Quantification of seasonal and diurnal dynamics of subglacial channels using seismic observations on an Alpine glacier The Cryosphere DOI 10.5194/tc-14-1475-2020 19 May 2020 Our study addresses key questions on the subglacial drainage system physics through a novel observational approach that overcomes traditional limitations. We conducted, over 2 years, measurements of the subglacial water-flow-induced seismic noise and of glacier basal sliding speeds. We then inverted for the subglacial channel’s hydraulic pressure gradient and hydraulic radius and investigated the links between the equilibrium state of subglacial channels and glacier basal sliding. Read more
Assimilation of surface observations in a transient marine ice sheet model using an ensemble Kalman filter The Cryosphere DOI 10.5194/tc-14-811-2020 17 March 2020 Marine-based sectors of the Antarctic Ice Sheet are increasingly contributing to sea-level rise. The basal conditions exert an important control on the ice dynamics. For obvious reasons of inaccessibility, they are an important source of uncertainties in numerical ice flow models used for sea-level projections. Here we assess the performance of an ensemble Kalman filter for the assimilation of transient observations of surface elevation and velocities in a marine ice sheet model. Read more
Cryoconite: an efficient accumulator of radioactive fallout in glacialenvironments The Cryosphere DOI 10.5194/tc-14-657-2020 25 February 2020 Cryoconite is the sediment found on the surface of glaciers. The paper presents cryoconite as an environmental matrix able to accumulate natural and artificial radioactivity with unprecedented efficiency. Only samples from sites where nuclear accidents and explosions occurred present a stronger radioactive contamination. The peculiarities of glacial environments are responsible for this extreme feature, making cryoconite a useful tool tool for the monitoring of environmental radioactivity. Read more
A decade of variability on Jakobshavn Isbræ: ocean temperatures pace speedthrough influence on mélange rigidity The Cryosphere DOI 10.5194/tc-14-211-2020 27 January 2020 Jakobshavn Isbræ, considered to be Greenland’s fastest glacier, has varied its speed and thinned dramatically since the 1990s. Here we examine the glacier’s behaviour over the last decade to better understand this behaviour. We find that when the floating ice (mélange) in front of the glacier freezes in place during the winter, it can control the glacier’s speed and thinning rate. A recently colder ocean has strengthened this mélange, allowing the glacier to recoup some of its previous losses. Read more
Understanding snow bedform formation by adding sintering to a cellular automata model The Cryosphere DOI 10.5194/tc-13-3239-2019 17 December 2019 Snow surfaces, under the action of wind, form beautiful shapes such as waves and dunes. This study is the first ever study to simulate these shapes using a state-of-the-art numerical modelling tool. While these beautiful and ephemeral shapes on snow surfaces are fascinating from a purely aesthetic point of view, they are also critical in regulating the transfer of heat and mass between the atmosphere and snowpacks, thus being of huge importance to the Earth system. Read more
New Last Glacial Maximum ice thickness constraints for the Weddell Sea Embayment, Antarctica The Cryosphere DOI 10.5194/tc-13-2935-2019 22 November 2019 We studied the history of ice masses at three locations in the Weddell Sea Embayment, Antarctica. We measured rare isotopes in material sourced from mountains overlooking the Slessor Glacier, Foundation Ice Stream, and smaller glaciers on the Lassiter Coast. We show that ice masses were between 385 and 800 m thicker during the last glacial cycle than they are at present. The ice masses were both hundreds of metres thicker and remained thicker closer to the present than was previously thought. Read more
Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler glaciers The Cryosphere DOI 10.5194/tc-13-2817-2019 15 November 2019 We used a number of computer simulations to understand the recent retreat of a rapidly changing group of glaciers in West Antarctica. We found that significant melt underneath the floating extensions of the glaciers, driven by relatively warm ocean water at depth, was likely needed to cause the large retreat that has been observed. If melt continues around current rates, retreat is likely to continue through the coming century and extend beyond the present-day drainage area of these glaciers. Read more
Calving cycle of the Brunt Ice Shelf, Antarctica, driven by changes in ice shelf geometry The Cryosphere DOI 10.5194/tc-13-2771-2019 15 November 2019 Two large icebergs are about to break off from the Brunt Ice Shelf in Antarctica. Rifting started several years ago and is now approaching its final phase. Satellite data and computer simulations show that over the past 2 decades, growth of the ice shelf has caused a build-up of forces within the ice, which culminated in its fracture. These natural changes in geometry coincided with large variations in flow speed, a process that is thought to be relevant for all Antarctic ice shelf margins. Read more
Contrasting thinning patterns between lake- and land-terminating glaciers in the Bhutanese Himalaya The Cryosphere DOI 10.5194/tc-13-2733-2019 29 October 2019 We investigate thickness change of Bhutanese glaciers during 2004–2011 using repeat GPS surveys and satellite-based observations. The thinning rate of Lugge Glacier (LG) is > 3 times that of Thorthormi Glacier (TG). Numerical simulations of ice dynamics and surface mass balance (SMB) demonstrate that the rapid thinning of LG is driven by both negative SMB and dynamic thinning, while the thinning of TG is minimised by a longitudinally compressive flow regime. Read more
Estimating Greenland tidewater glacier retreat driven by submarine melting The Cryosphere DOI 10.5194/tc-13-2489-2019 26 September 2019 The ocean’s influence on the retreat of Greenland’s tidewater glaciers is a key factor determining future sea level. By considering observations of ~200 glaciers from 1960, we find a significant relationship between retreat and melting in the ocean. Projected forwards, this relationship estimates the future evolution of Greenland’s tidewater glaciers and provides a practical and empirically validated way of representing ice–ocean interaction in large-scale models used to estimate sea level rise. Read more
