CR
Cryospheric Sciences

Image of the Week

Image of the Week – Searching for clues of extraterrestrial life on the Antarctic ice sheet

Fig. 1: A meteorite in the Szabo Bluff region of the Transantarctic mountain range, lying in wait for the 2012 ANSMET team to collect it [Credit: Antarctic Search for Meteorites Program / Katherine Joy].

Last week we celebrated Antarctica Day, 50 years after the Antarctic Treaty was signed. This treaty includes an agreement to protect Antarctic ecosystems. But what if, unintentionally, this protection also covered clues of life beyond Earth? In this Image of the Week, we explore how meteorites found in Antarctica are an important piece of the puzzle in the search for extraterrestrial life.


Meteorites in Antarctica

Year after year, teams of scientists from across the globe travel to Antarctica for a variety of scientific endeavours, from glaciologists studying flowing ice to atmospheric scientists examining the composition of the air and biologists studying life on the ice, from penguins to cold-loving microorganisms. Perhaps a less conspicuous group of scientists are the meteorite hunters.

Antarctica is the best place on Earth to find meteorites. Meteorites that fall in this cold, dry desert are spared from the high corrosion rates of warmer, wetter environments, preserving them in relatively pristine condition. They are also much easier to spot mainly due to the contrast between their dark surfaces on the white icy landscape (see our Image of the Week), but also because the combination of Antarctica’s climate, topography and the movement of ice serves to concentrate meteorites, as if lying in wait to be found.

The targeted search for meteorites has taken place annually since the late 1960s, leading to the recovery of over 50,000 specimens from the continent, and counting. The most prolific of these search teams is the US-led Antarctic Search for Meteorites ANSMET), which lay claim to over half of these finds. Comprising only a handful of enthusiasts, this team camps out on the slopes of the Transantarctic Mountains for around 6 weeks hunting for meteorites. The finds include rocks originating from asteroids, the Moon and Mars.

 

Evidence of life in a meteorite?

There has long been a link between meteorites and the potential for life beyond Earth. Perhaps the most famous, or rather infamous, meteorite found in Antarctica is the Alan Hills 84001 meteorite (ALH84001). Found by the 1984 ANSMET team, this meteorite was blasted from the surface of Mars some 17 million years ago as a result of an asteroid or meteorite impact, falling to Earth around 13,000 years ago. This piece of crystallised Martian lava is roughly 4.5 billion years old. The reason for its infamy is the widely publicised claim made a decade after its discovery that it harbours evidence of Martian life [McKay et al 1996]. Specifically, application of high resolution electron microscopy unearthed microstructures comprising magnetite crystals that looked, to the NASA scientist David McKay and his team, like fossilised microbial life, albeit at the nanoscale (see Fig. 2).

Fig.2: A nanoscale magnetite microstructure that was interpreted as fossilised microbial life from Mars [Credit: D McKay (NASA), K. Thomas-Keprta (Lockheed-Martin), R. Zare (Stanford), NASA].

Such a finding of evidence for extraterrestrial life has huge implications for the presence of life beyond Earth, a subject that has captivated humankind since ancient times. This extraordinary claim made headline news across the globe. It even gained acknowledgement by the then US president Bill Clinton. In the words popularised by Carl Sagan, “extraordinary claims require extraordinary evidence”, and this one garnered considerable controversy that endures today. At the time, there was no known process that did not involve life that could result in these types of structures. Subsequent research, triggered by this claim, has since indicated otherwise. The debate rolls on, and it seems we will never really know whether the crystals structures are fossils of Martian life or not, with no conclusive evidence on either side of the argument. Nevertheless, the interest and attention gained through this story kick-started a flurry of hugely successful Mars exploration missions, as well as reinvigorated the search for life beyond Earth.

 

Meteorites as microbial fuel

The ALH840001 is an unusual connection between meteorites and the search for extraterrestrial life. Much subtler, but more wide-reaching, is the potentially important connection between organic-containing meteorites and the existence of life elsewhere. The chondrite class of meteorites originates from the early solar system, specifically from primitive asteroids that formed from the accretion of dust and grains. They are the most common type of meteorite that falls to Earth, and contain a wide array of organic compounds, including nucleotides and amino acids, the so-called building blocks of life. In addition, a number of organic compounds that reside in these meteorites are also common on Earth, and are known to fuel microbial life by serving as a source of energy and nutrients for an array of microorganisms [Nixon et al 2012]. These meteorites have fallen to Earth and Mars for billions of years, since before the emergence and proliferation of life as we understand it. A significant quantity of these meteorites, and the organic matter contained within them, has therefore accumulated on Mars. In fact, owing to the thinner atmosphere of Mars, a larger quantity is expected to have accumulated there than on Earth, and with more of its organic content intact. It is a therefore a distinct possibility that these meteorites may play an important role in the emergence, or even persistence, of life on Mars, if such life has ever existed [Nixon et al 2013].

The search for life on Mars is very much an active pursuit. As we continue this search using robotic spacecraft, such as NASA’s Curiosity rover and the upcoming European Space Agency’s ExoMars rover, we seek to better define whether environments on Mars are habitable for life. But our understanding of habitability on Mars and beyond is defined by our knowledge of the limits of life here on Earth, such as the microbial lifeforms that can make a living on and under the Antarctic ice sheet (see this previous post), but also in terms of the chemical energy able to support life. The search for meteorites on Antarctica has an important role to play here, and long may the hunt continue.

 

References and further reading

Edited by Joe Cook and Clara Burgard


Sophie Nixon is a postdoctoral research fellow in the Geomicrobiology group at the University of Manchester. She completed her PhD in Astrobiology in 2014 at the University of Edinburgh, the subject of which was the feasibility for microbial iron reduction on Mars. Sophie’s research interests since joining the University of Manchester are varied, focussing mainly on the microbiological implications of anthropogenic engineering of the subsurface (e.g. shale gas extraction, nuclear waste disposal), as well as life in extreme environments and the feasibility for life beyond Earth. Contact: sophie.nixon@manchester.ac.uk

Image of the Week – Antarctica Day

Image of the Week – Antarctica Day

Today, 1st December 2017, marks the 58th anniversary of the signing of the Antarctic Treaty in 1959. The Antarctic Treaty was motivated by international collaboration in Antarctica in the International Geophysical Year (IGY), 1957-1958. During the IGY over 50 new bases were established in and around Antarctica by 12 nations- including this one at Halley Bay which was maintained for over a decade before being replaced. These nations signed the Treaty to keep Antarctica as a continent of peace and scientific research. Since 2010, this date has been marked by Antarctica Day, which is used to promote awareness of Antarctica as an international space with benefits for all.


Antarctica as a continent of peace and scientific collaboration

In the year 1957-1958, 67 countries participated in the International Geophysical Year (IGY). This was (a bit confusingly) 18 months of international coordinated observations and data retrieval. The goal was to exploit new tools and techniques to advance science in a huge range of geophysical disciplines. The results, direct and indirect, were widespread. For example it is no coincidence that the first artificial satellite, Sputnik 1, was launched by the USSR in October 1957, after the USA had announced they would launch a satellite as part of IGY activities.

Fig.2: Territorial claims in Antarctica [Credit: Australian Antarctic Data Centre ]

Expeditions in Antarctica were a major activity of the IGY. Seven countries had territorial claims in Antarctica at the time, some of them overlapping (Fig. 2). To make sure that territorial disputes did not hinder scientific progress, it was established that these political goals for Antarctica would be set aside during the IGY, and scientific goals prioritized. As a result, 12 countries operated around Antarctica during the IGY: Argentina, Australia, Belgium, Chile, France, Japan, New Zealand, Norway, South Africa, United Kingdom, United States and USSR. This included those with previous claims as well as those like the USA and USSR who had not previously had activities in Antarctica.

Out of concern for maintaining the scientific legacy of this fantastic year of collaboration, these same 12 countries gathered in 1959 for the “Conference on the Antarctic” in Washington D.C.
The original Treaty had two main components:

  • Antarctica should be used for ‘peaceful means only’. It would not be permitted to establish military bases, carry out military maneuvers, or test weapons.
  • There should be ‘freedom of scientific investigation’. In particular, the Treaty laid out terms of collaboration, such that personnel, information about activities, and the results of scientific observations, should be shared freely.

The Antarctic Treaty covers the area from 60 to 90 degrees south, enclosing the entire Antarctic continent as well as many Antarctic islands and a large area of the Southern Ocean.

 

Future Treaties: Protecting the Environment

The Antarctic Treaty didn’t directly include protections for the environment. However, it did state that future meetings would consider actions related to the Treaty, including those ‘regarding preservation and conservation of living resources in Antarctica’. In the following decades, three major agreements were made to ensure the protection of different aspects of the Antarctic environment.
The first two were the Convention for the Conservation of Antarctic Seals, in 1972, and the Convention for the Conservation of Antarctic Marine Living Resources, in 1982.

The third is the ‘Environmental Protocol’ (full and lengthy name “The Protocol on Environmental Protection to the Antarctic Treaty”). This wide-ranging protocol was signed in 1991 and came into force in 1998, and established the Committee for Environmental Protection. The overarching purpose of the protocol is a commitment “to the comprehensive protection of the Antarctic environment and dependent and associated ecosystems and hereby designate Antarctica as a natural reserve, devoted to peace and science“. It covers all activities in the Antarctic Treaty region, south of 60°S. It lays out reasons for protecting Antarctica – as a home to ecosystems, a unique wilderness, and as a crucial location for scientific research and for understanding the global environment. It outlines types of adverse impact to be avoided; for example, pollution, environmental change, damage to significant locations, and disruption of ecosystems by exploiting them or by introducing foreign species. And, the protocol establishes how such impacts are to be avoided, for example by requiring Environmental Impact Assessments before any activity is carried out.

 

Celebrating the Treaty: Antarctica Day

Inspired by 50 successful years of the Antarctic Treaty, Antarctica Day was launched on the 1st December 2010 and is celebrated on this date each year. Its goals are to celebrate the success of this international coordination treaty and the resulting international peaceful co-operation in Antarctica, raise awareness of the uniqueness of Antarctica, and to encourage conversation and collaboration between students, scientists and officials.

A number of particular activities take place each year. One is an ‘Antarctic flags’ event, organized by the Association of Polar Early Career Researchers (APECS), and currently managed by its UK branch, the UK Polar Network. School children design flags ready for Antarctica Day, which are then proudly displayed by researchers visiting Antarctica over the Antarctic summer (northern hemisphere winter!).

Fig.3: “Los niños de 5to año de la Escuela 163 “Japón” de La Paz- Uruguay”: Antarctica Day 2017 flags designed by school children in Uruguay. [credit: Valentina Cordoba. Provided by Sammie Buzzard.]

If you’re going to Antarctica in the next couple of months and can take a photo of yourself with one of the flags while there, please email education@polarnetwork.org

 

Happy Antarctica day!

 

Further Reading

Edited by Sophie Berger


Caroline Holmes is a postdoctoral researcher at the British Antarctic Survey, UK. She investigates how well sea ice is represented in coupled climate models. The climate models used to project the evolution of the earth system under climate change represent very differing behaviors in terms of the seasonal cycle of sea ice cover at each pole, and trends in the recent past and projected future. Caroline’s work seeks to understand these differing behaviors by examining sea ice processes and atmosphere-ocean-ice linkages. Twitter @CHolmesClimate. Contact Email: calmes@bas.ac.uk

Image of the Week – Does size really matter? A story of ice floes and power laws

Figure 1: Sea ice extent in 2014 during the melting season. The pink lines mark the inner and outer extent of the marginal ice zone. The data comes from the CPOM setup of the CICE sea-ice model run with 9 years spin up from 2005. [Credit: Adam Bateson]

The retreating Arctic sea ice is one of the most well-known facets of Climate Change. Images of polar bears desperately swimming through polar seas searching for somewhere to rest and feed resonate strongly with the public. Beyond these headlines however, the Arctic Ocean is displaying a rapid transition from having mostly permanent ice cover to a more seasonal cover.


The Marginal Ice Zone

As both atmospheric and ocean average temperatures increase over the 21st century, the region of the Arctic considered either marginal or seasonal i.e. regions where sea ice is present for at least some of the year but with periods of either no or incomplete sea ice cover, is projected to increase significantly. Our image of the Week (Fig. 1) shows how the Marginal Ice Zone (defined here as regions with 15 % – 80 % ice coverage) evolves through the melting season. This means that the thermodynamic (i.e. melting, freezing) and dynamic (i.e. mechanical) processes which dominate the marginal ice zone are likely to become more important in influencing how the sea ice evolves in future.

Floe size matters

A key parameter to describe the behaviour of this region is the size of the individual ice floes – sheets of floating sea ice – which form the sea ice cover (see also a previous post on this topic). Floe size impacts melt rate, floe mechanical response, atmosphere-ocean momentum exchange and wave-ice interactions (Fig. 2). The sea ice component of climate models usually assumes all floes have the same, constant size; this assumption removes the ability of sea ice models to represent the complexity of the marginal ice zone. As a result processes which influence floe size such as wave induced break up of floes and lateral melting can’t be represented adequately in current climate models.

Figure 2: Video shows significant wave height in 2014 (darker blue colours indicate bigger waves; note also that a white colour indicates no waves, not necessarily sea ice cover). The purple/pink lines mark the inner and outer extent of the Marginal Ice Zone respectively. The data come from the CPOM setup of the CICE sea-ice model run with 9 years spin up from 2005. [Credit: Adam Bateson]

How can we represent different floe sizes in models?

Given the changing Arctic environment, representing floe size as a variable quantity is likely to be important for future accuracy of sea ice modelling. Currently sea ice models tend to divide the Polar Regions into grid cells, with properties defined as an average across the grid cell. However floe sizes can vary significantly over sub kilometre scales. There are four alternative approaches to representing such a non-uniform distribution of floe sizes within a grid cell:

  1. Define floes individually within the model and allow each floe to evolve independently.
  2. Use a categorical floe size distribution i.e. assign floes to size categories of 1 – 10 m, 10 – 20 m etc. (e.g. Horvat et. al, 2015).
  3. Impose a floe size distribution on each grid cell which evolves over time driven by relevant processes such as lateral melting or floe break-up (e.g. Williams et. al, 2013 a & b).
  4. A single floe size for each grid cell is diagnosed from the fractional ice coverage.

 

Option 1 would be the ideal approach from a Physics perspective. It assumes nothing about what form the floe size distribution may take and allows us to properly assess the impact of different processes for floes of different sizes. This approach is computationally expensive however, which means it will take longer for models to run. Option 4 would the simplest option and wouldn’t have negligible impacts on model run times, however it wouldn’t be possible to include in the model any processes which influence floe size. Option 2 and option 3 represent intermediates between these two extremes. In particular option 3 would be a preferred compromise if floes can be represented as a coherent distribution which evolves over time at the grid length scale.

We should now look at whether observations support the use of such a distribution.

The power law distribution

Figure 3: The cumulative number density for floe size can be represented by a power law. Note that both scales are log scales, and that C in the equation is a constant. The blue and green lines show the distribution for smaller and larger exponents respectively. Note the cumulative number density for a given floe diameter, x, is the fraction of floes size x and larger. [Credit: Adam Bateson]

The floe size distribution is most commonly fitted to a power law (Fig. 3). Power law systems have the property of self-similarity, a term attributed to a system which looks the same over different scales (e.g. the metre or kilometre scale). Power law distributions are relatively easily to investigate mathematically, and can easily be incorporated into a model without significant computational expense.

Do observations support the use of a power law?

Many individual experiments to assess the floe size distribution have shown a good fit to the power law. However, a large range of values for the power law exponent have been reported with observations ranging from 0.9 to 4. Other papers have proposed two power laws over different size ranges, with smaller exponents used for the smaller floe range. Herman et. al (2010) proposed that a distribution with a variable exponent would produce a better fit than a power law. There are further questions we need to consider as well. Over what scale are power laws a valid approximation? What determines the exponent of the power law and can it be assumed that this is constant? Is the power law only valid over a certain range of floe sizes and if so what determines this range?

These questions are not trivial, and the available observations are not sufficient to answer them. However, there is still value in testing different distributions and approaches within models. This can provide information about how sensitive the sea ice cover is to different distributions and which processes in particular are important to accurately model winter ice growth and summer ice loss in the marginal ice zone.

References/Further Reading

Edited by Sophie Berger


Adam Bateson is a PhD student at the University of Reading (United Kingdom), working with Danny Feltham. His project involves investigating the fragmentation and melting of the Arctic seasonal sea-ice cover, specifically improving the representation of relevant processes within sea-ice models. In particular he is looking at lateral melting and wave induced fragmentation of sea-ice as drivers of break up, as well as the role of the ocean mixed layer as either an amplifier or dampener to the impacts of particular processes. Contact: a.w.bateson@pgr.reading.ac.uk or @a_w_bateson on twitter.

Image of the Week – Ice Stupas: a solution for Himalayan water shortage?

Image of the Week – Ice Stupas: a solution for Himalayan water shortage?

As the world searches for practical innovations that can mitigate the impact of climate change, traditional methods of environmental management can offer inspiration. In Hindu Kush and Karakoram region, local people have been growing, or grafting, glaciers for at least 100 years. Legend has it that artificial glaciers were grown in mountain passes as early as the twelfth century to block the advance of Genghis Khan and the Mongols!


 

What exactly are we talking about?

People in the Himalayas need water for the irrigation of their crops. Naturally, they get this water during the melting period of local glaciers. Glacial melt, however, is insufficient to satisfy the demands in early spring (April-June). Artificial ice structures can increase the availability of water for crop irrigation during this period. They are grown during the winter season preventing the water to waste away into the ocean. The Ice Stupa project is bringing these practices back from the realm of folklore for the everyday use of mountain farmers again.

 

How it works

An artificial glacier is built following a simple technique. Water is piped away from high altitude reservoirs (glacial lakes or streams) in winter. Further downstream, the water is allowed to “leave” the pipe. Due to gravity, the pressure that has built up on the way forces the water to leave the pipe as a water fountain. In contact with subzero temperatures, the water fountain freezes, building a huge cone of ice. In its final form, this artificial glacier looks like a traditional buddhist building, hence the name “stupa“. In the following video, you can get a better visual idea of the process!

 

 

An ice stupa is needed for crop irrigation. The water contained in the stupa should therefore also be released during the right time of the year. To this purpose, it is also designed to conserve water in ice form as long into the summer as possible. It can then, as it melts, provide irrigation to the fields until the real glacial melt waters are sufficient in June. Since these ice cones extend vertically upwards towards the sun, they receive less of the sun’s energy per unit of volume of water stored. Hence, they will take much longer to melt compared to an artificial glacier of the same volume formed horizontally on a flat surface.

 

Further reading

Edited by Clara Burgard


Suryanarayanan Balasubramanian is a mathematician who has been managing the Ice Stupa Project for the past three years. He studies the life cycle of Ice Stupas through field measurements and dynamic models. He is currently developing the project in Peru, Switzerland, Nepal and India. Contact Email: gayashiva91@gmail.com

Image of the Week — Climate change and disappearing ice

The first week of the Climate Change summit in Bonn (COP 23  for those in the know) has been marked by Syria’s decision to sign the Paris Accord, the international agreement that aims at tackling climate change. This decision means that the United States would become the only country outside the agreement if it were to complete the withdrawal process vowed by President Trump.

In this context, it has become a tradition for this blog to use the  United Nations climate talks as an excuse to remind us all of some basic facts about climate change and its effect on the part we are most interested in here: the cryosphere! This year we have decided to showcase a few compelling animations, as we say “a picture is sometimes worth a thousand words”…


Arctic sea ice volume

Daily Arctic sea ice volume is estimated by the PIOMAS reconstruction from 1979-present [Credit: Ed Hawkins]

The volume of Arctic sea ice has declined over the last 4 decades and reached a record low in September 2012. Shrinking sea ice has major consequences on the climate system: by decreasing the albedo of the Arctic surface, by affecting the global ocean circulation, etc.

More information about Arctic sea ice:

Land ice losses in Antarctica and Greenland

Change in land ice mass since 2002 (Right: Greenland, Left: Antarctica). Data is measured by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites. [Credit: Zack Labe]

Both the Antarctic and Greenland ice sheets have been losing ice since 2002, contributing to global sea-level rise (see previous post about sea level) .  An ice loss of 100 Gt raises the  sea level by ~0.28 mm (see explanations  here).

More information about ice loss from the ice sheets:

 

The cause: CO2 emissions and global warming

Finally we could not close this post without showing  how the concentration of carbon dioxide have evolved  over the same period and how this has led to global warming.

CO₂ concentration and global mean temperature 1958 – present. [Credit:Kevin Pluck]

More information about CO2 and temperature change

  • Global Temperature | NASA: Climate Change and Global Warming
  • Carbon dioxide | NASA: Climate Change and Global Warming

More visualisation resources

Visualisation resources | Climate lab

 

Edited by Clara Burgard

Image of the Week – Sea-ice dynamics for beginners

Image of the Week – Sea-ice dynamics for beginners

When I ask school children or people who only know about sea ice from remote references in the newspapers: ‘How thick do you think is the Arctic sea ice?’, I often get surprising answers: ’10 meters? No, it must be thicker – 100 meters!’. It seems like sea ice, often depicted as a uniform white cover around the North Pole and as a key element in accelerated warming of the Polar Regions, imposes a majestic image. Unfortunately, sea ice is much more fragile.


Growing in the current

Actually, sea ice is on average just about 2 m thick. It used to be thicker, up to 3 m, but such ice needs several winters to grow and is quite rare in the modern-day Arctic as winters are warmer than they used to be (see this previous post). Currently, more than half of the Arctic sea-ice area melts away completely during summer and grows back during the next winter. Such a thin layer of frozen water floating on the ocean is not strong enough to resist the forces of the wind, which pushes it around in ocean surface currents. In order for the ice to move, it has to deform and breaks into ice floes (read more in this previous post). Some ice floes move apart (divergence) in leads and polynyas (see this previous post), while others are pressed together (convergence) in pressure ridges, where blocks of ice pile up against and on top of each other (see our Image of the Week).

Ice grows from the ocean surface layer by water freezing. This is called thermodynamical growth. Thermodynamical growth produces most of the ice forming in the time from freeze-up in fall until the ice becomes about 1 to 2 m thick in mid-winter. At that point, sea ice approaches equilibrium thickness, i.e. the sea ice is thick enough to insulate the cold atmosphere from the relatively warm ocean. But because sea ice deforms, it can continue growing during the rest of the winter too. Pressure ridges sails can stick several meters out of the icy landscape, while their much larger and bulkier keels are hidden below the surface. Ridges can store large volume of sea ice – about a third (Hansen et al, 2013)! At the same time, new ice can grow in leads where open water is exposed to the atmosphere.

The following video is a collection of movies showing consequences and acts of sea-ice deformation. The first part is taken from R/V Lance – the ice-strengthened research ship of Norwegian Polar Institute, while she is navigating along a lead in late winter. Observe how much space is taken by pressure ridges! The second part of the movie shows a pressure ridge growing. Listen to the sound of deforming ice!

Another positive feedback

In winter, temperatures are so low that all the fractures, leads and pressure ridges freeze back – they heal. In summer, however, these damages are the first to appear again. Dark water with low albedo (read more about the albedo feedback in this post) is exposed and the ice melts faster in such regions. Because the Arctic sea ice became relatively thin over the recent decades, it also became less resistant to the forces of the wind. Such thin ice breaks more easily (e.g. Itkin et al, 2017). This means that, as more of such damaged ice is present in summer, the ice cover melts faster. So, here is an additional positive feedback for the Arctic ice under climate change: thinner ice melts faster also because it has become weaker and therefore breaks up easier.

Further reading

Edited by Clara Burgard


Polona Itkin is a Post-doctoral Researcher at the Norwegian Polar Institute, Tromsø. She investigates the sea ice dynamics of the Arctic Ocean and its connection to the sea ice thickness. In her work she combines the information from in-site observations, remote sensing and numerical modeling. Polona is part of the social media project ‘oceanseaiceNPI’ – a group of scientists that communicates their knowledge through social media channels:

Instagram.com/OceanSeaIceNPI, Twitter.com/OceanSeaIceNPI, Facebook.com/OceanSeaIceNPI, contact Email: polona.itkin@npolar.no

Image of the Week – Of comparing oranges and apples in the sea-ice context

Image of the Week – Of comparing oranges and apples in the sea-ice context

In the last fifty years, models and observations have enabled us to better understand sea-ice processes. On the one hand, global climate models have been developed, accounting for the sea-ice component in the climate system. On the other hand, satellite instruments have been developed to monitor the “real” sea-ice evolution. These satellite observations are often used to evaluate climate models. However, lately, doubts have arisen to whether comparing model output to observations is the most reasonable method. Are we sometimes comparing oranges to apples? To discuss this matter, sea-ice modelers and sea-ice observers met over three days in Hamburg earlier this month at the Workshop on improved satellite retrievals of sea-ice concentration and sea-ice thickness for climate applications.


How do we measure past and current seaice changes?

The great advantage of satellites over in-situ measurements is that they measure changes in sea-ice concentration (fraction of ocean covered by sea ice in a given area) and sea-ice thickness in a continuous way with an almost complete spatial coverage of the polar regions (see this previous post) and with a high temporal resolution.
Of course, satellites do not directly measure sea-ice concentration. Rather, they measure the brightness temperature (left part of Fig. 2), which is a measure of the radiation emitted by the Earth’s surface and atmosphere, with passive microwave sensors (such as SSM/I). From this brightness temperature, it is possible to compute sea-ice concentration (see this article for further information). Microwave sensors are used because they can “see” the surface through clouds and during polar night, which is not possible with visible sensors (such as MODIS).

In a similar way, satellites do not directly measure sea-ice thickness. Rather, they measure sea-ice freeboard (right part of Fig. 2), i.e. the height of the ice above the sea surface, with different kinds of sensors (laser altimetry [e.g. ICESat], radar altimetry [CryoSat]). Sea-ice thickness is then retrieved through appropriate algorithms (see e.g. this article).

 

Fig. 2: Satellite measurement techniques that lead to the observed brightness temperatures and sea-ice freeboard [Credit: C. Burgard].

 

Are the satellite retrievals accurate?

Each method of deriving sea-ice concentration or thickness from satellite measurements has its own uncertainties. For example, algorithms to retrieve sea-ice concentration use several assumptions about the state of the atmosphere and surface emissivity. Also, melt ponds and thin ice show up as lower concentration regions. Similarly, different assumptions about snow depth on ice and about sea-ice density impact the retrieved sea-ice thickness. Therefore, the sea-ice variables retrieved from satellite observations may deviate from their actual “real” state.

 

How do we project future sea-ice changes?

In order to project the future sea-ice evolution, different climate models are used (see this article for example). These climate models are usually evaluated against satellite observations in order to assess their performance. While all models present biases compared to observations, it cannot always be concluded that this is necessarily a problem of the models as observations also have uncertainties as previously said. Therefore, the main discussions at the workshop in Hamburg (Fig. 3) were about reducing uncertainties in the comparison between observations and models.

 

How can we better compare satellite observations and models?

The discussion in Hamburg was very lively as modelers and observers exchanged about how they actually reach the results they provide, explaining in detail their models and algorithms. It became rapidly clear that comparing observed sea-ice concentration to modeled sea-ice concentration might be like comparing apples to oranges under certain circumstances.

Thomas Lavergne, a researcher at the Norwegian Meteorological Institute, gave a presentation related to this discussion by presenting the picture that is our Image of the Week. The classical method up to now has always been to transform the measured satellite signal into a “satellite product”, a quantity that is directly computed by models (direction from right to left in the Image of the Week), so that we can compare this quantity to the corresponding model variable. As already mentioned, this can lead to assumptions and introduce errors into the observations, while one would expect observations to be the best representation of the “real” world.

Another possible approach, already well accepted in the community of weather forecasting, is to transform the model variables all the way into simulated brightness temperatures and compare these to satellite data (direction from left to right in the Image of the Week). The algorithms that transform model variables into simulated satellite quantities are observation operators. Although an active field of research, the observation operators for sea ice are not ready, and the comparison of sea-ice simulations to satellite observations will for the foreseeable future rely on satellite “products”.

At the workshop, Lavergne advocated for a middle-ground solution, where satellite products “take a step back” and climate models “take a step forward” using tailored observation operators. This would reduce the need for assumptions in the satellite products but still be manageable for modelers, and would most likely offer the best consensus for the two communities. This way, observed and modeled quantities can still be compared with each other and uncertainties introduced into the comparison can be reduced.

Fig. 3: Happy sea-ice observers and sea-ice modelers in Hamburg [Credit: Julika Doerffer, CEN, Universität Hamburg]

 

Perspectives

The workshop aim was to bring together sea-ice observers and modelers. While no real consensus on the proposed approach was found, the reflection has been launched and probably deserves some more attention in the future in order to better compare sea-ice models and satellite observations. This might move the debate from an apple-to-oranges comparison to a pear-to-pear one. This will hopefully improve sea-ice models and satellite observations and improve future projections of sea-ice evolution.

 

Further reading

With contributions by Thomas Lavergne and Clara Burgard

Edited by Clara Burgard and Sophie Berger


David 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 — Think ‘tank’: oceanography in a rotating pool

Miniature ocean at the Coriolis facility in Grenoble. [Credit: Mirjam Glessner]

To study how the ocean behaves in the glacial fjords of Antarctica and Greenland, we normally have to go there on big icebreaker campaigns. Or we rely on modelling results, especially so to determine what happens when the wind or ocean properties change. But there is also a third option that we tend to forget about: we can recreate the ocean in a lab. This is exactly what our Bergen-Gothenburg team has been doing these last weeks at the Coriolis facility, in sunny Grenoble.


How to build your own miniature ocean

Take a 13m diameter (circular) swimming pool. Install it on a rotating platform, and start turning to simulate the Coriolis force, i.e. the impact of the Earth rotation on the flow. Fill it so that the water level reaches 90cm. Actually, the exact value does not matter and can be changed; just make sure that your tank width is an order of magnitude larger than your depth, and that you do not overflow everywhere on the lab floor. Congratulations, you have an ocean! But for now it is a bit boring.

Let’s add some stratification and density-driven currents. As we explained in a previous entry, all you need to do for that is change the temperature and/or salinity of your water. The people here at the Coriolis facility say that changing the salinity is easier than the temperature, so ok, put a source somewhere in your tank that will spit out salty water. Make it even more realistic: have some trough, underwater mountains, solid ice shelves etc. Or rather, some Plexiglas of the corresponding shape. Now you have a beautiful part of the ocean with realistic currents!

But how do you observe it? You can lower probes into the water at specific locations, as if you were doing miniature CTD casts in your miniature ocean. Or you can visualise the whole full-depth flow: add tracer particles to the water flowing from the source (in our case, biodegradable plastic), shoot lasers at it at various depth levels, and take high resolution pictures as you do so. Then, you can track the particles from one image to the next to infer their velocity, using a method called PIV.

 

By the way, it looks way neater than on this image – that one is just from our overview camera, for fun. [Credit: Céline Heuzé]

What does it look like when you fire lasers at a large rotating tank?

In a nutshell, it looks like this:

The water flows from the source on the right of the image, towards the ‘ice shelf’ on the left. We are watching the scene from above, from our office that rotates with the tank. The laser successively illuminates several levels from the bottom of the channel to the water surface, revealing the changing structure of the flow with depth. In our real experiment, it took more than 10 minutes for the water to reach the ‘ice shelf’ – here, I have slightly accelerated it.

It is surprisingly peaceful and relaxing to watch. Well, there is tension and suspense regarding what the flow will do since this is, after all, why we are here. But otherwise you are in the dark, with particles shining all around you, in the silence except for the low-squeeking noise of the rotating tank, gently rocked by the vibrations of the platform, and there is not much you can do but wait and enjoy the view. You can also count how many undesired bubbles and dead insects floating at the surface you can see!

Why do we need rotating tank experiments?

As we explained in this blog, the future of the Antarctic ice sheet is unknown due to marine ice sheet instability. We do not know under which conditions the floating ice shelves that block (‘buttress’) the big land-based ice sheet may collapse. In particular, we do not know what controls the flow of comparatively warm waters that melt the ice shelves:

  •  under which conditions do these waters penetrate under the ice?
  •  at which depths do they sit?
  •  what are the impacts of stratification and the shape of the ice shelf itself?

These questions cannot easily be answered by going in the field. We would need access to many ice shelves, year round, and the ability to observe the flow everywhere –including under the ice– synoptically. Instead in the lab, we just need to adjust our flow speed, or the rotation speed of the tank, or the amount of salt in the source, and we are ready to observe!

Further reading:

The blog of the team: https://skolelab.uib.no/blogg/darelius/

Our blog post about the video game Ice Flows!, illustrating the marine ice sheet instability

Edited by Sophie Berger

Image of the Week – Karthaus Summer School 2017

Gloriously cloudless day for the fieldtrip to the Ötztal Alps [Credit: C. Reijmer].

Glaciologists often undertake fieldwork in remote and difficult to access locations, which perhaps explains why they happily travel to similar locations to attend meetings and workshops. The Karthaus Summer School, which focuses on Ice Sheets and Glaciers in the Climate System, is no exception. The idyllic village of Karthaus, located in the narrow Schnalstal valley in Südtirol (Italy), has been hosting this 10-day glaciology course nearly every year since 1995. In September, an international crowd of some 30+ PhD students and postdocs, and 11 lecturers assembled in Karthaus for the 2017 edition of this famous course, for an intensive program of lectures, food, some science, more food (with wine!), and lots of socialising.


The lecture theatre with a backdrop of green hills, on the day the cows came down from the hills [Credit: D. Medrzycka].

The morning sessions

A typical morning of the course involved four hours of lectures, which covered a wide range of topics including continuum mechanics, thermodynamics, ice-ocean interactions, ice cores, geophysics, and geodynamics, with a special focus on numerical modelling and its applications for investigating ice-climate interactions. The lectures covered fundamentals processes, their applications and limitations, and current knowledge gaps for a wide range of complex concepts related to ice dynamics. All our lecturers happily answered our (many) additional questions during the coffee and cake breaks, enjoyed in the fresh mountain air outside the lecture theatre.

 
 
 
 
 
 
 

The biggest challenge was not the group work itself, but trying to not get distracted by the sun and the hills surrounding us [Credit: V. Zorzut].

The afternoon sessions

After a three-course lunch, we spent the afternoon sessions applying the theory learned in the morning lectures. The group projects were designed to get us to go into more detail on certain topics, and work on real-world applications for specific research problems. We presented the results of our work at the end of the course during a 15 minute group presentation. For those who could afford a bit of free time after these sessions, the rest of the afternoon could be spent either hiking or trail running in the steep hills overlooking the village (trying to beat I. Hewitt’s time up Kruezspitze), playing football, chilling in the sauna, or catching up on some sleep before dinner.

 

The evenings

Everyone who has ever attended the Karthaus course mentions the food, complementing both the quality and (legendary) quantity of it. Every evening, we were served a memorable five course meal accompanied by generous amounts of local wine. Dessert was followed by musical entertainment, with inspired performances by Frank Pattyn on the piano. On the last evening, Frank was accompanied by Johannes Oerlemans who treated us to two of his original tango arrangements on the guitar, followed by a passionate rendition of Jacques Brel’s Le port d’Amsterdam by our own Kevin Bulthuis (vocals). We wrapped up each day of the course in the local bar, socialising, playing card games, sampling the local beers, and making our way through the many different flavours of schnaps and grappa. Big thanks to the owners, Paul and Stefania Grüner, and staff (with a special shout-out to Hannes) of the Goldene Rose Hotel, and the village of Karthaus, for taking great care of us!

Frank Pattyn (piano) and Johannes Oerlemans (guitar) performing an original tango arrangement [Credit: D. Medrzycka].


 

Out and about

On the penultimate day of the course the group headed to a number of glaciers in the Ötztal Alps. The excursion, which happened to take place on a perfectly cloudless day, gave us the opportunity to observe first hand the changes affecting glaciers in the region, and the impact of these retreating ice masses on the landscape and humans inhabiting it. It also provided a much needed break from the intense week! After walking down the ski slopes of the Hochjochferner, a small valley glacier accessible by cable car from Kurzras, we stopped to enjoy the sun and have lunch at the Schöne Aussicht (Bellavista) hut (2845 m a.s.l.). Those with more energy scrambled up to the ridge running along the Italian/Austrian border (3270 m a.s.l.), through at times knee-deep snow, to take a peak at the Hintereisferner, a valley glacier on the Austrian side of the border. Four of us continued on along the ridge, and by chance visited the laser scanner (LiDAR) system operated by researchers from the University of Innsbruck, used to monitor changes in surface elevation on the glacier.

Standing on the ridge running along the Italian/Austrian border. View onto the Hintereisferner [Credit: D. Medrzycka].


 

Final thoughts

The 10 day course was certainly an intensive (and intense) experience, and I would recommend it to all glaciology students without reservations, whether they are looking for a basic introduction to ice dynamics, or aiming to fill a few knowledge gaps. Whilst some of the topics covered in the course were only remotely related to my own PhD research (and far out of my comfort zone!), the lectures and project work forced me to think in alternate ways. Although I may have finished the course with more questions than I had at the start, I now know where to go look for the answers!

A big part of the experience was without a doubt the social aspect of the course. Between the never ending and excellent food (as a result of which some of us developed “food babies”), and the long evenings at the local bar (resulting in increasing amounts of sleep deprivation), there were plenty of opportunities to talk science, gain new insights into our ongoing research, and discuss ideas for future projects. As with all great Summer Schools, one of the major perks was the opportunity to hang out with fellow students, expand our network of fellow researchers, and establish the groundwork for continued professional collaborations. Huge thanks to the convenor, Johannes Oerlemans, the village of Karthaus, and all the lecturers and fellow students for a memorable 10 days! I am looking forward to working with all of you in the future.

The crowd of the Karthaus summerschool: 2017 edition [Credit: C. Reijmer].

Edited by Morgan Gibson and Clara Burgard


Dorota Medrzycka is a PhD candidate at the University of Ottawa (Canada), working with Luke Copland. Her research focuses on the dynamics of glaciers and ice caps in the Canadian High Arctic, with a focus on ice flow instabilities (including glacier surging). Her project combines field studies and remote sensing techniques to monitor ice motion, and gain insight into the factors controlling the variability in ice dynamics in the Canadian Arctic. Contact: dorota.medrzycka@uottawa.ca.

Image of the Week – The true size of Greenland

Fig. 1: Greenland is slightly bigger than  Austria, Belgium, Denmark, France, Germany, Ireland, Italy, Poland, Portugal, the Netherlands and the United Kingdom together [Credit: The True Size].

Greenland is a critical part of the world, which is regularly covered on this blog, because it hosts the second largest ice body on Earth – the Greenland Ice Sheet. This ice sheet, along with its small peripheral ice caps, contributes by 43% to current sea-level rise.

However, despite being the world’s largest island Greenland, appears disproportionately large on the most common world maps (Fig. 2). Our new image of the week takes a look at the true size of Greenland…


Fig. 2: World (Mercator) map used by many online mapping applications. [Credit: D. Strebe/Wikimedia commons]

How big is Greenland?

We could simply tell you that Greenland stretches over ~2 million km². For most people, this figure would however not speak for itself.   Luckily, The True Size is a web application that comes to our rescue by enabling us to compare the true size of all the countries in the world.

As we can see in Fig. 1, Greenland is in fact only slightly bigger than Austria, Belgium, Denmark, France, Germany, Ireland, Italy, Poland, Portugal, the Netherlands and the United Kingdom together.

Similarly, Greenland is also (Fig. 3):

  • roughly the size of the Democratic Republic of Congo

  • could fit 1.4 times in India

  • 4.2 times smaller than than the United States

  • could fit 3.5 times in Australia

Fig. 3: Greenland vs Democratic Republic of Congo, Australia, the United States and India. [Credit: The True Size]

 Greenland is therefore big but not as big as what is suggested by the most common maps (Fig. 2). As a result, one can therefore wonder why the most popular world maps distort the size of the countries.

All maps are wrong but some are useful

To map the world, cartographers must project a curved surface on a flat piece of paper. There are different approaches to do so but all distort the earth surface in some ways. For instance, conformal projections preserve angles and shapes but change the size of the countries, whereas equal-area projections conserve the sizes but distort the shapes. As a result, a map projection that suits all purposes does not exist. Instead, the choice of the projection will depend on the use of the map.

Fig. 4: Mercator cylindrical projection [Credit: National Atlas of the United States]

The most popular projection, the Mercator projection (Fig. 2),  is used by many online mapping applications (e.g. google maps, OpenStreetMap, etc.). In Mercator maps, the Earth’s surface is projected on a cylinder that surrounds the globe (Fig. 4). The cylinder is then unrolled to produce a flat map that preserves the shapes of landmasses but tends to stretch countries towards the poles. This is why the size of Greenland is exaggerated in many world maps.

Why does google map use the Mercator projection then?

If Google Maps and other web mapping services rely on the Mercator projection, it is not to make countries at high latitudes appear bigger, but, because those tools are mainly intended to be used at local scales. The fact that the Mercator projection preserves angles and shapes therefore ensures minimal distortions at the city-level: two perpendicular streets will always appear perpendicular in Google Maps. This is not necessarily the case at high latitudes with projections that preserves areas (as can be seen here).

Interested in this topic? Then, you might enjoy this video !