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Cryospheric Sciences

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Image of the Week – Life in blooming melting snow

Melting snowfields in a forested catchment of glacial lake in Šumava (mid-April), the Czech Republic [Credit: Lenka Procházková]

The new snow melting season has just started in the mountains of Europe and will last, in many alpine places, until the end of June. Weather in the middle of April is changeable. In the last few days sub-zero air temperatures have prevailed in the mountains during the day. In a frame of an international research project, me (Charles University) and Daniel Remias (Applied University Upper Austria), are both packing warm winter clothes as well as all the research equipment necessary for a new field mission: the aims are to find blooming spots of snow algae and to collect it for analyses. Upon our arrival in Šumava, a surprising but wonderful sunny day welcomes the expedition and we regret not taking the sun cream with us. While we are walking on still-compact partly frozen snowfields, our heads feel that they are exposed to hot summer.


Snow blooms – what do they look like?

Red snow colouration at nearly all ice-covered parts of a high-alpine glacial lake (mid-June), High Tatras (Slovakia). Detailed view of red snow after harvest [Credit: Daniel Remias and Lenka Procházková, see study Procházková et al. 2018a]

Snow blooms – see the figure above – can be found in polar and alpine regions worldwide. Availability of liquid water is a key factor for the development of a snow algae population. In our experience, only wet and slowly melting snowfields are suitable.  This colourful phenomenon can appear in different colour shades, as green, yellow, pink, orange or blood-red (Procházková et al., 2018a). Snow blooms are currently a focus of an increasing number of studies because of their significant effects on albedo reduction and subsequent acceleration of snow and ice melting.

Why are they colourful?

A few representatives of microalgae forming blooming snow – a coloured frame of each of these species corresponds with a colour of blooming snowfields [Credit: Lenka Procházková and Daniel Remias]

The macroscopic blooms are caused by microalgae of a cell size ranging from ~5 µm up to ~100 µm. During the melting season, cells live in a water film microhabitat surrounding large snow grains. The main genera that form these blooms are Chloromonas, Chlamydomonas and Chlainomonas, each associated with a specific bloom color (see the figure above).  A massive population development of golden algae can also occur.

When in the season do blooms occur?

Typical seasonal life cycle of a snow alga (Chloromonas nivalis), based on observation over many seasons in European Alps [Figure modified with permission from Sattler et al. 2010]

I would like to reveal a few secrets of snow algae.
The first strategy represents their seasonal life cycle. At the beginning the season in late April, one can hardly see any snow colouration. Snow algae from the previous seasons are lying at the interface between snow and soil in a resistant stage (called cyst). Snow is starting to melt slowly, and the cysts recognize the availability of liquid water and germinate. Flagellates are released and migrate upwards to the sub-surface layers, where they mate. With proceeding melting the cysts are accumulated and exposed at the snow surface. After total snowmelt these resistant stages should survive over summer in soil or at bare rock, where they can be subject to long-distance transport by wind.

The red colour of snow is caused by astaxanthin

A cross-section of a typical snow algal cyst, Chloromonas nivalis-like species, with abundant lipid bodies (“L”) with astaxanthin and plastids (“P”) [transmission electron microscope, credit: Lenka Procházková]

The next strategy of snow algae is an accumulation of the red pigment astaxanthin during their maturation, which has many benefits to life of these microorganisms. For example, astaxanthin is a powerful antioxidant, and its synthesis is not limited by the supply of nitrogen.
Another big advantage of astaxanthin is its protective action against excessive visible and harmful ultraviolet irradiation which are characteristic for snow surfaces in alpine and polar regions. This “sunscreen” effect of astaxanthin – which has maximum absorbance in the visible light region and also a significant capability of UV protection – is supported by the algae’s clever intracellular arrangement (shown in the figure above), namely that sensitive compartments of the algae, like chloroplast or nucleus, are located in the central part, whereas lipid bodies, which accumulate the astaxanthin, are in the periphery.

Our mission

Sequence-related sampling in Lower Tauern, Austria. Checking of a qualitative composition of a sampled spot using light microscope already in field. [Credit: Linda Nedbalová]

Do you wonder why we explore the physiology and biodiversity of snow algae? Because these extremophilic organisms cope with high ultraviolet radiation, repeated freeze-thaw cycles, desiccation, mechanical abrasion, limited nutrients and short season and are well adapted to it! Because of their ability to adapt to these extreme conditions, pigments of snow algae (as the astaxanthin presented above) are even used as biomarkers to detect life on Mars! Moreover, these microalgae are essential primary producers in such an extreme ecosystem, where phototrophic life is restricted to a few specialised organisms. For instance, they provide a basic ecosystem for snow bacteria, fungi and insects. Snow algae communities play an important role in supraglacial and periglacial snow food webs and supply nutrients that will be delivered throughout the glacial ecosystem.

 

Further reading

                               Edited by Jenny Turton


Lenka Procházková is a PhD Student at the Charles University, Prague, the Czech Republic. She investigates biodiversity and ecophysiology of snow algae. Her favourite algal group is in her focus in a lab as well as in field samplings in the European Alps, High Tatras, Krkonoše, Šumava and Svalbard. Contact Email:  lenkacerven@gmail.com

 

Image of the Week – Cryo Connect presents: The top 50 media-covered cryosphere papers of 2018

Discover which cryospheric research articles were most successful in attracting media attention in 2018 according to the Altmetric score.


Cryo Connect and Altmetric

Scientists are generally aware of each others’ studies. But when a scientific study generates media interest, its impact can be boosted beyond the scientific community. The media can push the essence of scientific study to the broader public through newspapers and news websites, television and social media. It all counts, and Altmetric tracks mentions of scientific studies across many media outlets. 

Cryo Connect is all about boosting outreach communication in cryospheric sciences, and developing a joint AGU- and EGU-endorsed community outreach platform for cryospheric researchers. So we comb through Altmetric data each year to see which cryospheric studies are garnering top media coverage. Visit https://CryoConnect.net to learn how to help boost your cryospheric research, or simply tag @CryoConnect on Twitter.

The colors of the Altmetric badges represent the different types of media coverage.

Cryospheric Top 50

What does the top 3 look like?
A Nature study that developed a consensus estimate of the mass balance of the Antarctic Ice Sheet garnered the most attention of any cryosphere study in 2018. This study was authored by the 80-author “IMBIE”, or Ice Sheet Mass Balance Inter-comparison Exercise, team. The second most media-featured cryosphere study of 2018 was a Science Advances study, which described an impact crater beneath the Hiawatha Glacier in Northwest Greenland, by Kurt Kjaer and 22 colleagues. The third most media-featured study of 2018 was a Nature study that documented a non-linear increase in meltwater runoff from the Greenland Ice Sheet since the industrial revolution, by Luke Tusel and eight colleagues.

The five most popular scientific journals of the top-50 list are: Nature Communications (9 studies), Geophysical Research Letters (8 studies), Nature (6 studies), and Science Advances and Nature Geoscience (5 studies each). Together, these five journals published two-thirds of the 50-top cryospheric science studies. Perhaps interestingly, Nature Communications and Science Advances are both relatively new journals — both less than eight years old — that provide gold open-access venues. Both EGU (The Cryosphere) and AGU (Geophysical Research Letters) journals are featured on the top-50 list.

There is a notable year-on-year increase in Altmetric scores comprising the top-50 list. At the low end, the rank #50 cut-off Altmetric score increased from 201 in 2017 to 293 in the 2018 list presented here. At the high end, the rank #1 Altmetric score increased from 1330 in 2017 to 3379 in 2018. Overall, the average top-50 Altmetric score increased from 442 in 2017 to 744 in 2018. We used the same methodology, described below, to generate the 2017 and 2018 top-50 lists.

It is difficult to precisely explain this year-on-year increase in Altmetric scores within the cryospheric sciences. There could be an increasing trend in cryosphere science coverage in the media, or improved detection of media coverage by Altmetric, or perhaps 2018 just had an unusually strong batch of cryospheric studies published. In any case, we congratulate all the authors of 2018’s top media-covered cryospheric studies on the well-deserved media attention that they have received, and the exposure they have given to cryospheric science!

Rank Altmetric Score Publication title Journal
1 Mass balance of the Antarctic Ice Sheet from 1992 to 2017 Nature
2 A large impact crater beneath Hiawatha Glacier in northwest Greenland Science Advances
3 Nonlinear rise in Greenland runoff in response to post-industrial Arctic warming Nature
4 Viable nematodes from late Pleistocene permafrost of the Kolyma River Lowland, Doklady Biological Sciences
5 Arctic sea ice is an important temporal sink and means of transport for microplastic Nature Communications
6 Exposed subsurface ice sheets in the Martian mid-latitudes Science
7 Direct evidence of surface exposed water ice in the lunar polar regions Proceedings of the National Academy of Sciences
8 Warm Arctic episodes linked with increased frequency of extreme winter weather in the United States Nature Communications
9 Net retreat of Antarctic glacier grounding lines Nature Geoscience
10 The Greenland and Antarctic ice sheets under 1.5 °C global warming Nature Climate Change
11 Trends and connections across the Antarctic cryosphere Nature
12 Permafrost stores a globally significant amount of mercury Geophysical Research Letters
13 Near-surface environmentally forced changes in the Ross Ice Shelf observed with ambient seismic noise Geophysical Research Letters
14 Reduced probability of ice-free summers for 1.5 °C compared to 2 °C warming Nature Climate Change
15 21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes Nature Communications
16 Observed rapid bedrock uplift in Amundsen Sea Embayment promotes ice-sheet stability Science
17 Formation of metre-scale bladed roughness on Europa’s surface by ablation of ice Nature Geoscience
18 On the propagation of acoustic–gravity waves under elastic ice sheets Journal of Fluid Mechanics
19 The influence of Arctic amplification on mid-latitude summer circulation Nature Communications
20 Topographic steering of enhanced ice flow at the bottleneck between East and West Antarctica Geophysical Research Letters
21 Warming of the interior Arctic Ocean linked to sea ice losses at the basin margins Science Advances
22 Evidence of an active volcanic heat source beneath the Pine Island Glacier Nature Communications
23 Experimental evidence for superionic water ice using shock compression Nature Physics
24 Variation in rising limb of Colorado River snowmelt runoff hydrograph controlled by dust radiative forcing in snow Geophysical Research Letters
25 Vulnerability of Arctic marine mammals to vessel traffic in the increasingly ice-free Northwest Passage and Northern Sea Route Proceedings of the National Academy of Sciences
26 Stopping the flood: could we use targeted geoengineering to mitigate sea level rise? The Cryosphere
27 Limited influence of climate change mitigation on short-term glacier mass loss Nature Climate Change
28 Degrading permafrost puts Arctic infrastructure at risk by mid-century Nature Communications
29 Seismology gets under the skin of the Antarctic Ice Sheet Geophysical Research Letters
30 Dark zone of the Greenland Ice Sheet controlled by distributed biologically-active impurities Nature Communications
31 Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water Science Advances
32 Ice core records of west Greenland melt and climate forcing Geophysical Research Letters
33 Arctic warming hotspot in the northern Barents Sea linked to declining sea-ice import Nature Climate Change
34 Path-dependent reductions in CO2 emission budgets caused by permafrost carbon release Nature Geoscience
35 Discovery of a hypersaline subglacial lake complex beneath Devon Ice Cap, Canadian Arctic Science Advances
36 Cascading lake drainage on the Greenland Ice Sheet triggered by tensile shock and fracture Nature Communications
37 Global sea-level contribution from Arctic land ice: 1971–2017 Environmental Research Letters
38 Discovery of moganite in a lunar meteorite as a trace of H2O ice in the Moon’s regolith Science Advances
39 The world’s largest High Arctic lake responds rapidly to climate warming Nature Communications
40 Mass loss of Totten and Moscow University Glaciers, East Antarctica, using regionally optimized GRACE mascons Geophysical Research Letters
41 A 400-Year ice core melt layer record of summertime warming in the Alaska Range Journal of Geophysical Research: Atmospheres
42 What drives 20th century polar motion? Earth & Planetary Science Letters
43 Response of Pacific-sector Antarctic ice shelves to the El Niño/Southern Oscillation Nature Geoscience
44 Dynamic response of Antarctic Peninsula Ice Sheet to potential collapse of Larsen C and George VI ice shelves The Cryosphere
45 Increased West Antarctic and unchanged East Antarctic ice discharge over the last 7 years The Cryosphere
46 Change in future climate due to Antarctic meltwater Nature
47 Antarctic ice shelf disintegration triggered by sea ice loss and ocean swell Nature
48 Heterogeneous and rapid ice loss over the Patagonian Ice Fields revealed by CryoSat-2 swath radar altimetry Remote Sensing of Environment
49 Persistent polar ocean warming in a strategically geoengineered climate Nature Geoscience
50 Ice loss from the East Antarctic Ice Sheet during late Pleistocene interglacials Nature

Methodology

This top-50 cryospheric articles list was compiled using access to the Altmetric Explorer database provided by Altmetric. Similar to the 2017 top-50 list of cryospheric studies, we searched Altmetric Explorer for all peer-reviewed articles published between 1 January and 31 December 2018 that were within the field-of-research codes for Atmospheric Science (0401), Geochemistry (0402), Geology (0403), Geophysics (0404), Physical Geography and Environmental Science (0406), Environmental Science and Management (0502), Soil Sciences (0503) or Other Environmental Sciences (0599). We further limited qualifying articles to those with keywords of Antarctic, Arctic, Cryosphere, Firn, Frozen, Glacier, Glaciology, Ice, Iceberg, Permafrost, Polar and Snow.

The resulting articles were then ranked by Altmetric score. The Altmetric scores shown here are characteristic of 29 March 2019, and will tend to grow over time with subsequent media coverage. Please contact info@cryoconnect.net if you have questions about methodology or oversights.

This is a joint post, published together with Cryo Connect.

Edited by Sophie Berger and Violaine Coulon


Cryo Connect is an initiative run by Dirk van As, Faezeh Nick, William Colgan and Inka Koch.

Image of the Week – 5th Snow Science Winter School

The participants to the 5th Snow Science Winter School [Credit: Anna Kontu]

 

From February 17th to 23rd, 21 graduate students and postdoctorate researchers from around the world made their way to Hailuoto, a small island on the coast of Finland, to spend a week learning about snow on sea-ice for the 5th Snow Science Winter School. The course, jointly organized by the Finnish Meteorological Institute and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, brought together a wide range of scientists interested in snow: climate modellers, large-scale hydrologists, snow microstructure modellers, sea-ice scientists and remote sensing experts studying the Arctic, Antarctica and various mountain ranges. The week was spent between field sessions out on the sea-ice, daily lectures, and data analysis sessions, punctuated by amazing food and Finnish saunas to finish the day!


Field sessions

Our field sessions focused on learning to use both standard snow measurement techniques and advanced state-of-the-art methods. We first practiced sampling the thin, crusty snowpack with traditional methods: digging snow pits and recording grain size, temperature profile and density. We then moved to advanced techniques, learning about micro-tomography – which generates 3D images of the snow without destroying the way the individual ice crystals are arranged, near-infrared imagery and the measurement of specific surface area of the snow crystals by recording how a laser beam is reflected and modified as it passes through the snow sample.  These techniques all give information on how the snow crystals are arranged in the snow pack that are not obtainable with the traditional techniques. They also give important parameters for remote sensing validation and snowpack modelling.

The lecturers had brought with them some of the most advanced instruments, in some cases their own unique prototypes, giving us an amazing opportunity to practice working with these instruments. Amongst them was the SLF SnowMicroPen, which can measure the mechanical resistance of the snowpack, the optical sensors IRIS and SnowCube which use the reflection from a laser beam to calculate the surface area of the snow crystals, and a small radar which relates the conductivity of snow to the amount of liquid water mixed in with the snow and the density. On top of that, we honed our sea-ice drilling and measurement skills.  During our field sessions, we were exposed to all the conditions a field researcher might experience, from cloudy skies, over to high winds threatening to blow away all your equipment to crisp, cold blue skies.

The students braving the winds to collect data [Credit: Guillaume Couture]

Practicing snow crystal identification under blowing snow conditions [Credit: Anika Rohde].

Lectures

Our daily lectures covered a range of topics, leaning on the expertise of the instructors of the course. After a short introduction about sea-ice, a well-needed refresher considering the wide range of backgrounds of the participants, we jumped into snow-science. We learned about snow measurements from a field, remote sensing, and modelling perspective. The lectures sparked multiple discussions, from the continual need for more ground-validation for remote sensing data, over spatial representativeness and accuracy of the field samples to modelling approaches and a consideration of the limitations of the observational datasets.

Final projects

After learning how to use these fancy and expensive instruments and using our newly gained knowledge of snow on sea-ice, we were given a day to plan our own field session, collect data, analyze the results and present our result to the other groups on the final afternoon. Some very ambitious projects were quickly checked by reality in the field and the snow conditions were exceptionally challenging. This meant that our data might not perhaps yield any scientific breakthroughs in the field of snow science, but that we certainly learned how to adapt measurement and analysis designs on the fly and will hopefully all have an all-weather plan for the next expedition out into the snow for our various projects at home.

Calculating specific area with the SnowCube [Credit: Anika Rohde].

More than the science

On our second evening, we braved the elements for the ice breaker held in a tent on the sea ice. Luckily, only the ice between the students and lecturers broke so that everyone appeared again at breakfast the next day. The delicious food kept us warm for the duration of the trip and anyone still feeling cold could enjoy the sauna for a truly Finnish experience. Our knowledge gained over the week was tested on the final evening with a sea-ice themed trivia organized by the instructors.

Being this far north provides a great opportunity to witness some elusive northern lights.  During the entire week, we kept a close eye on the aurora borealis forecast, and we finally had a good chance of seeing them on our last night. Needless to say, we put our field gear back on to head outside and were rewarded by a beautiful display of dancing green and pink lights in the skies. A wonderful way to finish a successful week of learning, meeting fellow researchers and sparking new research questions!

The elusive northern lights appearing on our last night in Hailuoto [Credit: Anika Rohde]

The accommodation treated us to some beautiful sunsets! [Credit: Caroline Aubry-Wake]

To finish on a high not, here is a short video summarizing our incredible week in Hailuto! [Credit: Caroline Aubry-Wake]

Edited by Violaine Coulon


Caroline Aubry-Wake is a mountain hydrology PhD candidate at the University of Saskatchewan, Canada. By combining mountain fieldwork in the Canadian Rockies with advanced computer modelling, she aims to further understand how melting glaciers and a changing landscape will impact water resources in the future.

 

 

 

Maren Richter is a PhD student at the Department of Physics of the University of Otago. A physical oceanographer by training, she has turned her focus on the solid state of water to study ice-ocean interactions in Antarctica. Specifically, the effect of platelet ice formed near ice shelf cavities on landfast sea ice thickness evolution and variability on interannual to decadal timescales.

 

Image of the Week — Into Iceberg Alley

Tabular iceberg, Ross Sea, Antarctica [Credit: Marlo Garnsworthy]

Crew in hardhats and red safety gear bustle about, preparing our ship for departure. A whale spouts nearby in the Straits of Magellan, a fluke waving in brief salute, before it submerges again. Our international team of 29 scientists and 2 science communicators, led by co-Chief Scientists Mike Weber and Maureen Raymo, is boarding the JOIDES Resolution, a scientific drilling ship. We’re about to journey on this impressive research vessel into Antarctic waters known as Iceberg Alley for two months on Expedition 382 of the International Ocean Discovery Program.

Not only are these some of the roughest seas on the planet, it is also where most Antarctic icebergs meet their ultimate fate, melting in the warmer waters of the Antarctic Circumpolar Current (ACC), which races unimpeded around the vast continent. And there, in the Scotia Sea, we will drill deep into the sea floor to learn more about the history of the Antarctic Ice Sheet.


The Drilling Ship

The JOIDES Resolution, our scientific drilling ship [Credit: William Crawford and IODP]

The JOIDES Resolution is a 134-meter-long research vessel topped by a derrick towering 62 meters above the water line. It can drill hundreds of meters into the sea floor to retrieve long cylinders of mud called cores. Analyzing this sediment can tell scientists much about geology and Earth’s history, including the history of Climate Change.

“Sediment cores are like sedimentary tape recorders of Earth’s history,” says Maureen Raymo. “You can see how the climate has changed, how the plants have changed, how the temperatures have changed. Imagine you had a multilayer cake and a big straw, and you just stuck your straw into your cake and pulled it out. And that’s essentially what we do on the ocean floor.”

Our drilling sites in the Scotia Sea. [Figure modified from Weber, et al (2014)]

Our expedition is “going to a place that’s never really been studied before,” adds Maureen Raymo. “In fact, we don’t even know what the age of the sediment at the bottom will be.” Nevertheless, we hope to retrieve a few million years’ worth of sediment, perhaps even more. The sediment cores will provide a nearly continuous history of changes in melting of the Antarctic Ice Sheet.

What can these cores tell us?

As icebergs melt, the dust, dirt, and rocks they carry—known as “iceberg rafted debris”—fall down through the ocean and are deposited as sediment on the seafloor. Analyzing this sediment can tell us when the icebergs that deposited it calved from the ice sheet, and even where they came from. At times when more debris was deposited, we know more icebergs were breaking away from the Antarctic Ice Sheet, which tells us the ice sheet was less stable.

Much shorter cores previously collected at our drilling sites reveal high sedimentation rates, allowing us to observe changes in the ice sheet and the climate on short timescales (from just tens to hundreds of years).

We now know that rapid discharge of icebergs—caused by rapid melting of Antarctic ice shelves and glaciers—occurred in the past, and that episodes of massive iceberg discharge can happen abruptly, within decades. This has huge implications for how the Antarctic Ice Sheet may behave in the future as our world warms.

Where do icebergs come from?

Ok, let’s back up a little—back to where these icebergs were born. Icebergs break off or “calve” from the margins (edges) of ice shelves and glaciers. Ice shelves are floating sheets of ice around the edges of the land. They are important because they have a “buttressing” effect—that is, they act as a wall, holding back the ice behind them. Glaciers are great flowing rivers of ice that grind their way across the land, picking up the rocks and dirt that become iceberg-rafted debris.

Thwaites velocity map animation [Credit: Kevin Pluck, Pixel Movers & Maker]

Most Antarctic icebergs travel anti-clockwise around Antarctica and converge in the Weddell Sea, then drifting northward into the warmer waters of the Antarctic Circumpolar Current.

Iceberg flux 1976-2017  [Credit: Kevin Pluck & Marlo Garnsworthy, Pixel Movers & Makers]

As our planet warms due to our greenhouse gas emissions, warmer ocean currents are melting Antarctica’s massive glaciers from below, thinning, weakening, and destabilizing them. In fact, the rate of Antarctic ice mass loss has tripled over the last decade alone.

Polar researchers predict that global sea level will rise up to one meter (around 3.2 feet) by the end of this century, and most of this will be due to melting in Antarctica. And if vulnerable glaciers melt, the West Antarctic Ice Sheet is more likely to collapse, raising sea level even further.

Blue is old ice, Mc Murdo Sound, Antarctica [Credit: Marlo Garnsworthy]

 

A Hazardous Voyage

We face several hazards on this journey. We are hoping we won’t encounter sea ice, as our vessel is not ice-class, but it’s something we must watch for, especially later in the cruise as winter draws nearer. It is certain that, at times, we’ll experience a sea state not conducive to coring—or to doing much but swallowing sea-sickness medication and retiring to one’s bunk. In heave greater than 4–6 meters, operations must stop for the safety of the crew and equipment.

Of course, our highly experienced ice observer will be ever on the lookout for our greatest hazard—icebergs, of course! We are likely to encounter everything from very small “growlers” to larger “bergy bits” to massive tabular bergs. In fact, it is the smaller icebergs that present the most danger to the ship, as large icebergs are both visible to the eye and are tracked by radar, while smaller ones can be more difficult to detect, especially at night. Nevertheless, we are intentionally sailing into the area of highest iceberg concentration and melt.

“My hope,” says Mike Weber, “is that our expedition will unravel the mysteries of Antarctic ice-sheet dynamics for the past, and this may tell is something about its course in the near future.”

“Bergy bit”, Ross Sea, Antarctica [Credit: Marlo Garnsworthy]

Edited by Sophie Berger


The JOIDES Resolution is part of the International Ocean Discovery Program and is funded by the US National Science Foundation.

Marlo Garnsworthy is an author/illustrator, editor, science communicator, and Education and Outreach Officer for JOIDES Resolution Expedition 382 and previously NBP 17-02. She and Kevin Pluck are co-founders of science communication venture PixelMoversAndMakers.com, creator of the animations in this article.

The hidden part of the cryosphere – Ice in caves

The hidden part of the cryosphere – Ice in caves

The cryosphere can be found in various places in many forms and shapes… in the atmosphere, on land and sea. A lesser known part of the cryosphere is hidden deep in the dark, in the cold-karstic areas of the planet: Ice caves! The ongoing climate change affecting ice all over the world is now rapidly melting these hidden ice masses as well. We therefore need to hurry up and try to collect as much information as we can before all will melt away…


The big melting

The ice masses around the globe, in ice sheets, sea ice, and mountain glaciers, have been melting away in past decades (see this previous post). The reduction of the cryosphere, both in terms of area and mass, has particularly been visible in the European Alps over the last 30 years. On the one hand, large and small Alpine glaciers decline, fragment and even disappear, and this trend has accelerated since the mid 1980s. Mountain glaciers are therefore considered to be sensitive indicators for climate variability. On the other hand, the warming climate is also acting on permafrost degradation, mostly affecting the stability of rock-slopes and cliffs.

What makes the international scientific community worry at the moment is how fast this abrupt glacial reduction is occurring globally. However, not all the natural environments respond in the same way to sudden changes in the climate system! Fortunately for us scientists, there are physical environments and ecological niches more resilient to external perturbations. This aspect has sometimes allowed the preservation of environments and information in the Earth’s climatic history that would have been otherwise destroyed.

Caves are resilient

Among the most resilient natural environments there are caves, “protected” by the rocky mass within which they were formed. In the mountains, high-altitude karst cavities can contain huge deposits of ice representing a lesser known part of the cryosphere. Speleologists face such ice in caves both as a joy and a damnation: fascinating by their beautiful shapes and morphologies, they also see it as an unwieldy presence that prevents explorations of still unknown voids in the alpine karstic systems.

Fig. 2: An ice deposit in a cave of the southeastern Alps [Credit: Renato R. Colucci].

 

But ice in caves is not just something beautiful (but isn’t it? Look at Fig. 2!). It rather represents a precious natural archive, sometimes with high temporal resolution, able to tell the climate history of large part of the Holocene (the last 11700 years of the Earth’s history). The permanent ice deposits, i.e. the ice staying longer than just a winter season, often defined in a colorful way as “fossil ice” by speleologists, is what counts the most. As it typically gets older than 2 years, which is one threshold for the general definition of permafrost, this phenomenon is part of the mountain permafrost… right or wrong, ice in caves is ground ice!

Fig. 3: Huge entrance of a cave opening in the Dachstein limestones of the Canin-Kanin massif, southeastern Alps [Credit: Renato R. Colucci].

 

Generally in the Alps such ice deposits lie in caves having their opening at altitudes above 1,000 m (Fig. 3), but locally even lower. The formation of these unique environments depends on a combination of geomorphological and climatic characteristics, which allow for accumulation and preservation of ice also in places where this would be very unlikely.

Now, although the caves are resilient environments, ice melting due to climate change is rapidly increasing there as well. This is why it is important to save as much information as possible from the remaining ice, before it is definitely lost!

The C3 project – Cave’s Cryosphere and Climate

The C3-Cave’s Cryosphere and Climate project is under the scientific guidance of the National Research Council (CNR) of Italy, and precisely the climate and paleoclimate research group of ISMAR Trieste. It aims to monitor and study ice deposits in caves. Such ice deposits store several information related to the paleoclimate, the biology, the chemistry and ecology of these environments.

Fig. 4: Drilling ice cores with the aim to extract the CCC layer from this ice body in a cave of the southeastern Alps [Credit: Arianna Peron].

The project started in 2016, following the discovery of a coarse cryogenic calcite deposit (CCCcoarse) in an ice layer (in-situ) in a cave of the Canin-Kanin massif, in the Julian Alps, located between Italy and Slovenia. This finding, representing the first evidence of CCC in the southern Alps, provides an important opportunity to understand the processes associated to the formation of these particular calcite crystals (Fig. 4). Previously, the CCC (Fig. 5) was only found on the floor in caves where ice had already melted away. What makes it interesting is the fact that it is possible to date these crystals using the isotopic ratio of some trace elements in radioactive materials, typically Uran and Thorium.

Fig. 5: Millimetric crystals of coarse cryogenic calcite found in-situ in the southern Alps [Credit: Renato R. Colucci].

The strongest financial and logistic support to the project is given by the Alpine Society of the Julian Alps through its speleological group, the E. Boegan Cave Commission. In addition to the CNR and other Italian institutions such as the University of Trieste, University of Bologna, Insubria University in Varese, Milano Bicocca University and the Natural Park of the Julian Prealps, the project involves research institutes and universities from Germany (Institute of Physics of Heidelberg University), Switzerland (Paul Scherrer Institut; Swiss Institute for Speleology and Karst Studies), Austria (Innsbruck University; Palynology and Archaeobotany Research Group), and Slovenia (Geological survey of Slovenia).

Many activities and several results already unveiled few of the secrets hidden in such environments: the realization of the first thermo-fluido-dynamic model in an ice cave, the development of innovative techniques for studying the mass balance of the ice, the study of the thermal characteristics of the rock and therefore of the permafrost and the active layer, the development of innovative and multidisciplinary methods of ice dating.

But there is little time to do all, and we must exploit it to the fullest!

Further reading

Edited by Clara Burgard


Renato R. Colucci works in the climate and paleoclimate research group of ISMAR-CNR, Department of Earth System Sciences and Environmental Technology. He is also adjunct Professor of glaciology at the University of Trieste (Italy). During his PhD he honed his skills in glacial and periglacial geomorphology at UNIS (University Center in Svalbard). His research centers around the interactions between cryosphere (glaciers, permafrost, ice caves) and the climate, spanning from the end of the Last Glacial Maximum to the present days.

Image of the Week – When “Ice, Ice Baby” puts rocks “Under Pressure”

Image 1: Composite image of the Aiguille Verte, the heavily-fractured headwall of the Glacier d’Argentière near Chamonix, France [Credit: D. Dennis].

Bowie and Queen said it first, and Vanilla Ice brought it back. But now, I’ve set out to quantify it: Pressure. Rocks in glacial landscapes can experience many different kinds of pressure (forces), from sources like regional tectonics or even the weight of the glacier itself. Our hypothesis is that smaller-scale pressures, caused by the formation of ice in small bedrock cracks (frost-weathering), have a large effect on the sculpting of landscapes in cold regions. This post will share how we evaluate these processes and their dependence on temperature, as well as discussing the broader effects for glacier and glacial landscape evolution.


Walking through the valley in the shadow of glaciers

Growing up just outside Glacier National Park, USA, at nearly the exact edge of the former Laurentide Ice Sheet, I became familiar with the romantic lore of how we understand glacial landscapes (Images 2, 3). Observing these glacial landscapes later throughout my formal Earth science education, I came to understand mountains as passive resistors to the relentless efficiency of glacier advance, erosion, and retreat—offering evidence of past glaciations but nonetheless devoid of agency in the rise and fall of icy stadials.

My current PhD research, however, investigates a slightly-modified premise: that glaciers and their landscapes respond in concert with climate, and that dividing the dynamics governing the ice and the rock may not be as straightforward as once thought. My work is a sub-project of the Climate Sensitivity of Glacial Landscape Dynamics (COLD) project, funded by the European Research Council (ERC) and lead by Dirk Scherler at the Deutches GeoForschungsZentrum (GFZ) in Potsdam, Germany.

Image 2: The author on holiday in Glacier National Park, Montana, circa 2001, demonstrating an early aptitude for glacial geomorphology and cosmogenic nuclide geochemistry. His affinity for popular German footwear at a young age foreshadowed his eventual move to Germany to study glaciology and geomorphology [Credit: D. Dennis].

Image 3: This image of Chamonix Valley and the M. Blanc massif conceptually outlines how average annual temperature may change with elevation in steep hillslopes. The highest peaks in the massif tower up to nearly 4000 m over Chamonix Valley, which sits at appx.1000m. This corresponds to a nearly ~20 °C difference in annual average temperature. [Image adapted from Google Earth].

Temperature as a control in glacial landscapes

Glaciers exist in locations with temperatures that are, for some portion of the year, below freezing, as this is a condition required for snow to persist through the melt season and to form ice. Temperature is therefore an important primary control on the stability of glaciers. These cold temperatures, however, impact mountain environments beyond just the formation/decline of glaciers, and several decades of recent research have shown that temperature is an important controlling factor on the type and magnitude of erosion (the act of dislodging and transporting rock) in cold landscapes.

Mountain glacier valleys are commonly characterized by steep head- and sidewalls which frame the glacier within (like in our Image of the Week). At our field sites in the French, Swiss, and Italian Alps, these rockwalls can tower up to 1500 m above the surface of the glaciers, corresponding to a temperature gradient of ~10 degrees (Image 3). Therefore, the rocks at different elevations are exposed to different temperature conditions, which could lead to differences in the rate of erosion.

Image 4: Permafrost degradation and frost-weathering in the steep hillslopes of the M. Blanc massif commonly lead to the deposition of debris on the glaciers at the base of the mountains. Shown here is Glacier d’Argentière (France) with patches of surface debris [Credit: D. Dennis].

Erosion in steep rockwall faces

Frost-weathering processes occur only at temperatures at or below zero, therefore requiring the same cold temperature conditions that form glaciers. At these temperatures, liquid water present in small cracks in the bedrock freezes. The pressure exerted on the rock by the ice as it freezes causes the rock to fracture, leading to large cracks in the bedrock (Image 5). Erosion occurs when the ice in the crack becomes large enough and its corresponding fracture wide enough that the rock can no longer remain attached and it falls from the rockwall surface.

Erosion can also occur when the ice in the crack melts and no longer “cements” the surface together. Because temperatures in glacial landscapes are commonly quite cold, much of the bedrock is considered permafrost (permanently-frozen ground), and remains frozen throughout the year. In the Alps, however, warmer temperatures over the past decades have caused the permafrost to thaw, melting the lenses of ice and causing larger and more frequent rockfalls.

Temperature conditions are therefore important for both the rate at which cracks form in rocks (and erode from the surface) in addition to permafrost stability and the size/frequency of rockfalls. As temperatures change in mountain regions due to global warming, this could lead to considerable changes in debris production.

Image 5: A cropped version of our Image of the Week, showing the base of the Aiguille Verte, headwall of Glacier d’Argentière. Large fractures in the bedrock are clearly visible. These may have grown from much smaller cracks that formed due to frost-weathering.

The hillslope/glacier surface connection

After material erodes from the surface of the headwall, it is often deposited onto the surface of the glacier (Image 3). As mentioned above, the deposition of material can occur both at a constant rate or sporadically (as in the case of permafrost-thaw rockfalls), depending on the controlling process. As such, determining the actual representative rate at which these headwalls erode is challenging.

Though this work can be complicated, we believe it to be important, as debris deposited on the surface of glaciers can insulate the ice from the effects of temperature (Image 4, Video 1). Though the global distribution of debris-covered glaciers is much smaller than debris-free glaciers, debris-covered glaciers make up a non-trivial fraction of the glaciers in populated mountain regions where they may be important fresh water sources, contribute to glacial hazards, or allow for the generation of hydropower. Understanding the supply of debris to these glaciers (via erosion), and how it may change, is therefore an important component of forecasting their evolution under warming climates.

Video 1: This drone footage from the Arolla Glacier, Switzerland, shows the steep relief which can develop as a result of differential melting. Debris thicker than 2-4 cm insulate ice, leading to topographic relief on the glacier surface as exposed ice melts and covered ice is protected. [Credit: D. Gök, GFZ]

Re-evaluating the dynamic glacial landscape

Though studies of frost-cracking and debris-covered glaciers individually are not necessarily brand new inventions, our methods for combining the two are rather novel. In doing so, we are linking the evolution of glacier with the evolution of the landscape itself, and investigating an interesting feedback loop induced by changes in climate. Should erosion rates increase with warmer temperatures, and the mountains therefore supply more debris to glacier surfaces, this could extend the “lifetime” of the glacier by insulating it; likewise, if erosion rates decrease, less debris supplied to already-covered glaciers could lead to less insulation and (comparatively) higher melt rates. This interplay demonstrates the complexity of Earth system processes, and the need to take these complexities into account when considering the effects of climate changes.

To summarize

Pressure, pushing down on rock,
Pushing laterally against rock, can cause them to fall.
Under (thick) debris, glacier melt will slow,
Despite higher temperatures,
And global warming.

Will it ever stop? I don’t know.
Turn up the temperatures, then no more (ice and) snow.
At the end of the day, frost-weathering needs ice,
When water can’t freeze, ice-cracking’s no dice.

Edited by David Docquier


Donovan Dennis is a PhD student at the Deutches GeoForschungsZentrum in Potsdam, Germany. He is interested in many aspects of glaciology and glacial geomorphology, and currently investigates the geomorphic feedbacks on glacial landscape erosion. He previously worked on post-deposition alteration of stable water isotope signals in snow and ice. He tweets as @donovan__dennis.

Contact Email: dennis@gfz-potsdam.de

 

Image of the Week – Seven weeks in Antarctica [and how to study its surface mass balance]

Figure 1 – Drone picture of our field camp in the Princess Ragnhild coastal region, East Antarctica. [Credit: Nander Wever]

After only two months of PhD at the Laboratoire de Glaciologie of the Université libre de Bruxelles (ULB, Belgium), I had the chance to participate in an ice core drilling campaign in the Princess Ragnhild coastal region, East Antarctica, during seven weeks in December 2018 – January 2019 for the Mass2Ant project. Our goal was to collect ice cores to better evaluate the evolution of the surface mass balance in the Antarctic Ice sheet. Despite the sometimes-uncomfortable weather conditions, the ins and outs of the fieldwork and the absence of friends and family, these seven weeks in Antarctica were a wonderful experience…


Mass2Ant

Mass2Ant is the acronym of the project: “East Antarctic surface mass balance in the Anthropocene: observations and multiscale modelling”. This project aims to better understand the processes controlling the surface mass balance in East Antarctica, its variability in the recent past and, ultimately, improve the projections of mass balance changes of the East Antarctic ice sheet.

What exactly is the surface mass balance?

The mass balance of an ice sheet (see Fig. 2) is the net balance between the mass gained by snow accumulation and the loss of mass by melting (either at the surface or under the floating ice shelves) and calving (breaking off of icebergs at the ice shelves fronts).

The surface mass balance on the other hand only considers the surface of the ice sheet. It is thus, for a given location, the difference between:

  • incoming mass: snowfall, and
  • outgoing mass, due to melting processes (fusion and sublimation), meltwater runoff and transport or erosion by wind at the ice sheet interface.

Figure 2 – Representation of the mass balance of an ice sheet [Credit: Figure adapted from NASA, Wikimedia Commons].

Overall, the ice sheet mass balance – the principal indicator of the “health state” of an ice sheet – is the balance between the surface mass balance, iceberg calving and basal melt under the ice shelves. A good evaluation of these three factors is thus essential to better quantify the evolution of the Antarctic mass balance under anthropogenic warming and therefore its contribution to future sea level rise.

However, the surface mass balance is characterized by strong temporal and spatial variations (see Figure 3) and is poorly constrained. In order to improve future projections for Antarctica, it is essential to better assess the variability of the Antarctic surface mass balance by directly collecting data in the field. Within this framework, the goal of the Mass2Ant project is to study the surface mass balance in the Princess Ragnhild coastal region (marked in the Figure 3).

Figure 3 – Surface mass balance (1989-2009) from RACMO2 (a regional climate model) of Antarctica (left) and Greenland (right) in kg/m².yr. Contour levels (dashed) are shown every 500 m. Black dot is the approximative position of the drilling site on the Tison Ice Rise. [Credit: adapted from Figure 1 of van den Broeke et al. (2011)].

Collecting the data [or how can we use ice cores to infer surface mass balance?]

Surface mass balance can be determined by analyzing ice core records. As a part of our expedition, ice cores were collected on the summit of the so-called “Tison Ice Rise” (a non-official name) – 70°S 21°E, near the Belgian Princess Elisabeth Station. We drilled to a depth of 260.1 m, which we expect to date back to the 15th century.
The drilling system, named the Eclipse drill, contains a motor on top of a drill barrel – which is composed of an inner barrel that cuts the ice core with 3 knives and collects it and an outer barrel (a tube) that collects the chips created. Due to the overlaying ice, pressure increases very quickly with depth. Deep ice cores are thus subject to much higher pressure than the atmospheric pressure. In order to reduce these strong pressure differences as the ice core is brought to the surface, drilling fluid was poured in the boreholes, a technique called “wet-drilling”. This was the first time the wet-drilling technique was used by our team, and it significantly improved the quality of our ice cores compared to the traditional method used during the previous campaigns!

Figure 4 – A part of our team in the drilling tent. An ice core can be observed in the inner barrel of the drilling system. A wooden box is placed on top of the trench, under the drill barrel to collect the chips contained in the outer barrel. [Credit: Hugues Goosse]

The 329 collected ice cores will be analyzed in our lab in Brussels. More specifically, we will focus on

  • the water stable isotopes: the seasonal cycle of stable isotopes of water in ice will be used for relative dating of the ice core;
  • the major ions (Na+, nssSO4, Na+/SO42-, NO3…) present in the ice: the reconstruction of the seasonal cycle of these ions allows us to refine the isotopic dating and therefore infer the annual snow/firn/ice thickness.
  • the conductivity of the ice, which also shows a clear seasonal signal used for dating. Moreover, the conductivity signal is also reacting to localized extra inputs – for example from past volcanic eruptions – therefore providing an absolute dating, which reduces our dating method uncertainties.

The seasonality of these signals will allow us to infer the yearly ice thicknesses (see this post). By taking into account the deformation of the ice, we will then be able to reconstruct the evolution of the surface mass balance in the Princess Ragnhild Coast region since the 15th century.

Life in the field

What was a typical day like for us? In fact, it strongly depended on the team to which you belonged as we were divided into two groups:

  • The “day group” was working on measurements such as snow density and radar analyses and worked roughly between 8 AM and 8 PM.
  • The second group – the drilling team, including me – worked during nights (between 9 PM and 9 AM) because of the too high temperatures during day, which would lead to ice core melt.

The drilling team adapted quite easily to this timing as the sun was shining 24 hours a day. In order to spend a common moment, a joint meal was organized every day at 8.30 AM, with some of us having their dinner while others were having breakfast.
The everyday life mainly occurred in two equipped containers. The first container was our living space, which we used as kitchen, dining room and working space. The second container consisted of a cloakroom, the toilets and the bathroom (with a real shower, a luxury in the field!). Each of us had a tent to sleep, with adapted sleeping bag, making it quite comfortable. As we stayed 5 weeks at the drilling site, we spent Christmas and New Year’s Eve on the field. It was a good occasion to eat fondue while sharing some fun stories and jokes (Fig. 5).

Figure 5 – Christmas time spent together, giving presents and eating fondue. [Credit: Nander Wever]

Why should you too go to Antarctica?

I’ll keep many memories of the time we all spent together, but also of the amazing landscapes and the calm and peacefulness of this white immensity… Despite the sometimes-uncomfortable weather conditions (a full week of whiteout days, lucky us!), this unique experience was wonderful! I’ve learned so much, from a scientific but also personal point of view. It was also a chance to participate in the collection of the samples that I will study during the next four years of my PhD. Before I left for Antarctica, someone told me that “When you went to Antarctica once, you usually want to go again”. Well, that’s definitely true for me!

Many thanks to belspo for funding this project, to the International Polar Foundation and Princess Elisabeth Antarctica staffs for the work both in Cape Town and in the station, and last but not least, thanks to the Mass2Ant team in the field that made this experience an amazing adventure.

Further reading

Edited by Violaine Coulon


Sarah Wauthy is a PhD student at Laboratoire de Glaciologie, Université Libre de Bruxelles, Belgium. Her PhD is part of the Mass2Ant project and aims at determining paleo-accumulation in the region of the Princess Ragnhild Coast (Dronning Maud Land, East Antarctica) as well as the paleo-extension of sea ice before and across the Anthropocene transition (ca. last 3 centuries), by performing high-resolution multiparametric analyses on ice cores collected during field campaigns.

Image of the Week – Permafrost features disappearing from subarctic peatlands

Image of the Week – Permafrost features disappearing from subarctic peatlands

Some of the most remarkable, marginal features of permafrost – palsas – are degrading and disappearing metre by metre from North European peatlands, and are driven close to extinction by the climate change.


What are these permafrost features?

A palsa is a peat mound with an icy core, which stays frozen throughout summer due to the insulating property of dry peat. These mounds can rise up to 10 metres above the surface of surrounding mire (wet terrain dominated by peat-forming vegetation), and they may occur as just a single palsa, group of palsas or as an extensive, but not very high (ca. 1 to 2 m) peat “platform”. The occurrence of palsas is limited by such factors as: low mean annual air temperature (< 0 °C), low annual precipitation (< 500 mm) and at least 40–50 cm thickness of peat layer, which is needed to sufficiently insulate the core during summer (Seppälä, 2011).

The established theory on palsas formation (Seppälä, 2011) is the following:

  1. The formation of a palsa begins when a part of mire freezes deeper in a windblown area with thinner snow cover, which normally protects the ground below from freezing temperatures.

  2. If the frozen peat doesn’t melt completely during summer, an ice lens forms inside the peat layer resulting in uplifting of the mire surface in this area.

  3. In the following winters, the snow is even more likely to be windblown from the mound, which again fosters deeper penetration of frost and formation of new ice lenses.

  4. As soon as a part of mire rises above the water level, the vegetation starts to change and the peat dries out, which contributes to the survival of the ice core during summers.

 

Breaking of the surface and erosion is a natural “step” for mature palsas, when the permafrost has reached the mineral ground below the peat. The melting of a palsa is a form of thermokarst, i.e. thawing of ice-rich permafrost (see this post for more details about thermokarst).

Block-erosion of peat on ridge-type palsa in Nierivuoma mire in Enontekiö, Finland [Credit: Mariana Verdonen].

Palsa, peat hummock or permafrost plateau?

The terminology used when speaking about these permafrost mounds varies, usually according to the continent the research was conducted on or the background of the authors. The term “palsa” comes from Lapland, and was used by Sami and northern Finns to refer to “hummock rising out of a bog with a core of ice” (Seppälä, 1972). In Fennoscandia, this term is used commonly for all main types: ridges, mounds and plateau palsas, whereas in North America the more common terms are either ‘peat or permafrost plateau’ or ‘wooded palsa’ depending on the shape and vegetation cover of the feature (Luoto et al, 2004).

Degrading permafrost of Fennoscandia

More often than not, one may encounter a desolate sight in North European palsa mires: most of the permafrost mounds are degrading by block erosion and/or melting away as a result of thawing of their frozen core. The vegetation that once was growing on hummocks above the wet mire surface, is now dead black in shallow thermokarst ponds surrounding palsas here and there. Although, in some places the conditions may still be favorable for new palsas to form, the general picture is devastating. Palsas are disappearing in most of their area of existence, and it is happening fast.

Thawing palsas of Nierivuoma captured from drone in July 2018. This peatland sprawls across ~7 km2 and is the largest palsa mire in Finland [Credit: Timo Kumpula].

Why should we care?

As climatic change is likely to increase winter and summer precipitation, and is already notable in rising mean annual air temperatures, palsas are predicted to disappear in Fennoscandia almost completely by the end of the 21st century (Fronzek et al, 2010).

It is noteworthy, that the palsa mire is the only mire and bog habitat that is listed as “critically endangered” in the 2016 European Red List of Habitats. While some other cold climate ecosystems may shift to higher latitudes and altitudes, palsa mires seem to be restricted from developing in higher areas, especially because of the required peat layer thickness (Luoto et al, 2004).

If just the loss of this diverse ecosystem type is not alarming by itself, there are couple of issues that I want to highlight:

  • Thawing of the perennially frozen peat changes the carbon fluxes of palsa mires as carbon previously trapped by permafrost becomes available for decay. As the area of dry peat surface decreases, more carbon is released into the atmosphere in the form of more effective greenhouse gas methane (CH4) instead of carbon dioxide (CO2). Recently, also the effects of permafrost thaw on the emissions of nitrous oxide (N2O), which is a strong greenhouse gas, have gained more attention (Marushchak et al, 2011).

  • The heterogeneity formed by variety of mire surfaces, thermokartst ponds and dry palsa mounds creates favorable conditions for species richness in these subarctic environments. In particular, the number and density of bird species seems to be high in the zone of palsa mires compared to more southern mire zones in Fennoscandia, even though no species have been reported to be exclusive to palsa mires (Luoto et al, 2004). This relationship, as well as overall significance of palsa mires for biodiversity is still poorly understood, however.

References

 

Edited by Clara Burgard


Mariana Verdonen is an Early Stage Researcher at the University of Eastern Finland. She focuses on optical, multi-temporal and multiscale remote sensing of environmental changes in Arctic and Subarctic areas. Mariana’s scientific interests are generally in geomorphology, permafrost-landscape dynamics and remote sensing of the Cryosphere. She tweets as @MarianaVerdonen. Contact Email: mariana.verdonen@uef.fi

Ice-hot news: The cryosphere and the 1.5°C target

Ice-hot news: The cryosphere and the 1.5°C target

Every year again, the Conference of Parties takes place, an event where politicians and activists from all over the world meet for two weeks to discuss further actions concerning climate change. In the context the COP24, which started this Monday in Katowice (Poland), let’s revisit an important decision made three years ago, during the COP21 in Paris, and its consequences for the state of the cryosphere…


1.5°C target – what’s that again?

Last October, the International Panel on Climate Change (IPCC) released a special report (SR15) on the impacts of a 1.5°C global warming above pre-industrial levels. This target of 1.5°C warming was established during the 21st conference of the parties (COP21), in a document known as the Paris Agreement. In this Agreement, most countries in the World acknowledge that limiting global warming to 1.5°C warming rather than 2°C warming would significantly reduce the risks and impacts of climate change.

But wait, even though achieving this target is possible, which is not our subject today, what does it mean for our beloved cryosphere? And how does 1.5°C warming make a difference compared to the 2°C warming initially discussed during the COP21 and previous COPs?

A reason why the cryosphere is so difficult to grasp is the nonlinear behaviour of its components. What does this mean ? A good basic example is the transition between water and ice. At 99.9°C, you have water. Go down to 0.1°C and the water is colder, but this is still water. Then go down to -0.1°C and you end up with ice. The transition is very sharp and the system can be deeply affected even for a small change in temperature.

As a main conclusion, studies conducted in the context of SR15 show that, below 1.5°C of global warming, most components of the cryosphere will be slightly affected, while above that level of warming, there is more chance that the system may respond quickly to small temperature changes. In this Ice Hot News, we review the main conclusions of the SR15 concerning ice sheets, glaciers, sea ice and permafrost, answering among others the question if achieving the 1.5°C target would prevent us to trigger the potential nonlinear effects affecting some of them.

Ice sheets

The two only remaining ice sheets on Earth cover Greenland and Antarctica. If melted, the Greenland ice sheet could make the sea level rise by 7 m, while the Antarctic ice sheet could make it rise by almost 60 m. A recent review paper (Pattyn et al., 2018), not in SR15 because published very recently, shows that keeping the warming at 1.5°C rather than 2°C really makes the differences in terms of sea level rise contribution by the two ice sheets.

Greenland is a cold place, but not that cold. During the Holocene, the surface of the ice sheet always melted in summer but, in the yearly mean, the ice sheet was in equilibrium because summer melt was compensated by winter accumulation. Since the mid-1990s, Greenland’s atmosphere has warmed by about 5°C in winter and 2°C in summer. The ice sheet is thus currently losing mass from above and its surface lowers down. In the future, if the surface lowers too much, this could accelerate the mass loss because the limit altitude between snow and rainfalls may have been crossed, further accelerating the mass loss. The temperature threshold beyond which this process will occur is about 1.8°C, according to the Pattyn et al., 2018 paper.

Antarctica is a very cold continent, much colder than Greenland, but it has been losing mass since the 1990s as well. There, the source of the retreat is the temperature increase of the ocean. The ocean is in contact with the ice shelves, the seaward extensions of the ice sheet in its margins. The warmer ocean has eroded the ice shelves, making them thinner and less resistant to the ice flow coming from the interior. And if you have read the post about the marine ice sheet instability (MISI), you already know that the ice sheet can discharge a lot of ice to the ocean if the bedrock beneath the ice sheet is deeper inland than it is on the margins (called retrograde). MISI is a potential source of nonlinear acceleration of the ice sheet that, along with other nonlinear effects mentioned in the study, could trigger much larger sea level rise contribution from the Antarctic ice sheet above 2 to 2.7°C.

You can find complementary informations to the Pattyn et al., 2018 paper in SR15, sections 3.3.9, 3.5.2.5, 3.6.3.2 and in FAQ 3.1.

Glaciers crossing the transantarctic mountains, one of them ending up to Drygalski ice tongue (left side) in the Ross sea. The ice tongue is an example of those ice shelves that form as grounded ice flows toward the sea from the interior. Ice shelves are weakened by a warmer ocean, which accelerates upstream ice flow [Credit: C. Ritz, PEV/PNRA]

Glaciers

Over the whole globe, the mass of glaciers has decreased since pre-industrial times in 1850, according to Marzeion et al., 2014. At that time, climate change was a mix between human impact and natural variability of climate. Glacier response times to change in climate are typically decades, which means that a change happening, for instance, today, still has consequences on glaciers tens of years after. Today, the retreat of glaciers is thus a mixed response to natural climate variability and current anthropogenic warming. However, since 1850, the anthropogenic warming contribution to the glacier mass loss has increased from a third to more than two third over the last two decades.

Similarly to the Greenland ice sheet, glaciers are prone to undergo an acceleration of ice mass loss wherever the limit altitude where rainfall occurs more often than snowfall is higher and at the same time the glacier surface lowers. However, as opposed to ice sheets, glaciers can be found all over the world under various latitudes, temperature and snow regimes, which makes it difficult to establish a unique temperature above which all the glaciers in the world will shrink faster in a nonlinear way. There are, however, model-based global estimates of ice mass loss over the next century. The paper from Marzeion et al., 2018, shows that under 1.5-2°C of global warming, the glaciers will lose the two thirds of their current mass, and that for a 1°C warming, our current level of warming since pre-industrial times, the glacier are still committed to lose one third of their current mass. This means the actions that we take now to limit climate change won’t be seen for decades.

You can find complementary informations in SR15, sections 3.3.9, 3.6.3.2 and in FAQ 3.1.

Sea ice

As very prominently covered by media and our blog (see this post and this post), the Arctic sea-ice cover has been melting due to the increase in CO2 emissions in past decades. To understand the future evolution of climate, climate models are forced with the expected CO2 emissions for future scenarios. In summer, the results of these climate model simulations show that keeping the warming at 1.5°C instead of 2°C is essential for the Arctic sea-ice cover. While at 1.5°C warming, the Arctic Ocean will be ice-covered most of the time, at 2°C warming, there are much higher chances of a sea-ice free Arctic. In winter, however, the ice cover remains similar in both cases.

In the Antarctic, the situation is less clear. On average, there has been a slight expansion of the sea-ice cover (see this post). This is, however, not a clear trend, but is composed of different trends over the different Antarctic basins. For example, a strong decrease was observed near the Antarctic peninsula and an increase in the Amundsen Sea. The future remains even more uncertain because most climate models do not represent the Antarctic sea-ice cover well. Therefore, no robust prediction could be made for the future.

You can find all references were these results are from and more details in Section 3.3.8 of the SR15. Also, you can find the impact of sea-ice changes on society in Section 3.4.4.7.

Caption: Sea ice in the Arctic Ocean [D. Olonscheck]

Permafrost

Permafrost is ground that is frozen consecutively for two years or more. It covers large areas of the Arctic and the Antarctic and is formed or degraded in response to surface temperatures. Every summer, above-zero temperatures thaw a thin layer at the surface, and below this, we find the boundary to the permafrost. The depth to the permafrost is in semi-equilibrium with the current climate.

The global area underlain by permafrost globally will decrease with warming, and the depth to the permafrost will increase. In a 1.5°C warmer world, permafrost extent is estimated to decrease by 21-37 % compared to today. This would, however, preserve 2 millions km2 more permafrost than in a 2°C warmer world, where 35-47 % of the current permafrost would be lost.

Permafrost stores twice as much carbon (C) as the atmosphere, and permafrost thaw with subsequent release of CO2 and CH4 thus represents a positive feedback mechanism to warming and a potential tipping point. However, according to estimates cited in the special report, the release at 1.5°C warming (0.08-0.16 Gt C per year) and at 2°C warming (0.12-0.25 Gt C per year) does not bring the system at risk of passing this tipping point before 2100. This is partly due to the energy it takes to thaw large amounts of ice and the soil as a medium for heat exchange, which results in a time lag of carbon release.
The response rates of carbon release is, however, a topic for continuous discussion, and the carbon loss to the atmosphere is irreversible, as permafrost carbon storage is a slow process, which has occurred over millennia.

Changes in albedo from increased tree growth in the tundra, which will affect the energy balance at the surface and thus ground temperature, is estimated to be gradual and not be linked to permafrost collapse as long as global warming is held under 2°C.

The above-mentioned estimates and predictions are from the IPCC special report Section 3.5.5.2, 3.5.5.3 and 3.6.3.3.

Slope failure of permafrost soil [Credit: NASA, Wikimedia Commons].

So, in summary…

In summary, what can we say? Although the 1.5°C and 2°C limits were chosen as a consensus between historical claims based on physics and a number that is easy to communicate (see this article), it seems that there are some thresholds for parts of the cryosphere exactly between the two limits. This can have consequences on longer term, e.g. sea-level rise or permanent permafrost loss. Additionally, as the cryosphere experts and lovers that we are here in the blog team, we would mourn the loss of these exceptional landscapes. We therefore strongly hope that the COP24 will bring more solution and cooperation for the future against strengthening of climate change!

Further reading

Edited by Clara Burgard and Violaine Coulon


Lionel Favier is a glaciologist and ice-sheet modeller, currently occupying a post-doctoral position at IGE in Grenoble, France. He’s also on twitter.

 

 

 

Laura Helene Rasmussen is a Danish permafrost scientist working at the Center for Permafrost, University of Copenhagen. She has spent many seasons in Greenland, working with the Greenland Ecosystem Monitoring Programme and is interested in Arctic soils as an ecosystem component, their climate sensitivity, functioning and simply understanding what goes on below.

 

 

Clara Burgard is a PhD student at the Max Planck Institute for Meteorology in Hamburg. She investigates the evolution of sea ice in general circulation models (GCMs). There are still biases in the sea-ice representation in GCMs as they tend to underestimate the observed sea-ice retreat. She tries to understand the reasons for these biases. She tweets as @climate_clara.

 

Image of the Week – (Un)boxing the melting under the ice shelves

Image of the Week – (Un)boxing the melting under the ice shelves

The Antarctic ice sheet stores a large amount of water that could potentially add to sea level rise in a warming world (see this post and this post). It is currently losing ice, and the ice loss has been accelerating in the past decades. All this is linked to the melting of ice – not at the surface but at the base, underneath the so-called ice shelves which form the continuation of the Antarctic ice sheet over the ocean. These floating ice shelves (represented in color in our Image of the Week) are melted by ocean water from underneath. How can this process called ‘sub-shelf melting’ be included in ice-sheet models? One simple way is to divide the ice-shelf cavity into a number of ocean boxes. Let’s briefly see how it works.


How to model sub-shelf melting in ice-sheet models?

There are three main ways to do so – which way is most suitable depends on the application:

  1. The most elaborated approach is to use ocean models that resolve ocean dynamics underneath the ice shelves. However, they need a lot of computational power.

  2. As an alternative, simple parameterizations in which melting is a function of the depth of the ice-shelf base can be used. However, such parameterizations are for many applications too simple…

  3. Recently, intermediate approaches that include the basic ocean dynamics have been developed (e.g. Lazeroms et al., 2018; Pelle et al., in review). One such approach is the ocean box model (Olbers and Hellmer, 2010) that we extended for the use in an ice-sheet model. Our extension is called Potsdam Ice-shelf Cavity mOdel (PICO, Reese et al., 2018).

In the following, we take a closer look into the approach of PICO…

“Boxing” the cavity circulation

In Antarctic ice-shelf cavities (i.e. the water below the ice shelves), in general, an overturning circulation transports ocean water from the sea floor along the ice-shelf base towards the calving front (see Figure 2). It is driven by the “ice-pump” (Lewis and Perkin, 1986): ice melting near the grounding line (separation between the grounded ice sheet and the floating ice shelf) reduces the density of the ambient water. It becomes buoyant and rises along the shelf base towards the ocean. Through this process, new water from outside of the ice-shelf cavity is “pumped” along the continental shelf towards the grounding line. This leads to the typical pattern of highest melting near the deep grounding lines and lower melting towards the calving front.

 

Figure 2: Schematic showing the ocean boxes following the ice-shelf base, with the first box B1 near the grounding line, and the last box Bn at the calving front. The arrows indicate the overturning circulation. The ocean water enters the cavity from box B0 which is at depth of the continental shelf, in front of the ice shelf. [Credit: Fig. 1 of Reese et al. (2018)]

 

By dividing the ice-shelf cavity into 2 to 5 ocean boxes, the transport of the overturning circulation is simplified while the sub-shelf melt pattern is captured. The open ocean conditions are simply represented by the ocean reservoir box B0 (Figure 2). And the circulation is driven by the differences in water density between the ocean reservoir (B0 in Figure 2) and the first box near the grounding line (B1 in Figure 2). The model computes sub-shelf melting successively over the ocean boxes, starting near the grounding line.

Sub-shelf melting with PICO

Sub-shelf melting can vary a lot in-between ice shelves (Figure 1). Antarctic ice-shelf cavities can roughly be sorted into two types (Joughin et al., 2012). The first category are the cold cavities in which the ocean water is close to the freezing point and in which sub-shelf melting is generally low, about 0.1 meter per year. The second category are warm cavities which have a temperature of about 1 degree – that does not sound like much, but for an ice shelf, this feels like being in a sauna – and sub-shelf melting can easily exceed 10 meters per year. Small changes in ocean temperatures can hence have large effects on sub-shelf melting. An increase in sub-shelf melting thins the ice shelf, as for example observed in the Amundsen Sea region in West Antarctica (see this post). The ice shelves there are examples for warm cavities, and a cold cavity is, for instance, underneath the Filchner-Ronne Ice Shelf (see Figure 1 for the specific locations).

In reality, of course, things are much more complicated than simulated by our PICO model. For example, the Coriolis effect can influence ocean circulation in the cavities, sills in the bed can block access of warm water to the grounding line and so on…

Applications of PICO

To summarize, PICO is a simple and efficient modeling tool that can capture the general pattern of sub-shelf melting observed in Antarctica today. Being implemented in the Parallel Ice Sheet Model, it is openly available, so if you got excited about what it can do and want to use it yourself, you’re welcome to download it!

Further reading

Edited by David Docquier


Ronja Reese is a postdoctoral researcher at the Potsdam Institute for Climate Impact Research, Germany, in the group of Prof. Dr. Ricarda Winkelmann. She investigates ice dynamics in Antarctic with a focus on ice-ocean interactions and ice-shelf buttressing. She developed and implemented PICO together with Ricarda Winkelmann, Torsten Albrecht, Matthias Mengel and Xylar Asay-Davis. Contact Email: ronja.reese@pik-potsdam.de