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Cryospheric Sciences

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Image of the Week – Super-cool colours of icebergs

Image of the Week – Super-cool colours of icebergs

It is Easter weekend! And as we do not want you to forget about our beloved cryosphere, we provide you with a picture nearly as colourful as the Easter eggs: very blue icebergs! What makes them so special? This is what this Image of the Week is about…


What are icebergs made of?

Fig.2: An iceberg with ‘scallop’ indentations [Credit: Stephen Warren].

Icebergs are chunks of ice which break off from land ice, such as glaciers or ice sheets (as you’ll know if you remember our previous post on icebergs). This means that they are mostly made up of glacial ice, which is frozen freshwater from accumulated snowfall. However, in some places where ice sheets extend to the coastline, making an ice shelf, icebergs can be made up of a different type of ice too.

 

Ice shelves can descend far down into the ocean. Seawater in contact with the ice at depth in the ocean is cooled to the freezing temperature. Because the freezing temperature decreases with decreasing pressure, if the seawater moves upwards in the ocean, it will have a temperature lower than the freezing temperature at that depth. That means it’s super-cooled – the seawater temperature is below the freezing temperature, but it hasn’t become a solid. The seawater cannot last for long in this state and freezes to the base of ice shelves as marine ice, which is seawater frozen at depth. The marine ice can help stabilize the ice shelf as it is less susceptible to fractures than glacial ice. Icebergs that calve from Antarctic ice shelves can sometimes be mixtures of glacial ice (on the top) and marine ice (on the bottom).

 

What can icebergs tell us?

Icebergs which tip over can tell us about processes that happen at the base of ice shelves. For example, scallops on the ice (the small indentations that can be seen in the second picture) can show the size of turbulent ocean eddies in the ocean at the ice shelf base. Basal cavities or channels show where oceanic melt had a large impact. Any colours visible in the iceberg can also give us information.

Fig.3: Marine ice containing organic matter, giving a greenish appearance [Credit: Stephen Warren].

Why are icebergs different colours?

Like snow (see this previous post), different types of ice appear different colours. A typical iceberg is white because it is covered with dense snow, and snowflakes reflect all wavelengths of ice equally. The albedo of snow, which is the proportion of the incident light or radiation that is reflected by a surface, is very high (nearly 1). Glacial ice is compressed snow, meaning it has fewer light-scattering air bubbles, so light can penetrate deeper than in snow, and more yellows and reds from the visible spectrum are absorbed. This results in a bubbly blue colour, with a slightly lower albedo than snow. Marine ice does not have bubbles, but light can be scattered by cracks, resulting in clear blue ice (see our Image of the Week). However, if the seawater from which the marine ice was formed contained organic matter, like algae and plankton, the resulting marine ice can have a yellowish or even green appearance (Fig. 3). If the marine ice formed near the base of an ice shelf where it meets the sea floor, it could contain sediment, giving it a dirty or black appearance.

So the colour of icebergs can tell us something about how ice was formed hundreds of metres below the ocean surface. You could even say that was super-cool…

Further reading

  • Warren, S. G., C. S. Roesler, V. I. Morgan, R. E. Brandt, I. D. Goodwin, and I. Allison (1993), Green icebergs formed by freezing of organic-rich seawater to the base of Antarctic ice shelves, J. Geophys. Res., 98(C4), 6921–6928, doi:10.1029/92JC02751.
  • Morozov, E.G., Marchenko, A.V. & Fomin, Y.V. Izv. (2015): Supercooled water near the Glacier front in Spitsbergen, Atmos. Ocean. Phys. 51(2), 203-207. https://doi.org/10.1134/S0001433815020115
  • Image of the Week – Ice Ice Bergy
  • Image of the Week – Fifty shades of snow

This post is based on a talk by Stephen Warren presented at AMOS-ICSHMO2018

Edited by Clara Burgard


Lettie Roach is a PhD student at Victoria University of Wellington and the National Institute for Water and Atmospheric Research in New Zealand. Her project is on the representation of sea ice in large-scale models, including model development, model-observation comparisons and observation of small-scale sea ice processes.  

 

Image of the Week – Geothermal heat flux in Antarctica: do we really know anything?

Spatial distributions of geothermal heat flux: (A) Pollard et al. (2005) constant values, (B) Shapiro and Ritzwoller (2004): seismic model, (C) Fox Maule et al. (2005): magnetic measurements, (D) Purucker (2013): magnetic measurements, (E) An et al. (2015): seismic model and (F) Martos et al. (2017): high resolution magnetic measurements. The color scale is truncated at 30 and 80 mW m-2. The black line locates the grounding line. Note, (B)-(F) are in order of publication from oldest to most recent. [Credit: Brice Van Liefferinge, (2018), PhD thesis]

Geothermal heat flux is the major unknown when we evaluate the temperature and the presence/absence of water at the bed of the Antarctic Ice Sheet. This information is crucial for the Beyond Epica Oldest Ice project, which aims to find a continuous ice core spanning 1.5 million years (see this previous post). A lot of work has been done* to determine geothermal heat flux under the entire Antarctic Ice Sheet, and all conclude that additional direct measurements are necessary to refine basal conditions! However direct measurements are difficult to obtain, due to the thick layer of ice that covers the bedrock. Our new image of the week goes over what we currently know about the geothermal heat flux in Antarctica and presents the five data sets that currently exist. But first, let’s see where this heat flux come from?


What determines geothermal heat flux and how can we estimate it?

Heat flux measured at the surface of the Earth has two sources: (i) primordial heat remaining from when the Earth formed and (ii) contemporary-sourced heat coming from radioactive isotopes present in the mantle and the crust. This heat, concentrated in the Earth’s centre, can propagate to the surface through both conduction in the solid earth (inner core and crust) and convection in the liquid-viscous earth (outer core, lower and upper mantles). The net heat flux to reach the surface of the crust and penetrate the overlying ice is what we refer to as the ‘geothermal heat flux’. Wherever the crust is thinner, convection in the mantle can transfer heat more efficiently to the surface. In those locations, the net geothermal heat flux is higher, and vice versa. At mid-ocean ridges and in active volcanic areas, the heat can be delivered almost directly to the surface by advection (i.e. by the movement of magma), therefore leading to a higher net surface geothermal heat flux (think of Iceland, where the shallow crust allows them to take advantage of geothermal heat flux directly).

As a result, we know that the geology determines the magnitude of the geothermal heat flux and the geology is not homogeneous underneath the Antarctic Ice Sheet:  West Antarctica and East Antarctica are significantly distinct in their crustal rock formation processes and ages.

Nowadays, five independent global geothermal heat flux data sets exist: Shapiro and Ritzwoller, (2004); Fox Maule et al., (2005); Purucker, (2013); An et al., (2015); Martos et al., (2017) (see image of the week). All geothermal heat flux data sets compiled and currently used have been inferred from the properties of the crust and the upper mantle, as geology dictates the magnitude of geothermal heat flux spatially. Let’s see together how the estimation of geothermal heat flux has evolved over the years….

Using constant values (Panel A)

The simplest method, which consists in using a constant value of geothermal heat flux over the entire continent, was common at first and is still sometimes used (e.g. sensitivity tests and model intercomparison projects) as it facilitates model inter-comparisons. Pollard et al. (2005), in panel A, used bands of constant geothermal heat flux values (70, 60, 55 and 41 mW m-2), with geothermal heat flux decreasing from West Antarctica to East Antarctica, consistent with the known geology.

2004, a seismic model (Panel B)

Shapiro and Ritzwoller (2004) are the first to propose a geothermal heat flux distribution map based on seismic methods, and not strictly on rock composition. They extrapolate the geothermal heat flux from a global seismic model of the crust and the upper mantle which is an analysis of seismicity all over the world. Regions of the globe are grouped by their similarity in seismic structure. Assuming that a certain magnitude of seismicity represents a certain geothermal heat flux value, they assign geothermal heat flux value to regions where geothermal heat flux cannot be directly measured by using geothermal heat flux data from regions of similar seismicity. The geothermal heat flux spatial distribution obtained, with values up to 80 mW m-2 in West Antarctica and 48 mW m-2 in East Antarctica, agrees with that of Pollard et al. (2005). However, errors associated with this method are quite large, reaching 50% of the geothermal heat flux value.

 

2005, magnetic measurements (Panel C)

A year later, Fox Maule et al. (2005) derive a geothermal heat flux map based on satellite magnetic measurements and a thermal model. The objective is to determine the depth to the Curie temperature, the temperature at which a material loses its permanent magnetic properties. They set the Curie temperature to 580 °C, while the temperature at the ice-bedrock interface is set at 0 °C. Satellite magnetic measurements allow the calculation of the depth of each of these boundaries. The geothermal heat flux is then obtained using a thermal model of the crust between the depth of the two boundary temperatures. This method also has a large associated error, 60% of the geothermal heat flux value for the East Antarctic interior.

2013, reanalysis of magnetic measurements (Panel D)

In 2013, Purucker updates the Fox Maule et al. (2005) geothermal heat flux map with new magnetic data. The spatial geothermal heat flux pattern obtained still retains the characteristic pattern of low values in West Antarctica and high values in East Antarctica, but predicts lower absolute values for East Antarctica and around the West Antarctic coast.

2015, new seismic model (Panel E)

More recently, An et al. (2015) derive a new geothermal heat flux distribution based on seismic velocities. The method is similar to that used by Shapiro and Ritzwoller (2004). They analyse the Earth’s mantle properties using a new 3D crustal shear velocity model to calculate crustal temperatures and the surface geothermal heat flux. However, their spatial distribution of geothermal heat flux differs quite a bit from the other data sets, particularly in East Antarctica where geothermal heat flux values differ by 10 mW m-2 from those of Shapiro and Ritzwoller (2004). An et al. (2015) find very low geothermal heat flux values at the domes, which is good news for the search of Oldest Ice, but rather high overall values for East Antarctica compared to the other data sets. They explain that the model is invalid for geothermal heat flux values exceeding 90 mW m-2. But such high values should only impact young crust areas, mainly West Antarctica and therefore the variability observed in East Antarctica cannot be explained.

2017, high resolution magnetic measurements (Panel F)

In 2017, Martos et al. provide a high resolution geothermal heat flux map based on the spectral analysis of airborne magnetic data. They use a compilation of all existing airborne magnetic data to determine the depth to the Curie temperature and infer the geothermal heat flux using a thermal model. Their continent-wide spatial distribution of geothermal heat flux obtained agrees with previous studies, but they show higher overall magnitudes of geothermal heat flux including East Antarctica. They report an error of 10 mW m-2 which is interestingly smaller than for the other data sets. However, their data set does not take into account point measurements of geothermal heat flux. The same year, Goodge (2017) calculates an average geothermal heat flux value of 48 mW m-2 for East Antarctica with a standard deviation of 13.6 mW m from the analysis of clasts in the region between Dome A and the Ross Sea. A geothermal heat flux value of 48 mW m-2 is consistent with the mean value of the data sets described above.

All in all

To sum up, although all geothermal heat flux data sets agree on continent scales (with higher values under the West Antarctic ice sheet and lower values under East Antarctica), there is a lot of variability in the predicted geothermal heat flux from one data set to the next on smaller scales. A lot of work remains to be done …

* (e.g. Shapiro and Ritzwoller, 2004; Fox Maule et al., 2005; Purucker, 2013; An et al., 2015; Fisher et al., 2015; Parrenin et al., 2017; Seroussi et al., 2017; Martos et al., 2017; Goodge, 2017)

References

Van Liefferinge, B., Pattyn, F., Cavitte, M. G. P., Karlsson, N. B., Young, D. A., Sutter, J., and Eisen, O.: Promising Oldest Ice sites in East Antarctica based on thermodynamical modelling, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-276, in review, 2018.

Van Liefferinge, B. Thermal state uncertainty assessment of glaciers and ice sheets: Detecting promising Oldest Ice sites in Antarctica, PhD thesis, Université libre de Bruxelles, Brussels, 2018.

Edited by Sophie Berger


Brice Van Liefferinge  has just earned his PhD at the Laboratoire de Glaciology, Universite Libre de Bruxelles, Belgium. His research focuses on the basal conditions of the ice sheets. He tweets as @bvlieffe.

Image of the Week – Broccoli on Kilimanjaro!

Image of the Week – Broccoli on Kilimanjaro!

On the plateau of Kilimanjaro, Tanzania, the remnants of a glacier can be found and the ice from that glacier contains a rather interesting feature – Broccoli! Not the vegetable, but bubbles that look a lot like it. Our Image of the Week shows some of these strange “Broccoli Bubbles”. Read on to find out more about where these were found and how we can see them.


Figure 2: Kilimanjaro northern ice field, Tanzania, 5800 m a.s.l. Red arrow indicates where ice samples were collected [Credit: Adapted from a Google Earth image]

There is not much ice left on the mountain plateau of Kilimanjaro (Fig. 2), the highest mountain in Africa (5895 m a.s.l.), which is also a dormant volcano. Very likely the last remnants of glacier ice will have gone soon (Thompson et al., 2009). However, a recent expedition to Kilimanjaro’s Northern Ice Field in 2015 (Bohleber et al., 2017) brought home some ice block samples cut with a chain saw from the accessible southern ice cliff 5800 m a.s.l. (red arrow, Fig. 2) . These block were then studied in  ice laboratory at AWI in Germany and an interesting observation was made…Broccoli bubbles!

These irregularly shaped bubbles, which look like broccoli, were seen in the polished ice slabs using close-up photography and an LASM (Large Area Scan Macroscope). This type of bubble intrigued scientists as it is certainly not a common one! When looking from above onto a horizontal section the broccoli bubbles appear to have pointy tips (Fig. 3.), which are all directed towards the glacier face.

Figure 3: “Broccoli” bubbles seen from above. RHS: A horizontal section of ice, area in image is approx. 2 cm high, image is a close-up photograph with a metal plate in the background. The pointed tips of the bubbles (up in this photo) are directed towards the ice cliff face (from which the samples were taken). LHS: Large Area Scan Macroscope (LASM) cross-section through the sample (LHS). The black pore spaces are the Broccoli bubbles [Credit: Johanna Kerch].

Another type of bubble makes also an appearance: the disk- or bowl-shaped bubble (Fig. 1). It is rather regular but not rounded. Instead it is flattened on one or both sides and a little angular, maybe even leaning towards a hexagonal shape. Disk bubbles found close together are oriented in the same direction, one explanation for this could be that the crystal orientation of the ice (the way the ice crystal align during ice flow) plays a role in the bubble formation.

How do the broccoli and disk bubbles evolve? Although we suspect it has something to do with the temperate ice and some temperature gradient at the ice cliff, we do not know for certain. Nonetheless, it is a marvellous thing to discover – before the Kilimanjaro glacier ice is gone for good!

Edited by Emma Smith


Johanna Kerch is a postdoctoral researcher at Alfred-Wegener-Institute in Bremerhaven. Her research focus is on crystal-preferred orientation and microstructure of glacier ice and how it links to other physical properties in ice and the deformation mechanisms in glacier ice. She has studied cold and temperate glacier ice from various sites in the Alps and has recently been involved in making measurements of the physical properties of the EGRIP ice core. She tweets as @JohannaKerch.

Image of the Week – The colors of sea ice

Image of the Week – The colors of sea ice

The Oscars 2018 might be over, but we have something for you that is just as cool or even cooler (often cooler than -20°C)! Our Image of the Week shows thin sections of sea ice photographed under polarized light, highlighting individual ice crystals in different colors, and is taken from a short video that we made. Read more about what this picture shows and watch the movie about how we got these colorful pictures…


Sea ice can vary in salinity

Sea ice forms differently than fresh water ice due to its salt content. When sea water begins to freeze, the ice crystals aren’t able to incorporate salt into their structure and hence reject salt into the surrounding water. This increases the density of the remaining sea water which sinks (see this previous post). Some salty water gets trapped between the crystals though. This water will also slowly freeze, always rejecting the salts into the remaining water. The saltier the water, the lower its freezing point. This means the remnant very salty water, which we call brine, remains liquid even at temperatures below -20oC!

Sea ice crystals can vary in shape

The first layer of sea ice is typically granular – the crystals are small and round, with a diameter around one centimeter. This is because this layer is formed in open seas, where the crystals which go on to form this layer are spun and broken up by surface waves. This granular structure includes lots of ‘pockets’ of trapped brine. Under this surface ice layer, which is typically 10-30 cm thick, ice starts growing in more sheltered conditions. Such sea ice is columnar. The crystals are flat and elongated – like layers in a vertical cake. The brine is trapped between these layers in brine channels. When ice is relatively warm, for example shortly after freezing or before it starts melting, such channels are wide and can be connected. Brine can then escape from them at the lower end into the ocean. The channels also allow small, hardy microscopic plants and animals to travel through the ice. Often air bubbles are trapped in them too.

Sea ice can vary in how it looks too!

The size and form of sea ice crystals – sea ice texture – impacts various properties of the sea ice including its salt content, density and suitability as a habitat. It also influences the optical properties of ice, however. While pure water ice is transparent (see this previous post), sea ice appears milky. That is because of brine channels and bubbles between the crystals.

When looking at large regions of sea ice from space by sensors mounted on satellites, sea ice texture will be important too. Visible light has a short wavelength and this means it only penetrates into the top millimeter of ice. Images collected in the visible light range (see this previous post) will show features dominated by the surface properties of the ice. In comparison, microwaves have a longer wavelength and can penetrate deeper into the ice. Hence imagery of the sea ice cover collected in the microwave spectrum of light (see this previous post) will display features influenced by the internal structure of the sea ice in addition to the surface features.

 

The video below shows how the sea ice samples are analyzed for texture and how we got the colorful pictures for our Image of the Week…

 

Further reading

Edited by Adam Bateson and 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 – A Hole-y Occurrence, the reappearance of the Weddell Polynya

Image of the Week – A Hole-y Occurrence, the reappearance of the Weddell Polynya

During both the austral winters of 2016 and 2017, a famous feature of the Antarctic sea-ice cover was observed once again, 40 years after its first observed occurrence: the Weddell Polynya! The sea-ice cover exhibited a huge hole (of around 2600 km2 up to 80,000 km2 at its peak!), as shown on our Image of the Week. What makes this event so unique and special?


Why does the Weddell Polynya form?

The Weddell Polynya is an open ocean polynya (a large hole in the sea ice, see this previous post), observed in the Weddell Sea (see Fig.2). It was first observed in the 1970s but then did not form for a very long time, until 2016 and 2017…

 

Fig. 2: Map of the sea ice distribution around Antarctica on 25th of September 2017, derived from satellite data. The red circle marks the actual Weddell Polynya [Credit: Modified from meereisportal.de]

In the Southern Ocean, warm saline water masses underlie cold, fresh surface water masses. The upper cold fresh layer acts like a lid, insulating the warmer deep waters from the cold atmosphere. While coastal polynyas (see this previous post) are caused by coastal winds, open ocean polynyas are more mysteriously formed as it is not as clear what causes the warm deep water to be mixed upwards. In the case of the Weddell polynya, it forms above an underwater mountain range, the Maud Rise. This ridge is an obstacle to the water flow and can therefore enhance vertical mixing of the deeper warm saline water masses. The warm water that reaches the surface melts any overlying sea ice, and large amounts of heat is lost from the ocean surface to the atmosphere (see Fig. 3).

 

Fig. 3: Schematic of polynya formation. The Weddell polynya is an open ocean polynya [Credit: National Snow and Ice Data Center].

 

Why do we care about the Weddell Polynya?

Overturning and mixing of the water column in the Weddell Polynya forms cold, dense Antarctic Bottom Water, releasing heat stored in the ocean to the atmosphere in the process. Antarctic Bottom Water is formed in the Southern Ocean (predominantly in the Ross and Weddell Seas) and flows northwards, forming the lower branch of the overturning circulation which transports heat from the equator to the poles (see Fig. 4). Antarctic Bottom Water also carries oxygen to the rest of the Earth’s deep oceans. The absence of the Weddell polynya could reduce the formation rate of Antarctic Bottom water, which could weaken the lower branch of the overturning circulation.

Fig.4: Schematic of the overturning (thermohaline) circulation. Deep water formation sites are marked by yellow ovals. Modified from: Rahmstorf, 2002 [©Springer Nature. Used with permission.]

How often does the Weddell Polynya form?

The last time the Weddell Polynya was observed was during the austral winters of 1974 to 1976 (see Fig. 5). It was then absent for nearly 40 years (!) up until austral winter 2016. In a modelling study, de Lavergne et al. 2014 suggested that the Weddell Polynya used to be more common before anthropogenic CO2 emissions started rising at a fast pace. The increased surface freshwater input from melting glaciers and ice sheets, and increased precipitation (as climate change increases the hydrological cycle) have freshened the surface ocean. This freshwater acts again as a lid on top of the warm deeper waters, preventing open ocean convection, reducing the production of Antarctic Bottom Water.

Fig. 5: Color-coded sea ice concentration maps derived from passive microwave satellite data in the Weddell Sea region from the 1970s. The Weddell Polynya is the extensive area of open water (in blue) [Credit: Gordon et al., 2007, ©American Meteorological Society. Used with permission.].

The reappearance of the Weddell Polynya over the past two winters despite the increased surface freshwater input suggests that other natural sources of variability may be currently masking this predicted trend towards less open ocean deep convection. Latif et al. 2013 put forward a theory describing centennial scale variability of Weddell Sea open ocean deep convection, as seen in climate models. In this theory, there are two modes of operation, one where there is no open ocean convection and the Weddell Polynya is not present. In this situation, sea surface temperatures are cold and the deep ocean is warm, and there is relatively large amount of sea ice. The heat at depth increases with time, as it is insulated by the sea ice and freshwater lid. Then, eventually, the deep water becomes warm enough that the stratification is decreased sufficiently so that open water convection begins again, forming the Weddell Polynya. This process continues until the heat reservoir depletes and surface freshwater forcing switches off the deep convection. Models show that the timescale of this variability is set by the stratification, and models with stronger stratification tend to vary on longer timescale, as the heat needs to build up more in order to overcome the stratification.

 

In the end, the Weddell Polynya is still surrounded by some mystery… Only the next decades will bring us more insight into the true reasons for the appearance and disappearance of the Weddell Polynya…

 

Further reading

Edited by Clara Burgard


Rebecca Frew is a PhD student at the University of Reading (UK). She investigates the importance of feedbacks between the sea ice, atmosphere and ocean for the Antarctic sea ice cover using a hierarchy of climate models. In particular, she is looking at the how the importance of different feedbacks may vary between different regions of the Southern Ocean.
Contact: r.frew@pgr.reading.ac.uk

Image of the Week – The world in a grain of cryoconite

Fig 1: A single grain of cryoconite (top left) is home to a microscopic city of microbes, revealed here by chlorophyll fluorescence microscopy – a technique that causes photosynthesising microbes to emit light (top right) and portable DNA sequencing (bottom panel) [credit: Arwyn Edwards]

Microbes growing on glaciers are recognized for their importance in accelerating glacier melting by darkening their surface and for maintaining biogeochemical cycles in Earth’s largest freshwater ecosystem. However, the microbial biodiversity of glaciers remains mysterious. Today, new DNA sequencing techniques are helping to reveal glaciers as icy hotspots of biodiversity.


To see a world in a grain of…cryoconite

Earth’s glaciers and ice sheets are among its most impressive features, yet this majesty conceals their microscopic riches. We must turn to the microscope and the DNA sequencer to reveal the natural history of glaciers. Rather than a grain of sand, this world lies hidden in a grain of cryoconite. Cryoconite ecosystems are microbe-mineral aggregates which darken the surface of glaciers world-wide which – along with algae – enhance absorption of solar energy and promote glacier melting through so-called bioalbedo feedbacks. Microscopy studies from the late 19th and early 20th century reveal that a diverse range of algae, cyanobacteria, heterotrophic bacteria, protists, fungi and even tardigrades live within cryoconite, but it is only in the last decade that we have started to resolve the genetic diversity of life within cryoconite.

From glaciers to genomes…and back again

Considering glaciers are Earth’s largest freshwater ecosystems, we know very little about the genetic diversity of their inhabitants. Of all known glaciers, fewer than 0.05% have any form of DNA datasets associated with them. Such DNA datasets are commonplace for other environments, as demonstrated by the Earth Microbiome Project. From the limited studies performed, it appears the microbial ecosystems of glaciers are no less diverse than temperate environments: even dark, cold and isolated subglacial lakes harbour thousands of bacterial species. As climatic warming increasingly threatens glaciers, unpicking the interactions between microbes and melt is vital, as is establishing the extent to which glacier biodiversity is threatened. Sequencing microbial genomes from glacial ecosystems is therefore urgent.

Fig 2: Preserving microbial samples from cryoconite for return to the author’s home lab is a conventional approach to studying genetic diversity on glaciers, but the portability of MinION DNA sequencing brings the lab to the field [Credit: Arwyn Edwards].

A DNA sequencer in your rucksack

Such genetic studies have required the collection of samples from glaciers and their return to state-of-the-art laboratories equipped with high throughput DNA sequencers. However, new, portable DNA sequencers are being trialled on cryoconite to permit sequencing of DNA in field labs. Using a pocket-sized DNA sequencer called a MinION connected to the USB port of a laptop, it is possible to extract, sequence and analyse microbial genomes while still in the field. While Nanopore DNA sequencing using MinION devices are increasingly applied to medical emergencies such as Ebola or antibiotic resistance, their highly portable nature means that glacier scientists will be able to collect and analyse microbial genomes while in the field, making the genetic diversity of glaciers accessible.

Who’s who in cryoconite?

Using MinION for DNA sequencing in a field lab at the UK Arctic Station in Ny Ålesund, it was possible to generate rapid profiles of microbial diversity in cryoconite. So who lives in Arctic cryoconite? The most abundant bacterial group identified is a close match to Phormidesmis priestleyi, a filamentous cyanobacterium responsible for engineering the growth of cryoconite grains on Arctic glaciers. In Figure 1 above, Phormidesmis is visible as the bright red, chlorophyll-rich filaments binding together the cryoconite grain. Other cyanobacteria are present, including a species matching sequences from Phormidium autumnale found in an Antarctic lake. However, MinION sequencing is useful in revealing less charismatic microbes. Also abundant within the community are members of the Polaromonas genus. Found in both cold and highly polluted environments worldwide, Polaromonas bacteria are highly flexible in their lifestyles, able to adapt to using highly poisonous compounds as food sources, or even anoxygenic phototrophy (photosynthesis without using water or producing oxygen) on alpine glaciers. Cryoconite sequences matching DNA from Methylibium found in Tibetan permafrost also hint at the need for flexible metabolism to survive on glacier surfaces. Finally, Ferruginibacter sequences best matching DNA data from iron-rich dust aggregates forming on snow in the Japanese mountains suggest that cold-tolerant iron cycling may be occurring within cryoconite.

In a grain of cryoconite, we see relatives of cyanobacteria from Arctic glaciers, but also Antarctic lakes, metabolically flexible bacteria found in cold and contaminated environments, and even bacteria living by respiring iron on snow in the Japanese mountains. We see a world.

Edited by Joe Cook and Sophie Berger


Dr Arwyn Edwards is a Senior Lecturer in Biology at Aberystwyth University and the present Royal Geographic Society’s Walters Kundert Arctic Fellow. His research on genomic diversity in glacial environments is supported by the Leverhulme Trust.

Image of the week – Skiing, a myth for our grandchildren?

Image of the week – Skiing, a myth for our grandchildren?

Ski or water ski? Carnival season is typically when many drive straight to the mountains to indulge in their favorite winter sport. However, by the end of the century, models seem to predict a very different future for Carnival, with a drastic reduction in the number of snow days we get per year. This could render winter skiing something of the past, a bedtime story we tell our grandchildren at night…


Christoph Marty and colleagues investigated two Swiss regions reputed for their great skiing resorts and show that the number of snow days (defined as a day with at least 5 cm of snow on the ground) could go down to zero by 2100, if fuel emissions and economic growth continue at present-day levels, and this scenario is less dramatic than the IPCC’s most pessimistic climate change scenario (Marty et al., 2017). They show that temperature change will have the strongest influence on snow cover. Using snow depth as representative for snow volume, they predict that snow depth maxima will all be lower than today’s except for snow at elevations of 3000 m and higher. This implies that even industrially-sized stations like Avoriaz in the French Alps, with a top elevation of 2466 m, will soon suffer from very short ski seasons.

Marty et al. (2017) predict a 70% reduction in total snow volume by 2100 for the two Swiss regions, with no snow left for elevations below 500 m and only 50% snow volume left above 3000 m. Only in an intervention-type scenario where global temperatures are restricted to a warming of 2ºC since the pre-industrial period, can we expect snow reduction to be limited to 30% after the middle of the century.

Recent work by Raftery et al (2017) shows that a 2ºC warming threshold is likely beyond our reach, however limiting global temperature rise, even above the 2ºC target, could help stabilize snow volume loss over the next century. We hold our future in our hands!

Further reading/references

  • Marty, C., Schlögl, S., Bavay, M. and Lehning, M., 2017. How much can we save? Impact of different emission scenarios on future snow cover in the Alps. The Cryosphere, 11(1), p.517.
  • Raftery, A.E., Zimmer, A., Frierson, D.M., Startz, R. and Liu, P., 2017. Less than 2 C warming by 2100 unlikely. Nature Climate Change, 7(9), p.637.
  • Less snow and a shorter ski season in the Alps | EGU Press release

Edited by Sophie Berger


Marie Cavitte just finished her PhD at the University of Texas at Austin, Institute for Geophysics (USA) where she studied the paleo history of East Antarctica’s interior using airborne radar isochrone data. She is involved in the Beyond EPICA Oldest Ice European project to recover 1.5 million-year-old ice. She tweets as @mariecavitte.

Image of the Week – The Gap, the Bridge, and the Game-changer

The Gap, the Bridge, and the Game-changer, together with many of the passive microwave satellite missions relevant for sea ice concentration mapping for the period 1980s to 2030s [Credit: T. Lavergne].

The Gap, the Bridge, and the Game-changer are three series of satellites. They carry instruments that measure the microwave radiation emitted by the Earth (called passive microwave instruments), while flying 800 km above our heads at 7,5 km/s. Since the late 1970s, most sea ice properties (concentration, extent, area, velocity, age and more!) have been measured with such passive microwave instruments.
So who are the Gap, the Bridge, and the Game-changer? Their story is what this Image of the Week is about…


The Gap

Since 1978, the U.S. equipped 11 satellites with passive microwave instruments to observe global sea ice. These instruments are called SMMR, SSM/I and SSMIS. Their measurements have produced a continuous, almost 40 year long climate data record of sea ice (see how satellite observations are converted into sea ice properties in this previous post). However, as described late last year in a Nature article, the remaining three of these instruments are ageing, already beyond their expected lifetime, and with no planned continuation from the U.S (see SSMIS F16-18 on our Image of the Week).

Europe will be operating a series of similar instruments (the MicroWave Imagers, MWI) on their 2nd Generation Polar System from 2023. A (looming future) gap is feared if the last U.S. instruments fail before the European ones are fully operating.

The decline of summer sea ice extent in the Arctic is an iconic indicator of climate change and U.S. satellites have enabled and sustained its monitoring for all these years (see this earlier post). More than a news magnet, the satellite time series is a back-bone for our understanding of the evolution of global sea ice. It is a key asset for developing and evaluating our climate models. The possibility of a data gap understandably caught the attention of the scientific community and the general public. This (looming future) «Gap» is the first character in our story.

The Bridge

The «Bridge» is known under the code name Feng Yun 3 (FY3) MWRI and is Chinese. The FY3 programme, operated by the Chinese Meteorological Administration (CMA), is a series of satellites with passive microwave instruments very similar to the ones on the American and European satellites. FY3D -the 4th satellite in the FY3 series- was successfully launched in late 2017, bridging the data gap that was feared to happen, even if the remaining U.S. SSMIS satellites would fail next month.

Over the past few months, scientists at the EUMETSAT OSI SAF (the European Organization for the Exploitation of Meteorological Satellites – Ocean and Sea Ice Satellite Application Facility) have been investigating the quality of FY3 passive microwave data. They adapted their algorithms to retrieve sea ice concentration from raw satellite measurements, so that they yield very similar accuracy to the sea ice concentration data they obtain from the SSMIS. An example sea ice concentration map using the OSI SAF algorithm on raw FY3 data is shown below. Such maps can extend the climate data record released in early 2017, should the last SSMIS fail.

Sea Ice Concentration maps for February 6th 2018 (left: Northern Hemisphere, right: Southern Hemisphere). These are computed by the OSI SAF algorithms applied on raw FY3 MWRI data [Credit: A. Sørensen].

Access to the FY3 data was facilitated by bi-lateral agreements between EUMETSAT and CMA. National and international space agencies coordinate their activities in a variety of forums such as CEOS (Comittee on Earth Observation Satellites), CGMS (Coordination Group for Meteorological Satellites) or WMO PSTG (the World Meteorological Organization Polar Space Task Group) to cite a few. This global-scale coordination goes mostly unnoticed to the public and the scientific community. It is, however, a great aid for our ability to continuously monitor and predict the global environment.

You might think that, now that the Gap is Bridged, I have nothing more to tell you about passive microwave satellites for sea ice observations? Well, think again. There is a third character to our story: the «game-changer».

The Game-changer

Without further teasing you, our «game-changer» is CIMR. CIMR stands for the «Copernicus Imaging Microwave Radiometer». It might get selected for joining the family of Copernicus satellites some time in the late 2020s.

Before I tell you what makes CIMR so special, we need a short introduction on what passive microwave instruments are, why we like them for observing sea ice, and how they work:

T. Lavergne (2018) Passive Microwave Remote Sensing of Sea Ice : a crash-course in just four list items, Int. J. of Short Lists

  1. The best satellite instruments for measuring sea ice use the microwave part of the electromagnetic spectrum (from ~1 to ~100 GHz). This type of radiation does not depend on Sun light, and is not blocked by clouds.

  2. Passive microwave instruments record a tiny amount of radiation naturally emitted at the surface of the Earth and in the atmosphere. Aboard the satellite, the radiation is reflected by an antenna towards a recording instrument: the radiometer.

  3. Radiometers can measure at several frequencies. Once the images are back at the processing centers on Earth, algorithms are applied to compute geophysical products such as sea ice concentration.

  4. Radiometers with low frequencies (e.g. 6 GHz) yield best accuracy for sea ice concentration products. The bigger the antenna, the better the final resolution of the product.

One of a kind, the CIMR will focus on the low frequencies (6, 10, and 18 GHz), and fly an antenna big enough to ensure much better resolution than any of the passive microwave instruments we ever used before. This requires the antenna of CIMR to be substantially larger than that of SSMIS (60cm diameter), MWI (75cm) or even AMSR2 (2.1m)! The AMSR-E instrument and its followers were game-changers 15 years ago, and still offer the best resolution today… but future operational models and polar applications will require better sea ice products all too soon.

An exciting time opens for satellite-based observations of polar sea ice, as the pre-studies for CIMR are started by the European Space Agency this spring! Will industry take-up the challenge and build a big enough antenna for CIMR? Will CIMR be selected as EU’s future polar Copernicus mission? If “yes” to both, Europe will have a game-changer: high-resolution all-weather daily global accurate mapping of sea ice concentration.

I will definitely follow the developments with CIMR! Maybe I’ll tell you how it went in a future blog post? 🙂

Note: Were there too many acronyms in this blog? Well, we are sorry about that. Those satellite-people just LOVE their acronyms! A good resource for searching what satellite acronyms mean is the “Space capability” page from the World Meteorological Organization: https://www.wmo-sat.info/oscar/spacecapabilities (enter the acronym in the Quick Search, top-right for the page).

Further reading

Edited by David Docquier and Clara Burgard


Thomas Lavergne is a research scientist at the Norwegian Meteorological Institute. His main interest is in improving algorithms to improve sea ice satellite products, and help towards a better understanding between observation and model communities. He recently worked with EUMETSAT OSI SAF and ESA CCI to produce Climate Data Records for Sea Ice Concentration. He tweets as @lavergnetho.

Image of the Week – Microbes have a crush on glacier erosion

Image of the Week – Microbes have a crush on glacier erosion

Glacier erosion happens at the interface between ice and the ground beneath. Rocks are ground down to dust and landscapes shaped by the flowing ice. While these might be hotspots for erosion, the dark and nutrient-poor sites are unlikely environments for biological activity. However, experiments suggest there may be novel sources of energy powering subglacial microbial life…


Where there is water, there is life…

Glaciers, ice sheets and ice caps cover around 11% of the earth’s land surface. At least 50% of the beds of these ice masses have temperatures at melting point due to the high pressure beneath the weight of the ice masses (Oswald and Gogineni, 2012). Liquid water is therefore present at the ice-bedrock interface in these areas. Additionally, erosion is a frequent feature of larger ice masses, and involves crushing and fracturing of bedrock. Consequently, recently crushed and wetted rock is a common feature of glacier and ice sheet beds. The adage that “where there is water, there is life” holds true for all glacier beds sampled to date, and for the only subglacial lake directly sampled beneath Antarctica, Subglacial Lake Whillans. Still, there is a large spectrum of different aquatic subglacial habitats beneath glaciers and ice sheets. The subglacial environments host genetically and functionally diverse microbial ecosystems capable of accelerating rock weathering (Montross et al., 2013), influencing global carbon cycles (Wadham et al., 2012) and productivity in adjacent oceans (Death et al., 2014).

How long can life survive beneath large ice masses?

However, the maintenance and longevity of these ecosystems is currently an area of uncertainty. Subglacial debris contains chemicals such as sulphides and organic matter that provide energy to sustain subglacial life (Hamilton et al., 2013). This is particularly important in areas close to the margin where melting water from the surface enters through moulins and crevasses and transports O2 and other biologically useful compounds such as DOC (dissolved organic carbon), POC (particulate organic carbon) and nutrients (such as Nitrogen and Phosphorus) to the bed. However, in the interior zones of ice sheets, the direct input of these species to the bed is negligible because hydrological connections between surface and bed do not exist. The O2 that is added to the bed in these locations is limited to gas bubbles in the basal ice which is geothermally melted or melts as regelation waters form and refreeze as ice flows around irregularities of the bedrock . This is problematic for the longer term maintenance of life in subglacial lakes and other aquatic environments beneath the ice sheet interiors, such as swamps and ice stream beds, because there is a lack of dissolved oxygen, and there is little energy derived from oxidants interacting with organic matter and sulphides. Further, the supply of potentially reactive organic matter, for example within former marine sediments, is finite and decreases over time, Therefore, subglacial life beneath ice sheet interiors is destined to expire unless new and sustainable sources of energy can be generated at the bed.

Hydrogen seems to be the miraculous diet!

A major advance in our understanding of the maintenance of life in subglacial environments was the recent discovery that H2 is produced by subglacial crushing. This is an important energy source for microbial food chains, because physical energy is transferred, via surface chemical (free-radical) energy, to biological activity and energy. Experiments show that  around 10-20 nmol H2 is produced per gram of crushed rock after 120 hours (Telling et al., 2015). Even if they sound very small, these concentrations are significant since only sub-nanomolar concentrations of H2 are required to sustain microbial growth near 0°C (Hoehler, 2004). Hydrogen is utilized by many types of microbes, and is generated abiotically via the interaction of silica surface radicals with water.

Next time you look at an otherwise dull grey meltwater stream draining a glacier, think of the crushing and the hydrogen that has been liberated by glacier erosion. The grey coloration arises from suspended sediment concentrations of about 1kg/m3 of meltwaters, and the sediment is typically silt- to clay-sized [Credit: Martyn Tranter].

Production of H2 supports the base of microbial food webs in fault and hydrothermal zones. Therefore, it is no stretch to suppose that this could be the case beneath glaciers. The H2 production rate from experimental rock crushing exceeds that required to support measured rates of methane production in the upper centimetre of South Western Greenland subglacial sediments. Additionally, rates of methane production in these subglacial sediments increased 10 times with the addition of excess H2 at 1°C (Stibal et al., 2012). A range of aerobic and anaerobic bacteria thought to be capable of oxidizing H2 as a source of energy have been found in subglacial sediments. Adding H2 to subglacial sediments from Robertson Glacier provided compelling evidence that the non-biological H2 produced during rock crushing could provide the sustain H2-oxidizing microbes (Telling et al., 2015).

Subglacial Lake Whillans is the first Antarctic subglacial lake to be sampled via a direct access hole. Water and sediment from the lake contain microbial life (Christner et al., 2013). Examination and experimentation on these unique samples is currently ongoing at the University of Bristol, where we hope to show that even already heavily weathered sediment produces hydrogen and supports microbial ecosystems when crushed and wetted. Subglacial microbes really do have a crush on glacier erosion, but don’t say it with chocolate or flowers, say it with hydrogen.

Edited by Joe Cook and Clara Burgard


Martyn Tranter is a polar biogeochemist, resident at the Bristol Glaciology Centre, University of Bristol, UK. Contact Email: m.tranter@bristol.ac.uk.

Image of the Week – Ice caps on Mars?!

Image of the Week – Ice caps on Mars?!

Much like our Planet Earth, Mars has polar ice caps too, one for each pole: the Martian North Polar Ice Cap (shown on our image of the week) and the Southern Polar Ice Cap. Yet, their composition and structure reveals these ice caps are quite different from those of Planet Earth…


Mars refresher

 

Planet Earth and planet Mars [Credit : NASA]

As a refresher, here are some Mars facts:

  • Mars is the 4th planet from the sun.
  • Its equatorial diameter is half the size of the Earth’s, but is bigger than our moon’s.
  • Its mean surface temperature is -63°C (the Earth’s surface is around 14°C)
  • Mars’ atmosphere is 96% carbon dioxide, less than 2% argon, less than 2% nitrogen and less than 1% other gases.
  • Mars’ rotational axis has a tilt similar to Earth’s giving it four seasons as well .

For more detailed pictures and facts about Mars, go have a look on the NASA website here.

What are these Martian ice caps like?

Like Earth, both of Mars’ poles are frozen. It is the only place in the solar system besides Earth where you can find permanent ice caps. These two Martian ice caps are primarily made of frozen water… but not only! During the winter season, the poles permanent bulk of “water ice” are covered by a seasonal layer of frozen carbon dioxide (commonly known as dry ice).

How come? Similar to Earth, during each pole’s respective winter, these ice caps experience continuous darkness for several months. The temperature becomes so cold (freezing point is -126°C !) that carbon dioxide in its atmosphere freezes and falls onto the ground, forming layers of dry ice. In the summer when the sun returns and temperatures warm, the dry ice begins sublimating back into the atmosphere. At the North pole almost all the dry ice turns back into gas and the ice caps shows its water ice, while a layer of frozen carbon dioxide always remains at the South pole. Seasonal variations can thus be observed like those on Earth.

Martian North (left) et South (right) poles [Credit: NASA ]

The northern ice cap on Mars is much bigger than the southern one. It is about 1,000 kilometers wide (roughly the width of Greenland at its widest point) while the South pole is only 350 kilometers in diameter. Yet… they both contain the same amount of ice! If all of this ice was to melt, Mars’ surface would be covered by an ocean that was 18 meters deep. They are thus the currently largest known water reservoirs on the planet.

But… what are these spiral forms on Mars’ ice caps?!

The ice caps at both Martian poles show spiral throughs. According to the ESA, these unique features are the result of strong winds that spiral at the surface of the ice caps due to the same Coriolis effect that exists on Earth. This makes every fluid rotate to the right in the North Hemisphere and to the left in the South Hemisphere.

In the North Pole, one of these throughs, called Chasma Boreale, is particularly big. This 100-kilometer-wide and 2-kilometer-deep canyon roughly cuts the Northern Martian ice cap in half.

Chasma Boreale on the Northern ice cap [Credit: NASA ]

Drilling ice cores on Mars?

The seasonal melting and accumulation of ice occurs while dust deposits, which explain why both Martian polar caps exhibit layered features. They are thus composed of layers of ice mixed with dust (in the scientific jargon, Mars ice caps are called “Polar Layered Deposits”). As for ice cores on Earth, information about the past climate of Mars might be “trapped” in these dust layers. These are essential if we want to find proof of a time when liquid water existed on Mars! Unfortunately, ice cores have not been drilled… yet!

Layers in North Martian Ice Cap (The more dust, the darker the surface) [Credit: NASA/JPL/University of Arizona ]

Further Reading

Edited by David Rounce


Violaine Coulon is a PhD student of the glaciology unit, at the Université Libre de Bruxelles (ULB), Brussels, Belgium. She is using a numerical ice sheet model to investigate the dynamics and stability of the Antarctic Ice Sheet for the past 1.5 million years.