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Cryospheric Sciences

Cryospheric Sciences

Katabatic winds – A load of hot (or cold) air?

Katabatic winds – A load of hot (or cold) air?

It might seem obvious that a warming world will lead to a reduction in glacial ice cover, but predicting the response of glaciers to climatic change is no simple task (even within the short term). One way to approach this problem is to come up with relationships which describe how glaciers interact with the world around them, for example, how the ice interacts with the air above it. Our post today delves into the world of ice-air interaction and describes some of the problems encountered by those who are investigating it, in particular the problem of modelling katabatic winds! Not sure what we are talking about…then read on to find out more! 


What are katabatic winds?

Anyone who has stood on, or in front of a glacier on a clear, sunny day has no doubt felt the bitter chill of a katabatic wind, forcing them to don a warm jacket and lose their chance at that lovely “glacier tan”. Katabatic winds (derived from the Greek word katabasis, meaning ‘downhill’) develop over snow and ice surfaces because the 0°C ice surface cools the air just above it. This cold, dense air then flows downhill under the force of gravity (Fig. 1 and Fig. 2). This is not recent news and such wind chill has no doubt punished glaciologists and explorers for the last century or more –  Mawson’s Description of the 1911-1914 Australian Antarctica Expedition is aptly named “The Home of the Blizzard“. However, despite being well known, this phenomenon still causes much uncertainty when it comes to modelling the melting of glacier ice surfaces around the world.

Soon gusts swept the tops of the rocky ridges, gradually descending to throw up the snow at a lower level. Then a volley raked the Hut, and within a few minutes we were once more enveloped in a sea of drifting snow, and the wind blew stronger than ever. – Mawson, 1915, The Home of the Blizzard

Figure 2: The view from the upper reaches of Tsanteleina Glacier in the western Italian Alps (Val d’Rhemes, Aosta). Katabatic winds generally flow in a down-glacier direction – here, from right to left [Credit: T Shaw].

Challenges for modelling

Air temperature is really important in determining how much a glacier melts and we need to know as much about it as possible to provide accurate predictions now and into the future. This is particularly relevant because the warmer it gets, the more energy is available to melt ice and seasonal snow. Unfortunately though, we don’t have an infinite supply of meteorological observations (e.g. air temperature, wind speed etc) at many locations we are interested in. As a result, we have to make simple assumptions about what the weather is doing at a remote, far away glacier. One such simple assumption is based upon the fact that air temperature typically decreases with increasing elevation, and so if we know the elevation of a location we are interested in, we can assume a ‘likely’ temperature. The rate of change in temperature with elevation is known as a ‘lapse rate’.

Air temperature is really important in determining how much a glacier melts…the warmer it gets, the more energy is available to melt ice and seasonal snow.

When predicting glacier melt, it is common practice to use a lapse rate which stays constant in time and space. This is convenient as we often don’t know the actual lapse rate at a given location, but this often ignores things happening at the surface of the Earth. An important example of this is when we have katabatic winds over glaciers!

When conditions are warm, and skies are clear, the cooling of the air above the ice surface, means that the application of a lapse rate is fairly useless, or close to it [Greuell and Böhm, 1998]! That is because the cooling from the surface continues as air flows down the glacier, typically creating colder temperatures at lower elevations, the opposite of the typical lapse rate assumption that models will apply.

‘Bow-shaped’ temperature vs. elevation relationships

To complicate matters for people trying to model the air temperature over glaciers, the effect of surface cooling is not just dependent on the amount of time an air parcel is in contact with the ice surface but also the characteristics of the ice surface it has been in contact with. In fact, after cooling on their descent down-glacier, air parcels have been documented to warm again, leaving interesting slightly “bow-shaped” curves to the temperature-elevation relationship. This effect has been found for the Swiss Haut Glacier d’Arolla and the Italian Tsanteleina Glacier (Fig. 3c,d). A new model approach to tackling this bow-shaped problem has been presented by recent research [Ayala et al., 2015] and offers a means of accounting for katabatic winds in glacier models. Nevertheless, more data and more work are still needed to generalise these models [Shaw et al., in review].

Figure 3: Relationship between elevation and air temperature on three different glaciers in the western Alps. Miage (Italy), Tsanteleina (Italy) and Arolla (Switzerland). Glaciers are represented using the mean of all data available (green), the top 10% of off-glacier temperatures (P90 – red) and the bottom 10% of off-glacier temperatures (P10 – blue), plus one standard deviation. The debris-covered Miage Glacier does not demonstrate a classic katabatic flow regime and therefore temperature corresponds well to elevation even under warm conditions [Credit: T Shaw, unpublished].

after cooling on their descent down-glacier, air parcels have been documented to warm again, leaving interesting slightly “bow-shaped” curves to the temperature-elevation relationship.

Air temperatures across debris-covered glaciers

As you may have read in our previous post on the topic, debris-covered glaciers behave in a different way to those with a clean ice surface. Detailed observations of air temperature across a debris-covered glacier show that the glacier responds to the heating of surface debris in the sunlight and a consequent warming of the lower atmosphere [Shaw et al., 2016]. Because of this, air temperature conforms very strongly to the elevation dependency that is assumed when using a lapse rate. Although very local variations of air temperature on other debris-covered glaciers cannot be well estimated by a lapse rate [Steiner and Pellicciotti, 2016], the insulating effect of thick debris cover means that the current approach to using simple lapse rates for estimating air temperature over debris-covered glaciers could be suitable.

Nevertheless, challenges for accurately representing air temperature above glaciers without debris cover remain. The fact that globally averaged temperatures are expected to rise over the current century (areas at high latitudes have shown a stronger warming trend) [Collins et al, 2013], the applicability of using lapse rates could further diminish. Recent patterns of warmer-than-average temperatures also suggest a difficulty of accurately estimating on-glacier temperatures in the short-term. For example, for the period of May 2015 – August 2016, every month beat the previously held record for warmest globally average temperature (GISTEMP). Imagine the bow-shaped problem to that!

Edited by Matt Westoby and Emma Smith


Thomas Shaw is a PhD student in the Department of Geography at Northumbria University, UK. His research is focused on the spatial and temporal variance in near-surface air temperature across debris-covered and debris-free glaciers in the western Italian Alps. As well as conducting research in the Alps, he is also very interested in glaciers and their processes on Svalbard (Norwegian Arctic) and has spent plenty of time studying above, or within (!), ice at high latitudes. Contact e-mail: thomas.shaw@northumbria.ac.uk

Image of the Week – For each tonne of CO2 emitted, Arctic sea ice shrinks by 3m² in summer

Image of the Week – For each tonne of CO2 emitted, Arctic sea ice shrinks by 3m² in summer

Declining sea ice in the Arctic is definitely one of the most iconic consequences of climate change. In a study recently published in Science, Dirk Notz and Julienne Stroeve find a linear relationship between carbon dioxide (CO2) emissions and loss of Arctic sea-ice area in summer. Our image of this week is based on these results and shows the area of September Arctic sea ice lost per inhabitant due to CO2 emissions in 2013.


What did we know about the Arctic sea ice before this study?

Since the late 1970s, sea ice has been dramatically shrinking in the Arctic, losing 3.8% of its area per decade. Sea-ice area is at its minimum in September, at the end of the melting season.

The main cause of this loss is the increase in surface temperature over the recent years (Mahlstein and Knutti, 2012), which has been more pronounced in the Arctic compared to other regions on Earth (Cohen et al., 2014). The use of statistical methods involving both observations and climate models shows that the recent warming in the Arctic can be attributed to human activity, i.e. mainly greenhouse gas emissions (Gillett et al., 2008). This suggests a direct link between human activity and Arctic sea-ice loss, which is confirmed in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).

How exactly is sea-ice loss related to CO2 emissions ?

Notz and Stroeve (2016) relate the Arctic sea-ice decline to cumulative CO2 emissions since 1850 (i.e. the total amount of CO2 that has been emitted since 1850) for both observations and climate models. Cumulative CO2 emissions constitute a robust indicator of the recent man-made global warming (IPCC, 2014).

The two quantities are clearly linearly related (see Figure 2). From 1953 to 2015, about 3.5 million km² of Arctic sea ice have been lost in September while 1200 gigatonnes (1 Gt = 10e9 tonnes) of CO2 have been emitted to the atmosphere. This means that for each tonne of CO2 released into the atmosphere, the Arctic loses 3 m² of sea ice.

Fig 2: Monthly mean September Arctic sea-ice area against cumulative CO2 emissions since 1850 for the period 1953-2015. Grey circles and diamonds show the results from in-situ (1953-1978) and satellite (1979-2015) observations, respectively. The thick red line shows the 30-year running mean and the dotted red line represents the trend of 3 m² sea-ice area loss per tonne of CO2 emitted. [Credit: D. Notz, National Snow and Ice Data Center ]

Starting from the relationship between cumulative CO2 emissions and sea-ice area, it is then easy to attribute to each country in the world their own contribution to sea-ice loss based on their CO2 emissions per capita. The countries that stand out in the map are thus the countries emitting the most in relation to their population.

Could the Arctic be ice-free in the future?

If this relationship holds in the future (in other words, if we extend the red dotted line to zero sea-ice area in Figure 2), adding 1000 Gt of CO2 in the atmosphere would free the Arctic of sea ice in September. Since we are currently emitting about 35 Gt CO2 per year, it would take less than 30 years to have the Arctic free of sea ice in the summer (which confirms previous model studies (e.g. Massonnet et al., 2012)).

Edited by Clara Burgard and Sophie Berger

Further reading

DavidDavid 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.

Polar Exploration: Perseverance and Pea Sausages

Polar Exploration: Perseverance and Pea Sausages

Born on this Day

Portrait of Ludvig Mylius-Erichsen by Achton Friis. [Credit: Danish Arctic Institute].

On this day in 1872 – 145 years ago –Ludvig Mylius-Erichsen, Danish author and polar explorer, was born. He led two expeditions to Greenland and successfully mapped the then unknown northeastern part of the country. The second expedition was his last. The expedition was surprised by an early onset of spring and could no longer use their dog sledges. The two Danes, Mylius-Erichsen and Høeg Hagen died in November 1907 of cold and hunger. Their bodies have never been found. The last remaining expedition member, the Greenlander Brønlund, continued the journey alone but perished a few weeks later. His body and the expedition diary was found in 1908.

Thousands of Pea Sausages

The tin on the image above contains “pea sausage” and was essentially the world’s first ready meal: A mixture of ground peas, beef fat, bacon, spices and salt. Pea sausage was invented in 1867 in Germany and was a common part of military and expedition rations up until the beginning of the 20th century.

Mylius-Erichsen’s expedition brought along 1756 tins of this kind. Each tin contained 6 tablets of pea sausage, that mixed with ¼ water would make a nourishing soup. And the taste? On his first expedition, Mylius-Erichsen wrote:

“The evening meals in the three boxes consisted mainly of different kinds of sturdy soups, black pudding, meat pie, beef, pea sausage and sizeable portions of vegetable such as cabbage, beans and carrots. We only used one third of the evening meal rations on the way out. We did not like the taste of the meat but black pudding, peas and the different kinds of soup were heavenly”.

And later:

“Jørgen and I had dinner at Amarfik’s, and dinner consisted both days of little auks boiled in our last portion of pea sausage – a wonderful dish…”

Members of Mylius-Erichsen’s first expedition: Brønlund, Bertelsen, Mylius-Erichsen, Rasmussen and Moltke. [Credit: Danish Arctic Institute].

Photos and descriptions are from the Danish Arctic Institute (@arktiskinstitut) where you can also see a full 360 degrees photo of the tin.

Check out more historical footage from Greenland in a previous Image of the Week showing aerial photos from the 1930s.

Edited by: Sophie Berger

Image of the Week – It’s all a bit erratic in Yosemite!

Image of the Week – It’s all a bit erratic in Yosemite!

When you think of California, with its sun-soaked beaches and Hollywood glamour, glaciers may not be the first thing that spring to mind – even for ice nerds like us. However, Yosemite National Park in California’s Sierra Nevada is famous for its dramatic landscape, which was created by glacial action. With our latest image of the week we show you some of the features that were left behind by ancient glaciers.


What do we see here?

Although Yosemite is now largely glacier-free the imprint of large-scale glaciation is evident everywhere you look. During the last glacial maximum (LGM), around 26,000 to 18,000 years ago, much of North America was covered in ice. Evidence of this can be seen in the strange landscape, shown in our image of the week. The bedrock surface in this area is polished and smoothed due to a huge ice mass that was moving over it, crushing anything in it’s path. When this ice mass melted rocks and stones it transported were released from the ice and left strewn on the smoothed bedrock surface. These abandoned rocks and stones are know as glacial erratics. Some of these erratics will have travelled from far-away regions to their resting place today.

During the last glacial maximum (LGM), around 26,000 to 18,000 years ago, much of North America was covered in ice.

Glaciers that still remain!

There are still two glaciers in Yosemite, Lyell and Maclure, residing in the highest peaks of the National Park. Park rangers have been monitoring them since the 1930s (Fig. 2), so there is a comprehensive record of how they have changed over this period. Sadly, as with many other glaciers around the world this means a huge amount mass has been lost – read more about it here!

Figure 2: Survey on Maclure Glacier by park rangers in the 1930s [Credit: National Parks Service]

On a more cheerful note – Here at the EGU Cryosphere Blog we think it is rather fantastic that the park rangers of the 1930s conducted fieldwork in a suit, tie and wide-brimmed hat and we are hoping some of you might be encouraged to bring this fashion back! 😀

If you do please make sure to let us know, posting it on social media an tagging us @EGU_CR! Here are a few more ideas of historical “fieldwork fashion” to wet your appetite: Danish explorers in polar bear suits, 1864-65 Belgian-Dutch Antarctic Expedition and of course Shackleton’s Endurance expedition!


Imaggeo, what is it?

You like this image of the week? Good news, you are free to re-use it in your presentation and publication because it comes from Imaggeo, the EGU open access image repository.

Image of the Week — Looking back at 2016

Image of the Week — Looking back at 2016

Happy New-Yearcorn

I cannot believe that a full year has passed since this very cute pink unicorn wished you a Happy New Year.

Yet, over the past  12 months our blog has attracted more than 16,200 visits.  And the blog analytics show that you, our dear readers, are based not only in Europe but literally all over the world!

With 67 new posts published in only 52 weeks, it’s more than likely that you missed a few interesting ones. Don’t worry, today’s Image Of the Week highlights some of the most exciting content written, edited and published by the whole cryo-team during the year 2016!  

Enjoy and don’t forget to vote in the big EGU Blog competition (see below) !
(Remark
: all the images are linked to their original posts)


Get the most of 2016

Last glaciation in Europe, ~70,000-20,000 years ago [By S. Berger].

The 82 research stations in the Antarctic [By S. Berger].

 

 

 

  • We also launched our new “for dummies” category that aims at explaining complex glaciological concepts in simple terms. The first and most read “for dummies” is all about “Marine Ice sheet instability” and explains why West Antarctica could be destabilised.

Marine Ice Sheet Instability [By D. Docquier].

Three other “for dummies” have been added since then. They unravel the mysteries behind Water Masses, Sea Level and Ice Cores.

  • Drilling an ice core [By the Oldest Ice PhD students]

    Another welcomed novelty of 2016 was the first “ice-hot news” post, about the very exciting quest for the oldest ice in Antarctica. In this post — issued at the same time as the press release —  the 3 PhD students currently involved with the project explain how and where to find their holy grail, i.e. the 1 million year old ice!

The list goes on of course, and I could probably spend hours presenting each of our different posts one by one and explain why every single one of them is terrific. Instead, I have decided to showcase a few more posts with very specific mentions!

 

The oddest place for ice : inside a volcano! [By T. Santagata]

The quirkiest ice phenomenon  : ice balls [By E. Smith].

The most romantic picture : Heart-shaped bubbles for ValentICE’s day [By S. Berger]

The creepiest picture: Blood Falls, Antarctica [By E. Smith]

The funniest post : April Fools “do my ice deceive me” [By S. Berger]

The best incidental synchronisation: The Perito Moreno collapsed the day before our the post went live [By E. Smith]

 

The “do they really do that? ” mention for ballooning the ice [By N. Karlsson]

The best fieldwork fail : Skidoos sinking into the slush [By S. Berger]

The most epic story : Shackleton’s rescue [By E. Smith]

The most puntastic title “A Game of Drones (Part 1: A Debris-Covered Glacier” [By M. Westoby].

The most provocative title : “What an ice hole” [By C. Heuzé]

The soundest post where science is converted to music [By N. Karlsson]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Good resolutions for 2017

The beginning of a new year is a great opportunity to look back at the previous year, and one of the logical consequences is to come with good resolutions for the coming year.  Thinking of a good resolution and then achieving it can however be tricky.  This is why we have compiled a few resolutions, that YOU dear cryo-followers could easily make 🙂

 Cryoblog stronger in the E(G)U blog competition

To celebrate the excellent display of science writing across all the EGU blogs, a competition has been launched.

Olaf the snowman begs you to vote for “the journey of a snowflake”

From now until Monday 16th January, we invite you, the cryo-readers, to vote for your favourite post of 2016, which should be “journey of a snowflake” (second-to last option). I am obviously being totally objective but if you’re not convinced, the little guy on the right might be more persuasive. If you’re really adventurous, you could also consider clicking on other posts to check what they look like, after having voted for the cryo-one, of course.

Get involved

Hopefully by now:

  1. You are convinced that the cryosphere is amazing and that the EGU cryoblog enables you to seize some of the cryo-awesomeness
  2. You have read and elected the “journey of a snowflake”  as the best post of 2016
  3. You would like to contribute to the blog (because you would like to be part of this great team or simply because you think your sub-field is not represented well enough).

Not to confuse you with a long speech, the image below explains how to get involved. We always welcome contributions from scientists, students and professionals in glaciology, especially when they are at the early stage of their career.

Thank you for following the blog!

PS: this is one of my favourite tweets from the EGU cryospheric division twitter account. What is yours?

Edited by Nanna Karlsson

Image of the Week – The Sound of an Ice Age

Image of the Week – The Sound of an Ice Age

New Year’s Eve is just around the corner and the last “image of the week” of 2016 will get you in the mood for a party. If your celebration needs a soundtrack with a suitably geeky touch then look no further. Here is the music for climate enthusiasts: The sound of the past 60,000 years of climate. Scientist Aslak Grinsted (Centre for Ice and Climate, University of Copenhagen, Denmark) has transformed the δOxygen-18 values from the Greenland NorthGRIP ice core and the Antarctic WAIS ice core into music (you can read more about ice cores in our Ice Cores for Dummies post). Using the Greenlandic data as melody and the Antarctic data as bassline, Aslak has produced some compelling music.

You can listen to his composition and read more about his approach here.

The δOxygen-18 values are a measure of the isotopic composition of the ice, and they are a direct indicator of temperature. The image of the week above shows the isotope values for the past 20,000 years as measured by polar ice cores. On the left-hand side, we are in present-day: an inter-glacial. The δOxygen-18 values are high indicating high temperatures. In contrast, on the right-hand side of the figure we are in the last glacial with lower δOxygen-18 values and lower temperatures. One remarkable thing about these curves is how fast the temperature changes in Greenland (top) compared to Antarctica (bottom). This delayed coupling is called the Bipolar Seesaw.

The clefs are our own addition of course. We have not included the time signature because who knows what the rhythm of the climate might be? (Personally, I think it might be in ¾ like a waltz: An unrestrained movement forward with small underlying variations).

The data from Antarctica is published by WAIS Divide Project Members, 2015. The Greenlandic data can be found on the Centre for Ice and Climate website and in publications by Vinther et al., 2006, Rasmussen et al., 2006, Andersen et al., 2006 and Svensson et al., 2006.

Happy New Year!

 

Image of the Week – Let it snow, let it snow, let it snow…

Image of the Week – Let it snow, let it snow, let it snow…

Christmas is coming to town and in the Northern Hemisphere many of us are still dreaming of a white Christmas, “just like the ones we used to know”. But how likely is it that our dreams will come true?


What is the definition of a White Christmas ?

Usually Christmas can be defined as a “White Christmas” if the ground is covered by snow on either Christmas Eve or Christmas Day depending on local traditions. If you believe Christmas movies, it seems like Christmas was accompanied by snow much more often in the past than today! But is this really the case, or is it just the “Hollywood” version of Christmas? According to the UK Met Office White Christmases were more likely in the past. Due to climate change, average global temperatures are higher, which in many places reduces the chance of a White Christmas. However, the chances of a White Christmas also depend strongly on where you live…

Living in Western or Southern Europe, the Southern US or the Pacific coast of the US? Unlucky you!

Not too surprisingly, most of the inhabitants of Portugal, Southern Spain, and Southern Italy have probably never experienced White Christmas in their hometown. Maybe more counter intuitively the probability of a White Christmas is also low in most of France, the Netherlands, Ireland, and the Southern UK! In the US, the probability of a White Christmas increases from South to North, except on the Pacific Coast, which has a very low probability of a White Christmas.

Probability of a White Christmas in Europe (snow on the ground on 25th of December), inferred from reanalysis data (ERA Interim from 1979-2015). Probability [in %] increases from white to blue [Credit : Clara Burgard, Maciej Miernecki. We thank the ECMWF for making the data available]

What influences the probability of snowfall on Christmas?

The mean air temperature decreases with altitude and latitude, meaning that chances of a white Christmas increase the further North and at the higher you travel. However, coastal regions represent an exception. The air often has traveled over the ocean before reaching land. As the ocean is often warmer than the land surface in winter, the air in coastal regions is often too warm for snow to form. Additionally, in the Northern Hemisphere, ocean currents on the Western coast of the continents tend to carry warm water to high latitudes, while ocean currents on the Eastern coast tend to carry cold water to low latitudes. The probability of snowfall is therefore even lower in Western coastal regions (e.g. Pacific coast of the US, Atlantic coast of Europe).

Don’t despair !

If you want to increase your chances of experiencing a White Christmas, you have three solutions:

    1. You already live in an area with high probability of White Christmas (lucky you!) – Sit tight and do a “snow dance”, here is one suggestion that we have heard works well:

    2. Travel or move to one of these 10 suggested destinations (e.g. St. Moritz, Swizerland)

      Frozen Lake St. Moritz in Winter 2013 [Credit: Wikimedia Commons]

    3. Build your own snow with this simple recipe!

We hope that you find a satisfactory solution that makes you happy this Christmas. Otherwise, remember that snow is not the only thing that defines Christmas. Enjoy the relaxed time with family and friends and prepare yourself for the coming new year! If you find yourself at a loose end, then there is always the back catalogue of EGU Cryosphere Blog posts to read – and we guarantee a healthy dose of snow and ice can be found here.

So, this is it from the EGU Cryosphere blog team for 2016. See you in 2017 – after all, the snow must go on…

Further reading:

      •  MetOffice website with interesting facts around White Christmas!

Edited by Emma Smith

Image of the Week — Allez Halley!

Image of the Week — Allez Halley!

On the Brunt Ice Shelf, Antarctica, a never-observed-before migration has just begun. As the pale summer sun allows the slow ballet of the supply vessels to restart, men and machines alike must make the most of the short clement season. It is time. At last, the Halley VI research station is on the move!


Halley, sixth of its name

Since 1956, the British Antarctic Survey (BAS) has maintained a research station on the south eastern coast of the Weddell Sea. Named after the 17th century British astronomer Edmond Halley (also the namesake of Halley’s comet), this atmospheric research station is, amongst other things, famous for the measurements that led to the discovery of the ozone hole (Farman et al., 1985).

Due to the inhospitable nature of Antarctica, there have been six successive Halley research stations:

  • Halley I to IV had to be abandoned and replaced when they got buried too deeply beneath the snow that accumulated over their lifetimes (up to ten years per station).
  • Halley V was built on steel platforms that were raised periodically, so the station did not end up buried under snow. However, Halley V was flowing towards the ocean along with the ice shelf when a crack in the ice formed. To avoid finishing up as an iceberg, the station was demolished in 2012.
  • Halley VI, active since 2012, can be raised above the snow and also features skis, so that it can be towed to a safer location if the ice shelf again threatens to crack. However, no one expected that this would have to be put in practice less than 5 years after the station’s opening…

The relocation project, featuring the new October crack. Inset, timeline of the awakening of Chasm 1. The ice shelf flows approximately from right to left. [Credit: British Antarctic Survey].

The awakening of the cracks

The project of moving Halley VI was announced a year ago. A very deep crack in the ice (“Chasm 1” in the map above) upstream of the station and dormant for 35 years, started growing again barely a year after the opening of Halley VI. The risk of losing the station if this part of the ice shelf broke off as an iceberg became obvious, and it was decided to move the station upstream – beyond the crack.

Additionally, there is another problem, or rather another crack, which appeared last October. This one is located north of the station and runs across a route used to resupply Halley VI. This means that of the two locations where a supply ship would normally dock, one is no longer connected to the research station and hence rather useless. Not only is the station now encircled by deep cracks, now it also has only one resupply route remaining; to bring equipment, personnel and food and fuel supplies to the station – all of which are needed to successfully pull off the station relocation.

Bringing Halley VI to its new location before the end of the short Antarctic summer season will be a challenge. We shall certainly keep you up-to-date with Halley news as well as with news about the rapid changes of the Brunt Ice Shelf (because we’re the Cryosphere blog after all!). In the meantime, you can feel like a polar explorer and enjoy this (virtual) visit of Halley VI.

References and further reading

Edited by Clara Burgard, Sophie Berger and Emma Smith

Ice Cores “For Dummies”

Ice Cores “For Dummies”

Ice cores are important tools for investigating past climate as they are effectively a continuous record of snowfall, which preserves historical information about climate conditions and atmospheric gas composition. In this new “For Dummies” post, we discuss the history and importance of ice-core science, and look at the way we can use ice core chemistry to reconstruct past climate.


Ice sheets, archives of our past

When snow falls on the surface of an ice sheet it begins to compact the snow beneath it – eventually it will be compacted enough to be transformed into ice. Simultaneously, atmospheric air held between the snowflakes is slowly trapped in the ice – forming small air bubbles. In areas where mean annual temperatures at the ice surface remain below 0C, such as Greenland and Antarctica, there is little surface melting, so this snow builds up to form thick ice sheets – up to 3000 metres in some part of East Antarctica! Low surface melt means that the snow that is compressed into ice each year forms a continuous record of the annual snowfall and atmospheric gas concentrations at the time of deposition, but how do we access this record..?

Snow that is compressed into ice each year forms a continuous record of the annual snowfall and atmospheric gas concentrations at the time of deposition

…We drill ice cores – of course!

An ice core is a cylinder of ice that is retrieved from the ice sheet by drilling vertically downwards. The core is drilled in sections from the surface, deep into the ice sheet (Fig. 1) using a rotating drill. Each section of the core is processed at the drill site and often cut further into shorter sections of ~55 cm for more practical transport and analysis in labs. A great deal of equipment is needed to achieve this and drilling is a slow and careful process often taking several field seasons to drill a deep core. An example of a drilling camp is shown in Fig. 2, housing scientists and engineers involved in drilling an ice core on the Fletcher Promontory, West Antarctica.

Figure 1: a) Ice core drill being lowered into the ice on Pine Island Glacier [Credit: Alex P. Taylor] b) Dr Rob Mulvaney processing the Berkner Island ice core, Weddell Sea, Antarctica [Credit: R. Mulvaney]

Figure 2: The layout of the Fletcher Promontory ice-drilling project, Weddell Sea, Antarctica. In the background the large Weatherhaven tent houses the drill rig, the central Weatherhaven tent is used for storage and equipment and a simple shower, the nearest Polarhaven tent is the mess tent, and the Polarhaven tent to the left houses the main generator. The pyramid tents in the foreground are the sleeping tents, and the two to the right are used for toilet facilities [Credit: Mulvaney et al., 2014]

Where to drill an ice core for the best record?

To get a good record of climate we want to find an area of ice that has many annual layers (good temporal resolution) that has not been disturbed by high ice flow velocities, usually these conditions can be found at an ice dome or divide. An ice sheet is a large plateau with a relatively stable rate of annual snowfall; the dome (or ice divide) is the point in the ice sheet where there is only vertical flow (compression) of ice (Fig. 3). Horizontal flow of ice is greater with the greater distance from the dome. Therefore, domes are the ideal site on the ice sheet or ice cap to drill for an ice core to ensure no interference with the snowfall history at the site. It is reasonable to assume that the ice-core record taken from a site with high annual snowfall will not extend the furthest back in time; similarly, a low annual snowfall and a large ice-sheet thickness will offer a record spanning much further back in time.

Figure 3: Ice flow within the ice sheet showing the zero flow at the ice divide – the ideal site for an ice core [Credit: Snowball Earth]

For Antarctica, the amount of snowfall across the ice sheet depends on the distance from the coast and sources of moisture; the highest mean annual snowfall is found at West Antarctic ice sheet sites whilst the lowest values are inland on the East Antarctic ice sheet, one of the driest deserts on Earth. In addition to the West and East Antarctic ice sheets, the Antarctic Peninsula is the third and final sector of the continent with high mean annual snowfall comparable to West Antarctica. In comparison to Antarctica, the Greenland ice sheet has a relatively high present-day mean annual snowfall, varying across the ice sheet between 10 and 30 cm per year. Therefore, if your aim is to find the oldest ice on Earth, East Antarctica is a good place to start looking, see our post on the quest to drill an ice core that contains ice which is over a million years old. Additionally, for the longest records it is paramount to find a drilling location with no (or at least very low) annual melting at the bedrock.

If your aim is to find the oldest ice on Earth, East Antarctica is a good place to start looking

What does an ice core actually record?

Once an ice core has been drilled and cut into sections, some of the sections are analysed and others are preserved. This is particularly important as some of the analysis is destructive (e.g. melting of the ice to extract water and gas). Therefore an archive of the ice core itself is needed. So, what information can we obtain from analysing the core and how is it done?

Annual layers, past snowfall and past temperatures!

Reconstructing the past surface temperature and snowfall is incredibly useful for understanding climate processes and changes through time in order to assess any present-day local and regional changes in climate. We can do this by:

          • Measuring the thickness of the annual layers: This is done by counting layers in the core, either by visual identification of the peaks in deposition or use of a computer algorithm. The thickness of a specific year depends on how much snow fell at the site and on how much the snowfalls of the following years compacted this specific layer. We can estimate the strain caused by compaction which allows us to extract historical annual snowfall.
          • Past air temperatures (Stable Water Isotope Record): An additional method to reconstruct past snowfall is from the ratios of the stable water isotopes from the water that forms snow and precipitation. The ratio of stable water isotopes has a linear relationship with surface temperature (see box below). Mathematical reconstructions of accumulation using the temperature reconstructions from stable water isotopes are employed in ice core profiles where the compaction of annual snowfall results in an annual layer thickness beyond standard laboratory resolution, such as Antarctic sites. Following the accumulation reconstruction, the rate of compaction of the annual snowfall to ice and subsequent ‘thinning’ of the deposited snowfall layer must be estimated by glaciological modelling.
          • Trace-element analysis: For the upper depths of a deep ice core, or an ice core with an easily-resolvable annual layer thickness, the continuous analysis of an ice core for stable water isotopes offers a sub-annual view of the climate record.

            Figure 4: Seasonal deposition of four chemical species in the WAIS Divide ice core. Pink: electrical conductivity measurements; Black: Black Carbon; Red: non-sea salt Sulphur; Blue: Sodium. Each panel, shows the averaged annual record for 2 different periods: the Antarctic Cold Reversal (ACR, 13-14,000 years ago – bold line) and the Holocene, (10-11,000 years ago – thin line) the [Credit: Fig. 2, Sigl et al., 2016 ]

            The deposition of a number of chemical elements increases during the summer season and decreases during the winter.When these elements are measured in the ice core they can be depicted as an almost-sinusoidal record, indicating the historical seasons. High-resolution ice-core profiles can be dated by counting these annual layers, and have been done so across Greenland and at the West Antarctic Ice Sheet (WAIS) Divide ice core site. Fig. 4 shows two annual signals over 24 months for four different chemicals that are deposited in ice cores (Sigl et al., 2016). The peak in seasonal deposition is shown twice for each chemical, at different times in history, but the seasonality of these species remains strong throughout time.
Reconstructing Past Temperatures
We commonly think of water as H2O - a molecule containing two hydrogen atoms and one oxygen atom. However, atoms (i.e. Hydrogen and Oxygen) come in several forms, known as isotopes - atoms with the same number of protons, but differing numbers of neutrons. Those isotopes that don't decay over time and are preserved in the ice core are know as stable water isotopes. It is possible to measure the amount of each different stable water isotope present in an ice core by melting the ice core and using a mass spectrometer to analyse the water produced.

The snow that eventually forms ice cores starts its life as ocean water which is evaporated and transported to the polar regions. Water isotopes with more neutrons are heavier and therefore require more energy to evaporate and transport. The amount of energy available to do this is related to temperature. Therefore heavier isotopes are found in ice cores in higher amounts at warmer periods in the planet's history! Find out more  here!

Atmospheric gas

Ice-core measurements of atmospheric gases correlate well with direct measurements taken from the atmosphere dating back to 1950. As a result of this, ice-core scientists can assume that the atmospheric gas concentrations measured in ice cores reflects the atmospheric conditions at the time the gas was entrapped in the ice core. Hence, ice cores tell us that carbon dioxide concentrations have been relatively stable for the last millennia until around 1800 AD but since then a rise of almost 40% has been measured in both ice cores and direct atmospheric measurements (Fig. 5).

Figure 5: 1000 years of atmospheric CO2 concentrations from various Antarctic ice cores (DML, South Pole, Law Dome and Siple Dome) and the direct measurements in Mauna Loa Observatory [Credit: Ashleigh Massam, compiled from open access data sources]

Carbon dioxide concentrations have been relatively stable for the last millennia until around 1800 AD but since then a rise of almost 40% has been measured

In addition to comparison with present-day measurements, the trapped gases offer a record of direct atmospheric and greenhouse gas concentrations, including methane, carbon dioxide and nitrous oxide (Fig. 6) on a longer timescale – up to 800,000 years (Loulergue et al., 2008). Records show the connection between fluctuations in the atmosphere and long-term global climate variations (e.g. temperature) on a millennial timescale (Kawamura et al., 2007). The long-term trends show a pattern in the gas concentrations that compare well with glacial-interglacial climate. The phasing and timing of the eight glacial cycles covered by this record are dominated by the orbital cycle of the Earth on a 96,000-year periodicity, with a warm, interglacial period between each cold period. However, as we will see later in this blog post, this may not be the case when we look further back in time!

Figure 6: Variations of temperature (from present day mean temperature, black), atmospheric carbon dioxide (in part per million by volume — blue) and methane (in part per billion per volume red) over the past 800,000 years, from the EPICA Dome C ice core in Antarctica. Modern value (of 2009) of carbon dioxide and methane are indicated by arrows. [Credit : Centre for Ice and Climate , University of Copenhagen. Re-used with permission ]

Other climate proxies

Chemistry preserved in the ice also offers a proxy (=a means) to reconstruct other seasonally-deposited tracers:

                        • Information on past sea-ice extent can be obtained from chemicals found in ice cores which are also present in sea salt such as sodium, chlorine and methanesulphonic acid (MSA) (Sommer et al., 2000; Curran et al., 2003; Rothlisberger et al., 2003).
                        • The seasonal deposition of elements such as iron, magnesium and calcium, which are linked to dust from far-afield and the short-term climate variability such as atmospheric circulation (Fuhrer et al., 1999).
                        • Finally, volcanic layers in the ice core such as tephra and sulphate deposit provides a unique timestamp to a specific depth. These layers were deposited at the same time, all over the world and can be pinpointed to a specific volcanic eruption. Deposits of the same layer outside of a glaciated landscape, (e.g. within rock layers ) can often be dated using radiocarbon (Carbon-14) or another radiogenic dating methods. Additional age horizons can be interpreted by events assumed to occur in the world at the same time, such as rapid climate events. Age constraints are beneficial to interpreting deep ice-core records that are not analysed at a sub-annual resolution by offering pinpoint age horizons to an ice-core record.

Current knowledge from ice-core records

As we have seen, ice core are important because they put the current climate variations into the context of a long-term climate history. Additionally, polar ice cores can allow us to looks at variations between the northern and southern hemisphere. Ice cores also extend back much, much further in time than terrestrial weather stations or satellite records:

Figure 7: Deep ice core locations in Greenland and Antarctica [Credit and more details: NSIDC ]

The current past climate record tells us about glacial and inter-glacial periods (Fig. 6) but also allows us to look at finer detail – i.e. the variability within these periods, which were previously assumed stable.  For example, ice cores have led to the discovery of Dansgaard-Oeschger events; which are are rapid climate fluctuation events, characterised by rapid warming followed by gradual cooling to return to glacial conditions, 25 of these events have happened during the last glacial period.

Records from the Northern and Southern hemisphere also allow us to link these small and large scale changes in climate in the two hemispheres. For example, ice cores analysed from both poles show a ‘call and response’ signal between Dansgaard-Oeschger events in the Northern Hemisphere and events in the Antarctic climate record. The southern hemisphere cooled during the warm phases of Dansgaard-Oeschger events in the northern hemisphere (Buizert et al., 2015), and vice versa during northern hemispheric cooling (see our previous blog post on the subject).

There are already over a dozen ice cores taken from Greenland and Antarctica (Fig. 7), offering a clear and detailed history of the climate during the Late Quaternary period (Fig. 6), going back up to 800,000 years (Quaternary = last 2.6 million years). As we mentioned earlier the timing of glacial and inter-galcial cycles in this 800,000 year old record is dominated by the orbital cycle of the Earth (96,000-year periodicity). However, marine records show that frequency of glacial-interglacial cycles was different before this time (Lisiecki and Raymo, 2005). It is in order to better understand these changes that the quest for the oldest was formed – beginning last month the mission aims to drill an ice core of ice older than 800,000 years to gain detailed information about the climate even further back in time.

Detailed records from high-resolution ice cores improves our understanding of the response of the planet to deglaciation events

The continuous and high-resolution of ice-core records, together with marine and terrestrial records, offers a global view of coupled processes from ice sheet calving events, changes to ocean circulation and heat transport and the subsequent cooling events across the Earth. Detailed records from high-resolution ice cores improves our understanding of the response of the planet to deglaciation events from the large ice sheets that once covered much of the northern hemisphere. Melting ice sheets pose a significant threat to the planet from rising sea levels and the freshwater input leading to inevitable changes in climate.

Edited by Emma Smith and Sophie Berger


Ashleigh Massam is a final-year PhD student based in the Ice Dynamics and Palaeoclimate group at the British Antarctic Survey and with the Department of Geography at Durham University. Her project is developing the age-depth profiles of three ice cores drilled at James Ross Island, Fletcher Promontory and Berkner Island, West Antarctica, by a combination of high-resolution trace-element analytical techniques and modelling ice-sheet processes.

Image of the Week – Blood Falls!

Image of the Week – Blood Falls!

If glaciers could speak, you might imagine them saying – “HELP!” The planet continues to warm and this means glaciers continue to shrink. Our new image of the week shows a glacier that appears to be making this point in a rather dramatic and gruesome way – it appears to be bleeding!


If you went to the snout of Taylor Glacier in Antarctica’s Dry Valley region (see map below) you would witness a bright red waterfall, around 15m high, flowing from the glacier into Lake Bonney. Due to it’s colour, this waterfall has acquired the somewhat graphic name: Blood Falls!

The Dry Valleys

Location of Taylor Glacier in Taylor Valley – one of the Antarctic Dry Valleys. The American McMurdo Research Station is located a short distance away [Credit: USGS via Wikimedia Commons ]

The dry valleys, as the name suggests, are considered one of the driest and most arid places on Earth – which seems like an unusual location for waterfall! The area is completely devoid of animals and complex plants, however, in finding an explanation for the colour of Blood Falls, scientists have also gained an insight into a whole ecosystem hidden beneath the Dry Valley glaciers.

Why is the water red?

The water that feeds Blood Falls is salty and rich in iron. This water is forced out from underneath the glacier by the pressure of the overlying ice (see schematic below) and as it emerges the iron in the water comes into contact with oxygen causing it to rust (oxidise) and turn the water red. But why is this water so salty and iron-rich in the first place? The story of how this unusual water came to be starts around five million years ago…

At this time, it is thought that the dry valleys were submerged beneath the ocean as part of a system of fjords (Mikucki et al., 2015). Subsequent uplift of this land and climatic cooling causing a drop in sea level left some of this salty ocean water isolated as a lake. Around 1.5 million – 2 million years ago a glacier started to form on top of this lake. The ice cut the lake off from the atmosphere and caused the lake water to become even more salty by the process of cryoconcentration (lake water in contact with the glacier ice is frozen, the salt is left behind in the lake increasing the concentration). Iron was introduced into the water from the bedrock beneath the lake, which was ground up as the ice moved over the top of it. There was also something else in this ancient sea water, that surprised scientists when they began to analyse the water from Blood Falls – microbes!

A schematic cross-section of Blood Falls showing how microbial communities survive in this hostile environment [Credit: Zina Deretsky, NSF ]

Life in the lake – Microbes

When it was covered in ice, this subglacial lake was very cold and cut off from the out side world – meaning no sun light and oxygen, which are normally essential for microbes to survive. However, the microbes in this lake are thought to have adapted to survive using sulphates and iron in the water (Mikucki et al., 2009).  This strange ecosystem is surviving in extreme conditions and shows how adaptable microbes can be. An area once thought to be too inhospitable to support much life has been shown to be much more “lively” than first thought – sparking up ideas about lifeforms in other inhospitable environments, such as Mars.

Further Reading

 

Edited by Sophie Berger

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