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Back to the Front – Larsen C Ice Shelf in the Aftermath of Iceberg A68!

Back to the Front – Larsen C Ice Shelf in the Aftermath of Iceberg A68!

Much of the Antarctic continent is fringed by ice shelves. An ice shelf is the floating extension of a terrestrial ice mass and, as such, is an important ‘middleman’ that regulates the delivery of ice from land into the ocean: for much of Antarctica, ice that passes from land into the sea does so via ice shelves. I’ve been conducting geophysical experiments on ice for over a decade, using mostly seismic and radar methods to determine the physical condition of ice and its wider system, but it’s only in the last couple of years that I’ve been using these methods on ice shelves. The importance of ice shelf processes is becoming more widely recognised in glaciological circles: after hearing one of my seminars last year, a glaciology professor told me that he was revising his previous opinion that ice shelves were largely ‘passengers’ in the grand scheme of things and this recognition is becoming more common. Slowly, we are coming to appreciate that ice shelves have their own specific dynamics and, moreover, that they are the drivers of change on other ice masses.


The MIDAS Project

In 2015, I joined the MIDAS project – led by Swansea and Aberystwyth Universities and funded by the Natural Environment Research Council – dedicated to investigating the effects of a warming climate on the Larsen C ice shelf in West Antarctica (Fig. 1). My role was to to assist with geophysical surveys (Fig. 2) on the ice shelf – but more about that later!

Figure 2: Adam Booth overseeing seismic surveys on the Larsen C ice
shelf in 2015 [Credit: Suzanne Bevan].

Larsen C is located towards the northern tip of the Antarctic Peninsula, and is one of a number of “Larsen neighbours” that fringe its eastern cost. MIDAS turns out to have been an extremely timely study, culminating in 2017 just as Larsen C hit the headlines by calving one of the largest icebergs – termed A68 – ever recorded. On 12th July 2017, 12% of the Larsen C area was sliced away by a sporadically-propagating rift through the eastern edge of the shelf, resulting in an iceberg with 5800 km2 area (two Luxembourgs, one Delaware, one-quarter Wales…). As of 14th October 2017 (Fig. 1), A68 is drifting into the Weddell Sea, with open ocean between it and Larsen C. See our previous post “Ice ice bergy” to find out more about how and why ice berg movement is monitored.

The aftermath of A68

As colossal as A68 (Fig, 1) is, its record-breaking statistics are only (hnnngh…) the tip of the iceberg, and of greater significance is the potential response of what remains of Larsen C. This potential is best appreciated by considering what happened to Larsen B, a northern neighbour of Larsen C. In early 2002, over 3000 km2 of Larsen B Ice Shelf underwent a catastrophic collapse, disintegrating into thousands of smaller icebergs (and immortalised in the music of the band British Sea Power). Rewind seven years further back, to 1995: Larsen B calved an enormous iceberg, exceeding 1700 m2 in area. An ominous extrapolation from this is that large iceberg calving somehow preconditions ice shelves to instability, and several models of Larsen C evolution suggest that it could follow Larsen B’s lead and become more vulnerable to collapse over the coming years.

The enormous mass of the intact ice shelf acts like a dam that blocks the delivery of terrestrial ice into the ocean, and the disappearance of the ice shelf removes so-called ‘backstress’ – essentially ‘breaking the dam’.

Then what? Well, ice shelves are in stress communication with their terrestrial tributaries, therefore processes affecting the shelf can propagate back to the supply glaciers. The enormous mass of the intact ice shelf acts like a dam that blocks the delivery of terrestrial ice into the ocean, and the disappearance of the ice shelf removes so-called ‘backstress’ – essentially ‘breaking the dam’. In the aftermath of Larsen B’s collapse, its tributary glaciers were seen to accelerate, thereby delivering more of their ice into the Weddell Sea. It is this aftermath that we are particularly concerned about, since it’s the accelerated tributaries that promote accelerated sea-level rise. Ice shelf collapse has little immediate impact on sea-level: since it is already floating, the shelf displaces all the water that it ever will. But, in moving more ice from the land to the sea, we risk increased sea levels and, with them, the associated socio-economic consequences.

How can we improve our predictions?

Figure 3: Computational model of the changed stress state, Δτuu, of Larsen C following the calving of A68 (output from BISICLES model, from Stephen Cornford, Swansea University). The stress change is keenly felt at the calving front, but also propagates further upstream [Credit: Stephen Cornford]

A key limitation in our ability to predict the evolution of Larsen C is a lack of observational evidence of how ice shelf stresses evolve in the short-term aftermath of a major calving event. These calving events are rare: we simply haven’t had much opportunity to investigate them, so while our computer predictions are based on valid physics (e.g., Fig. 3) it would be valuable to have actual observations to constrain them. Powerful satellite methods are available for tracking the behaviour of the shelf but these provide only the surface response; Larsen C is around 200 m thick at its calving front so there is plenty of ice that is hidden away from the satellite ‘eye in the sky’, but that is still adapting to the new stress regime. So how can we “see” into the ice?

To address this, we’ve recently been awarded an “Urgency Grant” – Response to the A68 Calving Event (RA68CE) – from NERC to send a fieldcrew to the Larsen C ice shelf, involving researchers from Leeds, Swansea and Aberystwyth, together with the British Geological and British Antarctic Surveys.

Figure 4: Emma Pearce and Dr Jim White preparing seismic equipment – intrepid geophysicists ready to wrap-up warm for field deployment on Larsen C! [Credit: Adam Booth]

The field team – Jim White and Emma Pearce (Fig. 4) – will undertake seismic and radar surveys at two main sites (Fig. 3) to assess the new stress regime around the Larsen C calving front. One of these sites is being reoccupied after seismic surveying in 2008-9, during the Swansea-led SOLIS project, allowing us to make a long-term comparison. These, and two other sites, will also be instrumented with EMLID REACH GPS sensors, to track small-scale ice movements than can’t be captured in the satellite data. The field observations will be supplied to a team of glacial modellers at Swansea University, to allow them to improve future predictions (e.g. Fig. 3), while their remote sensing team continues to monitor the evolving stress state at surface.

It’s truly exciting to be coordinating the first deployment, post A68, on Larsen C. Our data should provide a unique missing piece from the predictive jigsaw of Larsen C’s evolution, ultimately improving our understanding of the causes and effects of large-scale iceberg calving – both for Larsen C and beyond!

 

For ice-hot news from the field, follow Emma Pearce on twitter: @emm_pearce

 

Edited by Emma Smith


Further Reading

  • More information on Larsen C at the project MIDAS website
  • Learn more about ice shelf evolution with the Ice Flows game – eduction by stealth! Also check out the EGU Cryoblog post about it!
  • Borstad et al., 2017; Fracture propagation and stability of ice shelves governed by ice shelf heterogeneity; Geophysical Research Letters, 44, 4186-4194.
  • Wuite et al., 2015; Evolution of surface velocities and ice discharge of Larsen B outlet glaciers from 1995 to 2013. The Cryosphere, 9, 957-969.
  • Cornford et al., 2013; Adaptive mesh, finite volume modelling of marine ice sheets; Journal of Computational Physics, 232, 1, 529-549.

Adam Booth is a lecturer in Exploration Geophysics at the University of Leeds, UK. He is the PI on the NERC-funded project “Ice shelf response to large iceberg calving” (NE/R012334/1). After obtaining his PhD from the University of Leeds in 2008, he held postdoctoral positions at Swansea University and Imperial College London, in which he worked with diverse research applications of near-surface geophysics. He tweets as: @Geophysics_Adam

Image of Week: Inside the Greenland Ice Sheet

Image of Week: Inside the Greenland Ice Sheet

The image shows a cross section of the Greenland Ice Sheet, where a recent study by MacGregor et al. have mapped the layers imaged by radar. Thanks to ice core measurements the age of the layers have been determined, and in the image the layers from the Holocene period (the past 11.700 years) are shown in green. The ice formed during the last ice age, that spanned 11.700 to 115.000 years ago are coloured blue, and finally, the ice from the last interglacial, the Eemian period, more than 115.000 years ago, are red. The grey areas show parts where the age is unknown.

For more details see:
MacGregor et al., 2015, Journal of Geophysical Research
NASA Goddard

For more beautiful visualisations of the data:
NASA’s Scientific Visualization Studio

My first journey to Antarctica – Brice Van Liefferinge

My first journey to Antarctica – Brice Van Liefferinge
(Credit B. Van Liefferinge)

(Credit B. Van Liefferinge)

19 November 2014, the Iliuchine 76 gently lands on the runway of the Russian Antarctic station, Novolazarevskaya, in Dronning Maud Land. For the first time, I’m in Antarctica! It is 4 o’clock in the morning and we need to hurriedly offload 2 tons of material intended for our field mission near the Belgian Princess Elisabeth Station. I’m deeply impressed by the landscape although it is dotted with containers, people and machines. I am impressed by the fuzz. I am impressed by the novelty. I am impressed by the icescape. It is cold, but I don’t feel it.

(Credit B. Van Liefferinge)

(Credit B. Van Liefferinge)

I take part in an expedition lasting five weeks and led by the Laboratoire de Glaciologie of the Université Libre de Bruxelles (ULB) in the framework of the Icecon project.The project aims at constraining past and current mass changes of the Antarctic ice sheet in the coastal area of Dronning Maud Land (East Antarctica) to better understand past and present ice volumes and the extension of the Antarctic ice sheet across the continental shelf during the last glacial period. This year we are a team of 5 to do the job: GPS measurements, ice-core drilling, high- and low-frequency radar measurements (GSSI and ApRES), televiewer measurements … The ApRES radar is a new phase-sensitive radar developed by British Antarctic Survey (BAS), capable of detecting internal structures in the ice and changes in the position of internal layering over time.

After a couple of hours at the Russian base, it’s time to fly to the Princess Elisabeth Station (the Belgium base, PEA). The arrival in a Bassler (a former DC3 re-equipped with turbo-props) with stunning views of the Sor Rondane Mountains and the Princess Elisabeth station on the Utsteinen rim is simply magnificent. Alain Hubert, the base manager, gives us the first security rules and shows us the different parts of the base.

(Credit B. Van Liefferinge)

(Credit B. Van Liefferinge)

 

After following the various field training and especially an exercise that aims at pulling yourself out of crevasses, it’s time to inspect, to set up, and to test our equipment. While one part of the team sets up the drill, Frank Pattyn and I test the GPS and radar equipment, mainly the ApRES that is a new “toy” for us. The first results are promising, we can clearly identify the bed topography and internal layers. The two GPS systems sponsored by the “10km of the ULB”, a run organised by the students of our Faculty, are also tested next to the L1L2 GPS systems for precise positioning. As our departure is imminent, I’m excited (even though my level of Coca-cola are getting low – I ‘m an avid consumer of this “evil drink” and Frank was afraid that I wouldn’t survive without sufficient sugar intake).

(Credit B. Van Liefferinge)

(Credit B. Van Liefferinge)

On 27 November, we leave PEA in the evening for one night and one day across the Roi Baudouin Ice Shelf to Derwael ice rise. We are 6 scientists, 2 field guides and 1 technician. After 25 hours of travel, we set up the camp on the top of the divide. We start immediately with the radar measurements to locate potential drill sites. However, we get caught in a storm the following day and as Frank says “not a nice one”.

(Credit F. Pattyn and B. Van Liefferinge)

(Credit F. Pattyn and B. Van Liefferinge)

 

The snow drift is just amazing and the atmospheric pressure drops frighteningly (“can this still go lower?”). The whiteboard installed in the living container is not wide enough to draw the graph of pressure change, nor is it high enough to accommodate the lowest values. Furthermore, it’s quite warm, meaning that snow melts in contact with persons and goods. Despite efforts of everyone to clear away the snow, we leave our tents and sleep in the containers for 2 days. Not the most comfortable nights, because we share a two-bunk space with three people, and despite a container it remains very shaky! After three days of amazing experience, we clean up the camp and the science restarts. For one week Frank and I perform radar and GPS measurements in a 10km radius around the camp. These measurements will be repeated in 2015-2016 to provide new data on ice compaction, density and flow. While Frank thoroughly checks the collected data, I have some time to get familiar with the drill, which should prove to be very useful thereafter. The “drill part” led by Jean-Louis Tison and Morgane Philippe aims at drilling two 30 m deep ice cores on Derwael Ice Rise, 2 km on each side of the divide. We want to investigate the spatial variability of snow accumulation induced by this ice rise that sticks approximately 300 m above the surrounding flat ice shelf and therefore perturbs the surface mass balance distribution (Lenaerts et al., 2014).

Blog_EGU (12)_mod

(Credit B. Van Liefferinge)

(Credit F. Pattyn and B. Van Liefferinge)

I use this week to improve my knowledge on other scientific techniques, such as the coffee-can method (will complement the results from the ApRES) or geodetic GPS measurements with Nicolas Bergeot. I also learn the basics of snowmobile mechanics (it’s surprising to see the amount of snow that can be put in an engine!). Unfortunately we get stuck for another 2 days by a new storm event. We use this time to have a look on the first radar profiles and to prepare the second part of the expedition.

 

 

On 9 December, we leave the camp on Derwael ice rise and move towards the Roi Baudouin Ice Shelf, 40km to the west. We set up the camp in a longitudinal depression (like a trench) on the ice shelf that stretches from the grounding line to the coast.

The purpose of this part of the field work is twofold: first of all, determine the mass budget of ice shelves. To do that, we need to map carefully the flow speed of the ice-shelf. Secondly, understand the formation of the trench in evaluating if under the ice-shelf, the ice is melting or accreting (formation of marine ice) and analyze the surface melt history by investigating near-surface melt layers.

The first three days are devoted to make radar measurements (ApRES) in the center and on the sides of the trench. The thickness of ice and the reflection at the interface with the ocean is different from the one on the ice rise; we take some time to develop a robust method and determine the best settings of the radar. Together with Frank Pattyn and Jan Lenaerts (InBev Baillet Latour fellowship, http://benemelt.blogspot.be/) I perform a 120km transect with a high-frequency radar towed by a snowmobile to map the near-surface internal structure along the ice shelf and link the drill site with the grounding zone. Driving at 8 km per hour for 8 hours a day, it’s an opportunity for me to think about how lucky I am to be here. Alone in the vastness of the Roi Baudouin ice-shelf, I feel very small. Back in camp, we find out that the drill got stuck at a depth of 54m in the borehole and preparations to free the drill are on their way. During this time I carry out a number of high-frequency radar measurements with Alain Hubert (the base manager) to fine-tune the equipment to potentially detect crevasses near the surface. To our surprise, we stumble upon a crevasse more than 500m long, 10m wide and 20m high. Moreover, we can safely descend through the apex of the crevasse to discover its vastness. Truly a magic moment!

(Credit A. Hubert)

(Credit A. Hubert)

 

Thirty-six hours later, and thanks to antifreeze, the drill restarts. This small technical incident pushes us to work the next couple of days through the day and the night (under the sun at 3am is rather special) and we take turns in operating the drill. We reach a depth of 107m, not far from the 155 meters needed to reach the bottom of the ice shelf, but the brittle ice makes progress very difficult. Nevertheless, this is the third core of the (short) season, and as valuable as the previous ones. We can clearly identify every single ice layer over 200 years as well as the surface melting history.

(Credit A. Hubert)

(Credit A. Hubert)

Before leaving back to the base, we finish the installation of the famous Tweetin’IceShelf project (http://tweetiniceshelf.blogspot.com); a project also presented at the EGU General Assembly in 2015. We deploy two GPSes on the flanks of the trench and one in the center. These are simple GPS systems that record their position every hour. They are named GPS CGEO (from Cercle de Géographie et de Géologie de l’ULB) and GPS CdS (from Cercle des Sciences). In the center of the trench, the ApRES is installed which measures once a day the radar signal through the ice. All systems will be effective throughout the Antarctic winter. Data are sent via Twitter to be followed by a larger community. Just follow the @TweetinIceShelf on Twitter. You will not be disappointed.

(Credit F. Pattyn)

(Credit F. Pattyn)

It’s time to go back to the station, which is reached after 20 hours of travel across the ice shelf and the coastal ice sheet. Over 2 days we will be at Cape Town and we have to clean up everything for the next field season.

(Credit N. Bergeot)

(Credit N. Bergeot)

 

I know it is my first time to Antarctica, and as most first-timers, an unforgettable experience of vastness, whiteness, silence, laughter, hard work and fun. When I board the plane I feel delighted and fulfilled and ready to find back green landscapes and city soundscapes in less than ten hours.

The text is based on the blog that was held during the mission: http://icecon2012.blogspot.be/

Edited by Sophie Berger


Brice Van Liefferinge is a PhD student and a teaching assistant at the Laboratoire de Glaciology, Universite Libre de Bruxelles, Belgium. His research focuses on the basal conditions of the ice sheets.

Glaciers on Mars

Glaciers on Mars

“I did not know that there is water on Mars!” This a sentence I hear surprisingly often when I talk about glaciers on Mars. In fact, it has been known for some time that water exists in the form of ice and water vapour on the planet. For example, water ice layers several kilometres thick cover the Martian poles, and the ground close to the Polar Regions has permafrost patterns very similar to what we see on Earth.

The glaciers on Mars were discovered in the 1970s on images from the Viking missions. From the images it was evident that features made up of a soft, deforming material existed in some parts of the planet. At the time, it was suggested that the features might consist of a mixture of water ice, CO2 ice or perhaps mud.

More than 10,000 water ice bodies (blue dots) have been found between 30 and 50 degrees (blue lines). Credit: Mars Digital Image Model, NASA/J. Levy/Nanna Karlsson

More than 10,000 water ice bodies (blue dots) have been found between 30 and 50 degrees (blue lines). Credit: Mars Digital Image Model, NASA/J. Levy/Nanna B. Karlsson

In 2005, NASA launched the satellite Mars Reconnaissance Orbiter that carried amongst other instruments the SHARAD (SHAllow RADar) sounder. The instrument emitted radar waves that could penetrate the surface of the planet, and return information on what was below the dusty surface. The mission proved successful and – amongst many other discoveries – the SHARAD measurements showed that the glaciers consist of more than 90% water ice .

We now know the composition of the glaciers but many questions remain. One extremely interesting observation is the fact that the glaciers are only found in particular latitude bands: between 30 and 50 degrees on both hemispheres. A recent study has mapped more than 10,000 features in these latitudes. In other words, the glaciers are much more abundant than initially thought, but why are they there in the first place? The answer is probably to be found somewhere in Mars’s past. More than 5 million years ago, the amount of solar insolation at the poles of Mars was dramatically different compared to today. Models have shown that during this time water ice at the poles would have been unstable and possibly migrated to the midlatitudes. When the climate changed, again the water migrated back to the poles. The glaciers could therefore be remnants of a past, large ice sheet.

CTX imagery of a glacier surrounding a central massif. Credit: CTX/JMars.

CTX imagery of a glacier surrounding a central massif. Credit: CTX/JMars.

How much water do the glaciers contain then? To answer this question, we can use knowledge of glaciers on Earth. A glacier is essentially a big chunk of ice, and when it flows, it obtains a shape that tells us something about how soft the ice is. Water ice moves and deforms in a certain way, and the slope of the surface of a glacier therefore reveals information about the bed under the glacier. Looking at images of the Martian surface, we can see where the glaciers are, and from the Mars Orbiter Laser Altimeter we know the surface elevation. This allows us to setup models for how the ice behaves on Mars.

Combining the models with the radar measurements and maps of the glaciers, it turned out that the glaciers contain more than 150 thousand cubic kilometres of ice. This amount of ice may cover the surface of the planet in a 1.1 metres thick ice layer.

Dust covered water ice close to the south pole and white CO2-ice.

Dust covered water ice close to the south pole and white CO2-ice. Credit: ESA/DLR/FU Berlin.

If you want to know more about glaciers on Mars check out my recent paper published in Geophysical Research Letters. You can also meet me at the EGU General Assembly next week and listen to my talk at 8:30am, Wednesday the 15th of April in Room R13 (Session CR6.1Modelling ice sheets and glaciers).