CR
Cryospheric Sciences

Image of the Week

Image of the Week – Ice on Fire (Part 2)

Image of the Week – Ice on Fire (Part 2)

This week’s image looks like something out of a science fiction movie, but sometimes what we find on Earth is even more strange than what we can imagine! Where the heat of volcanoes meets the icy cold of glaciers strange and wonderful landscapes are formed. 


Location of the Kamchatka Peninsula [Credit: Encyclopaedia Britannica]

The Kamchatka Peninsula, in the far East of Russia, has the highest concentration of active volcanoes on Earth. Its climate is cold due to the Arctic winds from Siberia combined with cold sea currents passing through the Bearing Strait, meaning much of it is glaciated.

Mutnovsky is a volcano located in the south of the peninsula, which last erupted in March 2000. At the base of the volcano are numerous labyrinths of caves within ice. The caves are carved into the ice by volcanically heated water. The roof of the cave shown in our image of the week is thin enough to allow sunlight to penetrate. The light is filtered by the ice creating a magical environment inside the cave, which looks a bit like the stained glass windows of a cathedral. It is not always easy to access these caves, but when the conditions are favourable it makes for a wonderful sight!

The Mutnovsky volcano is fairly accessible for tourists, around 70 km south of the city of Petropavlovsk-Kamchatsky. Maybe this could be the holiday destination you have been searching for?

Further Reading

We have featured a number of stories about ice-volcano interaction on our blog before, read more about them here, here and here!

Edited by Sophie Berger

Image of The Week – Ice Flows!

Image of The Week – Ice Flows!

Portraying ice sheets and shelves to the general public can be tricky. They are in remote locations, meaning the majority of people will never have seen them. They also change over timescales that are often hard to represent without showing dramatic images of more unusual events such as the collapse of the Larsen B Ice Shelf.  However, an app launched in the summer at the SCAR (Scientific Committee for Antarctic Research) Open Science Conference in Kuala Lumpur set out to change this through a game. Developed by Anne Le Brocq from the University of Exeter, this game is aptly named – Ice Flows!


The game in a nutshell!

Ice Flows is a game that allows the player to control various variables of an ice shelf (floating portion of an ice sheet) environment, such as ocean temperature and snowfall, and see the changes that these cause. For example, increasing the amount of snowfall increases the ice thickness but increasing the ocean temperature causes thinning of the ice shelf. The aim of the game is to help penguins feed by altering the variables to create ice shelf conditions which give them access to the ocean. Although the game is based around penguins, importantly, it is changing the ice shelf environment that the player controls, this allows a player to investigate how changing environmental conditions affect the ice. Our Image of the week shows a still from the game, where the player has created ice conditions which allow the penguins to dive down and catch fish.

What is the educational message?

The polar regions are constantly changing and assigning these changes to either natural cycles or anthropogenic (human induced) climate change can be tricky. Ice shelves tend to only hit the news when large changes happen, such as the recent development of the Larsen C rift which is thought to be unrelated to the warming climate of the region but may still have catastrophic consequences for the ice shelf. Understanding that changes like these can sometimes be part of a natural process can seem conflicting with the many stories about changes caused by warming. That’s why ice flows is a great way to demonstrate the ways in which ice shelves can change and the various factors that can lead to these changes. And the bonus chance to do this with penguins is never going to be a bad thing!

The game allows players to visualise the transformation of ice sheet to ice shelf to iceberg. This is an especially important educational point given the confusing ways that various types of ice can be portrayed by the media; reports, even if factually correct, will often jump from sea ice to ice shelves and back (see this example). It is also common for reports to cloud the climate change narrative by connecting processes thought to be due to natural causes (such as the Larsen C rift) to a warming climate (such as this piece). This confusion is something I often see reflected in people’s understanding of the cryosphere. In my own outreach work I start by explicitly explaining the difference between ice shelves and sea ice (my work is based on ice shelves). Even so, I can usually guarantee that many people will ask me questions about sea ice at the end of my talk.

Xue Long the Snow Dragon Penguin [Credit: Ice Flows game ]

Despite the messages that it is trying to convey, the app doesn’t come across as pushing the educational side too much. There is plenty of information available but the game also has genuinely fun elements. For example, you can earn rewards and save these to upgrade your penguins to some extravagant characters (my favourite has to be Xue Long – the snow dragon penguin!) Although the focus may be drawn towards catching the fish for the penguins while you’re actually playing, it would be hard for anyone to play the game and walk away without gaining an understanding of the basic structure of an ice shelf and how various changing environmental factors can affect it.

Developing the game…

The game was developed by Anne Le Broq in collaboration with games developers Inhouse Visual and Questionable Quality, using funding from the Natural Environment Research Council. Of course, many scientific researchers were also involved to ensure that the game was as scientifically accurate as possible whilst still remaining fun to play.

A key challenge in developing the game was modelling the ice flow. In order to be used in the app, the ice flow model needed to represent scientific understanding as well as being reactive enough to allow the game to be playable. This required some compromise, as one of the scientists involved in the development, Steph Cornford (CPOM, University of Bristol), explains on the CPOM Blog:

On one hand, we wanted the model to reflect contemporary understanding well enough for students to learn about ice sheets, ice shelves, and Antarctica in particular. On the other, the game had to be playable, so that any calculations needed to be carried out quickly enough that the animation appeared smooth, and changing any of the parameters (for example, the accumulation rate) had to lead to a new steady state within seconds, to make the link between cause and effect clear.

— Steph Cornford

The resulting model works really well, creating a fun, challenging and educational game! See for yourself by downloading the free to play game from your app store, or online at www.iceflowsgame.com!

Further reading

  • Find out more about the game on the University of Exeter website or visit the game’s own website here.
  • You can read in more detail about Steph’s modelling here.

Edited by Emma Smith


Sammie Buzzard has recently submitted her PhD thesis where she has developed a model of ice shelf surface melt, focusing on the Larsen C Ice Shelf. She is based at the Centre for Polar Observation and Modelling within the University of Reading’s Department of Meteorology. She blogs about her work and PhD life in general at https://iceandicing.wordpress.com/ and tweets as @treacherousbuzz.

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 – The Pulsating Ice Sheet!

Image of The Week – The Pulsating Ice Sheet!

During the last glacial period (~110,000-12,500 years ago) the Laurentide Ice Sheet (North America) experienced rapid, episodic, mass loss events – known as Heinrich events. These events are particularly curious as they occurred during the colder portions of the last glacial period, when we would intuitively expect large-scale mass loss during warmer times. In order to understand mass loss mechanisms from present-day ice sheets we need to understand what happened in the past. So, how can we better explain Heinrich events?


What are Heinrich Events?

During a Heinrich event large swarms of icebergs were discharged from the Laurentide Ice Sheet into the Hudson Strait and eventually into the North Atlantic Ocean. This addition of fresh water to the oceans caused a rise in sea level and a change in ocean currents and therefore climate.

We know about these events by studying glacial debris that was transported from the ice sheet into the oceans by the icebergs and eventually deposited on the ocean floor. From studying ocean-sediment records we know that Heinrich events occurred episodically during the last glacial period but not on at a regular intervals. Interestingly, when compared to temperature records from Greenland ice cores, it can be seen that the timing of Heinrich events coincides with the cold phases of Dansgaard–Oeschger (DO) cycles – rapid temperature fluctuations which occurred during the last glacial period (see our previous post).

the timing of Heinrich events coincides with the cold phases of Dansgaard–Oeschger (DO) cycles

What do we think causes them?

A new study, published last month in Nature, uses numerical modelling to show how pulses of warm ocean water could trigger Heinrich events. Our image of the week (Figure 1) illustrates the proposed mechanism for one event cycle:

  • a) Ice sheet at it’s full extent, grounded on a sill (raised portion of the bed, at the mouth of the Hudson Strait). Notice the sill is around 300m below sea level at this time.
  • b) A pulse of sub-surface water (purple) warms by a few degrees, encouraging iceberg calving at the glacier front and causing the ice begin to retreat from the sill.
  • c) As the ice retreats, it becomes unstable due to an inwards sloping bed (see our previous post on MISI). This leads to sudden rapid retreat of the ice – characteristic of Heinrich events.
  • d) Due to ice loss and thus less mass depressing the bed, the bed will slowly rise (Glacial Isostatic Adjustment), eventually the sill has risen to a level which cuts off the warmer water from the ice front and the ice can slowly advance again.

Once the ice has advanced back to it’s maximum extent (a) it will slowly depress the bed again, allowing deeper, warmer water to reach the ice front and the whole cycle repeats!

The authors of this study used this model to simulate Heinrich events over the last glacial period and were able to accurately predict the timing of Heinrich events, as known from ocean sediment records. Check out this video to see the model in action!!

Why is it important?

This study shows that the proposed mechanism probably controlled the onset of rapid mass-loss Heinrich events in the past and more generally that such mechanisms can cause the rapid retreat of marine terminating glaciers. This is important as it adds to our understanding of the stability (or instability) of present day marine terminating glaciers – such as the West Antarctic Ice Sheet! If such rapid mass loss happened regularly in the past we need to know if and how it might happen in the future!

such mechanisms can cause the rapid retreat of marine terminating glaciers.


Check out the full study and the news article summarising the findings here:

Image of the Week — The ice blue eye of the Arctic

Image of the Week — The ice blue eye of the Arctic

Positive feedback” is a term that regularly pops up when talking about climate change. It does not mean good news, but rather that climate change causes a phenomenon which it turns exacerbates climate change. The image of this week shows a beautiful melt pond in the Arctic sea ice, which is an example of such positive feedback.


What is a melt pond?

The Arctic sea ice is typically non-smooth, and covered in snow. When, after the long polar night, the sun shines again on the sea ice, a series of events happen (e.g. Fetterer and Untersteiner, 1998):

  • the snow layer melts;

  • the melted snow collects in depressions at the surface of the sea ice to form ponds;

  • these ponds of melted water are darker than the surrounding ice, i.e. they have a lower albedo. As a result they absorb more heat from the Sun, which melts more ice and deepens the pond. Melt ponds are typically 5 to 10 m wide and 15 to 50 cm deep (Perovich et al., 2009);

  • eventually, the water from the ponds ends up in the ocean: either by percolation through the whole sea-ice column or because the bottom of the pond reaches the ocean. Sometimes, it can also simply refreeze, as the air temperatures drop again (Polashenski et al., 2012).

Melt ponds cover 50-60% of the Arctic sea ice each summer (Eicken et al., 2004), and up to 90% of the first year ice (Perovich al., 2011). How do we know these percentages? Mostly, thanks to satellites.

Monitoring melt ponds by satellites

Like most phenomena that we discuss on this blog, continuous in-situ measurements are not feasible at the scale of the whole Arctic, so scientists rely on satellites instead. For melt ponds, spectro-radiometer data are used (Rösel et al., 2012). These measure the surface reflectance of the Earth i.e. the proportion of energy reflected by the surface for wavelengths in the visible and infrared (0.4 to 14.4 μm). The idea is that different types of surfaces reflect the sunlight differently, and we can use these data to then map the types of surfaces over a region.

In particular for the Arctic, sea ice, open ocean and any stage in-between all reflect the sunlight differently (i.e. have different albedos). The way that the albedo changes with the wavelength is also different for each surface, which is why radiometer measurements are taken for a range of wavelengths. With these measurements, not only can we locate the melt ponds in the Arctic, but even assess how mature the pond is (i.e. how long ago it formed) and how deep it extends. These values are key for climate change predictions.

Fig. 2: Melt pond seen by a camera below the sea ice. (The pond is the lighter area) [Credit: NOAA’s climate.gov]

Melt ponds and the climate

Let’s come back to the positive feedback mentioned in the introduction. Solar radiation and warm air temperature create melt ponds. The darker melt ponds have a higher albedo than the white sea ice, so they absorb more heat, and further warm our climate. This extra heat is also transferred to the ocean, so melt pond-covered sea ice melts three times more from below than bare ice (Flocco et al., 2012). This vicious circle heat – less sea ice – more heat absorbed – even less sea ice…, is called the ice-albedo feedback. It is one of the processes responsible for the polar amplification of global warming, i.e. the fact that poles warm way faster than the rest of the world (see also this post for more explanation).

The ice-albedo feedback is one of the processes responsible for the polar amplification of global warming

But it’s not all doom and gloom. For one thing, melt ponds are associated with algae bloom. The sun light can penetrate deeper through the ocean under a melt pond than under bare ice (see Fig. 2), which means that life can develop more easily. And now that we understand better how melt ponds form, and how much area they cover in the Arctic, efforts are being made to include more realistic sea-ice properties and pond parametrisation in climate models (e.g. Holland et al., 2012). That way, we can study more precisely their impact on future climate, and the demise of the Arctic sea ice.

Edited by Sophie Berger

Further reading

Image of the Week – Icelandic glaciers monitored from space!

Image of the Week – Icelandic glaciers monitored from space!

Located in the North Atlantic Ocean, just south of the polar circle, Iceland is a highly fascinating land. Covered by some of the largest glaciers in Europe and hosting active volcanoes, geothermal sites and subglacial lakes, it is extremely dynamic in nature and ever changing. With this Image of the Week we will tell you a bit about the changing ice caps of Iceland and how we can monitor them from space!


Icelandic ice caps since the mid-1990s

Iceland enjoys a mild and moist climate because of the relatively warm and saline Irminger current transporting heat to its southern coast, although the cold East Greenland and East Icelandic currents may cause sea ice to form to the north. Iceland’s ice caps, which receive abundant precipitation from North Atlantic cyclones, cover about 11% of the land, and contain ~3600 km2 of ice. If they completely melted they would contribute 1 cm to Sea Level Rise (SLR).

In the period 1995-2010, Icelandic glaciers shrank every year and lost mass at an average rate of 9.5±1.5 Gton a-1 – generally reflecting higher summer temperatures and longer melting seasons than in the early 1990s (Björnsson et al., 2013). Importantly, in recent decades Iceland has been the second largest source of glacier meltwater to the North Atlantic after Greenland and its peripheral glaciers. Furthermore, surge-type outlet glaciers – which have unpredictable dynamics – are present in all Icelandic ice caps and represent as much as 75% of the area of Vatnajökull (Bjornsson et al., 2003), the largest ice cap in Europe by volume. Therefore, it is important to continuously monitor Icelandic ice caps (>90% of the whole glaciated area) at high spatial resolution. Glaciological field surveys can yield accurate measurements and are routinely performed in Iceland on all ice caps and most glaciers. However, it is not always feasible to use field methods, depending on the remoteness and size of the glacier (e.g. several glaciers and ice caps in the Arctic). Continuous monitoring of such hardly accessible areas can be achieved from space at high spatial resolution.

Continuous health check from space

Since 2010, the ESA CryoSat-2 (CS2) mission has been fundamental in retrieving ice elevation data over glacial terrain characterised by complex topography and steep slopes – notoriously hard to monitor via satellite. CS2’s radar altimeter provides the elevation of the Point-Of-Closest-Approach (POCA) – the point at the surface closest to the satellite on a straight line – every ~400 m along the flight track. The main novelty of this mission is the use of a second antenna, which allows the use of interferometry across-track to accurately infer the location of a surface reflection in presence of a slope (read more about it here). Additionally, a new and exciting application of CS2 interferometric capabilities is that we can exploit the echos after the POCA, i.e. the reflections coming from the sloping surface moments after the first one. This approach generates a swath of elevations every ~400 m and provides up to two orders of magnitude more elevation data than with conventional POCA processing (Fig. 2; Gray et al., 2013, Foresta et al., 2016).

Since 2010, the ESA CryoSat-2 (CS2) mission has been fundamental in retrieving ice elevation data

Figure 2: Example of the improved elevation data using CS2 swath-processing. CS2 swath data (colors) and conventional (circles) heights over the Austfonna ice cap (Svalbard) for two satellite passes. Swath processing delivers up to two orders of magnitude more elevation data. [Credit: Dr. N. Gourmelen,University of Edinburgh, School of GeoSciences]

This rich dataset can be used to generate maps of surface elevation change rates at sub-kilometer resolution (Figs. 1 and 3). These maps show extensive thinning of up to -10 m a-1 in marginal areas of Iceland’s ice caps, while patterns of change are more variable in their interior. Fig. 3 shows the difference in spatial coverage between the POCA and Swath approaches, with the former sampling preferentially along topographic highs (see for example the Langjökull ice cap in Fig. 3). Using these high resolution maps, it is possible to independently infer the mass balance of each ice cap purely from satellite altimetry data. Based on CS2 swath-processed elevations, between glaciological years 2010/11 and 2014/15 Iceland has lost mass at an average rate of 5.8±0.7 Gton a-1 contributing 0.016±0.002 mm a-1 to SLR (Foresta et al., 2016). The rate of mass loss is ~40% less than during the preceding 15 years, partly caused by Vatnajökull (63% of the total mass loss) having had positive mass balance during the glaciological year 2014/15 due to anomalously high precipitation. Langjökull, with widespread thinning up to the ice divide (Figs. 1 and 3), is the fastest changing ice cap in terms of mass loss per unit area.

between glaciological years 2010/11 and 2014/15 Iceland has lost mass at an average rate of 5.8±0.7 Gton a-1 contributing 0.016±0.002 mm a-1 to SLR

Beside estimating mass change at the ice cap scale, the novel swath approach demonstrates the capability to observe glaciological processes at a sub-catchment scale. Different accumulation and thinning patterns over Vatnajökull and Langjökull, for example, are directly related to past surges or subglacial volcanic eruptions, some of which happened decades ago. Their long term lingering effects on the ice cap topography are now visible from space and as the satellite data record extends we will be able to gain an increased understanding of how these effects evolve over time.

Figure 3 – Comparison between swath-processed (Swath) and conventional (POCA) surface elevation change rates over the six largest ice caps in Iceland, representing 90% of the glaciated area. V (Vatnajökull), L (Langjökull),H(Hofsjökull),M(Mýrdalsjökull), D (Drangajökull), and E (Eyjafjallajökull). The inset shows the location of individual elevation measurements by using Swath and POCA approaches over Langjökull. [Credit: After Foresta et al. (2016).]

Edited by Emma Smith


Luca Foresta is a PhD student in the Glaciology and Cryosphere Research Group at the University of Edinburgh (@EdinGlaciology), and his research focuses on improving CryoSat-2 processing as well as exploiting swath-processed CryoSat-2 data to quantify surface, volume and mass changes over ice caps.

 

Image of the Week – Apocalypse snow? … No, it’s sea ice!

Image of the Week – Apocalypse snow? … No, it’s sea ice!

Sea ice brine sampling is always great fun, but sometimes somewhat challenging !

As sea water freezes to form sea ice, salts in the water are rejected from the ice and concentrate in pockets of very salty water, which are entrapped within the sea ice. These pockets are known as “brines”.

Scientists sample these brines to measure the physical and bio-geochemical properties, such as: temperature, salinity, nutrient, water stable isotopes, Chlorophyll A, algal species, bacterial number and DNA, partial pressure of CO2, dissolved and particulate Carbon and Nitrogen, sulphur compounds, and trace metals.  All of this helps to better understand how sea ice impacts the atmosphere-ocean exchanges of climate relevant gases.

In theory, sampling such brines is very simple: you just have to drill several holes in the sea-ice ensuring that the holes don’t reach the bottom of ice and wait for half an hour. During this time, the brine pockets which are trapped in the surrounding sea ice drain under gravity into the hole. After that, you just need to sample the salty water that has appeared in the hole. Simple…

…at least it would be if they didn’t have to deal with the darkness of the Antarctic winter, blowing snow, handling water at -30°C and all while wearing trace metal clean suits on top of polar gear…hence the faces!


This photo won the jury prize of the Antarctic photo competition, organised by APECS Belgium and Netherlands as part of Antarctica Day celebrations (1st of December).

All the photos of the contest can be seen here.

Edited by Sophie Berger and Emma Smith


Jean-Louis Tison is a professor at the Université libre de Bruxelles. His activities are focused on the study of physico-chemical properties of « interface ice », be it the « ice-bedrock » (continental basal ice) , « ice-ocean » (marine ice) or « ice-atmosphere » (sea ice) interface. His work is based on numerous field expeditions and laboratory experiments, and on the development of equipments and analytical techniques dedicated to the multi-parametric study of ice: textures and fabrics, stable isotopes of oxygen and hydrogen, total gas content and gas composition, bulk salinity, major elements chemistry…

 

Image of the Week – Supraglacial debris variations in space and time!

Image of the Week – Supraglacial debris variations in space and time!

There is still a huge amount we don’t know about how glaciers respond to climate change. One of the most challenging areas is determining the response of debris-covered glaciers. Previously, we have reported on a number of fieldwork expeditions to debris-covered glaciers but with this Image of The Week we want to show you another way to investigate these complex glaciers – numerical modelling!


Debris-covered glaciers

Debris-covered glaciers occur globally, with a great many being found in the Himalaya-Karakoram mountain range. For example, in the Everest Region of Nepal 33% of glacier area is debris covered (Thakuri et al., 2014). The response of debris-covered glaciers to future climate change in such regions has huge implications for water resources, with one fifth of the world’s population relying on water from the Himalayan region for their survival (Immerzeel et al., 2010).

Debris-covered glaciers respond to climate change differently to debris-free glaciers as the supraglacial debris layer acts as a barrier between the atmosphere and glacier (Reznichenko et al., 2010). The supraglacial debris layer has several key influences on the glacier dynamics:

  • Glacier ablation (loss of mass from the ice surface) is enhanced or inhibited depending on debris layer thickness and properties – see our previous post.
  • Supraglacial debris causes glaciers to reduce in volume through surface lowering rather than terminus retreat (typical of debris free mountain glaciers).

Understanding the influence of a supraglacial debris layer on mass loss or gain is, therefore, key in determining the future of these glaciers. The properties of supraglacial debris layers can vary in time and space both in debris layer thickness and distribution, as well as properties of the rocks which make up the debris (e.g. albedo, surface roughness, porosity, size and moisture content). It is these characteristics of the debris-cover which control the heat transfer through the debris and therefore the amount of thermal energy that reaches the underlying ice causing melting (Nicholson and Benn, 2006). In order to better predict the future of debris-covered glaciers we needs to be able to numerically model their behaviour. This means we need a better understanding of the variations in debris cover and how this affects the ice dynamics.

How does a supraglacial debris layer vary in time and space?

Our Image of the Week (Fig. 1) shows a schematic of how debris distribution can vary spatially across a glacier surface and also this can change through time. The main inputs of debris are:

  • Upper regions: snow and ice avalanches in the upper reaches of the glacier.
  • Mid and Lower regions: rock avalanches and rock falls (Mihalcea et al., 2006).

These irregular mass movement events vary in frequency and magnitude, and therefore affect debris distribution across the glacier surface but also through time. The irregularity of them makes it really hard to predict and simulate! Luckily, debris transport is a little more predictable.

Figure 2: An ice cliff emerging out of the supraglacial debris layer on Khumbu Glacier, Nepal, with Nuptse in the background. [Credit: M. Gibson]

Debris is initially transported along medial moraines (glacially transported debris)  in the upper and mid-sections of the glacier, this is known as entrained debris. The various sources of entrained debris combine to form a continuous debris cover in the lower reaches of the glacier (Fig. 1). As a supraglacial debris layer is forming, such as for Baltoro glacier (Fig. 1), the boundary between the continuous debris layer and entrained debris sections progresses further upglacier over time.

Eventually transported debris will reach the terminus of the glacier and be deposited (Fig. 1), mainly due to a decrease in surface velocity of the glacier towards the terminus. However, once debris is deposited it doesn’t just sit there; debris is constantly being shifted around as ablation (surface melting) occurs. As ablation occurs the debris surface ablates unevenly, as the thickness of the debris layer is spatially variable. Uneven ablation, otherwise known as differential surface lowering, causes the glacier surface to be made up of topographic highs and lows, the latter of which sometimes become filled with water, forming supraglacial ponds (Fig. 1) . Another product of debris shifting is that ice cliffs, such as the one seen in Fig. 2, are exposed. These features are initially formed when englacial channels collapse  or debris layers slide (Kirkbride, 1993). All this movement and shifting means that not only do glacier models have to consider variation in debris layers across the glacier and through time, but also the presence of ice cliffs and supraglacial ponds. They are important as they have a very different surface energy balance to debris-covered ice. To complicate things further the frequency and area of ice cliffs and supraglacial ponds also vary through time! You see the complexity of the problem…

Modelling spatially and temporally varying debris layers

Numerical modelling is key to understanding how supraglacial debris layers affect glacier mass balance. However, current numerical modelling often either omits the presence of a supraglacial debris layer entirely, or a debris layer that is static in time and/or space (e.g. Collier et al., 2013; Rowan et al., 2015; Shea et al., 2014). However, as outlined earlier, these supraglacial debris layers are not static in time or space. Understanding the extent to which spatiotemporal variations in supraglacial debris distribution occur could aid identification of when glaciers became debris-covered, glaciers that will become debris-covered glaciers in the future, and the timescales over which supraglacial debris layers vary. The latter is particularly relevant to numerical modelling as it would result in total glacier ablation being calculated more precisely throughout the modelling time period. Understanding the interaction between glacier dynamics and debris distribution is therefore key to reconstructing debris-covered glacier systems as accurately as possible.

Edited by Emma Smith


Morgan Gibson is a PhD student at Aberystwyth University, UK, and is researching the role of supraglacial debris in ablation of Himalaya-Karakoram debris-covered glaciers. Morgan’s work focuses on: the extent to which supraglacial debris properties vary spatially; how glacier dynamics control supraglacial debris distribution; and the importance of spatial and temporal variations in debris properties on ablation of Himalaya-Karakoram debris-covered glaciers. Morgan tweets at @morgan_gibson, contact email address: mog2@aber.ac.uk.

Image of the Week – On the tip of Petermann’s (ice) tongue

Image of the Week – On the tip of Petermann’s (ice) tongue

5th August 2015, 10:30 in the morning. The meeting had to be interrupted to take this picture. We were aboard the Swedish icebreaker Oden, and were now closer than anyone before to the terminus of Petermann Glacier in northwestern Greenland. But we had not travelled that far just for pictures…


Petermann’s ice tongue

Petermann is one of Greenland’s largest “marine terminating glaciers”. As the name indicates, this is a glacier, i.e. frozen freshwater, and its terminus floats on the ocean’s surface. Since Petermann is confined within a fjord, the glacier is long and narrow and can be referred to as an “ice tongue”.

Petermann Glacier is famous for its recent calving events. In August 2010, about a quarter of the ice tongue (260 km2) broke off as an iceberg (Fig. 2). In July 2012, Petermann calved again and its ice tongue lost an extra 130 km2.

These are not isolated events. Greenland’s marine terminating glaciers are all thinning and retreating in response to a warming of both air and ocean temperatures (Straneo et al., 2013), and Greenland’s entire ice sheet itself is threatened. Hence, international fieldwork expeditions are needed to understand the dynamics of these glaciers.

Fig. 2: The 2010 calving event of Petermann. Natural-color image from the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite ( August 16, 2010).  [Credit: NASA’s Earth Observatory]

The Petermann 2015 expedition

In summer 2015, a paleoceanography expedition was conducted to study Petermann Fjord and its surroundings, in order to assess how unusual these recent calving events are compared to the glacier’s past. Our small team focused on the present-day ocean, and specifically investigated how much of the glacier is melted from below by the comparatively warm ocean (that process has been described on this blog previously). In fact, this “basal melting” could be responsible for up to 80% of the mass loss of Petermann Glacier (Rignot, 1996). Additionally, we were also the first scientists to take measurements in this region since the calving events.

Our results are now published (Heuzé et al., 2017). We show that the meltwater can be detected and tracked by simply using the temperature and salinity measurements that are routinely taken during expeditions (that, also, has been described on this blog previously). Moreover, we found that the processes happening near the glacier are more complex than we expected and require measurements at a higher temporal resolution, daily to hourly and over several months, than the traditional summer single profiles. Luckily, this is why we deployed new sensors there! And since these have already sent their data, we should report on them soon!

Edited by David Rounce and Sophie Berger

References and further reading

Image of the Week – For each tonne of CO2 emitted, Arctic sea ice shrinks by 3m² in summer

Image of the Week – For each tonne of CO2 emitted, Arctic sea ice shrinks by 3m² in summer

Declining sea ice in the Arctic is definitely one of the most iconic consequences of climate change. In a study recently published in Science, Dirk Notz and Julienne Stroeve find a linear relationship between carbon dioxide (CO2) emissions and loss of Arctic sea-ice area in summer. Our image of this week is based on these results and shows the area of September Arctic sea ice lost per inhabitant due to CO2 emissions in 2013.


What did we know about the Arctic sea ice before this study?

Since the late 1970s, sea ice has been dramatically shrinking in the Arctic, losing 3.8% of its area per decade. Sea-ice area is at its minimum in September, at the end of the melting season.

The main cause of this loss is the increase in surface temperature over the recent years (Mahlstein and Knutti, 2012), which has been more pronounced in the Arctic compared to other regions on Earth (Cohen et al., 2014). The use of statistical methods involving both observations and climate models shows that the recent warming in the Arctic can be attributed to human activity, i.e. mainly greenhouse gas emissions (Gillett et al., 2008). This suggests a direct link between human activity and Arctic sea-ice loss, which is confirmed in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).

How exactly is sea-ice loss related to CO2 emissions ?

Notz and Stroeve (2016) relate the Arctic sea-ice decline to cumulative CO2 emissions since 1850 (i.e. the total amount of CO2 that has been emitted since 1850) for both observations and climate models. Cumulative CO2 emissions constitute a robust indicator of the recent man-made global warming (IPCC, 2014).

The two quantities are clearly linearly related (see Figure 2). From 1953 to 2015, about 3.5 million km² of Arctic sea ice have been lost in September while 1200 gigatonnes (1 Gt = 10e9 tonnes) of CO2 have been emitted to the atmosphere. This means that for each tonne of CO2 released into the atmosphere, the Arctic loses 3 m² of sea ice.

Fig 2: Monthly mean September Arctic sea-ice area against cumulative CO2 emissions since 1850 for the period 1953-2015. Grey circles and diamonds show the results from in-situ (1953-1978) and satellite (1979-2015) observations, respectively. The thick red line shows the 30-year running mean and the dotted red line represents the trend of 3 m² sea-ice area loss per tonne of CO2 emitted. [Credit: D. Notz, National Snow and Ice Data Center ]

Starting from the relationship between cumulative CO2 emissions and sea-ice area, it is then easy to attribute to each country in the world their own contribution to sea-ice loss based on their CO2 emissions per capita. The countries that stand out in the map are thus the countries emitting the most in relation to their population.

Could the Arctic be ice-free in the future?

If this relationship holds in the future (in other words, if we extend the red dotted line to zero sea-ice area in Figure 2), adding 1000 Gt of CO2 in the atmosphere would free the Arctic of sea ice in September. Since we are currently emitting about 35 Gt CO2 per year, it would take less than 30 years to have the Arctic free of sea ice in the summer (which confirms previous model studies (e.g. Massonnet et al., 2012)).

Edited by Clara Burgard and Sophie Berger

Further reading

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.

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