CR
Cryospheric Sciences

monitoring sea ice

Image of the Week – The 2018 Arctic summer sea ice season (a.k.a. how bad was it this year?)

Sea ice concentration anomaly for August 2018: blue means less ice than “normal”, i.e. 1981-2010 average. Credit: NSIDC.

With the equinox this Sunday, it is officially the end of summer in the Northern hemisphere and in particular the end of the melt season in the Arctic. These last years, it has typically been the time to write bad news about record low sea ice and the continuation of the dramatic decreasing trend (see this post on this blog). So, how bad has the 2018 melt season been for the Arctic?  


Yes, the 2018 summer Arctic sea ice was anomalously low

Before we give you the results for this summer, let us start with the definitions of the three most common sea ice statistics:

  • Sea ice concentration: how much of a given surface area (e.g. 1 km2) in the ocean is covered by sea ice. The concentration is 100% if there is nothing but sea ice, 50% if half of this area is covered by ice, and 0% if there is nothing but open water. Read more about how satellites measure sea ice concentration on this blog here.
  • Sea ice extent: typically defined as the ocean area with at least 15% sea ice concentration.
  • Sea ice volume: the whole volume of sea ice, i.e. total area times thickness of sea ice. This is probably the most difficult of the three statistics to measure since satellite measurements of sea ice thickness are only starting to be trustworthy.

So, how did summer 2018 perform regarding these three statistics?
As shown on today’s Image of the Week, the sea ice concentration has been anomalously low in most parts of the Arctic, with many areas in dark blue showing they had more than 50% less sea ice than normal (1981-2010 average).

The resulting extent was anomalously low as well (see figure below), but not record-breaking low. The volume however was the fourth lowest recorded or 50% lower than normal, with 5000 km3 of sea ice missing. In a more meaningful unit, that is one trillion elephants of ice, or 64 000 elephants per km2 of the Arctic Ocean.

But as we discussed in a previous post, talking about the Arctic as a whole is not enough to understand what happened this summer. So let us have a closer look at the area north and east of Greenland.

Summer 2018 Arctic sea ice extent up till 19th September (blue) compared to the “normal” extent (grey) and the all-time record of 2012 (green dashed). Credit: NSIDC.

North of Greenland: open water instead of multiyear ice

Until recently, most of the Arctic Ocean was covered by multiyear / perennial ice. That is, most sea ice would not melt in summer and would stay until the next winter. But with climate change and the warming of the Arctic, the multiyear ice cover has shrunk and became limited to the area north of Greenland.

The situation has been even more dramatic this summer. For the entire month of August 2018, there was open water north of Greenland where there should have been thick multiyear ice (see picture below). As nicely explained here, that area had already unexpectedly melted in February this year when the Arctic was struck with record high air temperatures; when the sea ice closed again, it was thinner and more brittle than it should have been, and did not withstand strong winds in August. Therefore, this unusual winter melting could have contributed to the formation of open water north of Greenland.

It is really bad news, and it does feel like yet another tragic milestone: even the last areas of multiyear ice are melting away. Most worryingly, we do not know what the consequences of this disappearance will be on the ecosystem and the entire climate. Or rather, we know that everything from local sea ice algae to European weather patterns will be affected, but more research is needed over the coming years before we can assess the full impact over our complex fully coupled climate system.

Optical satellite image of the northern half of Greenland, 19 August 2018. Dark colour is open water, and should not have been here. Credit: NASA.

Reference/Further reading

For near real time analysis of the sea ice conditions: https://nsidc.org/arcticseaicenews/

For checking sea ice data from home: https://seaice.uni-bremen.de/databrowser/

For simple visualisations of sea ice statistics: http://sites.uci.edu/zlabe/arctic-sea-ice-volumethickness/

 

Edited by David Docquier

Image of the Week – Icy expedition in the Far North

Image of the Week – Icy expedition in the Far North

Many polar scientists who have traveled to Svalbard have heard several times how most of the stuff there is the “northernmost” stuff, e.g. the northernmost university, the northernmost brewery, etc. Despite hosting the four northernmost cities and towns, Svalbard is however accessible easily by “usual-sized” planes at least once per day from Oslo and Tromsø. This is not the case for the fifth northernmost town: Qaanaaq (previously called Thule) in Northwest Greenland. Only one small plane per week reaches the very isolated town, and this only if the weather permits it. And, coming from Europe, you have to change plane at least twice within Greenland! It is near Qaanaaq, during a measurement campaign, that our Image of the Week was taken…


Who, When and Where?

In January 2017, a few German and Danish sea-ice scientists traveled to Qaanaaq to set up different measurement instruments on, in and below the sea ice covering the fjord near Qaanaaq. While in town, they stayed in the station ran by the Danish Meteorological Institute. After a few weeks installation they traveled back to Europe, leaving the instruments to measure the sea-ice evolution during end of winter and spring.

 

What and How?

The goal of the measurement campaign was to measure in a novel way the evolution of the vertical salinity and the temperature profiles inside the sea ice, and the evolution of the snow covering the ice. These variables are not measured often in a combined way but are important to understand better how the internal properties of the sea ice evolve and how it affects or is affected by its direct neighbors, the atmosphere and the ocean. The team had to find a place remote enough from human influence, and with good ice conditions. As there are only few paved roads in Qaanaaq, cars are not the best mode of transport. The team therefore traveled a couple of hours on dog sleds (in the dark and at around -30°C!), with the help of local guides and their well-trained dogs (see Fig. 2 and 3).

 

Fig. 2: While the humans were working, the dogs could take a well-deserved break [Credit: Measurement campaign team].

Once on the spot, the sea-ice measurement device was introduced into the ice by digging a hole of 1m x 1m in the ice, placing the measurement device in it, and waiting until the ice refroze around it. Additionally, a meteorological mast and a few moorings were installed nearby (see Image of the Week and Fig. 3) to provide measurements of the atmospheric and oceanic conditions during the measurements. Further, a small mast was installed to enable the data to be transferred through the IRIDIUM satellite network.

 

Fig. 3: Small meteorological mast with dog sleds in the background [Credit: Measurement campaign team].

Finally, the small instrument family was left alone to measure the atmosphere-ice-ocean evolution for around four months. After this monitoring period, in May, the team had to do this trip all over again to get all the measurement devices back. Studying Greenlandic sea ice is quite an adventure!

 

Further reading

Edited by Violaine Coulon

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

European Space Agency Living Planet Symposium 2016

European Space Agency Living Planet Symposium 2016

Living Planet Symposium

Between the 9th and 13th May, Prague played host to the European Space Agency’s (ESA) fourth Living Planet Symposium. The event, the largest in its history with over 3300 attendees, brought together the earth observation community across multiple disciplines to discuss significant scientific results and the future developments of earth observation missions. Earth Observation  of the Cryosphere over the last few decades has revolutionised our understanding of these regions, allowing us to monitor and assess ice sheet dynamics at unprecedented spatial and temporal scales.

ESA & Observation of the Cryosphere

The role of Earth Observation in Cryospheric sciences is set to increase further thanks to the European Commission and ESA Copernicus program; a series of satellites called Sentinels which all feature different sensor instrumentation, allowing researchers to monitor various aspects of the Earth System. The program will consist of 6 separate sentinel missions and will allow us to measure various Ice Sheet and Glacier dynamics continuously at a high temporal resolution. In addition, the Earth Explorer mission CryoSat-2 has been transforming our knowledge of the polar regions since it’s launch in 2010.

As a result, the conference had a wide range of exciting scientific results related to the Cryosphere from these missions; ranging from data products to be used by the community to the exploitation of mission data to further our knowledge of key processes and outstanding scientific questions.

Don’t worry if you weren’t able to make the symposium, as this post will highlight a selection of interesting results and the impact they will have on Cryospheric research!

CryoSat-2: Transforming Knowledge of the Cryosphere

CryoSat-2, an ESA Earth Explorer satellite that carries onboard a radar altimeter to measure ice elevation (Credit : ESA – P. Carril)

CryoSat-2, an ESA Earth Explorer satellite that carries onboard a radar altimeter to measure ice elevation (Credit : ESA – P. Carril)

CryoSat-2 is the ESA Earth Explorer radar altimetry mission dedicated to monitoring changes in surface elevation of earth’s ice sheets, sea-ice thickness and extent; which it has been routinely monitoring since November 2010. The combination of its unique polar orbital characteristics and novel dual antenna interferometric mode of operation has allowed it to overcome  many of the issues associated with previous altimetry missions over ice sheets.

Major results from CryoSat-2 included the application of swath processing techniques to the interferometric data to dramatically increase the number of surface elevation measurements available to researchers (Gray et al, 2013). Traditionally, the radar instrumentation would record a single elevation measurement at the point of closest approach (POCA) to the satellite. However, this technique analyses the whole radar return to produce measurements across the satellite footprint. By exploiting this increased data density it allows researchers to investigate ice sheet changes at much finer spatial and temporal resolution, allowing for an increase in the range of scientific questions the satellite is able to address. Examples of this include glacier thinning as a result of surging events that have previously occurred on time scales not possible to be captured by the satellite. It will also allow us to get a more complete picture of mass balance using the altimetry method.

Ice-shelf thickness in Antarctica

Furthermore, a contemporary continental ice shelf thickness dataset (Chuter and Bamber, 2015) derived from CryoSat-2 was presented; which provides large accuracy improvements over the previous ERS-1 derived dataset (Griggs and Bamber, 2011), particularly in the grounding zone, a key region for monitoring ice sheet stability. The results from this work will allow the community to improve accuracy in mass balance estimations from the input-output method, sub-ice shelf ocean modelling and for parameterisations in ice sheet models.

Ish_thick

Antarctic ice shelf thickness Derived from CryoSat-2 radar altimetry (Credit: subset of fig S1 from Chuter and Bamber, 2015). 

Monitoring sea ice

Sea ice monitoring is also a key mission objective, with the satellite already delivering on these aims through studies of continuous monitoring of the Arctic Sea Ice over the past five years.  Work presented at the symposium by Rachel Tilling (CPOM/University College London) makes use of the Near Real Time data products from ESA to deliver knowledge of sea ice thickness and extent as quick as two days after data acquisition, providing benefits to the shipping industry in addition to aiding arctic climate predictions (see also Tilling et al, 2015).

Antarctic mass balance

For the Antarctic ice sheet, mass balance estimates obtained from altimetry, gravimetry, and mass-budget methods can yield conflicting results with error bars that do not always overlap.

Some of these techniques use models to isolate and remove the effects of glacio-isostatic adjustment and surface mass balance (SMB) processes,  introducing another source of uncertainty which is hard to quantify.

a) Estimates of mass balance for the Amundsen Sea Embayment (ASE) sector in Antarctica from different techniques, including estimates from the RATES project. b) Estimates of the mass loss due to ice dynamics (red) and SMB (blue) for the ASE, compared with modeled values from RACMO2.3 (red dots) and ice discharge (blue line) (Credit: fig 9a from Martín-Español, et al. 2016)

a) Estimates of mass balance for the Amundsen Sea Embayment sector in West Antarctica from different techniques, including estimates from the RATES project. [IOM = Input-Output Method] b) Estimates of the mass loss due to ice dynamics (red) and Surface Mass Balance (SMB — blue) for the Amundsen Sea Sector, compared with modeled values from RACMO2.3 (red dots) and ice discharge (D — blue line) (Credit: fig 9 from Martín-Español et al. 2016)

To address both these issues, the RATES project presented a statistical modelling approach to the problem (Martin-Español et al., 2016). They combined the observational data (including satellite altimetry, GRACE, GPS and InSAR), and used prior information to separate out the mass balance signal into its main components.  For instance, we know that the glacio-isostatic adjustment has a large spatial length-scale, but  changes in ice dynamics may vary from one glacier to the next. We thus can `look’ for these components within the data and attribute them to the correct process. For the period 2003-2013, they estimated a mean mass balance rate of -82±23 Gt/yr with a sustained negative mean trend of dynamic imbalance to which West Antarctica is the largest contributor, mainly triggered by high thinning rates of glaciers draining into the Amundsen Sea Embayment. The Antarctic Peninsula has experienced a dramatic increase in mass loss in the last decade following the destabilization of the Southern Antarctic Peninsula. The total mass loss is partly compensated by a significant mass gain in East Antarctica due to a positive trend of SMB anomalies.

4th Cryosat User workshop

In addition to major scientific results and products, the conference combined with the 4th CryoSat User Workshop, bringing together users from all cryospheric disciplines to discuss a variety of issues such as: Product Calibration and Validation campaigns, future data product releases and further serving the needs of the scientific community. In addition, with the satellite currently being operated beyond in it’s initial commissioning timespan, initial discussions were held regarding whether there would be the possibility of a follow up and the form it could possibly take.

Sentinel 1A/B – A New Era for Ice sheet Velocity Mapping

sentinel

Sentinel 1A/B is the Copernicus Synthetic Aperture Radar (SAR) mission, providing global radar imagery currently at a 12 day repeat period, free from the limitations posed by multispectral imagery such as cloud cover. The launch of Sentinel 1B on the 25th April this year to join in constellation with 1A will reduce this repeat period to 6 days. This will allow for continuous, long term monitoring of the Earth’s Cryosphere at a high temporal resolution.

Sentinel 1 results presented at the conference exemplified the transformative power this mission will have on Cryospheric sciences. Firstly, it will allow us to produce continental velocity maps for both Greenland and Antarctica at sub-annual resolution. This will allow for monitoring of seasonal velocity changes in outlet glaciers, better estimations of mass balance and improved parameterisations of conditions in ice sheet models.  Additionally, the mission is now providing researchers with a near real time data stream of ice velocities for key outlets of the Greenland and Antarctic ice sheets, allowing them to track changes and investigate changes in behaviour at 12-day scale (reducing to 6 days with 1B) (Hogg et al, 2016).

Ice Sheet velocity across the Antarctic peninsula derived from Sentinel 1 data from December 2014 to March 2016. Image Credit ESA and ENVEO: http://www.esa.int/spaceinimages/Images/2016/05/Antarctic_Peninsula_ice_flow

Ice Sheet velocity across the Antarctic peninsula derived from Sentinel 1 data from December 2014 to March 2016. (Credit: ESA and ENVEO)

The grounding line is a key region of the ice sheet to monitor due to it’s ability to indicate changes in the dynamics of the inland Ice Sheet and it’s potential instability. SAR missions allow us to map the grounding line with high accuracy by analysing the differences in vertical tidal displacement of the ice shelves between images via the formation of interferograms. Previously there has been discontinuous temporal coverage from various SAR missions; however with the advent of Sentinel 1 mission, it will possibly to routinely monitor grounding line flux position for an extended period of time, improving our understanding of key ice sheet processes and inland grounded ice stability.

Final Thoughts

The conference showed us the combined power offered by the new Sentinel missions and the continuation of CryoSat-2 in allowing us to monitor the Cryosphere at scales not previously possible, thus shedding more light on the dynamics of these key earth system regions. The new satellites have allowed researchers to produce new and improved datasets open for use by the scientific community, helping to accelerate and enable future discoveries. Additionally, when these datasets are used in combination, they can help us to better answer some of the subject’s biggest questions; such as the mass balance of the Ice Sheets and its changes over time. As a result, these missions promise for exciting times ahead in terms of greatly forwarding our understanding of the Cryosphere.

 With the new sentinel missions and the continuation of CryoSat-2 exciting times are ahead for remote sensers of the cryosphere

Aside from the Conference – City of Prague

Prague offered many sights and opportunities to explore during the downtime of the conference. Highlights of the City included the Charles Bridge built in 1390 and the old Town Square which hosts the famous astronomical clock. All of this is set to the backdrop of Prague Castle, the largest ancient castle in the world and residence of the President of the Czech Republic. The City also has a famous classical music and opera scene and offers some of the world’s best beer, providing the perfect opportunity to network and make contacts!


References

  • Chuter, S. J., and J. L. Bamber (2015), Antarctic ice shelf thickness from CryoSat-2 radar altimetry, Geophys. Res. Lett., 42(24), 10,721–10,729, doi:10.1002/2015GL066515.
  • Gray, L, D Burgess, L Copland, R Cullen, N Galin, R Hawley, and V Helm. 2013. “Interferometric Swath Processing of Cryosat Data for Glacial Ice Topography.” The Cryosphere 7 (6). Copernicus GmbH: 1857–67.
  • Griggs, J.A., and J.L. Bamber. 2011. “Antarctic Ice-Shelf Thickness from Satellite Radar Altimetry.” Journal of Glaciology 57 (203). International Glaciological Society: 485–98. doi:10.3189/002214311796905659.
  • Hogg, A., A. Shepherd, N. Gourmelen (2015) A first look at the performance of Sentinel-1 over the West Antarctic Ice Sheet, FRINGE 2015, Frascati, Italy, 23-27 March 2015.
  • Martín-Español, A. et al. (2016), Spatial and temporal Antarctic Ice Sheet mass trends, glacio-isostatic adjustment and surface processes from a joint inversion of satellite altimeter, gravity and GPS data, J. Geophys. Res. Earth Surf., 120, 1–18, doi:10.1002/2015JF003550.
  • Tilling, R. L., A. Ridout, A. Shepherd, and D. J. Wingham (2015), Increased Arctic sea ice volume after anomalously low melting in 2013 – supplementary Information, Nat. Geosci., 8(8), 643–646, doi:10.1038/ngeo2489.

Edited by Sophie Berger


steve

Stephen Chuter is a PhD Student at the University of Bristol, UK. He  Investigates the dynamics of the Antarctic Ice Shelves and grounding zone using the ESA CryoSat-2 satellite. The unique orbital characteristics and novel SARIn mode of operation allow us to study these areas in much greater detail than possible from previous radar altimetry missions, therefore allowing us to greater ascertain its role in ice sheet stability. He tweets as @StephenChuter.
Contact Email: s.chuter@bristol.ac.uk