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Cryospheric Sciences

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Image of the Week – Fifty shades of snow

Image of the Week – Fifty shades of snow

When I think of snow, I tend to either think about the bright white ski slopes in the mountains or the large white areas in the Arctic. However, natural phenomena can lead to colorful snow. Our Image of the Week shows snow can be green! Snow can also turn orange, pinkish, grey and even yellow… But where do these different shades of snow come from?


White

The most common color of snow is white (see Fig. 2). Snow generally appears white when it is pure snow, which means that it is only an aggregate of ice and snow crystals. When sunlight meets the snow surface, all frequencies of the sunlight are reflected several times in different directions by the crystals, leading to a white color of the snowpack.

 

Fig. 2: Fresh powder snow, snow crystals [Credit: Introvert, Wikimedia Commons]

 

 

If other particles or organisms are present in the snow though, they can alter the color of the snow’s surface…

Green

Snow can obtain a green color if it is host to an algal bloom (see our Image of the Week). Depending on the wetness of the snow, sunlight conditions and nutrient availability, unicellular snow algae can develop and thrive on the snow. Although it is not clear exactly how fast snow algae grow, algae populations from temperate regions have been found to grow sixteen-fold in one day! As the algae population increases, the snow turns green as the algae reflect the green light back.

 

Red/Pink

The pink-red-colored snow, commonly called “watermelon snow”, can also be caused by snow algae (see Fig. 3). The snow algae responsible for the pink color are similar to the ones responsible for green color. However, these algae use pigments of red color to protect their cells from high sunlight and UV radiation damage during the summer. Just like how we use sunscreen to protect our skin! The red pigments come either from iron tannin compounds or, more commonly, from orange to red-pigmented lipids.

There is also another origin for pink snow: Penguin poo! Indeed, the krill they eat contain a lot of carotenoids that give their poo a red color.

Fig. 3: Watermelon snow streaks [Credit: Wikimedia Commons].

 

Yellow

Yellow snow is the result of a different process (and no, it is not from Penguin pee!). Fig. 4 shows the Sierra Nevada in Spain before and after dust transported from the Sahara settled down on the snow-covered mountain tops. The dust was lifted up from the Sahara desert and blown north before ending its trip in Spain.

Fig. 4: Snow-covered Sierra Nevadas (Spain) before and after a dust deposition event [Credit: modified from NASA’s Earth Observatory]

 

Do these colors have an influence on snow cover?

In all cases of colored snow, the snow surface is darker than before. The darker surface absorbs more sunlight than a white surface, which causes the snow to melt faster… Therefore, although it looks artistic, colored snow is not necessarily healthy for the snow itself…

 

So, if you don’t like winter because everything is boring and white, just think about the variety of snow colors and try to look out for these special types! 🙂

 

Further reading

Edited by David Rounce

Image of the Week – Summer is fieldwork season at EastGRIP!

Image of the Week – Summer is fieldwork season at EastGRIP!

As the days get very long, summer is a popular season for conducting fieldwork at high latitudes. At the North East Greenland Ice Stream (NEGIS), the East Greenland Ice-core Project (EastGRIP) is ongoing. Several scientists are busy drilling an ice core through the ice sheet to the very bottom, in continuation to previous years (see here and here). This year, amongst others, several members from the European Research Council (ERC) supported synergy project ice2ice are taking part in the work at EastGRIP. Besides sleeping in the barracks that can be seen in our Image of the Week, the scientists enjoy the international and interdisciplinary setting and, of course, the work in a deep ice core drilling camp…


Life at the EastGRIP camp

In total, 22 people live in the camp (see Fig.2): 1 field leader, 5 ice core drillers, 4 ice core loggers, 3 people working with the physical properties of the ice, 2 are doing continuous water isotope analysis, 2 surface science scientists, 2 field assistants, and 1 mechanic, 1 electrical engineer and most important an excellent cook. We cover a variety of nationalities: British, Czech, Danish, French, German, Japanese, Korean, Norwegian, Russian and more. The crew changes every four weeks and the EastGRIP project aims to get as many young scientists (Master and PhD students) into camp as possible, so that it also works as a learning environment for new generations. In total, the number of people that have and will spent time at EastGRIP this season is almost 100, making it a buzzing science hub. This environment leads to extensive science discussions over the dinner table and therefore facilitates the interdisciplinary connections so vital in ice core science.

Fig.2: The current crew at EastGRIP dressed up for the Saturday party (tie and dress obligatory!) [Credit: EastGRIP diaries].

Science at the EastGRIP camp

The main aim of the EastGRIP project is to retrieve an ice core by drilling through the North East Greenland Ice Stream (NEGIS) up to a depth of 2550 m (!). Ice streams are responsible for draining a significant fraction of the ice from the Greenland Ice Sheet (see Fig. 3). We hope to gain new and fundamental information on ice stream dynamics from the project, thereby improving the understanding of how ice streams will contribute to future sea-level change. The EastGRIP project has many international partners and is managed by the Centre for Ice and Climate, Denmark with air support carried out by US ski-equipped Hercules aircraft managed through the US Office of Polar Programs, National Science Foundation.

Fig. 3: Ice velocities from RADARSAT synthetic aperture radar data are shown in color and illustrate the wedge of fast-flowing ice that begins right at the central ice divide and cuts through the ice sheet to feed into the ocean through three large ice streams (Nioghalvfjerds isstrømmen, Zachariae isbræ, and Storstrømmen). [Credit: EastGRIP, data from Joughin et al., 2010]

Currently, four Norwegian and Danish scientists from the ice2ice project have joined the EastGRIP project to conduct field work at the ice core drilling site. The ice2ice project focuses on how land ice and sea ice influence each other in past, present, and future. Thus, being at the EastGRIP site is a great opport

unity for us in ice2ice to learn more about how the fast-flowing ice stream in North East Greenland may influence the stability of the Greenland ice cap and to enjoy the collaborative spirit at an ice core drilling site.

 

This year’s fieldwork at EastGRIP started in May and will continue until August. We aim to make it through the brittle zone of the ice. This is a zone where the gas bubbles get enclosed in the ice crystals and thus the ice is, as the name indicates, more brittle than at other depths. Unfortunately for us, the brittle zone makes it very hard to retrieve the ice in a great quality. This is because of the pressure difference between the original depth of the ice and the surface, that causes the ice to fracture when it arrives at the surface. We are doing our very best to stabilize the core and several optimizations in terms of both drilling and processing of the ice core are being applied.

Fig. 4: Cross-section view of an ice core [Credit: Helle Astrid Kjær].

Still, a large part of the core can already be investigated (see Fig. 4) for water isotopes to get information about past climate. Also, ice crystals directions are being investigated through thin slices of the ice core to help better understanding the flow of the NEGIS. On top of the deep ice core, which is to be drilled to bedrock over the coming years, we are doing an extensive surface program to look at accumulation changes.

In the large white plains…

Despite all the fun science and people, when you are at EastGRIP for more than 4 weeks, you have a very similar landscape everyday and can miss seeing something else than just the great white. About a week ago, a falcon came by to remind us of the rest of the world (see Fig. 5). It flew off after a couple of days. We will follow its path to the greener parts of Greenland when we will soon fly down to Kangerlussuaq. Someone else will then take over our job at EastGRIP and enjoy the wonders of white…

Fig.5: Visit of a falcon [Credit: Helle Astrid Kjær].

Further reading

Edited by Clara Burgard


Helle Astrid Kjær is a postdoc at the Centre for Ice and Climate at the Niels Bohr Institute at University of Copenhagen. When she is not busy in the field drilling and logging ice cores, she spends most of her time in the lab retrieving the climate signal from ice cores. These include volcanic events, sea salts, dust with more by means of Continuous Flow Analaysis (CFA). Further she is hired to manage the ice2ice project.

Image of the Week — High altitudes slow down Antarctica’s warming

Elevations in Antarctica. The average altitude is about 2,500m. [Credit: subset of Fig 5 from Helm et al (2014)]

When it comes to climate change, the Arctic and the Antarctic are poles apart. At the north of the planet, temperatures are increasing twice as fast as in the rest of the globe, while warming in Antarctica has been milder. A recent study published in Earth System Dynamics shows that the high elevation of Antarctica might help explain why the two poles are warming at different speeds.


The Arctic vs the Antarctic

At and around the North Pole, in the Arctic, the ice is mostly frozen ocean water, also known as sea ice, which is only a few meters thick. In the Antarctic, however, the situation is very different: the ice forms not just over sea, but over a continental land mass with rugged terrain and high mountains. The average height in Antarctica is about 2,500 metres, with some mountains rising as high as 4,900 metres.

A flat Antarctica would warm faster

Mount Jackson in the Antarctic Peninsula reaches an altitude of 3,184 m  [Credit: euphro via Flickr]

Marc Salzmann, a scientist working at the University of Leipzig in Germany, decided to use a computer model to find out what would happen if the elevation in Antarctica was more like in the Arctic. He discovered that, if Antarctica were flat, there would be more warm air flowing from the equator to the poles, which would make the Antarctic warm faster.

As Antarctica warms and ice melts, it is actually getting flatter as time goes by, even if very slowly. As such, over the next few centuries or thousands of years, we could expect warming in the region to speed up.

Reference/further reading

planet_pressThis is modified version of a “planet press” article written by Bárbara Ferreira and originally published on 18 May 2017 on the EGU website
(a Serbian version is also available, why not considering adding a new language to the list? 🙂 )

Image of the Week – A rather splendid round-up of CryoEGU!

Image of the Week – A rather splendid round-up of CryoEGU!

The 2017 edition of the EGU general assembly was a great success overall and for the cryospheric division in particular. We were for instance thrilled to see that two of the three winning photos of the EGU Photo contest featured ice! To mark the occasion we are delighted to use as our image of this week,  one of these pictures, which  shows an impressive rapid in the Pite River in northern Sweden. Congratulations to Michael Grund for capturing this stunning shot.  You can find all photos entered in the contest on imaggeo — the EGU’s  open access geosciences image repository.

But being the most photogenic division (at least the ice itself is…not sure about the division team itself!) was not our only cryo-achievement during the conference. Read on to get the most of (cryo)EGU 2017!


EGU 2017 in figures

  • 17,399 abstracts in the programme (including 1179 to cryo-related sessions)
  • 14,496 scientists from 107 countries attending the conference
  • 11,312 poster, 4,849 oral and 1,238 PICO presentations
  • 649 scientific sessions and 88 short courses
  • 53% of early-career scientists

Polar Science Career Panel

During the week we teamed up with APECS to put on a Polar Science Career Panel. Our five panellists, from different backgrounds and job fields, engaged in a lively discussion with over 50 session attendees. With many key topics being frankly and honesty discussed by our panelists, who had some great comments and advice to offer. Highlights of the discussion can be found on the @EGU_CR twitter feed with #CareerPanel.

At the end we asked each panellist to come up with some final words of advice for early-career scientists, which were:

  • There is no right and wrong, ask other people and see what you like
  • Remember you can shape your own job
  • Take chances! Even if you are likely to fail and think outside the box
  • Remember that you are a whole human being… not only a scientist and use all your skills
  • And last but not least… come and work at Carbon Brief (thanks Robert McSweeney!!)

However, the most memorable quotation of the entire panel is arguably from Kerim Nisancioglu :

Social media

One of the things the EGU Cryosphere team has been recognised for is its great social media presence. We tweeted away pre-EGU with plenty of advice, tips and information about events during the week and also made sure to keep our followers up-to-date during the week.
If it is not yet the case, please consider following us on twitter and/or facebook to keep updated with the latest news about the cryosphere division, the EGU or any other interesting cryo-related news!

We need YOU for the EGU cryosphere division

Conferences are usually a great way to meet new people but did you know that getting involved with the outreach activities of the division is another way?

Each division has an ECS (early-career scientist) representative and a team to go with that and the Cryosphere division is one of the most active. Our new team of early-career scientists for 2017/18 includes some well known faces and some who are new to the division this year:

Nanna Karlsson : outgoing ECS representative and incoming coordinator for posters and PICOs awards

Emma Smith : incoming ECS representative and outgoing co-chief editor of the  cryoblog

Sophie Berger: chief-editor of the cryoblog and incoming outreach officer

Clara Burgard : incoming co-chief editor the cryoblog

 

 

 

We also have many more people (who aren’t named above) involved in the blog and social media team AND the good news is that we are looking for new people to either run our social media accounts and/or contribute regularly to this “award winning” cryoblog. Please get in touch with Emma Smith (ECS Representative and former blog editor) or Sophie Berger (Chief Blog Editor and Outreach Officer) if you would like to get involved in any aspect of the EGU Cryosphere team. No experience is necessary just enthusiasm and a love of bad puns!

And here is your “Save the Date” for EGU 2018 – which will be held between 8th – 13th April 2018.

Co-authored by Emma Smith and Sophie Berger

Quantarctica: Mapping Antarctica has never been so easy!

Quantarctica: Mapping Antarctica has never been so easy!

One of the most time-consuming and stressful parts of any Antarctic research project is simply making a map. Whether it’s plotting your own data points, lines, or images; making the perfect “Figure 1” for your next paper, or replying to a collaborator who says “Just show me a map!,” it seems that quick and effective map-making is a skill that we take for granted. However, finding good map data and tools for Earth’s most sparsely-populated and poorly-mapped continent can be exhausting. The Quantarctica project aims to provide a package of pre-prepared scientific and geographic datasets, combined with easy-to-use mapping software for the entire Antarctic community. This post will introduce you to Quantarctica, but please note that the project is organizing a Quantarctica User Workshop at the 2017 EGU General Assembly (see below for more details).


[Credit: Quantarctica Project]

What is Quantarctica?

Quantarctica is a collection of Antarctic geographic datasets which works with the free, open-source mapping software QGIS. Thanks to this Geographic Information System package, it’s now easier than ever for anyone to create their own Antarctic maps – for any topic and at any spatial scale. Users can add and plot their own scientific data, browse satellite imagery, make professional-quality maps and figures, and much, much more. Read on to learn how researchers are using Quantarctica, and find out how to use it to start making your own (Qu-)Antarctic maps!

Project Origins

When you make a sandwich, you start with bread, not flour. So why would you start with ‘flour’ to do your science?” — Kenny Matsuoka, Norwegian Polar Institute

Deception Island isn’t so deceptive anymore, thanks to Quantarctica’s included basemap layers, customized layer styles, and easy-to-use cartography tools. [Credit: Quantarctica Project]

Necessity is the mother of invention, and people who work in Antarctica are nothing if not inventive. When Kenny Matsuoka found himself spending too much time and effort just locating other Antarctic datasets and struggling with an expired license key for his commercial Geographic Information System (GIS) software in the field, he decided that there had to be a better way – and that many of his Antarctic colleagues were probably facing the same problems. In 2010, he approached Anders Skoglund, a topographer at the Norwegian Polar Institute, and they decided to collaborate and combine some of the critical scientific and basemap data for Antarctica with the open-source, cross-platform (Windows, Mac, and Linux) mapping software QGIS. Quantarctica was born, and was quickly made public for the entire Antarctic community.

Since then, maps and figures made with Quantarctica have appeared in at least 25 peer-reviewed journal articles (that we can find!). We’ve identified hundreds of Quantarctica users, spread among every country participating in Antarctic research, with especially high usage in countries with smaller Antarctic programs. We’ve been actively incorporating even more datasets into the project, teaching user workshops at popular Antarctic conferences – such as EGU 2017 – and building educational materials on Antarctic mapping for anyone to use.

A great example of a Quantarctica-made figure published in a paper. Elevation, imagery , ice flow speeds, latitude/longitude graticules, custom text and drawing annotations… it’s all there and ready for you to use! [Credit: Figs 1 and 2 from Winter et al (2015)].

What data can I find in Quantarctica?

  • Continent-wide satellite imagery (Landsat, MODIS, RADARSAT)
  • Digital elevation models and/or contour lines of bed and ice-surface topography and seafloor bathymetry
  • Locations of all Antarctic research stations and every named location in Antarctica (the SCAR Composite Gazetteer of Antarctica)
  • Antarctic and sub-Antarctic coastlines and outlines for exposed rock, ice shelf, and subglacial lakes
  • Magnetic and gravity anomalies
  • Ice flow velocities, catchment areas, mass balance, and firn thickness grids
  • Ancient UFO crash sites

…just to name a few!

Four examples of included datasets. From left to right: Ice flow speed, drainage basins, and subglacial lakes; bed topography; geoid height; modeled snow accumulation and surface blue ice areas [Credit: Quantarctica Project]

All of these datasets have been converted, imported, projected to a standard Antarctic coordinate system, and hand-styled for maximum visibility and compatibility with other layers. All you have to do is select which layers you want to show! The entire data package is presented in a single QGIS project file that you can quickly open, modify, save, and redistribute as your own. We also include QGIS installers for Windows and Mac, so everything you need to get started is all in one place. And finally, all of the data and software operates entirely offline, with no need to connect to a license server, so whether you’re in a tent in Antarctica or in a coffee shop with bad wi-fi, you can still work on your maps!

Quantarctica was used in traverse planning for the MADICE Project, a collaboration between India’s National Centre for Antarctic and Ocean Research (NCAOR) and the Norwegian Polar Institute (NPI), investigating mass balance, ice dynamics, and climate in central Dronning Maud Land. Check out pictures from their recently-completed field campaign on Facebook and Twitter! Base image: RADARSAT Mosaic; Ice Rises: Moholdt and Matsuoka (2015); Mapping satellite features on ice: Ian Lee, University of Washington; Traverse track: NCAOR/NPI. [Credit: Quantarctica Project]

Every dataset in Quantarctica is free for non-commercial use, modification, and redistribution – we get explicit permission from the data authors before their datasets are included in Quantarctica, always include any README or extra license/disclaimer files, and never include a dataset if it has any stricter terms than that. We always provide all metadata and citation information, and require that any Quantarctica-made maps or figures printed online or in any publication include citations for the original datasets.

How do I start using Quantarctica?

Quantarctica is available for download at http://quantarctica.npolar.no/. It’s a 6 GB package, so if your internet connection is struggling with the download, just contact us and we can send it to you on physical media. You can use the bundled QGIS installers for your operating system, or download the latest version of QGIS at http://qgis.org/ and simply open the Quantarctica project file, Quantarctica.qgs, after installation.

We’re actively developing Version 3 of Quantarctica, for release in Late 2017. Do you know of a pan-Antarctic dataset that you think should be included in the new version? Just email the Quantarctica project team at quantarctica@npolar.no.

Quantarctica makes it easy to start using QGIS, but if you’ve never used mapping software before or need to brush up on a few topics, we recommend QGIS Tutorials and Tips and the official QGIS Training Manual. There are also a lot of great YouTube tutorial videos out there!

 

Nobody said you could only use Quantarctica for work – you can use it to make cool desktop backgrounds, too! Foggy day in the Ross Island / McMurdo Dry Valleys area? Though it often is, the fog effects image was created using only the LIMA 15m Landsat Imagery Mosaic and RAMP2 DEM in Quantarctica, with the help of this tutorial. [Credit: Quantarctica Project]

Quantarctica Short Course at EGU 2017

Are you attending EGU 2017 and want to learn how to analyze your Antarctic data and create maps using Quantarctica? The Quantarctica team will be teaching a short course (SC32/CR6.15) on Monday, 24 April at 13:30-15:00 in room -2.31. Some basic GIS/QGIS experience is encouraged, but not required. If you’re interested, fill out the registration survey here: https://goo.gl/forms/mLaJg686tZq8bm2N2 and feel free to send any questions or comments to quantarctica@npolar.no. We’ll see you in Vienna!

Edited by Kenny Matsuoka and Sophie Berger

Reference/Further Reading

Data sources

[Read More]

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

Image of the Week – Climate Change and the Cryosphere

Image of the Week – Climate Change and the Cryosphere

While the first week of COP22 – the climate talks in Marrakech – is coming to an end, the recent election of Donald Trump as the next President of the United States casts doubt over the fate of the Paris Agreement and more generally the global fight against climate change.

In this new political context, we must not forget about the scientific evidence of climate change! Our figure of the week, today summarises how climate change affects the cryosphere, as exposed in the latest assessment report of the Intergovernmental Panel on Climate Change (IPCC, 2013, chapter 4)


Observed changes in the cryosphere

Glaciers (excluding Greenland and Antarctica)

  • Glaciers are the component of the cryosphere that currently contributes the most to sea-level rise.
  • Their sea-level contribution has increased since the 1960s. Glaciers around the world contributed to the sea-level rise from 0.76 mm/yr (during the 1993-2009 period) to 0.83 mm/yr (over the 2005-2009 period)

Sea Ice in the Arctic

  • sea-ice extent is declining, with a rate of 3.8% /decade (over the 1979-2012 period)
  • The extent of thick multiyear ice is shrinking faster, with a rate of 13.5%/decade (over the 1979-2012 period)
  • Sea-ice decline sea ice is stronger in summer and autumn
  • On average, sea ice thinned by 1.3 – 2.3 m between 1980 and 2008.

Ice Shelves and ice tongues

  • Ice shelves of the Antarctic Peninsula have continuously retreated and collapsed
  • Some ice tongue and ice shelves are progressively thinning in Antarctica and Greenland.

Ice Sheets

  • The Greenland and Antarctic ice sheets have lost mass and contributed to sea-level rise over the last 20 years
  • Ice loss of major outlet glaciers in Antarctica and Greenland has accelerated, since the 1990s

Permafrost/Frozen Ground

  • Since the early 1980s, permafrost has warmed by up to 2ºC and the active layer – the top layer that thaw in summer and freezes in winter – has thickened by up to 90 cm.
  • Since mid 1970s, the southern limit of permafrost (in the Northern Hemisphere) has been moving north.
  • Since 1930s, the thickness of the seasonal frozen ground has decreased by 32 cm.

Snow cover

  • Snow cover declined between 1967 and 2012 (according to satellite data)
  • Largest decreases in June (53%).

Lake and river ice

  • The freezing duration has shorten : lake and river freeze up later in autumn and ice breaks up sooner in spring
  • delays in autumn freeze-up occur more slowly than advances in spring break-up, though both phenomenons have accelerated in the Northern Hemisphere

Further reading

How much can President Trump impact climate change?

What Trump can—and can’t—do all by himself on climate | Science

US election: Climate scientists react to Donald Trump’s victory  | Carbon Brief

Which Trump will govern, the showman or the negotiator? | Climate Home

GeoPolicy: What will a Trump presidency mean for climate change? | Geolog

Previous posts about IPCC reports

Image of the Week — Ice Sheets and Sea Level Rise

Image of the Week —  Changes in Snow Cover

Image of the Week — Atmospheric CO2 from ice cores

Image of the Week — Ice Sheets in the Climate

Edited by Emma Smith

Sea Level “For Dummies”

Sea Level “For Dummies”

Looking out over the sea on a quiet day with no wind, the word “flat” would certainly pop up in your mind to describe the sea surface. However, this serene view of a flat sea surface is far from accurate at the global scale.

The apparent simplicity behind the concept of sea level hides more complex science that we hope to explain in a simple manner in today’s “For Dummies” post, which will give you the keys to understand the important aspects of past sea change, and an ability to look into and understand how sea level is a key factor in the future.

Everyone will be familiar with news stories about current sea level rise, but it can be very confusing to understand what this means in real terms; how fast it is happening and why we should care about it anyway. So to begin with, let’s have a look at what we mean by sea level?


Sea Level – It’s all about gravity!

[Read More]

Image of the Week — ice tsunamis !

Image of the Week — ice tsunamis !

Tsunami is a word that became world famous after the so-called Christmas tsunami in 2004, when enormous waves hit the shores around the Indian Ocean with disastrous consequences for countries such as Sri Lanka, Thailand, Somalia and many others.

But did you know that tsunamis can be icy?

An ice tsunami is one of the many names associated with ice shoves (or ivu, shore ice override, ice pile-up, ice ride-up). This rare but impressing phenomenon happens when strong winds rapidly push slabs of sea/lake ice towards the shore.

  • Once on shore, the ice shoves can ride up and advance up to a few hundreds metres inland as a large but thinner sheet of ice (Mahoney et al, 2004; Whiteman, 2011)

  • Alternatively, the ice slabs can also pile up, forming a big ridge on the beach that can rise up to 200m high (Mahoney et al, 2004; Whiteman, 2011).

 

Conditions to get an ice shove

  1. Partial thaw: Ice shoves can only happen when the ice has started to melt but has not completely disappeared yet.  Spring is therefore the best time of the year to observe such a phenomenon.
  2. Strong winds: Only strong winds in the direction of the shore can push piles of ice ashore.
  3. Gentle slope of the beach: The gentler the slope of the shore, the less it prevents the ice pile to advance inland, and the more it can pile up.

This is a common phenomenon in Northern Canada and in Alaska but as these places are sparsely populated, the damages it causes are often limited.

Modis satellite images of Lake Huron, Michigan before (top) and after (bottom) strong winds broke up the ice on the lake and caused an ice shove on Linwood. [Credit: NASA earth observatory]

Modis satellite images of Lake Huron, Michigan, before (top) and after (bottom) a wind storm broke up the ice on the lake and caused an ice shove on Linwood (NOTE: the resolution of the image is too coarse to display the ice piled up on the shore) . [Credit: NASA earth observatory]

Reference/further reading

Edited by N. Karlsson

Water Masses “For Dummies”

Water Masses “For Dummies”

Polar surface water, circumpolar deep water, dense shelf water, North Atlantic deep water, Antarctic bottom water… These names pop in most discussions about the ice-ocean interaction and how this will change in a warming climate, but what do they refer to?

In our second “For Dummies” article, we shall give you a brief introduction to the concept of “water mass”, explain how to differentiate water from more water, and why you would even need to do so.


Global heat budget and the need for an ocean circulation

The global climate is driven by differences between the incoming shortwave radiation and the outgoing longwave radiation (Fig. 1):

  • In the tropics, there is a surplus of energy: the Sun brings more heat, all year-round, than what is radiated out;
  • At the poles in contrast, there is a net deficit: more energy is leaving than is coming from the Sun (who is absent in winter).

The global ocean and atmosphere circulations act to reduce this imbalance, by transporting the excess heat from the tropics to the pole. Here we will focus on the global ocean circulation only, since this post is written by an oceanographer, but similar principles also apply to atmospheric circulation.

Fig 1 :Earth’s latitudinal radiation bugdet, The tropics show a surplus of energy that compensates the Poles’ deficit[Credit: National Oceanograpy Center

Fig 1 :Earth’s latitudinal radiation bugdet, The tropics show a surplus of energy that compensates the Poles’ deficit [Credit: National Oceanograpy Center].

The global ocean circulation

In a nutshell, surface waters bring heat towards the poles where they cool down, sink to the abyss, and return towards the tropics as deep waters where they can go back to the surface..…

We talk about “the global ocean circulation” because although the Earth officially has five oceans, they are not totally separate bodies of water. In fact, the Arctic, Atlantic, Indian, Pacific and Southern oceans are interconnected, with water circulating and moving between them. How does this happen?

The global ocean circulation has two components:

  • The wind-driven circulation, fast but limited to a few hundred metres below the surface of the ocean (read more about it here for example);
  • And the thermohaline circulation (shown on Fig. 2), slower but which affects the whole depth of the ocean.

Today’s post focuses on the latter, since we will talk about water properties. The thermohaline circulation, also called density-driven circulation, depends on two water properties:

  • The temperature (‘thermo’) is mostly controlled by heat exchange with the atmosphere or the ice. Cold water has a high density.
  • The salinity (‘haline’) can be modified by evaporation, precipitation, or addition of fresh water from melted glaciers/ice sheets or rivers. Salty water has a high density.
Fig 2- The global thermohaline circulation shows warm surface currents in red, cold deep currents in blue. Deep waters form in the North Atlantic and Southern oceans. [Credit: NASA]

Fig 2- The global thermohaline circulation shows warm surface currents in red, cold deep currents in blue. Deep waters form in the North Atlantic and Southern oceans [Credit: NASA].

Roughly speaking, a water mass is any drop of the ocean within a specific range of temperature and salinity, and hence specific density. Some water masses are found at particular locations or seasons, while others can be found all around the globe, all the time. Since density sets the depth (density MUST always increase with depth), water masses will lie and travel at particular depth levels.

A quick and dirty oceanography guide

Water masses are formed.

Some are the result of the mixing of other water masses. The others start at the water surface, where they exchange gas (notably oxygen and carbon) with the atmosphere. When a water mass becomes denser than the waters below it , for example, if it is cooled by the wind or ice, it sinks to its corresponding depth within the ocean.

Fig 3- The bathymetry of the Arctic Ocean forces dense (deep) water masses to enter the region via Fram Strait whereas lighter (shallower) waters can go through the Barents Sea [Credit: adapted from IBCAO bathymetry map, Jakobsson et al., 2012 ].

Water masses move all around the globe…

…provided their density allows it. The vertical distribution of density in the ocean must be “stably stratified”, which means that the density increases with depth. In practice, that means that dense waters cannot climb up a shallow bathymetric feature but have to find a way around it. For example to enter the Arctic Ocean (Fig 3), a dense water mass has no choice but to go via Fram Strait, whereas a less dense one can go via the Barents Trough. Similarly, there is a depth limit of about 500 m to reach the northwestern Greenland glaciers.

Water masses retain their properties

Or rather, not all these properties change considerably with space and time. We are not talking only about temperature and salinity, but also about gas and chemical concentrations. It is then possible to track a water mass as it travels around the globe or watch its evolution with time.

You should use T-S diagrams

Visualising water properties can either be done with one graph showing how the temperature varies with depth plus another one for the salinity (multiplied by the number of locations to be observed at the same time); or all of this information can be combined on one image (as done on Fig. 4). This image is called a T-S diagram it and shows how the temperature (T) varies as a function of the salinity (S). It is customary to also draw the lines of constant density (the ‘isopycnals’, black on Fig. 3). These isopycnals give information about the types of mixing happening and the stratification, but we will talk about that in another post.

Fig 4 - an example of how to combine several profiles (top) into a T-S diagram, for one of the randomly selected Arctic historical points that I work with.[Credit: C. Heuzé]

Fig 4 – an example of how to combine several profiles (top) into a T-S diagram, for one of the randomly selected Arctic historical points that I work with [Credit: C. Heuzé].

Because each water mass occupies a very specific region of the T-S diagram (see Fig 5 for an example in the Atlantic), identifying them is relatively easy once you have plotted your data on such diagrams.

Fig 5 – example of a reference T-S diagram with the different water masses of the Atlantic Ocean. Water massed are labelled by their acronym (e.g. AABW= Antarctic Bottom Water) [Credit: after Emery and Meincke (1986)]

Why do ocean water masses matter to the cryosphere?

  • Marine ice sheet instability, and more generally basal melting, is caused by warm dense waters melting floating glaciers from below; how dense the water mass is determines whether it can even reach the glacier.
  • Sea ice formation and melting can be largely affected by water masses moving up and down, especially is those going up are warm.

But there’s a reason why we always talk about “ice-ocean” interactions: it’s not just the ocean acting on the ice, but also the ice impacting the ocean:

  • The densest water mass in the world, Antarctic Bottom Water, forms in the middle of winter if a hole in the sea-ice cover opens (that is called a polynya), suddenly exposing the relatively warm ocean to the extremely cold atmosphere. The resulting strong heat loss and the increased salinity as sea ice reforms make this water sink straight to the bottom;
  • On the other hand, deep water formation can be stopped by the cryosphere: paleorecord evidence showed that it happened in the North Atlantic due to surging ice sheet / marine ice sheet instability (so called Heinrich events) or meltwater floods (Younger Dryas);
  • Less dramatically, icebergs, ice shelves or even sea ice, can cool or freshen water masses they meet, forming “modified” water masses (for example “modified Atlantic Water”),

Each aspect of these interactions is already experiencing climate change and is much more complex than this brief overview… but that will be the topic of another post!

Further reading

 Edited by Sophie Berger and Emma Smith

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