-induced firn air depletion is found in the grounding zone. Unlike the AP, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal EA high temperatures are caused by persistent katabatic winds originating from the ice sheet's interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining 〉3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared to its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in-situ observation of supraglacial flow and englacial storage of meltwater suggests that ice shelf grounding zones in EA, like their AP counterparts, are vulnerable to hydrofracturing.