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Cryospheric Sciences

Ice shelf

Image of the Week — Hidden lakes in East Antarctica !

Image of the Week — Hidden lakes in East Antarctica !

Who would have guessed that such a beautiful picture could get you interviewed for the national news?! Certainly not me! And yet, the photo of this englacial lake (a lake trapped within the ice in Antarctica), or rather science behind it, managed to capture the media attention and brought me, one of the happy co-author of this study,  on the Belgian  television… But what do we see on the picture and why is that interesting?


Where was the picture taken?

The Image of this Week shows a 4m-deep meltwater lake trapped 4 m under the surface of the Roi Baudouin Ice Shelf (a coastal area in East Antarctica). To capture this shot, a team of scientists led by Stef Lhermitte (TU Delft) and Jan Lenaerts (Utrecht University) went to the Roi Baudouin ice shelf, drilled a hole and lowered a camera down (see video 1).

Video 1 : Camera lowered into borehole to show an englacial lake 4m below the surface. [Credit: S. Lhermitte]

How was the lake formed?

In this region of East Antarctica, the katabatic winds are very persistent and come down from the centre of the ice sheet towards the coast, that is the floating ice shelf (see animation below). The effect of the winds are two-fold:

  1. They warm the surface because the temperature of the air mass increases during its descent and the katabatic winds mix the very cold layer of air right above the surface with warmer layers that lie above.
  2. They sweep the very bright snow away, revealing darker snow/ice, which absorb more solar radiation

The combination leads to more melting of the ice/snow in the grounding zone — the boundary between the ice sheet and ice shelf — , which further darkens the surface and therefore increases the amount of solar radiation absorbed, leading to more melting, etc. (This vicious circle is very similar to the ice-albedo feedback presented in this previous post).

Animation showing the processes causing the warm micro-climate on the ice shelf. [Credit: S. Lhermitte]

All the melted ice flows downstream and collects in depressions to form (sub)surface lakes. Those lakes are moving towards the ocean with the surrounding ice and are progressively buried by snowfalls to become englacial lakes. Alternatively, the meltwater can also form surface streams that drain in moulins (see video 2).

Video 2 : Meltwater streams and moulins that drain the water on the Roi Baudouin ice shelf. [Credit: S. Lhermitte]

Why does it matter ?

So far we’ve seen pretty images but you might wonder what could possibly justify an appearance in the national news… Unlike in Greenland, ice loss by surface melting has  often been considered negligible in Antarctica. Meltwater can however threaten the structural integrity of ice shelves, which act as a plug of the grounded ice from upstream. Surface melting and ponding was indeed one of the triggers of the dramatic ice shelves collapses in the past decades, in the Antarctic Peninsula . For instance, the many surfaces lakes on the surface of the Larsen Ice shelf in January 2002, fractured and weakened the ice shelf until it finally broke up (see video 3), releasing more grounded ice to the ocean than it used to do.

Of course surface ponding is not the only precondition for an ice shelf to collapse : ice shelves in the Peninsula had progressively thinned and weakened for decades, prior their disintegration. Our study suggests however that surface processes in East Antarctica are more important than previously thought, which means that this part of the continent is probably more vulnerable to climate change than previously assumed. In the future, warmer climates will intensify melt, increasing the risk to destabilise the East Antarctic ice sheet.

Video 3 : MODIS images show Larsen-B collapse between January 31 and April 13, 2002. [Credit:NASA/Goddard Space Flight Center ]

Reference/Further reading

Edited by Nanna Karlsson

Image of the Week — Allez Halley!

Image of the Week — Allez Halley!

On the Brunt Ice Shelf, Antarctica, a never-observed-before migration has just begun. As the pale summer sun allows the slow ballet of the supply vessels to restart, men and machines alike must make the most of the short clement season. It is time. At last, the Halley VI research station is on the move!


Halley, sixth of its name

Since 1956, the British Antarctic Survey (BAS) has maintained a research station on the south eastern coast of the Weddell Sea. Named after the 17th century British astronomer Edmond Halley (also the namesake of Halley’s comet), this atmospheric research station is, amongst other things, famous for the measurements that led to the discovery of the ozone hole (Farman et al., 1985).

Due to the inhospitable nature of Antarctica, there have been six successive Halley research stations:

  • Halley I to IV had to be abandoned and replaced when they got buried too deeply beneath the snow that accumulated over their lifetimes (up to ten years per station).
  • Halley V was built on steel platforms that were raised periodically, so the station did not end up buried under snow. However, Halley V was flowing towards the ocean along with the ice shelf when a crack in the ice formed. To avoid finishing up as an iceberg, the station was demolished in 2012.
  • Halley VI, active since 2012, can be raised above the snow and also features skis, so that it can be towed to a safer location if the ice shelf again threatens to crack. However, no one expected that this would have to be put in practice less than 5 years after the station’s opening…

The relocation project, featuring the new October crack. Inset, timeline of the awakening of Chasm 1. The ice shelf flows approximately from right to left. [Credit: British Antarctic Survey].

The awakening of the cracks

The project of moving Halley VI was announced a year ago. A very deep crack in the ice (“Chasm 1” in the map above) upstream of the station and dormant for 35 years, started growing again barely a year after the opening of Halley VI. The risk of losing the station if this part of the ice shelf broke off as an iceberg became obvious, and it was decided to move the station upstream – beyond the crack.

Additionally, there is another problem, or rather another crack, which appeared last October. This one is located north of the station and runs across a route used to resupply Halley VI. This means that of the two locations where a supply ship would normally dock, one is no longer connected to the research station and hence rather useless. Not only is the station now encircled by deep cracks, now it also has only one resupply route remaining; to bring equipment, personnel and food and fuel supplies to the station – all of which are needed to successfully pull off the station relocation.

Bringing Halley VI to its new location before the end of the short Antarctic summer season will be a challenge. We shall certainly keep you up-to-date with Halley news as well as with news about the rapid changes of the Brunt Ice Shelf (because we’re the Cryosphere blog after all!). In the meantime, you can feel like a polar explorer and enjoy this (virtual) visit of Halley VI.

References and further reading

Edited by Clara Burgard, Sophie Berger and Emma Smith

Image of the Week – Climate Change and the Cryosphere

Image of the Week – Climate Change and the Cryosphere

While the first week of COP22 – the climate talks in Marrakech – is coming to an end, the recent election of Donald Trump as the next President of the United States casts doubt over the fate of the Paris Agreement and more generally the global fight against climate change.

In this new political context, we must not forget about the scientific evidence of climate change! Our figure of the week, today summarises how climate change affects the cryosphere, as exposed in the latest assessment report of the Intergovernmental Panel on Climate Change (IPCC, 2013, chapter 4)


Observed changes in the cryosphere

Glaciers (excluding Greenland and Antarctica)

  • Glaciers are the component of the cryosphere that currently contributes the most to sea-level rise.
  • Their sea-level contribution has increased since the 1960s. Glaciers around the world contributed to the sea-level rise from 0.76 mm/yr (during the 1993-2009 period) to 0.83 mm/yr (over the 2005-2009 period)

Sea Ice in the Arctic

  • sea-ice extent is declining, with a rate of 3.8% /decade (over the 1979-2012 period)
  • The extent of thick multiyear ice is shrinking faster, with a rate of 13.5%/decade (over the 1979-2012 period)
  • Sea-ice decline sea ice is stronger in summer and autumn
  • On average, sea ice thinned by 1.3 – 2.3 m between 1980 and 2008.

Ice Shelves and ice tongues

  • Ice shelves of the Antarctic Peninsula have continuously retreated and collapsed
  • Some ice tongue and ice shelves are progressively thinning in Antarctica and Greenland.

Ice Sheets

  • The Greenland and Antarctic ice sheets have lost mass and contributed to sea-level rise over the last 20 years
  • Ice loss of major outlet glaciers in Antarctica and Greenland has accelerated, since the 1990s

Permafrost/Frozen Ground

  • Since the early 1980s, permafrost has warmed by up to 2ºC and the active layer – the top layer that thaw in summer and freezes in winter – has thickened by up to 90 cm.
  • Since mid 1970s, the southern limit of permafrost (in the Northern Hemisphere) has been moving north.
  • Since 1930s, the thickness of the seasonal frozen ground has decreased by 32 cm.

Snow cover

  • Snow cover declined between 1967 and 2012 (according to satellite data)
  • Largest decreases in June (53%).

Lake and river ice

  • The freezing duration has shorten : lake and river freeze up later in autumn and ice breaks up sooner in spring
  • delays in autumn freeze-up occur more slowly than advances in spring break-up, though both phenomenons have accelerated in the Northern Hemisphere

Further reading

How much can President Trump impact climate change?

What Trump can—and can’t—do all by himself on climate | Science

US election: Climate scientists react to Donald Trump’s victory  | Carbon Brief

Which Trump will govern, the showman or the negotiator? | Climate Home

GeoPolicy: What will a Trump presidency mean for climate change? | Geolog

Previous posts about IPCC reports

Image of the Week — Ice Sheets and Sea Level Rise

Image of the Week —  Changes in Snow Cover

Image of the Week — Atmospheric CO2 from ice cores

Image of the Week — Ice Sheets in the Climate

Edited by Emma Smith

Image of the Week — FRISP 2016

Image of the Week — FRISP 2016

The Forum for Research into Ice Shelf Processes, aka FRISP, is an international meeting bringing together glaciologists and oceanographers. There are no parallel sessions; everyone attends everyone else’s talk and comment on their results, and the numerous breaks and long dinners encourage new and interdisciplinary collaborations. In fact, each year, a few presentations are the result of a previous year’s question!

The location changes every year, moving around the institutions that are involved with Arctic and Antarctic research. The 2016 edition just occurred this week, 3rd – 6th October, in a marine research station of the University of Gothenburg, in the beautiful Gullmarn Fjord.

Each year, a few presentations are the result of a previous year’s question!

Fjord at the sunset [Credit: Céline Heuzé]

Gullmarn fjord at the sunset [Credit: Céline Heuzé]

70 participants from 37 institutions:

  • Attended 49 talks on model results, new observation techniques, and everything in between;

  • Spent more than 15h discussing these results, including 2h around 15 posters;

  • Drank 50 L of coffee, 60 L of tea, 20 L of lingon juice… and a fair amount of wine!

Poster session at the FRISP 2016 meeting. [Credit: Céline Heuzé]

Poster session at the FRISP 2016 meeting. [Credit: Céline Heuzé]

I can’t really choose THE highlight of the conference.
As an organiser, it was a real pleasure to simply see it happen after all the long hours of planning.
As a scientist, it was a great and productive meeting, giving me new ideas and the opportunity to discuss my recent work with the big names of the field in a friendly environment.
And as a human, I enjoyed most the under-ice footages, and in particular the general ”ooooh” that came from the audience.

It was a bit sad to say goodbye to the participants, old friends and new collaborators. But I know that I will see them again during FRISP 2017… and I hope to see you there as well!

 Edited by Sophie Berger and Emma Smith

Image of the Week – How ocean tides affect ice flow

Image of the Week – How ocean tides affect ice flow

Ice streams discharge approximately 90% of the Antarctic ice onto ice shelves , and ultimately into the sea into the sea (Bamber et al., 2000; Rignot et al., 2011). Whilst flow-speed changes on annual timescales are frequently discussed, we consider here what happens on much shorter timescales!

Previous studies have shown that ice streams can respond to ocean tides at distances up to 100km inland (e.g. Gudmundsson, 2006 ; Murray et al., 2007; Rosier et al, 2014); new high-resolution remotely sensed data provide a synpoptic-scale view of the response of ice flow in Rutford Ice Stream (West Antarctica), to ocean tidal motion.

These are the first results to capture the flow of an entire ice stream and its proximal ice shelf in all three spatial dimensions and in time.

The ocean controls the Antarctic ice sheet

The ice-ocean interface is very important as nearly all ice-mass loss occurs directly into the ocean in Antarctica (Shepherd et al., 2012). Many areas terminate on ice shelves (the floating ice that connects with the land ice), which are fed by the flow of ice from the ice sheet. Any changes to the floating ice shelf alter the forces acting on the grounded ice upstream, therefore directly affecting the ice sheet evolution (e.g. Gudmundsson, 2013; Scambos et al, 2004).

Because ocean tides are well-understood, we can use the response of grounded ice streams to ocean tidal uplift over the ice shelf to better understand how ice sheets respond to ocean-induced changes.

An ice stream and ice shelf respond to forcing by ocean tides

Floating ice shelves are directly affected by tides, as their vertical displacement will be altered. These tidal variations are on short timescales (hourly to daily) compared to the timescales generally associated with ice flow (yearly). The question therefore is, how much can the tides affect horizontal flow speeds, and how far inland of the ice shelf are these effects felt?

The movie below, by Brent Minchew et al, shows the significant response of Rutford Ice Stream and its ice shelf to forcing by the tides. Using high-resolution synthetic aperture radar data they are able to infer the significant spatio-temporal response of Rutford Ice Stream in West Antarctica to ocean tidal forcing. The flow is modulated by the ocean tides to nearly 100km inland of the grounding line. These flow variations propagate inland at a mean rate of approximately 30 km/day and are sensitive to local ice thickness and the mechanical properties of the ice-bed interface. Variations in horizontal ice flow originate over the ice shelf, indicating a change in (restraining force) over tidal timescales, which is largely attributable to the ice shelf lifting off of shallow bathymetry near the margins. Upstream propagation of ice flow variations provides insights into the sensitivity of grounded ice streams to variations in ice shelf buttressing.

Horizontal ice flow on Rutford Ice Stream inferred from 9 months of continuous synthetic aperture radar observations. (a) Total horizontal flow. Colormap indicates horizontal speed and arrows give flow direction. (b) Detrended horizontal flow variability over a 14.77-day period. Colormap indicates the along-flow component (negative values oppose flow) while arrows indicate magnitude and direction of tidal variability. Contour lines give secular horizontal speed in 20 cm/day increments. (c) Modelled vertical tidal displacement over the ice shelf. (Credit : Brent Minchew)

Reference

B. M. Minchew, M. Simons, B. V. Riel, and P. Milillo. Tidally induced variations in vertical and horizontal motion on Rutford Ice Stream, West Antarctica, inferred from remotely sensed observations. submitted to JGR, 2016

(Edited by Sophie Berger and Emma Smith)


facepic

Teresa Kyrke-Smith is a postdoctoral researcher at the British Antarctic Survey, on the iSTAR grant. She works on using inversion methods to learn about the nature of basal control on the flow of Pine Island Glacier in West Antarctica. She completed her PhD two years ago in Oxford; her thesis focused on the feedbacks between ice streams and subglacial hydrology.

Brent Minchew is an National Science Foundation Postdoctoral Fellow also now based at the British Antarctic Survey.


 

 

Marine Ice Sheet Instability “For Dummies”

Marine Ice Sheet Instability “For Dummies”

MISI is a term that is often thrown into dicussions and papers which talk about the contribution of Antarctica to sea-level rise but what does it actually mean and why do we care about it?

MISI stands for Marine Ice Sheet Instability. In this article, we are going to attempt to explain this term to you and also show you why it is so important.


Background

The Antarctic Ice Sheet represents the largest potential source of future sea-level rise: if all its ice melted, sea level would rise by about 60 m (Vaughan et al., 2013). According to satellite observations, the Antarctic Ice Sheet has lost 1350 Gt (gigatonnes) of ice between 1992 and 2011 (1 Gt = 1000 million tonnes), equivalent to an increase in sea level of 3.75 mm or 0.00375 m (Shepherd et al., 2012). 3.75 mm does not seem a lot but imagine that this sea-level rise is evenly spread over all the oceans on Earth, i.e. over a surface of about 360 million km², leading to a total volume of about 1350 km³, i.e. 1350 Gt of water… The loss over this period is mainly due to increased ice discharge into the ocean in two rapidly changing regions: West Antarctica and the Antarctic Peninsula (Figure 1, blue and orange curves respectively).

Figure 1: Cumulative ice mass changes (left axis) and equivalent sea-level contribution (right axis) of the different Antarctic regions based on different satellite observations (ERS-1/2, Envisat, ICESat, GRACE) from 1992 to 2011 (source: adapted from Fig. 5 of Shepherd et al., 2012 ) with addition of inset: Antarctic map showing the different regions ( source )

What are the projections for the future?

Figure 2: Ice velocity of the glaciers in the Amundsen Sea Embayment, West Antarctica, using ERS-1/2 radar data in winter 1996. The grounding line (boundary between ice sheet and ice shelf) is shown for 1992, 1994, 1996, 2000 and 2011 (source: Fig. 1 of Rignot et al., 2014 ).

Figure 2: Ice velocity of the glaciers in the Amundsen Sea Embayment, West Antarctica, using ERS-1/2 radar data in winter 1996. The grounding line (boundary between ice sheet and ice shelf) is shown for 1992, 1994, 1996, 2000 and 2011 (source: Fig. 1 of Rignot et al., 2014 ).

According to model projections from the Intergovernmental Panel on Climate Change (IPCC), global mean sea level will rise by 0.26 to 0.82 m during the twenty-first century (Church et al., 2013). The contribution from the Antarctic Ice Sheet in those projections will be about 0.05 m (or 50 mm) sea-level equivalent, i.e. 10% of the global projected sea-level rise, with other contributions coming from thermal expansion (40 %), glaciers (25 %), Greenland Ice Sheet (17 %) and land water storage (8 %).

The contribution from Antarctica compared to other contributions does not seem huge, however there is a high uncertainty coming from the possible instability of the West Antarctic Ice Sheet. According to theoretical (Weertman, 1974; Schoof, 2007) and recent modeling results (e.g. Favier et al., 2014; Joughin et al., 2014), this region could be subject to marine ice sheet instability (MISI), which could lead to considerable and rapid ice discharge from Antarctica. Satellite observations show that MISI may be under way in the Amundsen Sea Embayment (Rignot et al., 2014), where some of the fastest flowing glaciers on Earth are located, e.g. Pine Island and Thwaites glaciers (Figure 2). So what exactly is MISI?

What is marine ice sheet instability (MISI)?

 

Figure 3: Antarctic map of ice sheet (blue), ice shelves (orange) and islands/ice rises (green) based on satellite data (ICESat and MODIS). The grounding line is the separation between the ice sheet and the ice shelves. Units on X and Y axes are km (source: NASA ).

Figure 3: Antarctic map of ice sheet (blue), ice shelves (orange) and islands/ice rises (green) based on satellite data (ICESat and MODIS). The grounding line is the separation between the ice sheet and the ice shelves. Units on X and Y axes are km (source: NASA ).

To understand the concept of MISI, it is important to define both ‘marine ice sheet’ and ‘grounding line’:

 

  • A marine ice sheet is an ice sheet sitting on a bedrock that is below sea level, for example the West Antarctic Ice Sheet.
  • The grounding line is the boundary between the ice sheet, sitting on land, and the floating ice shelves (Figure 3 for a view from above and Figure 4 for a side view). The position and migration of this grounding line control the stability of a marine ice sheet.

 

 

The MISI hypothesis states that when the bedrock slopes down from the coast towards the interior of the marine ice sheet, which is the case in large parts of West Antarctica, the grounding line is not stable (in the absence of back forces provided by ice shelves, see next section for more details). To explain this concept, let us take the schematic example shown in Figure 4:

  1. The grounding line is initially located on a bedrock sill (Figure 4a). This position is stable: the ice flux at the grounding line, which is the amount of ice passing through the grounding line per unit time, matches the total upstream accumulation.
  2. A perturbation is applied at the grounding line, e.g. through the incursion of warm Circumpolar Deep Water (CDW, red arrow in Figure 4) below the ice shelf as observed in the Amundsen Sea Embayment.
  3. These warm waters lead to basal melting at the grounding line, ice-shelf thinning and glacier acceleration, resulting in an inland retreat of the grounding line.
  4. The grounding line is then located on a bedrock that slopes downward inland (Figure 4b), i.e. an unstable position where the ice column at the grounding line is thicker than previously (Figure 4a). The theory shows that ice flux at the grounding line is strongly dependent on ice thickness there (Weertman, 1974; Schoof, 2007), so a thicker ice leads to a higher ice flux.
  5. Then, the grounding line is forced to retreat since the ice flux at the grounding line is higher than the upstream accumulation.
  6. This is a positive feedback and the retreat only stops once a new stable position is reached (e.g. a bedrock high), where both ice flux at the grounding line and upstream accumulation match.
Figure 4: Schematic representation of the marine ice sheet instability (MISI) with (a) an initial stable grounding-line position and (b) an unstable grounding-line position after the incursion of warm Circumpolar Deep Water (CDW) below the ice shelf (source: Fig. 3 of Hanna et al., 2013 ).

Figure 4: Schematic representation of the marine ice sheet instability (MISI) with (a) an initial stable grounding-line position and (b) an unstable grounding-line position after the incursion of warm Circumpolar Deep Water (CDW) below the ice shelf (source: Fig. 3 of Hanna et al., 2013 ).

  • In summary, the MISI hypothesis describes the condition where a marine ice sheet is unstable due to being grounded below sea level on land that is sloping downward from the coast to the interior of the ice sheet.
  • This configuration leads to potential rapid retreat of the grounding line and speed up of ice flow from the interior of the continent into the oceans.

Is there evidence that MISI is happening right now?

 

Figure 5: Buttressing provided by Larsen C ice shelf, Antarctic Peninsula, based on a model simulation (Elmer/Ice). Buttressing values range between 0 (no buttressing) and 1 (high buttressing). The red contour shows the buttressing=0.3 isoline. Observed ice velocity is also shown (source: Fig. 2 of Fürst et al., 2016 ).

Figure 5: Buttressing provided by Larsen C ice shelf, Antarctic Peninsula, based on a model simulation (Elmer/Ice). Buttressing values range between 0 (no buttressing) and 1 (high buttressing). The red contour shows the buttressing=0.3 isoline. Observed ice velocity is also shown (source: Fig. 2 of Fürst et al., 2016 ).

In reality, the grounding line is often stabilized by an ice shelf that is laterally confined by side walls (see Figure 5, where Bawden and Gipps ice rises confine Larsen C ice shelf) or by an ice shelf that has a contact with a locally grounded feature (Figure 6). Both cases transmit a back force towards the ice sheet, the ‘buttressing effect’, which stabilizes the grounding line (Goldberg et al., 2009; Gudmundsson, 2013) even if the configuration is unstable, i.e. in the case of a grounding line located on a bedrock sloping down towards the interior (Figure 4b).

 

However, in the last two decades, the grounding lines of the glaciers in the Amundsen Sea Embayment (Pine Island and Thwaites glaciers for example) retreated with rates of 1 to 2 km per year, in regions of bedrock sloping down towards the ice sheet interior (Rignot et al., 2014). The trigger of these grounding-line retreats is the incursion of warm CDW penetrating deeply into cavities below the ice shelves (Jacobs et al., 2011), carrying important amounts of heat that melt the base of ice shelves (Figure 4). Increased basal melt rates have led to ice-shelf thinning, which has reduced the ice-shelf buttressing effect and increased ice discharge. All of this has led to grounding-line retreat. The exact cause of CDW changes is not clearly known but these incursions are probably linked to changes in local wind stress (Steig et al., 2012) rather than an actual warming of CDW.

 

 

Figure 6: Schematic representation of ice-shelf buttressing by a local pinning point (source: courtesy of R. Drews ).

Figure 6: Schematic representation of ice-shelf buttressing by a local pinning point (source: courtesy of R. Drews ).

There is currently no major obstacle to these grounding line retreats. Therefore, the Amundsen Sea Embayment is probably experiencing MISI and glaciers will continue to retreat if no stabilization is reached. This sector of West Antarctica contains enough ice to raise global sea level by 1.2 m.

 

What can we do about it?

MISI is probably ongoing in some parts of Antarctica and sea level could rise more than previously estimated if the grounding lines of the glaciers in the Amundsen Sea Embayment continue to retreat so fast. This could have catastrophic impacts on populations living close to the coasts, for example more frequent flooding of coastal cities, enhanced coastal erosion or changes in water quality.

Thus, it is important to continue monitoring the changes happening in Antarctica, and particularly in West Antarctica. This will allow us to better understand and project future sea-level rise from this region, as well as better adapt the cities of tomorrow.

Edited by Clara Burgard and Emma Smith


DavidDavid Docquier is a post-doctoral researcher at the Earth and Life Institute of Université catholique de Louvain (UCL) in Belgium. He works on the development of processed-based sea-ice metrics in order to improve the evaluation of global climate models (GCMs). His study is embedded within the EU Horizon 2020 PRIMAVERA project, which aims at developing a new generation of high-resolution GCMs to better represent the climate.

Image of the Week: Under the Sea

Image of the Week: Under the Sea

Always wondered how it looks like under the sea ice?
Getting an answer is simpler than you might think: Just go out to the front of McMurdo ice shelf in Antarctica and drill a tube into the sea ice. Then let people climb down and take pictures of the ice from below.
More information:
– Photo taken by Marcus Arnold, Gateway Antarctica, University of Canterbury during his November 2015, Antarctic Expedition.
– More photos of their expedition on https://instagram.com/the_ross_ice_shelf_programme/

Image of the Week: Antarctic ice-shelf thickness

Image of the Week: Antarctic ice-shelf thickness

Thickness of floating ice shelves in Antarctica. Ice thickness is greatest close to the grounding line where it can reach 1000 meters or more (red). Away from the grounding line, the ice rapidly thins to reach a few hundreds of meters at the calving front. Ice thickness varies greatly from one ice shelf to another. Within ice shelves, “streams of ice” can be spotted originating from individual tributary glaciers and ice streams.

This dataset was used to compute calving fluxes and basal melt rates of Antarctic ice shelves (see Depoorter et al, 2013). This ice thickness map was derived from altimetry data (ERS and ICESat) acquired between 1994 and 2009 and corrected for elevation changes during this period.

Follow this link to download the georeferenced map and see Depoorter et al (2013)‘s paper for more information.

Image of the week : formation of an ice rise

Image of the week : formation of an ice rise

Deglaciation and formation of an ice rise with the ice-sheet model BISICLES.  The simulation starts with an ice sheet in steady state that overrides a topographic high in the bed, close to the calving front. The sea level is then forced to rise steadily with 1 cm per year during 15 thousand years, and the simulation goes on until the ice sheet reaches steady state.
The animation below shows that the formation of an ice rise delays the grounding line retreat.

For more information see Favier and Pattyn (2015)‘s recent paper.

movieicerise

The  movie shows the ice sheet retreat and the ice rise formation and evolution in between the two steady states. The movie starts after 5 thousands years of sea level rise. The ice upper surface is colored as a function of the velocity magnitude. The ice lower surface is colored either in light gray for floating ice or dark gray for grounded ice. Credit: L. Favier.