CR
Cryospheric Sciences

Image of the Week

Image of the Week – The Lost Meteorites of Antarctica…

Image of the Week – The Lost Meteorites of Antarctica…

 When most people think of Antarctica, meteorites aren’t the first things that come to mind. Perhaps they imagine the huge ice shelves, the desolate interior, or perhaps penguin colonies near one of the scientific bases — but usually not meteorites. So why is our project looking for meteorites in Antarctica, and besides, aren’t they all lost until they are found?


Let’s start with the Antarctic part. Surprisingly, Antarctica is a great place to hunt for meteorites, with two-thirds of all known meteorites found there (see also this previous post). Despite the difficult searching conditions, the dark meteorites show up well on the bright white surface of the ice sheet. Also, due to the cold conditions, the weathering of meteorites is slower than in warmer regions, such as hot deserts. However, Antarctica is vast and most meteorites are small (a few cm in size) so finding them is still difficult. One thing that helps in this case is the presence of mountain ranges and nunataks near the perimeter of the continent. These slow the ice flow and cause stagnation points — blue ice areas (see Fig.1) — where meteorites can collect and accumulate on the surface usually at elevations of 1500m to 2500m or so.

To understand the “lost” part, you need to know that not all meteorites are created equally – some are stony, somewhat like the rocks found in the Earth’s crust, whilst others are more metallic, having a high iron content perhaps close to 90%. The latter tell a meteoriticist (yep, this is a real job definition!) about the cores of planets and the early formation of the solar system. In the rest of the world these rarer and more interesting iron meteorites usually make up about 5.2% of all samples found — but on the ice sheet, they only represent about 0.6%, an order of magnitude less.

This under-representation is a little odd and unexpected. We don’t expect any particular bias due to delivery to Earth, and if you’re out hunting for meteorites on your skidoo and spot a dark rock that’s potentially a meteorite, you’re still going to pick it up: so no bias in collection.

So where are the missing iron meteorites?

About 3 years ago a team from Manchester were looking at this problem and came up with a hypothesis that might explain it: as sunlight enters the blue ice and gets scattered below the surface it gets absorbed by meteorites and heats them up. This happens more on their upper surface, and due to the higher conductivity of iron meteorites in comparison to their stony counterparts, the heat is transferred to the ice below. Given the right conditions during the Austral summer, this process can provide enough energy so that iron meteorites melt the ice underneath them and sink a few centimetres below the surface whilst the stony ones stay on top. Though we put this on a mathematical footing by way of a model and confirmed the mechanism by some laboratory experiments, the only way to be sure that there is a layer of iron meteorites hiding below the surface is to go out and find them.

Fig. 2: Meteorite close-up: partially embedded in the blue ice surface [Credit: Katherine Joy/Lost Meteorites of Antarctica].

The current project

If you’re going to try and find iron meteorites hidden below the ice surface in Antarctica, then you’re going to need a new way of doing things. Ordinarily, searches are carried out by systematically searching an area of blue ice on skidoo and looking for dark rocks that might be potential meteorites (see Fig. 2). Obviously this won’t work for samples below the surface, so we had to come up with a new method that allows a good sized area to be covered (even in a relatively productive area we estimate the density of irons is <1 km-2) and can cope with the conditions up on the Antarctic plateau. Given that the key discriminating characteristic of the subsurface meteorites is their metallic content, it makes sense to use a system based on metal detector technology.

Our system is somewhat different to what you might use for hunting for archaeological coins or have to walk through at the airport, and instead the detector coils are embedded into an array of large polymer panels (the same material the British Antarctic Survey use for transporting fuel drums on). It’s entirely bespoke, including the pulse and detection electronics, data acquisition and analysis, and importantly, it’s designed to be able to deal with the conditions we expect down South.

Fig 3: The prototype detection system being tested at Sky-Blu Field Station during the 2018/19 season. Panels are on the left of the image, control electronics are beneath the photovoltaic panel in the centre, and an indicator box on the skidoo shows when something metallic is detected [Credit: Geoff Evatt/Lost Meteorites of Antarctica].

Even so, given the logistical challenges of remote working in Antarctica (the area we want to search is ~700 km from the nearest base), we thought it prudent to do some tests of the prototype equipment closer to home. To that end, we’ve had two field trips to the UK Arctic Research Station in Ny Ålesund on Svalbard for the initial testing of the detection equipment.

In addition, we need to figure out exactly where to search. We therefore need to confirm an area has surface meteorites before we can hope to find the subsurface layer. That was the point of last Austral summer’s expeditions: while one team kept close to the Sky-Blu base for the first Antarctic test of full detector array, the other team went out to the Recovery Glacier region for a visual search of surface meteorites. Thankfully both were a success, with our meteorite hunting team bringing back a total of 36 surface meteorites.

Fig 4: The meteorite search team’s home for a few weeks. 700 km from Halley and poor weather meant return to civilisation was delayed until the Twin Otter could fly in [Credit: Katherine Joy/Lost Meteorites of Antarctica].

A bit more planning and we’re lined up for next year’s expedition where it all comes together and we find out if the hidden layer is there – or there’s something else at work…

You can find out more about the project and what we’re up to on the project blog: https://ukantarcticmeteorites.com/blog/

Further reading

Edited by Clara Burgard


Andy Smedley trained as an atmospheric scientist measuring and modelling how sunlight interacts with the atmosphere. Recently his research interests have expanded to include sunlight’s interaction with, and impacts on, the cryosphere. He is currently working on the Leverhulme Trust funded “Lost Meteorites of Antarctica” project at the University of Manchester where he deals with the logistics of Antarctic field expeditions, mapping and analysis to select the field sites, and trying to better understand how solar radiation interacts with blue ice and light absorbing particles – including meteorites.

Image of the Week – Who let the (sun)dogs out?

Figure 1a: Atmospheric formations on the interior Antarctic plateau near Dome Fuji. Photo credit: B. Van Liefferinge

How peaceful it is to contemplate the sky … This is especially true of polar northern or southern skies where the low temperatures can engender unique light phenomena. We often tend call them all, wrongly, sundogs, but in fact, many more phenomena exist. To list a few, you can observe a parhelic circle, a 22° halo, a pair of sun dogs, a lower tangent arc, a 46° halo, a circumzenithal arc, a parry arc, … This year, I had the chance to observe several of these phenomena during my fieldwork on the Antarctic plateau. I am no cloud specialist or meteorologist, but I would like to give you some explanations to better understand this sky art you might see one day.


Figure 1b: Atmospheric formations on the interior Antarctic plateau near Dome Fuji. Photo credit: B. Van Liefferinge

Everything starts with the ice crystals inside the clouds. Ice crystals can be approximated as hexagonal prisms, and two shapes can be found naturally: plates and columns (Fig.2), mainly dependent on air temperature and humidity. Clouds formed from these ice crystals are relatively thin and therefore sun rays can pass through them easily. In cold regions (polar or not), the ice crystals can also be found at ground level (in that case, they are called diamond dust).

Figure 2: atmospheric halos in the Antarctic plateau, 27 ‎November ‎2018. Plate crystal (left) and column crystal (right), modified from Walter Tape, 1994. Photo credit: B. Van Liefferinge

The observed light patterns in the sky are caused by the refraction of sun rays on the ice crystals. As they hit the crystals, the sun rays are diverted from their trajectory. Depending on the orientation of the crystals in the cloud, and the type of crystal present in the cloud, this will affect the sun ray paths differently. The resulting halos or arcs seen in the sky will result from the combination of all the different ray paths through all the clouds’ crystals together. The sun ray paths through the crystals can become quite complex, as illustrated in Fig. 3.

Figure 3: Example of a complex ray path through a plate crystal which contributes to forming a left parhelic circle (left), example of a complex ray path through a hexagonal crystal which contributed to forming a tricker arc (right), (Walter Tape, 1994). Photo credit: B. Van Liefferinge

As an example, let’s try to understand how the 22° halo forms (see Fig.1 a and b), one of the most common halos observed. The 22° halo is formed in clouds that have randomly oriented column crystals (although this is still under debate). When a sun ray hits an ice crystal, the most common path it will take is to refract through the face of the hexagon it hits (e.g. face 1 on Fig.4) and refract back out of a face opposite (face 3 on Fig.4). The angle between face 1 and face 3 is of 60°. A light ray passing through two faces of an ice crystal inclined at 60° from each other is deflected through angles from 22° up to 50°. The deflection at 22° is the most probable and therefore creates the brightest circle in the sky (the 22° halo!). The other deflections above 22° are less common but occur nonetheless and form the fade disk (Fig. 4). No light can be refracted through smaller angles then 22° (this is a result of the air-to-ice index of refraction). This is why you see a “darker sky” inside the halo. Now, add to this that we have been considering white light in general. But in fact, visible white light is composed of visible red through blue rays, which do not deviate by the same amount (21.54° for red light to 22.37° for blue light). This explains why the 22° halo looks like a rainbow.

Figure 4: Sun ray path through an ice crystal (left), resulting 22° halo (right) [Credit: B. Van Liefferinge].

Now let’s go back to our famous sundog. If you understood the 22° halo, it will be a piece of cloud! Sundogs follow the same rule as the 22° halo: sun rays passing through two ice crystal faces inclined at 60° to each other are deflected through a minimum angle of 22°. The difference here is that for a sundog to form, the ice crystals must all be aligned along the horizontal direction. This is the case when the ice crystals are all plate crystals (Fig.5), which, as a result of their shape, tend to align horizontally in clouds. As sun rays traverse them, they are deflected into two specific spots either side of the sun, instead of along a circle when crystals are randomly oriented (like for the 22° halo).

Figure 5: Sundog formation [Credit: Atmospheric Optics website]

And finally, I’ll let you enjoy a light show, filmed recently over Svalbard on a perfect day for atmospheric formations (video courtesy of Ashley Morris)…

 

A few more fun facts:

Edited by Marie Cavitte


Brice Van Liefferinge is a trained geographer, glaciologist and modeller. With a background in geography at the Université libre de Bruxelles (ULB, Belgium), he pursued his interest in Earth sciences during his PhD looking at the thermal regime of the Antarctic Ice Sheet and working on the Beyond Epica Oldest Ice project. He is now working on the Oldest Ice Dome Fuji project with Dr. Kenny Matsuoka at the Norwegian Polar Institute (NPI, Tromsø, Norway) for which he just came back from 3 months of fieldwork at Dome Fuji, Antarctica.

 

Image of the Week – Kicking the ice’s butt(ressing)

Risk map for Antarctic ice shelves shows critical ice shelf regions, where local thinning increases the ice flow from the continent into the ocean [Credit: modified from Reese et al., 2018]

Changes in the ice shelves surrounding the Antarctic continent are responsible for most of its current contribution to sea-level rise. Although they are already afloat and do not contribute to sea level directly, ice shelves play a key role through the buttressing effect. But which ice shelf regions are most important for this?


The role of ice-shelf buttressing

Schematic ice-sheet-shelf system: buttressing arises when an ice shelf is laterally confined in an embayment or locally grounds at pinning points [Credit: Ronja Reese & Maria Zeitz]

In architecture, the term “buttress” is used to describe pillars that support and stabilize buildings, for example ancient churches or dams. In analogy to this, buttressing of ice shelves can stabilize the grounded ice sheet (see this blog article about the marine ice sheet instability). It can be understood as a backstress that the ice shelf exerts on the grounding line – the line that separates the grounded ice from the floating ice shelves. When an ice shelf thins or disintegrates, this stress can be reduced, then the ice flow upstream is less restrained and can increase.

This effect has been widely observed in Antarctica: the thinning of ice shelves in the Amundsen Sea is driven by the ocean and linked to ice loss there (see this blog article) and after the spectacular disintegration of Larsen A and B ice shelves the adjacent ice streams accelerated.

Which ice shelf regions are important?

Risk maps show how important each ice-shelf location is: if an ice shelf thins in this location, how much does the flux across the grounding line increase? We estimated this immediate increase using the numerical ice-flow model Úa. At first glance, one can see that all ice shelves have regions that influence upstream ice flow, and thus, provide buttressing. The highest responses occur near grounding lines of fast-flowing ice streams. Equally strong responses are found in the vicinity of ice rises or ice rumples – where the ice shelf re-grounds locally and is subject to basal drag. On the other hand, “passive” regions with negligible flux response are located towards the calving front, but also in spots close to the grounding line. Flux response signals can sometimes travel quite far – for example a perturbation near Ross Island accelerates the ice flow in almost the entire Ross Ice Shelf and reaches ice streams more than 900km away (not visible in the figure).

Risk maps for Antarctic ice shelves, as presented here, help us to get a better understanding of the critical ice shelf regions – if you are interested to read more, please see for example Gagliardini, 2018 and Reese et al., 2018.

Edited by Scott Watson and Sophie Berger


Ronja Reese is a postdoctoral researcher at the Potsdam Institute for Climate Impact Research, Germany, in the ice dynamics working group. She investigates ice dynamics in Antarctic with a focus on ice-ocean interactions and ice-shelf buttressing. She created the risk map together with Ricarda Winkelmann, Hilmar Gudmundsson and Anders Levermann. Contact Email: ronja.reese@pik-potsdam.de

.

Image of the Week – Fifty shades of May (Glacier)

Image of the Week – Fifty shades of May (Glacier)

With over 198 000 glaciers in the world, you can always find a glacier that fits your mood or a given occasion. So why not for example celebrate the first Image of the Week of May with a picture of the aptly named May Glacier?


May Glacier is in fact not named after the month, but after Mr May, an officer onboard the Flying Fish during her expedition to the East Antarctic coast in the 1840s. Apart from that, there is not much to say about this 9 x 11 km glacier located in East Antarctica around 130°E, except that it is really hard to find a picture with the keywords “may” and “glacier”… So I let you enjoy the Image of the Week, which combines three satellite images of May Glacier (at the centre) and its surroundings exactly a month ago, when the skies were clear and the sea ice pretty:

See you in a month to talk about the June(au) ice field!

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 — Cavity leads to complexity

Aerial view of Thwaites Glacier [Credit: NASA/OIB/Jeremy Harbeck].

 

A 10km-long, 4-km-wide and 350m-high cavity has recently been discovered under one of the fastest-flowing glaciers in Antarctica using different airborne and satellite techniques (see this press release and this study). This enormous cavity previously contained 14 billion tons of ice and formed between 2011 and 2016. This indicates that the bottom of the big glaciers on Earth can melt faster than expected, with the potential to raise sea level more quickly than we thought. Let’s see in further details how the researchers made this discovery.


Thwaites Glacier

Thwaites Glacier is a wide and fast-flowing glacier flowing in West Antarctica. Over the last years, it has undergone major changes. Its grounding line (separation between grounded ice sheet and floating ice shelf) has retreated inland by 0.3 to 1.2 km per year in average since 2011. The glacier has also thinned by 3 to 7 m per year. Several studies suggest that this glacier is already engaged in an unstoppable retreat (e.g. this study), called ‘marine ice sheet instability’, with the potential to raise sea level by about 65 cm.

Identifying cavities

With the help of airborne and satellite measurement techniques, the researchers that carried out this study have discovered a 10km-long, 4km-wide and 350m-high cavity that formed between 2011 and 2016 more than 1 km below the ice surface. In Figure 2B, you can identify this cavity around km 20 along the T3-T4 profile between the green line (corresponding to the ice bottom in 2011) and the red line (ice bottom in 2016). According to the researchers, the geometry of the bed topography in this region allowed a significant amount of warm water from the ocean to come underneath the glacier and progressively melt its base. This lead to the creation of a huge cavity.

Fig. 2: A) Ice surface and bottom elevations in 2014 (blue) and 2016 (red) retrieved from airborne and satellite remote sensing along the T1-T2 profile identified in Fig. 2C. B) Ice surface and bottom elevations in 2011 (green) and 2016 (red) along the T3-T4 profile. C) Changes in ice surface elevation between 2011 and 2017. The ticks on the T1-T2 and T3-T4 profiles are marked every km [Credit: adapted with permission from Figure 3 of Milillo et al. (2019)].

What does it mean?

In order to make accurate projections of future sea-level rise coming from specific glaciers, such as Thwaites Glacier, ice-sheet models need to compute rates of basal melting in agreement with observations. This implies a correct representation of the bed topography and ice bottom underneath the glacier.

However, the current ice-sheet models usually suffer from a too low spatial resolution and use a fixed shape to represent cavities. Thus, these models probably underestimate the loss of ice coming from fast-flowing glaciers, such as Thwaites Glacier. By including the results coming from the observations of this study and further ongoing initiatives (such as the International Thwaites Glacier Collaboration), ice-sheet models would definitely improve and better capture the complexity of glaciers.

Further reading

Edited by Sophie Berger


David Docquier is a post-doctoral researcher at the Earth and Life Institute of Université catholique de Louvain (UCL) in Belgium. He works on the development of processed-based sea-ice metrics in order to improve the evaluation of global climate models (GCMs). His study is embedded within the EU Horizon 2020 PRIMAVERA project, which aims at developing a new generation of high-resolution GCMs to better represent the climate.

 

Image of the Week – 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.

Image of the Week – The solid Earth: softer than you might think!

Rebounding beach in the Canadian Artic [Credit : Mike Beauregard distributed by Wikimedia Commons]

Global sea level is rising and will continue to do so over the next century, as has once again been shown in the recent IPCC special report on 1.5°C. But did you know that, in some places of our planet, local sea level is actually falling, and this due to rising of the continent itself?! Where is this happening? In places where huge ice sheets used to cover the land surface during the last ice age, such as Scandinavia, Canada, or Siberia. Even though these ice sheets melted several thousands of years ago, the land that once lied under them is still rising in reaction to the release of their previous burden. This is what we call Glacial Isostatic Adjustment or GIA. Where does this adjustment come from? Our Earth is not as solid as you would think…


Our Image of the Week represents a layered beach located in Nunavut, in the Canadian Arctic. This specific landform is caused by the glacial rebound of the Arctic coastline resulting from the response of the lithosphere to the melting of the Laurentide Ice sheet, an ice sheet that used to cover the North American continent until less than 10 000 years ago.

Earth during Last Ice Age [Credit: Wikimedia Commons]

What is Glacial Isostatic Adjustment?

Imagine sitting on a very comfy couch, watching a movie. At the end of the movie, the couch has perfectly adapted to the shape of your body. Once you get up, you’re still able to see where you’ve been sitting, as the couch takes a little time to get back to its original form. Well… this is exactly what happens with the Earth’s crust and mantle. To understand this, you need to visualize the internal structure of our planet Earth, which is layered in spherical shells: under our feet lie the rocky tectonic plates, which constitute the Earth’s crust. These crusty plates – whose thickness varies between a few kilometers under oceans to a few tens of kilometers under the continents – are floating on a viscous layer, called the mantle. It is almost 3000 kilometers thick and actually slowly flows like a liquid, at a speed of a few centimeters per year.

Even though the Earth’s crust is a very strong material, the pressure applied by an ice sheet thick of several kilometers is so important that the crust will locally deform under the heavy ice mass, sinking down into the viscous mantle. That’s what happened over large areas of the Northern Hemisphere that were covered by ice masses during the last ice age, and what is still happening in the remaining ice sheets of Greenland and Antarctica, which have been depressing the Earth’s crust beneath them for thousands of years.

Just like for the couch in the example above, when the weight is removed, the mantle rebounds, carrying with it the overlying crust. Over the 20 000 years since the last glacial maximum, lands now relieved of their previous ice-burden are gradually rebounding. The Earth’s delayed response to the variation of mass on its surface is explained by the viscous character of the Earth’s mantle.

Glacial Isostatic Adjustment [Credit: Wikimedia Commons]

Why is it important to take it into account?

Even though the Siberian, Scandinavian and Laurentide ice sheets melted several thousands of years ago (causing a rise in global sea level), these regions that were previously glaciated are still locally emerging to compensate the loss of their overlying weight. The level of the coastline relative to the local sea-level thus increases. One says that the “relative sea level” is falling, and this at a rate that is essentially determined by the rate of the post-glacial rebound (which can exceed 1 cm/year in some areas, as shown in the figure below!). The rates of relative sea level can be influenced even at sites that are quite far away from the centres of the last glaciation, although it is much less significant.

Rate of the post-glacial rebound [Credit: NASA, Wikimedia Commons]

A good understanding of glacial isostatic adjustment is important to distinguish the different components and contributors to a local sea-level evolution: what part is due to the uplift of the land? And what part is due to the rising of global sea-level?
In addition, glacial isostatic adjustment also impacts the behaviour of  modern Greenland and Antarctic ice sheets. By influencing the geometry of the underlying bedrock, it will impact the sensitivity of the ice sheet to global warming and thus the glacial isostatic adjustment itself: this is a vicious circle!

The problem is that glacial isostatic adjustment also depends on the local properties of the Earth’s crust and mantle, which are not constant at the Earth’s surface. A lot of work is still needed to understand all of this properly. Luckily, since NASA launched GRACE – a satellite mission that maps variations in the Earth’s gravity field –  in 2002, scientists have observations they can use to constrain their models and improve their understanding of this complicated matter.

Further reading

Edited by Clara Burgard and Sophie Berger