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Diurnal depth cycles of decimeter scale are observed in a supraglacial lake on the McMurdo Ice Shelf, Antarctica. We evaluate two possible causes: (1) tidal tilt of the ice shelf in response to the underlying ocean tide, and (2) meltwater input variation. We find the latter to be the most likely explanation of our observations. However, we do not rule out tidal tilt as a source of centimeter scale variations, and point to the possibility that other, larger supraglacial lake systems, particularly those on ice shelves that experience higher amplitude tidal tilts, such as in the Weddell Sea, may have depth cycles driven by ocean tide. The broader significance of diurnal cycles in meltwater depth is that, under circumstances where the ice shelf is thin, tidal-tilt amplitudes are high, and meltwater runoff rates are large, there may be associated flexure stresses that can contribute to ice-shelf fracture and destabilization. For the McMurdo Ice Shelf (~20–50 m thickness, ~ 1 m tidal amplitude and ~10 cm water-depth variations), these stresses amount to several 10's of kPa. [ABSTRACT FROM AUTHOR]

Supraglacial lakes are known to trigger Antarctic ice-shelf instability and break-up. However, to date, no study has focused on lakes on Greenland's floating termini. Here, we apply lake boundary/area and depth algorithms to Landsat 8 imagery to analyse the inter- and intraseasonal evolution of supraglacial lakes across Petermann Glacier's (81°N) floating tongue from 2014 to 2016, while also comparing these lakes to those on the grounded ice. Lakes start to fill in June and quickly peak in total number, volume and area in late June/early July in response to increases in air temperatures. However, through July and August, total lake number, volume and area all decline, despite sustained high temperatures. These observations may be explained by the transportation of meltwater into the ocean by a river, and by lake drainage events on the floating tongue. Further, as mean lake depth remains relatively constant during this time, we suggest that a large proportion of the lakes that drain, do so completely, likely by rapid hydrofracture. The mean areas of lakes on the tongue are only ~20% of those on the grounded ice and exhibit lower variability in maximum and mean depth, differences likely attributable to the contrasting formation processes of lakes in each environment. [ABSTRACT FROM AUTHOR]

On 2 March 2016, several small en échelon tabular icebergs calved from the seaward front of the McMurdo Ice Shelf, and a previously inactive rift widened and propagated by ~3 km, ~25% of its previous length, setting the stage for the future calving of a ~14 km2 iceberg. Within 24 h of these events, all remaining land-fast sea ice that had been stabilizing the ice shelf broke-up. The events were witnessed by time-lapse cameras at nearby Scott Base, and put into context using nearby seismic and automatic weather station data, satellite imagery and subsequent ground observation. Although the exact trigger of calving and rifting cannot be identified definitively, seismic records reveal superimposed sets of both long-period (>10 s) sea swell propagating into McMurdo Sound from storm sources beyond Antarctica, and high-energy, locally-sourced, short-period (<10 s) sea swell, in the 4 days before the fast ice break-up and associated ice-shelf calving and rifting. This suggests that sea swell should be studied further as a proximal cause of ice-shelf calving and rifting; if proven, it suggests that ice-shelf stability is tele-connected with far-field storm conditions at lower latitudes, adding a global dimension to the physics of ice-shelf break-up. [ABSTRACT FROM AUTHOR]

Supraglacial meltwater lakes trigger ice-shelf break-up and modulate seasonal ice-sheet flow, and are thus agents by which warming is transmitted to the Antarctic and Greenland ice sheets. To characterize supraglacial lake variability we perform a comparative analysis of lake geometry and depth in two distinct regions, one on the pre-collapse (2002) Larsen B ice shelf, Antarctica, and the other in the ablation zone of Paakitsoq, a land-terminating region of the Greenland ice sheet. Compared to Paakitsoq, lakes on the Larsen B ice shelf cover a greater proportion of surface area (5.3% cf. 1%), but are shallower and more uniform in area. Other aspects of lake geometry (e.g. eccentricity, degree of convexity (solidity) and orientation) are relatively similar between the two regions. We attribute the notable difference in lake density and depth between ice-shelf and grounded ice to the fact that ice shelves have flatter surfaces and less distinct drainage basins. Ice shelves also possess more stimuli to small-scale, localized surface elevation variability, due to the various structural features that yield small variations in thickness and which float at different levels by Archimedes' principle. [ABSTRACT FROM AUTHOR]

Three stations near the calving front of the Ross Ice Shelf, Antarctica, recorded GPS data through a full spring-neap tidal cycle in November 2005. The data revealed a diurnal horizontal motion that varied both along and transverse to the long-term average velocity direction, similar to tidal signals observed in other ice shelves and ice streams. Based on its periodicity, it was hypothesized that the signal represents a flow response of the Ross Ice Shelf to the diurnal tides of the Ross Sea. To assess the influence of the tide on the ice-shelf motion, two hypotheses were developed. The first addressed the direct response of the ice shelf to tidal forcing, such as forces due to sea-surface slopes or forces due to sub-ice-shelf currents. The second involved the indirect response of ice-shelf flow to the tidal signals observed in the ice streams that source the ice shelf. A finite-element model, based on viscous creep flow, was developed to test these hypotheses, but succeeded only in falsifying both hypotheses, i.e. showing that direct tidal effects produce too small a response, and indirect tidal effects produce a response that is not smooth in time. This nullification suggests that a combination of viscous and elastic deformation is required to explain the observations. [ABSTRACT FROM AUTHOR]

The article discusses a study of the role of the Honshu earthquake and tsunami in Japan in March 2011 in an Antarctic ice-shelf calving. The calving of the rift-bounded section of ice adjacent to Guest Peninsula from the Sulzberger Ice Shelf (SIS) occurred on March 13. The event was confirmed by European Space Agency (ESA) Envisat advanced synthetic aperture radar (ASAR) images. One of the factors that enabled the tsunami to act as a trigger for ice calving was the sea-ice condition. It emphasizes the key role of environmental and tectonic conditions in the far field in ice-shelf stability in the Antarctic.

The article discusses the study which examines the vertical motions of the large tidally modulated flow that interact with the ice streams feeding the Ross Ice Shelf in Antarctica. It states that the flow of the Ross Ice Shelf front ice streams exhibits smooth and sinusoidal motions corresponding to tidal modulation. It notes that the possible linking of the ice shelf with the ice streams to form a unified system has responded to small perturbations in stresses associated with ocean tides. It confirms the presence of the sinusoidal motion and damping of very high-frequency signals despite the absence of stick-slip motions.

The article focuses on the seismic observations of glaciogenic ocean waves on icebergs and ice shelves in the Ross Sea and on the Ross Ice Shelf in Antarctica. Investigation shows that the impulsive sources of ocean surface waves are frequent in the ice-shelf and iceberg-covered environment of coastal Antarctica. Field deployment of seismometers suggests that these impulsive events are generated through glaciological mechanisms. These mechanisms include small-scale calving and edge wasting of icebergs and ice-shelf fronts, edge-on-edge closing and opening associated with iceberg collisions and the impulsive opening of void space related to ice-shelf rifting. Observations offer a background of glaciogenic ocean-wave phenomena significant to the Ross Sea.

States that model simulations of the West Antarctic ice sheet suggest that sporadic, perhaps chaotic, collapse (complete mobilization) of the ice sheet occurred throughout the past one million years. Causes of the irregular behavior; Concern that the West Antarctic ice sheet might collapse in response to future climate warming; Presentation of a whole ice-sheet model; More.

Reviews the result of the study on the west antarctic ice sheet collapse. Lubricated surges of the Laurentide ice sheet in the Heinrich layers in the North Atlantic; Changes in the modern west antarctic ice sheet; Thinning of the modern ice sheet.

Surface debris covers much of the western portion of the McMurdo Ice Shelf and has a strong influence on the local surface albedo and energy balance. Differential ablation between debris-covered and debris-free areas creates an unusual heterogeneous surface of topographically low, high-ablation, and topographically raised ('pedestalled'), low-ablation areas. Analysis of Landsat and MODIS satellite imagery from 1999 to 2018, alongside field observations from the 2016/2017 austral summer, shows that pedestalled relict lakes ('pedestals') form when an active surface meltwater lake that develops in the summer, freezes-over in winter, resulting in the lake-bottom debris being masked by a high-albedo, superimposed, ice surface. If this ice surface fails to melt during a subsequent melt season, it experiences reduced surface ablation relative to the surrounding debris-covered areas of the ice shelf. We propose that this differential ablation, and resultant hydrostatic and flexural readjustments of the ice shelf, causes the former supraglacial lake surface to become increasingly pedestalled above the lower topography of the surrounding ice shelf. Consequently, meltwater streams cannot flow onto these pedestalled features, and instead divert around them. We suggest that the development of pedestals has a significant influence on the surface-energy balance, hydrology and flexure of the ice shelf. [ABSTRACT FROM AUTHOR]

Abstract: We present the results of an Antarctic spring field study of snow drift threshold measurements made using two custom drift sensors and a commercial parts-counting device. All three sensor types worked well at detecting drifting snow events, but the sensors recorded different magnitudes (particle count per unit time) of drift. Each sensor has a unique detection threshold for particle size, and responded differently to identical wind and snow conditions, although the particle counts from the different sensors are linearly related at low wind speeds. The drift threshold is defined here as the minimum friction velocity at which drifting snow was observed during more than 10% of measurements at that wind speed. The results of this multi-sensor study demonstrate that the drift threshold is lower (friction velocity of 0.2m/s) for very small particles that are likely transported in suspension than for coarse-grained saltating particles (0.25m/s). These friction velocities correspond to 10-meter wind speeds of 5.6 and 7.2m/s respectively for the conditions during this experiment. The commercially available parts counter is recommended as a low-cost alternative to custom-built drift sensors for use in future field studies of drifting and blowing snow. [Copyright &y& Elsevier]