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Cryospheric Sciences

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Image of the week — Making pancakes

A drifting SWIFT buoy surrounded by new pancake floes. [Credit: Maddie Smith]

It’s pitch black and twenty degrees below zero; so cold that the hairs in your nose freeze. The Arctic Ocean in autumn and winter is inhospitable for both humans and most scientific equipment. This means there are very few close-up observations of sea ice made during these times.

Recently, rapidly declining coverage of sea ice in the Arctic Ocean due to warming climate and the impending likelihood of an ‘ice-free Arctic’ have increased research and interest in the polar regions. But despite the warming trends, every autumn and winter the polar oceans still get cold, dark, and icy. If we want to truly understand how sea ice cover is evolving now and into the future, we need to better understand how it is growing as well as how it is melting.


Nilas or thin sheets of sea ice [Credit: Brocken Inaglory (distributed via Wikimedia Commons) ]

Sea ice formation

Sea ice formation during the autumn and winter is complex. Interactions between ocean waves and sea ice cover determine how far waves penetrate into the ice, and how the sea ice forms in the first place. If the ocean is still, sea ice forms as large, thin sheets called ‘nilas’. If there are waves on the ocean surface, sea ice forms as ‘pancake’ floes – small circular pieces of ice. As the Arctic transitions to a seasonally ice-free state, there are larger and larger areas of open water (fetch) over which ocean surface waves can travel and gain intensity. Over time, with the continued action of waves in the ice, pancake ice floes develop raised edges —  as seen in our image of the week — from repeatedly bumping into each other. Pancake ice is becoming more common in the Arctic, and it is already very common in the Antarctic, where almost all of the sea ice grows and melts every year.

Nilas vs pancakes

Nilas and pancake sea ice are different at the crystal level (see previous post), and regions of pancake ice and nilas of the same age may have different average ice thickness and ice concentration. As a result, the interaction of the ocean and atmosphere in these two ice types may be very different. Gaps of open water between pancake ice floes allow heat fluxes to be exchanged between the ocean and atmosphere – which can have very different temperatures during winter. Nilas and pancakes also interact with waves differently – nilas might simply flex with a low-intensity wave field, or break into pieces if disturbed by large waves, while pancakes bob around in waves, causing a viscous damping of the wave field. The two ice types have very different floe sizes (see previous posts here and here). Nilas is by definition is a large, uniform sheet of ice; pancake floes are initially very small and grow laterally as more frazil crystals in the ocean adhere to their sides, and multiple floes weld together into sheets of cemented pancakes.

How to make observations?

Sea ice models have only recently begun to be able to separate different sizes of sea ice. This allows more accurate inclusion of growth and melt processes that occur with the different sea ice types. However, observations of how sea ice floe size changes during freeze-up are required to inform these new models, and these observations have never been made before. Pancake sea ice floes are often around only 10 cm in diameter initially, which is far too small to observe by satellite. This means that observations of pancake growth need to be made close-up, but the dynamic ocean conditions in which pancakes are created makes it difficult to deploy instruments in-situ. So how can we observe pancake sea ice in this challenging environment?

In a recent paper (Roach et al, 2018), we used drifting wave buoys, called SWIFTs, to capture the growth of sea ice floes in the Arctic Ocean. SWIFTs are unique platforms (see image of the week) which drift in step with sea ice floes, recording air temperature, water temperature, ocean wave data and – crucially for sea ice – images of the surrounding ice. Analysis of the series of images captured has provided the first-ever measurements of pancake freezing processes in the field, giving unique insight into how pancake floes evolve over time as a result of wave and freezing conditions. This dataset has been compared with theoretical predictions to help inform the next generation of sea ice models. The new models will allow researchers to investigate whether describing physical processes that occur on the scale of centimetres is important for prediction of the polar climate system.

Edited by Sophie Berger


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.  

 

 

 

Maddie Smith is a PhD student at the Applied Physics Lab at the University of Washington in Seattle, United States. She uses observations to improve understanding of air-sea interactions in polar, ice-covered oceans.

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 – 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 – 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 – Understanding Antarctic Sea Ice Expansion

Fig. 1: Average monthly Antarctic sea ice extent time series in black, with the small increasing trend in blue. [Credit: NSIDC]

Sea ice is an extremely sensitive indicator of climate change. Arctic sea ice has been dubbed ‘the canary in the coal mine’, due to the observed steady decline in the summer sea ice extent in response to global warming over recent decades (see this and this previous posts). However, the story has not been mirrored at the other pole. As shown in our image of the week (blue line in Fig. 1), Antarctic sea ice has actually been expanding slightly overall!


The net expansion is the result of opposing regional trends

The small increasing trend in Antarctic sea-ice extent is the sum of opposing regional trends (click here for definitions of area, concentration and extent). Sea ice in the Weddell and Ross seas has expanded whereas in the Amundsen and Bellingshausen (A-B) seas the sea-ice cover has diminished (Holland 2014). The size of these trends varies with the seasons (Fig. 2). There are no significant trends in ice concentration – the fraction of a chosen area/grid box that is sea ice covered — if you look at (Southern hemisphere) winter values, however we do see trends when looking at a time series of summer values. The differences in trends between seasons suggests interactions with atmosphere and ocean (feedbacks) that amplify (in the spring) and dampen (in the autumn) changes in the ice cover, creating this seasonality. Some of this variability can be explained by changes in the winds (Holland and Kwok, 2012). But the complexity of the trends can’t be explained by one single change in forcing (e.g. winds, snowfall or temperature) or a single process (e.g. ice albedo feedback acting in the spring/summer).

 

Fig. 2: Seasonal trend in ice concentration. Maximum trends are seen in summer. Large increases are seen in the Weddell and Ross seas, and decreases in the Amundsen and Bellingshausen (A-B) seas. [Credit: Fig 2 from Holland (2014). , reprinted with permission by Wiley and Sons].

Why hasn’t Antarctic sea ice extent been decreasing?

There is no clear consensus on this. In short, we don’t really know… It is not as intuitive as the ‘warmer climate results in less ice’ narrative for the Arctic. We only have a time series of Antarctic sea ice extent from 1979 (the start of satellite observations). We therefore can’t be sure what role natural variability is having on decadal and longer timescales, i.e. if this is just natural ups and downs or an “unusual” trend related to climate change. Another difficulty is that we don’t have a reliable time series of sea ice volume as we have difficulties in getting reliable sea ice thickness measurements, because of the thick snow covering on sea ice in the Southern Ocean. For example, it could be that the ice is becoming thinner although the sea-ice area has increased.

There are important processes and/or feedbacks between sea ice and ocean or between sea ice and atmosphere that we are missing from our models

Currently, global climate models are poor at reproducing the observed Antarctic sea ice changes (Turner et al. 2013). Models simulate a decrease in the overall sea ice extent, instead of the observed increase. They also fail to reproduce the correct spatial variations, as shown in Fig. 2. This makes it very hard to make predictions about future changes in Antarctic sea ice from model results, and implies that there are important processes and/or feedbacks between sea ice and ocean or between sea ice and atmosphere that we are missing from our models, and therefore our understanding of the Southern Ocean climate system is incomplete.

 

However, there are some suggestions as to processes that could explain some of the observed Antarctic sea ice variability. The largely fall into two main categories: natural variability and anthropogenic changes.

 

1.Natural Variability

Natural variability refers to the repeating oscillations and patterns we see in the climate system. Some of these repeating patterns can be correlated with increases/decreases in Antarctic sea ice. In particular El Nino Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) have been linked to Antarctic sea ice changes. The SAM is a measure of the difference in pressure between 40°S and 65°S, a positive SAM indicates a stronger difference in pressure, driving stronger westerly winds around Antarctica, increasing the thermal isolation of Antarctica. Stronger westerlies are associated with cooler sea surface temperatures and expansion of the sea ice cover on short  timescales (seasons to years).

The SAM has been in a mostly positive phase since the mid-1990s, so is believed may have something to do with some of the small increase in sea ice extent we have seen. However, variability on longer time scales (decades or longer) could also explain some of the small increase, but this is tricky to assess without a longer observational time series.

 

2. Anthropogenic Changes

The main two human-induced changes on the Antarctic climate system are the ozone hole and increased melting of the Antarctic ice sheet.

  • Ozone hole
    The ozone hole causes the westerly winds to strengthen, making the sea ice cover expand. However it is more complicated than this, as the impact on the sea ice may depend on what timescale we look at. Over longer timescales (years to decades) the initial response may be outweighed by an increase in ocean upwelling (due to the stronger winds). This brings warm water from below the cold surface layer up to the surface, melting the sea ice from below, eventually resulting in a net sea ice area decrease in response to the ozone hole. See Ferreira et al. (2015) for details.
  • Increased melting of the Antarctic ice sheet
    This could also play a role in the observed sea ice expansion, by increasing the ocean stratification. This results in a cooler and fresher surface layer, favouring the growth of sea ice (Bintanja et al. 2015).

 

It is very tricky to distinguish what is natural variability, what is human induced, or a complicated combination of two.

 

It is very tricky to distinguish what is natural variability, what is human induced, or a complicated combination of two. This means we don’t really know whether the observed large decrease in Antarctic sea ice extent seen in 2016/2017 (read more about it here) is just an anomaly or the start of a decreasing trend. So, in summary Antarctic sea ice is confusing, and we still can’t claim to completely understand observed variability. But this makes it interesting and means there is still a wealth of secrets left to be discovered about Antarctic sea ice!

 

Further reading

 

Edited by Clara Burgard et Sophie Berger


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 – 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