CR
Cryospheric Sciences

Antarctica

Image of the Week – A Hole-y Occurrence, the reappearance of the Weddell Polynya

Image of the Week – A Hole-y Occurrence, the reappearance of the Weddell Polynya

REMARK: If you’ve enjoyed reading this post, please make sure you’ve voted for it in EGU blog competition (2nd choice in the list)!

During both the austral winters of 2016 and 2017, a famous feature of the Antarctic sea-ice cover was observed once again, 40 years after its first observed occurrence: the Weddell Polynya! The sea-ice cover exhibited a huge hole (of around 2600 km2 up to 80,000 km2 at its peak!), as shown on our Image of the Week. What makes this event so unique and special?


Why does the Weddell Polynya form?

The Weddell Polynya is an open ocean polynya (a large hole in the sea ice, see this previous post), observed in the Weddell Sea (see Fig.2). It was first observed in the 1970s but then did not form for a very long time, until 2016 and 2017…

 

Fig. 2: Map of the sea ice distribution around Antarctica on 25th of September 2017, derived from satellite data. The red circle marks the actual Weddell Polynya [Credit: Modified from meereisportal.de]

In the Southern Ocean, warm saline water masses underlie cold, fresh surface water masses. The upper cold fresh layer acts like a lid, insulating the warmer deep waters from the cold atmosphere. While coastal polynyas (see this previous post) are caused by coastal winds, open ocean polynyas are more mysteriously formed as it is not as clear what causes the warm deep water to be mixed upwards. In the case of the Weddell polynya, it forms above an underwater mountain range, the Maud Rise. This ridge is an obstacle to the water flow and can therefore enhance vertical mixing of the deeper warm saline water masses. The warm water that reaches the surface melts any overlying sea ice, and large amounts of heat is lost from the ocean surface to the atmosphere (see Fig. 3).

 

Fig. 3: Schematic of polynya formation. The Weddell polynya is an open ocean polynya [Credit: National Snow and Ice Data Center].

 

Why do we care about the Weddell Polynya?

Overturning and mixing of the water column in the Weddell Polynya forms cold, dense Antarctic Bottom Water, releasing heat stored in the ocean to the atmosphere in the process. Antarctic Bottom Water is formed in the Southern Ocean (predominantly in the Ross and Weddell Seas) and flows northwards, forming the lower branch of the overturning circulation which transports heat from the equator to the poles (see Fig. 4). Antarctic Bottom Water also carries oxygen to the rest of the Earth’s deep oceans. The absence of the Weddell polynya could reduce the formation rate of Antarctic Bottom water, which could weaken the lower branch of the overturning circulation.

Fig.4: Schematic of the overturning (thermohaline) circulation. Deep water formation sites are marked by yellow ovals. Modified from: Rahmstorf, 2002 [©Springer Nature. Used with permission.]

How often does the Weddell Polynya form?

The last time the Weddell Polynya was observed was during the austral winters of 1974 to 1976 (see Fig. 5). It was then absent for nearly 40 years (!) up until austral winter 2016. In a modelling study, de Lavergne et al. 2014 suggested that the Weddell Polynya used to be more common before anthropogenic CO2 emissions started rising at a fast pace. The increased surface freshwater input from melting glaciers and ice sheets, and increased precipitation (as climate change increases the hydrological cycle) have freshened the surface ocean. This freshwater acts again as a lid on top of the warm deeper waters, preventing open ocean convection, reducing the production of Antarctic Bottom Water.

Fig. 5: Color-coded sea ice concentration maps derived from passive microwave satellite data in the Weddell Sea region from the 1970s. The Weddell Polynya is the extensive area of open water (in blue) [Credit: Gordon et al., 2007, ©American Meteorological Society. Used with permission.].

The reappearance of the Weddell Polynya over the past two winters despite the increased surface freshwater input suggests that other natural sources of variability may be currently masking this predicted trend towards less open ocean deep convection. Latif et al. 2013 put forward a theory describing centennial scale variability of Weddell Sea open ocean deep convection, as seen in climate models. In this theory, there are two modes of operation, one where there is no open ocean convection and the Weddell Polynya is not present. In this situation, sea surface temperatures are cold and the deep ocean is warm, and there is relatively large amount of sea ice. The heat at depth increases with time, as it is insulated by the sea ice and freshwater lid. Then, eventually, the deep water becomes warm enough that the stratification is decreased sufficiently so that open water convection begins again, forming the Weddell Polynya. This process continues until the heat reservoir depletes and surface freshwater forcing switches off the deep convection. Models show that the timescale of this variability is set by the stratification, and models with stronger stratification tend to vary on longer timescale, as the heat needs to build up more in order to overcome the stratification.

 

In the end, the Weddell Polynya is still surrounded by some mystery… Only the next decades will bring us more insight into the true reasons for the appearance and disappearance of the Weddell Polynya…

 

Further reading

Edited by Clara Burgard


Rebecca Frew is a PhD student at the University of Reading (UK). She investigates the importance of feedbacks between the sea ice, atmosphere and ocean for the Antarctic sea ice cover using a hierarchy of climate models. In particular, she is looking at the how the importance of different feedbacks may vary between different regions of the Southern Ocean.
Contact: r.frew@pgr.reading.ac.uk

Image of the Week – Vibrating Ice Shelf!

Image of the Week – Vibrating Ice Shelf!

If you listen carefully to the Ekström ice shelf in Antarctica, a strange sound can be heard! The sound of a vibrating truck sending sounds waves into the ice. These sound waves are used to “look” through the ice and create a seismic profile of what lies beneath the ice surface. Read on to find out how the technique works and for a special Cryosphere Christmas message!


What are we doing with this vibrating truck on an ice shelf?

In early December a team from the Alfred Wegener Institute (AWI) made a science traverse of the Ekström ice shelf, near the German Neumayer III Station. Their aim was to make a seismic survey of the area. The seismic source (sound source) used to make this survey was a vibrating truck, known as a Vibroseis source (Fig. 2).

Fig. 2: The Vibroseis truck. It is attached to a “poly-sled” so that it can be easily towed across the ice shelf. The vibrating plate can be seen suspended below the centre of the truck. [Credit: Judith Neunhaeuserer]

It has a round metal plate, which is lowered onto the ice-shelf surface and vibrates at a range of frequencies, sending sound waves into the ice. When the snow is soft the plate often sinks a little, leaving a rather strange “footprint” in the snow (Fig. 3).

Fig. 3: The “footprint” of the Vibroseis truck plate in the snow [Credit: Olaf Eisen].

The sound waves generated travel through the ice shelf, through the water underneath and into the rock and sediment of the sea floor, they are reflected back off these different layer and these reflections are recorded back on the ice surface by a string of recording instruments – geophones (Fig 1). There are sixty geophones in a long string, a snow streamer, which can be towed behind the truck as it moves from location to location. By analyzing how long it takes the sound waves to travel from the source to the geophones an “image” of the structures beneath the ice can be made. For example, you can see a reflection from the bottom of the ice shelf and from the sea floor as well as different layers of rock and sediment beneath the sea floor. This allows the team to look into the geological and glaciological history of the area, as well as understand current glaciology and oceanographic processes!

 

As it happens, the team from AWI consists of your very own EGU Cryosphere Division President, Olaf Eisen and ECS Rep, Emma Smith! As this is the last post before Christmas, we wanted to wish you a merry Christmas from Antarctica!

Merry Christmas! As you can see the weather is beautiful here! [Credit: Jan-Marcus Nasse]

Edited by Sophie Berger

Image of the Week – Understanding Antarctic Sea Ice Expansion

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

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


The net expansion is the result of opposing regional trends

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

 

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

Why hasn’t Antarctic sea ice extent been decreasing?

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

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

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

 

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

 

1.Natural Variability

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

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

 

2. Anthropogenic Changes

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

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

 

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

 

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

 

Further reading

 

Edited by Clara Burgard et Sophie Berger


Rebecca Frew is a PhD student at the University of Reading (UK). She investigates the importance of feedbacks between the sea ice, atmosphere and ocean for the Antarctic sea ice cover using a hierarchy of climate models. In particular, she is looking at the how the importance of different feedbacks may vary between different regions of the Southern Ocean.
Contact: r.frew@pgr.reading.ac.uk

Image of the Week — Climate change and disappearing ice

The first week of the Climate Change summit in Bonn (COP 23  for those in the know) has been marked by Syria’s decision to sign the Paris Accord, the international agreement that aims at tackling climate change. This decision means that the United States would become the only country outside the agreement if it were to complete the withdrawal process vowed by President Trump.

In this context, it has become a tradition for this blog to use the  United Nations climate talks as an excuse to remind us all of some basic facts about climate change and its effect on the part we are most interested in here: the cryosphere! This year we have decided to showcase a few compelling animations, as we say “a picture is sometimes worth a thousand words”…


Arctic sea ice volume

Daily Arctic sea ice volume is estimated by the PIOMAS reconstruction from 1979-present [Credit: Ed Hawkins]

The volume of Arctic sea ice has declined over the last 4 decades and reached a record low in September 2012. Shrinking sea ice has major consequences on the climate system: by decreasing the albedo of the Arctic surface, by affecting the global ocean circulation, etc.

More information about Arctic sea ice:

Land ice losses in Antarctica and Greenland

Change in land ice mass since 2002 (Right: Greenland, Left: Antarctica). Data is measured by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites. [Credit: Zack Labe]

Both the Antarctic and Greenland ice sheets have been losing ice since 2002, contributing to global sea-level rise (see previous post about sea level) .  An ice loss of 100 Gt raises the  sea level by ~0.28 mm (see explanations  here).

More information about ice loss from the ice sheets:

 

The cause: CO2 emissions and global warming

Finally we could not close this post without showing  how the concentration of carbon dioxide have evolved  over the same period and how this has led to global warming.

CO₂ concentration and global mean temperature 1958 – present. [Credit:Kevin Pluck]

More information about CO2 and temperature change

  • Global Temperature | NASA: Climate Change and Global Warming
  • Carbon dioxide | NASA: Climate Change and Global Warming

More visualisation resources

Visualisation resources | Climate lab

 

Edited by Clara Burgard

Back to the Front – Larsen C Ice Shelf in the Aftermath of Iceberg A68!

Back to the Front – Larsen C Ice Shelf in the Aftermath of Iceberg A68!

Much of the Antarctic continent is fringed by ice shelves. An ice shelf is the floating extension of a terrestrial ice mass and, as such, is an important ‘middleman’ that regulates the delivery of ice from land into the ocean: for much of Antarctica, ice that passes from land into the sea does so via ice shelves. I’ve been conducting geophysical experiments on ice for over a decade, using mostly seismic and radar methods to determine the physical condition of ice and its wider system, but it’s only in the last couple of years that I’ve been using these methods on ice shelves. The importance of ice shelf processes is becoming more widely recognised in glaciological circles: after hearing one of my seminars last year, a glaciology professor told me that he was revising his previous opinion that ice shelves were largely ‘passengers’ in the grand scheme of things and this recognition is becoming more common. Slowly, we are coming to appreciate that ice shelves have their own specific dynamics and, moreover, that they are the drivers of change on other ice masses.


The MIDAS Project

In 2015, I joined the MIDAS project – led by Swansea and Aberystwyth Universities and funded by the Natural Environment Research Council – dedicated to investigating the effects of a warming climate on the Larsen C ice shelf in West Antarctica (Fig. 1). My role was to to assist with geophysical surveys (Fig. 2) on the ice shelf – but more about that later!

Figure 2: Adam Booth overseeing seismic surveys on the Larsen C ice
shelf in 2015 [Credit: Suzanne Bevan].

Larsen C is located towards the northern tip of the Antarctic Peninsula, and is one of a number of “Larsen neighbours” that fringe its eastern cost. MIDAS turns out to have been an extremely timely study, culminating in 2017 just as Larsen C hit the headlines by calving one of the largest icebergs – termed A68 – ever recorded. On 12th July 2017, 12% of the Larsen C area was sliced away by a sporadically-propagating rift through the eastern edge of the shelf, resulting in an iceberg with 5800 km2 area (two Luxembourgs, one Delaware, one-quarter Wales…). As of 14th October 2017 (Fig. 1), A68 is drifting into the Weddell Sea, with open ocean between it and Larsen C. See our previous post “Ice ice bergy” to find out more about how and why ice berg movement is monitored.

The aftermath of A68

As colossal as A68 (Fig, 1) is, its record-breaking statistics are only (hnnngh…) the tip of the iceberg, and of greater significance is the potential response of what remains of Larsen C. This potential is best appreciated by considering what happened to Larsen B, a northern neighbour of Larsen C. In early 2002, over 3000 km2 of Larsen B Ice Shelf underwent a catastrophic collapse, disintegrating into thousands of smaller icebergs (and immortalised in the music of the band British Sea Power). Rewind seven years further back, to 1995: Larsen B calved an enormous iceberg, exceeding 1700 m2 in area. An ominous extrapolation from this is that large iceberg calving somehow preconditions ice shelves to instability, and several models of Larsen C evolution suggest that it could follow Larsen B’s lead and become more vulnerable to collapse over the coming years.

The enormous mass of the intact ice shelf acts like a dam that blocks the delivery of terrestrial ice into the ocean, and the disappearance of the ice shelf removes so-called ‘backstress’ – essentially ‘breaking the dam’.

Then what? Well, ice shelves are in stress communication with their terrestrial tributaries, therefore processes affecting the shelf can propagate back to the supply glaciers. The enormous mass of the intact ice shelf acts like a dam that blocks the delivery of terrestrial ice into the ocean, and the disappearance of the ice shelf removes so-called ‘backstress’ – essentially ‘breaking the dam’. In the aftermath of Larsen B’s collapse, its tributary glaciers were seen to accelerate, thereby delivering more of their ice into the Weddell Sea. It is this aftermath that we are particularly concerned about, since it’s the accelerated tributaries that promote accelerated sea-level rise. Ice shelf collapse has little immediate impact on sea-level: since it is already floating, the shelf displaces all the water that it ever will. But, in moving more ice from the land to the sea, we risk increased sea levels and, with them, the associated socio-economic consequences.

How can we improve our predictions?

Figure 3: Computational model of the changed stress state, Δτuu, of Larsen C following the calving of A68 (output from BISICLES model, from Stephen Cornford, Swansea University). The stress change is keenly felt at the calving front, but also propagates further upstream [Credit: Stephen Cornford]

A key limitation in our ability to predict the evolution of Larsen C is a lack of observational evidence of how ice shelf stresses evolve in the short-term aftermath of a major calving event. These calving events are rare: we simply haven’t had much opportunity to investigate them, so while our computer predictions are based on valid physics (e.g., Fig. 3) it would be valuable to have actual observations to constrain them. Powerful satellite methods are available for tracking the behaviour of the shelf but these provide only the surface response; Larsen C is around 200 m thick at its calving front so there is plenty of ice that is hidden away from the satellite ‘eye in the sky’, but that is still adapting to the new stress regime. So how can we “see” into the ice?

To address this, we’ve recently been awarded an “Urgency Grant” – Response to the A68 Calving Event (RA68CE) – from NERC to send a fieldcrew to the Larsen C ice shelf, involving researchers from Leeds, Swansea and Aberystwyth, together with the British Geological and British Antarctic Surveys.

Figure 4: Emma Pearce and Dr Jim White preparing seismic equipment – intrepid geophysicists ready to wrap-up warm for field deployment on Larsen C! [Credit: Adam Booth]

The field team – Jim White and Emma Pearce (Fig. 4) – will undertake seismic and radar surveys at two main sites (Fig. 3) to assess the new stress regime around the Larsen C calving front. One of these sites is being reoccupied after seismic surveying in 2008-9, during the Swansea-led SOLIS project, allowing us to make a long-term comparison. These, and two other sites, will also be instrumented with EMLID REACH GPS sensors, to track small-scale ice movements than can’t be captured in the satellite data. The field observations will be supplied to a team of glacial modellers at Swansea University, to allow them to improve future predictions (e.g. Fig. 3), while their remote sensing team continues to monitor the evolving stress state at surface.

It’s truly exciting to be coordinating the first deployment, post A68, on Larsen C. Our data should provide a unique missing piece from the predictive jigsaw of Larsen C’s evolution, ultimately improving our understanding of the causes and effects of large-scale iceberg calving – both for Larsen C and beyond!

 

For ice-hot news from the field, follow Emma Pearce on twitter: @emm_pearce

 

Edited by Emma Smith


Further Reading

  • More information on Larsen C at the project MIDAS website
  • Learn more about ice shelf evolution with the Ice Flows game – eduction by stealth! Also check out the EGU Cryoblog post about it!
  • Borstad et al., 2017; Fracture propagation and stability of ice shelves governed by ice shelf heterogeneity; Geophysical Research Letters, 44, 4186-4194.
  • Wuite et al., 2015; Evolution of surface velocities and ice discharge of Larsen B outlet glaciers from 1995 to 2013. The Cryosphere, 9, 957-969.
  • Cornford et al., 2013; Adaptive mesh, finite volume modelling of marine ice sheets; Journal of Computational Physics, 232, 1, 529-549.

Adam Booth is a lecturer in Exploration Geophysics at the University of Leeds, UK. He is the PI on the NERC-funded project “Ice shelf response to large iceberg calving” (NE/R012334/1). After obtaining his PhD from the University of Leeds in 2008, he held postdoctoral positions at Swansea University and Imperial College London, in which he worked with diverse research applications of near-surface geophysics. He tweets as: @Geophysics_Adam

Mapping the bottom of the world — an Interview with Brad Herried, Antarctic Cartographer

Mapping the bottom of the world — an Interview with Brad Herried, Antarctic Cartographer

Mapping Earth’s most remote continent presents a number of unique challenges. Antarctic cartographers and scientists are using some of the most advanced mapping technologies available to get a clearer picture of the continent. We asked Brad Herried, a Cartographer and Web Developer at the Polar Geospatial Center at the University of Minnesota, a few questions about what it’s like to do this unique job both on and off the ice.


Before we go too much further… what is the Polar Geospatial Center, and what does it do for polar science and scientists?

The Polar Geospatial Center (PGC), founded in 2007 by Director Paul Morin, is a research group of about 20 staff and students at the University of Minnesota with a simple mission: solve geospatial problems at the poles (Antarctica and the Arctic). Because we are funded (primarily) through the U.S. National Science Foundation (NSF) and NASA Cryospheric Sciences, that is the community we support – other U.S.-funded polar researchers. We provide custom maps, high-resolution commercial satellite imagery, and Geographic Information System (GIS) support for researchers who would like to use the data for their research but may not have the expertise to do so.

Our primary service is providing high-resolution satellite imagery (i.e. from the DigitalGlobe, Inc. constellation) to U.S.-funded polar researchers – at no additional cost to their grants – through licensing agreements with the U.S. Government. It has proven beneficial to researchers to have a service so that we do the hard parts of data management, remote sensing, and automation of satellite imagery processing so that they don’t have to. So, a glaciologist or geomorphologist or wildlife ecologist studying at the poles may come to us and say: I would like to use satellite imagery to study phenomenon x or y. Some groups use it just for logistics (these are some of the least mapped places on Earth after all) to get to their site. Some groups’ entire research is done using remote sensing.

What kinds of data and resources do you use?

The PGC’s polar archive of high-resolution commercial imagery is absolutely astounding (like, in the thousands of terabytes). The imagery, although licensed to us by U.S. Government contracts, is collected by the DigitalGlobe, Inc. constellation of satellites (e.g. WorldView-2), much like the imagery where you can see your house/car in Google Earth. The benefit is that we can provide it at no cost to our users (researchers). That resource, along with the expertise of the staff at PGC, can provide solutions to users, whether it’s making a simple map of a remote research site or providing a time-series of satellite imagery for a researcher studying change detection (like, say for a glacier front in Greenland).

This also presents a challenge. How do we manage and effectively deliver that much data? We have relied on skilled staff, ingenuity, cheap storage, high-performance computing, and automation to become successful.

As the saying goes, automate or die.

What’s your role at the PGC? How did you find your way into a job like this?

I started at the PGC as a graduate student in 2008. I knew nothing about Antarctica or the Arctic, but my background and studies in GIS & cartography offered a wide range of jobs. After I graduated, I became a full-time employee as the lead cartographer of the (at the time, very small) group. Currently, I do a lot more GIS web application development and geospatial data management. We have recognized the need for more automated, “self-service” systems for our users to get the data they need in a timely manner, and less of asking a PGC employee for a custom product. As the saying goes, automate or die. But, of course, I still spend a fair bit of my times creating maps to keep my cartographic juices going.

Antarctica and the South Polar Regions. Map from the American explorer Richard Byrd’s second expedition in 1933. [Credit: Byrd Antarctic Expeditions]

What kind of work do PGC employees do in Antarctica?

The PGC staffs an office at the United States’ McMurdo Station annually from October to February, with 3-5 staff rotating throughout the field season. It is really an extension of our responsibilities, with a couple interesting twists, both good and bad. First, a majority of our users (NSF-funded researchers) come through McMurdo Station in preparation for their fieldwork. It’s a beneficial and unique experience to meet with them one-on-one and solve problems, ironically, faster than email exchanges back in the States. Second – and this is true of all of Antarctica – the internet bandwidth is very limited. So, we have to a) prepare more regarding what data/imagery we have on site and b) do more with less. That always proves to be a fun challenge because it is impossible to access our entire archive of imagery from down there.

How could I forget collecting Google Street View in Antarctica.

There have been several years, however, when we do get to go out into the field! In past years, we have conducted various field campaigns in the nearby McMurdo Dry Valleys to collect survey ground control to make our satellite imagery more accurate. And, how could I forget collecting Google Street View (with some custom builds of the typical car-camera system for snowmobiles, heavy-duty trucks, and backpacks). The Google Street View provides a window into the world of Antarctica – history, facilities, science, and of course its beautiful landscapes – to a wide audience who only dream of visiting Antarctica.

Brad on a snowmobile collecting Google Street View imagery [Credit: Brad Herried]

What are some of the interesting projects PGC has worked on? What’s exciting at PGC right now?

The PGC does a lot to contribute to polar mapping. There’s not exactly a ton of geospatial data or maps for the polar regions, especially Antarctica. What data or maps there are, it is not often of very high quality. For example, there are regions of Antarctica (especially in inland East Antarctica) which have not been properly mapped or surveyed since the 1960s. Those maps offer little help if you’re trying to land an aircraft in the area. So, PGC has done a lot to improve that geospatial data including creating more accurate coastlines, improving geographic coordinates of named features (sometimes the location can be off by 10s of kilometers!), organizing historic aerial photography, and digitizing map collections. These are important to have, but it all changes when you can collect data 100 times more accurate with satellites…

There’s not exactly a ton of geospatial data or maps for the polar regions, especially Antarctica.

Where it gets really interesting is how we can apply our archive of satellite imagery to help researchers solve problems or come up with cutting-edge solutions with the data. One example is the ArcticDEM project. In a private-public collaboration, PGC is using high performance computing (HPC) to develop a pan-Arctic Digital Elevation Model (DEM) at a resolution 10 times better than what exists now. This project requires hundreds of thousands of stereoscopic satellite imagery pairs to be processed using photogrammetry techniques to build a three-dimensional model of the surface for the entire Arctic. There are countless more applications for the imagery and we’ll continue to push the limits of the technology to produce innovative products to help measure the Earth and solve really important research questions.

ArcticDEM hillshade in East Greenland. DEM(s) created by the Polar Geospatial Center from DigitalGlobe, Inc. imagery. [Credit: Brad Herried/ Polar Geospatial Center].

 

What resources can cryosphere researchers and other polar scientists without US funding get from PGC to enhance their research?

Our website provides a wealth of non-licensed data, freely available to download. That includes our polar map catalog (with over 2,000 historic maps of the polar regions), aerial photography, and elevation data. The ArcticDEM project I mentioned before is freely available (see https://www.pgc.umn.edu/data/arcticdem/), as are all DEMs created (derived) from the optical imagery. Moreover, we work with the international community on a regular basis to continue mapping efforts across both poles.

 

What advice do you have for students interested in a career in science or geospatial science?

This might be a little bit of a tangent, but learn to code. I was trained in cartography ten years ago and we hardly touched the command line. Now? You certainly don’t have to be an expert, say, Python programmer, but you’re behind if you don’t know how to automate some of your tasks, data processing, analysis, or other routine workflows. It allows you to focus on the things you’re actually an expert in (and, employers are most certainly looking for these skills).

ArcticDEM hillshade of Columbia Glacier, Alaska. DEM(s) created by the Polar Geospatial Center from DigitalGlobe, Inc. imagery. [Credit: Brad Herried/ Polar Geospatial Center].

Personally, what has been the highlight of your time at PGC so far?

I will never forget the first time I stepped off the plane landing in Antarctica as a graduate student. A surreal, breathtaking (literally), and completely foreign feeling. To be able to experience the most remote places on Earth first-hand naturally leads to a better understanding of them. So, the highlight for me is this: I find myself asking more questions, talking to the preeminent researchers and students about their work, and discovering the purpose of it all. I may be a small piece in the puzzle of understanding our Earth’s poles, but I’m humbled to be a part.

Interview and Editing by George Roth, Additional Editing by Sophie Berger

Image of the Week – See sea ice from 1901!

Image of the Week – See sea ice from 1901!

The EGU Cryosphere blog has reported on several studies of Antarctic sea ice (for example, here and here) made from high-tech satellites, but these records only extend back to the 1970s, when the satellite records began. Is it possible to work out what sea ice conditions were like before this time? The short answer is YES…or this would be a very boring blog post! Read on to find out how heroic explorers of the past are helping to inform the future.


During the Heroic Age of Antarctic Exploration (1897–1917), expeditions to the “South” by explorers such as Scott and Shackleton involved a great deal of time aboard ship. Our image of the week shows one such ship – the ship of the German Erich von Drygalsk – captured from a hot air balloon in 1901.

These ships spent many months navigating paths through sea ice and keeping detailed logs of their observations along the way. Climate scientists at the University of Reading, UK have used these logs to reconstruct sea-ice extent in Antarctica at this time – providing key information to extend satellite observations of sea ice around the continent.

Why do we want to know about sea-ice extent 100 years ago?

In the last three decades, satellite records of Antarctic sea-ice extent have shown an increase, in contrast to a rapid decrease in Arctic sea-ice extent over the same period (see our previous post). It is not clear if this, somewhat confusing, trend is unusual or has been seen before and without a longer record, it is not possible to say. This limits how well the sensitivity of sea ice to climate change can be understood and how well climate models that predict future ice extent can be validated.

To help understand this increase in Antarctic sea-ice extent; records of ice composition and nature from ships log books recorded between 1897–1917 have been collated and compared to present-day ice conditions (1989–2014).

What does the study show?

The comparison between sea ice extent in the Heroic Age and today shows that the area of sea ice around Antarctica has only changed in size by a very small amount in the last ~100 years. Except in the Weddell sea, where ice extent was 1.71o (~80 km) further North in the Heroic Age, conditions comparable to present-day were seen around most of Antarctica. This suggests that Antarctic sea-ice extent is much less sensitive to the effects of climate change than that Arctic sea ice. One of the authors of the study, Jonny Day, summarises these findings in the video below:

References and Further Reading

Planet Press

planet_pressThis is modified version of a “planet press” article written by Bárbara Ferreira and originally published on 26th November 2016 on the EGU website .

It is also available in Dutch, Hungarian, Serbian, French, Spanish, Italian and Portuguese! All translated by volunteers – why not consider volunteering to translate an article and learn something interesting along the way?

 

Edited by Sophie Berger

Image of the Week – A new way to compute ice dynamic changes

Fig. 1: Map of ice velocity from the NASA MEaSUREs Program showing the region of Enderby Land in East Antarctica [Credit: Fig. 1 from Kallenberg et al. (2017) ].

Up to now, ice sheet mass changes due to ice dynamics have been computed from satellite observations that suffer from sparse coverage in time and space. A new method allows us to compute these changes on much wider temporal and spatial scales. But how does this method work? Let us discover the different steps by having a look at Enderby Land in East Antarctica, for which ice velocities are shown in our Image of the Week…


Mass balance of ice sheets

The mass balance of an ice sheet is the difference between the mass gain of ice, primarily through snowfall, and the mass loss of ice, primarily via meltwater runoff and ice dynamic processes (e.g. iceberg calving, melting below ice shelves). When the mass gain is equal to the mass loss, the ice sheet is in balance. However, if one exceeds the other, the ice sheet either gains or loses mass.

Measuring mass balance changes of ice sheets is crucial due to their potential contribution to sea level rise (see previous post). You can have a look at this nice review for further details about the recent changes in the mass balance of the two biggest ice sheets on Earth, i.e. Antarctica and Greenland.

Ice mass changes from snowfall and meltwater runoff (what we call ‘surface mass balance’ changes) are reasonably well simulated by regional climate models, which give good agreement with observations (see this study for Antarctica and this one for Greenland). Mass changes from ice dynamics are more complex to obtain. They are commonly estimated by combining ice velocity and ice thickness. Ice velocity is measured via satellite radar interferometry, while ice thickness is obtained thanks to airborne radar. Unfortunately, these measurements have sparse temporal and spatial coverage, especially in Antarctica, which makes the computation of mass changes from ice dynamics challenging.

A new method to estimate ice dynamic changes

Kallenberg et al. (2017) conducted a study focussing on Enderby Land in East Antarctica (see our Image of the Week) in which they use a novel approach to estimate ice dynamic changes. This region of Antarctica has experienced a slightly positive mass balance in past years, meaning that the ice sheet has slightly thickened in this region.

Kallenberg et al. (2017) first used satellite observations to compute the total changes in ice sheet mass. They took advantage of two high-technology datasets. The first one, “Gravity Recovery And Climate Experiment” (GRACE), measures changes in the Earth’s gravity field, from which ice mass changes can be derived. A summary explaining how GRACE works can be found in this previous post. The second satellite dataset, “Ice, Cloud, and land Elevation Satellite” (ICESat), measures changes in ice surface elevation, from which changes in ice mass can be computed by using ice density.

However, Kallenberg et al. (2017) were not interested in the total ice mass changes, as obtained from GRACE and ICESat satellites, but rather in ice dynamic changes. They subtracted two quantities from the total mass changes in order to obtain the remaining dynamic changes:

  1. Surface mass balance changes: changes from processes happening at the surface of the ice sheet (e.g. snow accumulation, meltwater runoff). These changes were obtained from model simulations using the Regional Atmospheric Climate Model (RACMO2), for which details can be found in this previous post.
  2. Glacial Isostatic Adjustment: changes in land topography due to ice loading and unloading. These changes were computed from Glacial Isostatic Adjustment models.

What does this study tell us?

The results of this study show that it is possible to compute changes in ice mass resulting from ice dynamics with higher spatial and temporal coverage than before, using a combination of satellite observations and models.

Also, the use of two different satellite datasets (GRACE and ICESat) shows that they agree quite well with each other in the region of Enderby Land (see Fig. 2). This means that using one or the other dataset does not make a big difference.

Finally, this new method also shows that differences between GRACE and ICESat reduce when using the newer version of RACMO2 for computing surface mass balance changes. This tells us that comparing results of ice dynamics from both satellites with different models is a good way to identify which models correctly simulate surface processes and which models do not.

Fig. 2: Ice dynamic changes (dH/dt, where H is ice thickness and t is time) computed from (a) GRACE and (b) ICESat and expressed in meters per year [Credit: Fig. 5 from Kallenberg et al. (2017) ].

Further reading

Edited by Clara Burgard and Emma Smith


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

Image of the Week — 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 – The birth of a sea-ice dragon!

Image of the Week – The birth of a sea-ice dragon!

Dragon-skin ice may sound like the name of an episode of the Game of Thrones fantasy franchise. However, this fantasy name hides a rare and bizarre type of ice formation that you can see in our Image of the Week. It has been recently observed by the “Polynyas, ice production and seasonal evolution in the Ross Sea” (PIPERS) research team in Antarctica. This bizarre phenomenon caused by strong wind conditions has not been observed in Antarctica since 2007.


PIPERS expedition observed dragon-skin ice

In early April, the Nathan B Palmer icebreaker (see Fig. 2) began its 65-day voyage to Antarctica to study sea ice in the Ross Sea during the autumn period. This expedition, named PIPERS, was carried out by a team of 26 scientists from 9 countries. Its goal was to investigate polynyas, ice production, and seasonal evolution with a particular focus on the Terra Nova Bay and Ross Sea Polynyas (see Fig. 3).

Fig.2 : The Nathan B Palmer icebreaker caught in sea ice [Credit: IMAS ].

A polynya is an area of open water or thin sea ice surrounded by thicker sea ice and is generally located in coastal areas [Stringer and Groves, 1991]. Ice formation in polynyas is strongly influenced by wind conditions whose action can lead to astonishing spatial patterns in sea ice appearance. Special wind conditions probably also lead to what the members of the PIPERS expedition had the opportunity to observe: ice patterns that resemble dragon scales, therefore called dragon-skin ice. Such a sighting is quite remarkable as the last one dates back from a decade. However, the sparsity of observations of dragon-skin ice phenomena is probably a consequence of the relatively small number of expeditions in Antarctica during the autumn and winter seasons…

Fig. 3: The Terra Nova Bay Polynya and Ross Sea Polynya explored by the PIPERS expedition. [Credit: PIPERS ].

Chaotic ice formation caused by strong winds

Dragon-skin ice is a chaotic result of the complex interplay between the ocean and the atmosphere. Coastal polynyas in Antarctica are kept open by the action of strong and cold offshore winds (see Fig. 4) known as katabatic winds, which blow downwards as fast as 100 km/h for several hours [McKnight and Hess, 2000]. Sea ice forming at the cold sea surface gets blown away by these strong winds, preventing a closed sea-ice cover in this area. As the ice is blown away, an area of open water gets in direct contact with the atmosphere, leading to strong cooling and new formation of ice, that gets blown away again, and so on… Therefore, in general, sea ice in polynyas consists of thin pancake ice (see Fig. 5) i.e. round pieces of ice from 0.3 to 3 meters in diameter, which results from the aggregation of ice crystals caused by the wave action. Due to the wind action, the pieces of ice are pushed out by the wind action to the edges of the polynya.  As these pieces push strongly against each other, dragon-like scales appear on sea ice giving birth to the so-called dragon-skin ice.

Fig.4: Formation of coastal polynyas due to the action of katabatic winds [Credit: Wikimedia Commons ].

Figure 5: Sea ice in polynyas takes the form of pancake ice due to the action of water waves [Credit: PIPERS ].

The importance of polynyas for ocean-atmosphere interactions

Besides providing us with dazzling pictures of the cryosphere, investigating sea-ice production and evolution in polynyas is essential to better understand the complex interactions between the ocean and the atmosphere.
As sea water freezes into sea ice, salt is expelled into the ocean, raising its local salinity. The incessant production of sea ice in polynyas leads to water masses with very high salinity inside the polynyas. As sea water cools down, it releases energy in the atmosphere, leading to a warming of the atmosphere in polar regions. Moreover, due to their high density, these masses of cold and salty water sink and mix with lower ocean layers.
First results from the PIPERS mission show that when sea ice is forming, polynyas release greenhouse gases to atmosphere, instead of capturing it, as it was previously assumed! But fully understanding what’s happening there will necessitate more time and analyses….

Further reading

 

Edited by Scott Watson and Clara Burgard
Modified by Sophie Berger on 3 July 2017 to account for remarks of Célia Sapart (Member of the PIPER expedition)


Kevin Bulthuis is a F.R.S.-FNRS Research Fellow at the Université de Liège and the Université Libre de Bruxelles. He investigates the influence of uncertainties and instabilities in ice-sheet models as a limitation for accurate predictions of future sea-level rise. Contact Email:kevin.bulthuis@ulg.ac.be.