Category Archives: Cryosphere

Sea Ice Conditions In the Weddell Sea

The ice is melting everywhere.

This spring researchers of the British Antarctic Survey report on recent measurements of the sea ice over the Weddell Sea off Antarctica [1].  Bottom line:  the sea ice was at a record low over the summers of 2016-9.

These measurements are based on satellite observations of the ice, weather stations reporting air temperatures, and ocean buoys reporting sea temperatures.

Obviously, sustained low ice is important, especially as the NYT headline put it, “The Iciest Waters Around Antarctica Are Less Icy[1].  Melting sea ice doesn’t directly raise sea level, but it does lower the albedo of the sea, possibly leading to warmer sea water, and follow on effects from that.  And the warmer the sea, the less ice that will form, in a feedback loop.

(This ice shelf is also an important habitat for penguins and seals among others, so lack of ice is really hard on wildlife.)

However, the research indicates that these conditions, while unprecedented “in the satellite era”,  are due to a combination of effects, not necessarily a sustained trend.  This is made pretty clear from their graphs of the estimates for last 40 years, which bounce up and down quite a bit.  The last three years are unusual, but it wouldn’t be surprising to see the ice extent bounce back.

Figure 1. (a) The 1978/1979–2019/2020 mean summer SIEs for the Weddell Sea. The x axis values refer to the year in which the December of each summer occurred. (b) Mean annual cycles of Weddell Sea SIE based on daily data for 2013–2015 (black) and 2017–2019 (red). The month indicators mark the midpoint of each month. (c) The monthly percentage SIE anomalies (from the monthly mean climatological SIEs for 1979–2008) since 2013. The year indicators mark the midpoint of each year (From [2])
However, with general warming and feedback effects, it is also possible that the sea ice will continue to melt each summer, which would be a significant indication of major climate change in Antarctica.

So, we’ll keep watching.

  1. Henry Fountain, The Iciest Waters Around Antarctica Are Less Icy, in New York times. 2020: New York.
  2. John Turner, Maria Vittoria Guarino, Jack Arnatt, Babula Jena, Gareth J. Marshall, Tony Phillips, C. C. Bajish, Kyle Clem, Zhaomin Wang, Tom Andersson, Eugene J. Murphy, and Rachel Cavanagh, Recent Decrease of Summer Sea Ice in the Weddell Sea, Antarctica. Geophysical Research Letters, 47 (11):e2020GL087127, 2020/06/16 2020.

Space Lasers Measuring the Cryosphere

The ice is melting everywhere.

This is important, and, fortunately we are science-ing the hell out of it.

The science includes computational modelling, remote sensing, and in situ measurements.

One important thrust has been increased satellite observation of the polar regions, to build a detailed, continuing record of the snow and ice cover.

Or, as the BBC headline put it, “NASA space lasers track melting of Earth’s ice sheets” [1].

Anything involving “space lasers” has got to be cool, right?

: – )

The space lasers in question are the ICESats, which have laser altimeters that have been measuring the height and thickness of the snow and ice around the world.

This spring researchers report on a careful analysis of ICESat data from 2003 – 2019 [2]. The study combined earlier data from ICESat with the improved and higher resolution data from ICESat-2.  The combined data is incomplete, but is a comprehensive record of the ice mass of ice shelves, glaciers, and interiors.

ICESat-2 has much higher resolution, which means the data can account for more of the real geography of the ice, such as large crevasses.  This is particularly important where the ice is in the process of melting, because it will lose mass by hollowing out before the total coverage changes.

IceSat-2’s resolution allows it to map crevasses in the ice sheet surface. (Image credit: NASA/SCRIPPS/S.ADUSUMILL) (From [1])
The total amount of ice is a critical factor, because if and when the ice decreases (melts), the water flows into the oceans, raising sea level.  And vice versa.  So, big changes in these icy areas mean, among other things, changes in sea level everywhere.

Current understanding tells us that there are a number of processes that contribute to the accumulation, retention, and loss of ice.  The temperature of the air, as well as humidity, prevailing winds, and the number of storms contribute to the amount of snowfall (new ice) and the melting of surface snow and ice.  Ocean temperature and currents contribute to the rate of melting of sea ice.  And there are plenty of complicated interactions between oceans and air, as well as the dynamic behavior of the ice, as glaciers flow faster or slower into the sea.  And, of course, as the ice melts, the exposed surfaces are darker, absorbing more solar energy, and heating the ocean and atmosphere even faster.

The upshot is that things are so complicated that we need as good of data as we can get to make sure the models are following reality, as well as to understand the state of play.

The new study  is broadly consistent with existing work, showing areas of loss and areas of gain. (e.g., this, this)  While there is increased snow accumulation in places, there is thinning and reduction in ice shelves, and increase flow in glaciers.

Overall, they see over 300 Gigatons of ice loss over this period, which they calculate contributed to a 14mm rise in global sea level.  (This is probably an underestimate, because the data does not cover everywhere for the whole period.)

The bottom line is that the ice was melting for the last 15 years, and looks to continue to melt, quite probably at a faster rate.  ICESat-2 will surely document the changes over the next few years.

  1. Jonathan Amos, NASA space lasers track melting of Earth’s ice sheets, in BBC News – Science & Environment, April 30, 2020.
  2. Ben Smith, Helen A. Fricker, Alex S. Gardner, Brooke Medley, Johan Nilsson, Fernando S. Paolo, Nicholas Holschuh, Susheel Adusumilli, Kelly Brunt, Bea Csatho, Kaitlin Harbeck, Thorsten Markus, Thomas Neumann, Matthew R. Siegfried, and H. Jay Zwally, Pervasive ice sheet mass loss reflects competing ocean and atmosphere processes. Science:eaaz5845, 2020.


Antarctic frogs!

The ice is melting in everywhere, including Antarctica.  We need to understand what is happening, so we are science-ing the hell out of polar regions, including Antarctica.

A side effect of all this work is that we are learning lots about the geological history of the area, and finding a lot of new fossils.

This spring, researchers report on the remains of a frog that lived in Antarctica some 40 million years ago [2].   Frogs don’t live anywhere near Antarctica these days, and this find is the first frog ever found on the continent.

“Our results demonstrate that eocene freshwater ecosystems in Antarctica provided habitats favourable for ectothermic vertebrates “ ([2], p. 1)

The main conclusion is that there must have been frog-friendly environments down Antarctica way at that time.  The frog and other fossils show that the Northern parts of Antarctica were pretty similar to Southern South America at the time.  Presumably, ancestors of these frogs lived in Pangea before Antarctica split off.

Similar ancient frog species are found in South America and Australia.  This new finding suggests that they may have spread through Antarctica when the continents were all connected.

  1. Lucas Joel, Fossil Shows Cold-Blooded Frogs Lived on Warm Antarctica, in New York Times. 2020: New York.
  2. Thomas Mörs, Marcelo Reguero, and Davit Vasilyan, First fossil frog from Antarctica: implications for Eocene high latitude climate conditions and Gondwanan cosmopolitanism of Australobatrachia. Scientific Reports, 10 (1):5051, 2020/04/23 2020.


Some great names for a band:

Antarctic Frogs
First Fossil Frog
Eocene High Latitude
Gondwanan Cosmopolitinism

A-68 is still going

We’ve been following the big A-68 iceberg, which has been wandering north from Antarctica since it broke off in 2017.   The main part of the berg, designated A-68A, is about 800 KM from its spawning point, having spent a lot of time sloshing back and forth in the currents. It now seems to be circling in an eddy [1].

Image credit: NASA Earth Observatory image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. (From [1])
This berg is actually holding together surprisingly well.  Many bergs break up much sooner.

But A-68A is in warmer water now, so it probably will break up in to a lot of pieces soon.

The article notes that B-15, the largest berg ever tracked by satellite, melted and disintegrated.  But 20 years after calving, one piece of B-15 is still large enough to be tracked.   So, pieces of A68 will probably be around for years.

  1. Kathryn Hansen, A-68A Holding it Together, in NASA Earth Observatory, April 22, 2020.


Tropic Antarctica in the Cretaceous

The dinosaurs flourished on a very warm Earth, with high levels of CO2 in the atmosphere, little, if any, ice, and sea levels more than 100m higher than present.  While the continents and oceans were different back then, the poles still had low angled sunlight, midnight sun in the summer, and a long, dark winter.

This spring, researchers report on a rare fossil find from Antarctica which records evidence of the plants around 80-90 millions years ago (the mid Cretaceous) [2].  The fossils show that there were abundant pines and ferns, as well as algae mats.  Together, the picture is a swampy rainforest.

Clearly, there wasn’t much ice even at the south pole at this time!

The researchers used this evidence to constrain models of paleo climate.  I.e., they explored what parameters have to be to support the inferred conditions in Antarctica at that time.  These studies are, of course, uncertain.  But these fossils do seem to point to very high levels of CO2 and low albedo (no ice) at the poles.

This paleoenvironment isn’t that different from a lot of Cretaceous areas.  However, this muggy rainforest was at 82 degrees south, and would have had long, dark winter months.  This is unlike any tropic forest we know of today, and must have been specially adapted to these conditions.  It also suggests that the air must have been very warm indeed, to stay warm enough for plants to survive a long Antarctic winter.

  1. Jonathan Amos, ‘Dinosaurs walked through Antarctic rainforests’, in BBC News – Science & Environment, April 1, 2020.
  2. Johann P. Klages, Ulrich Salzmann, Torsten Bickert, Claus-Dieter Hillenbrand, Karsten Gohl, Gerhard Kuhn, Steven M. Bohaty, Jürgen Titschack, Juliane Müller, Thomas Frederichs, Thorsten Bauersachs, Werner Ehrmann, Tina van de Flierdt, Patric Simões Pereira, Robert D. Larter, Gerrit Lohmann, Igor Niezgodzki, Gabriele Uenzelmann-Neben, Maximilian Zundel, Cornelia Spiegel, Chris Mark, David Chew, Jane E. Francis, Gernot Nehrke, Florian Schwarz, James A. Smith, Tim Freudenthal, Oliver Esper, Heiko Pälike, Thomas A. Ronge, Ricarda Dziadek, V. Afanasyeva, J. E. Arndt, B. Ebermann, C. Gebhardt, K. Hochmuth, K. Küssner, Y. Najman, F. Riefstahl, M. Scheinert, and The Science Team of Expedition PS104, Temperate rainforests near the South Pole during peak Cretaceous warmth. Nature, 580 (7801):81-86, 2020/04/01 2020.

On The Ice In Antarctica

Satellite remote sensing is really, really cool.  But it is very important to validate the results with additional measurements.  And the gold standard would be measurements from the actual area observed, AKA “ground truth”.

(Satellite instruments record photons and other physical phenomenon received from Earth.  These readings are interpreted through complicated computational models that essentially simulate how that photon or whatever got to the satellite.  This involves very complicated physics of energy, matter, and the dynamic Earth.  So a lot of effort goes into continuously checking the correctness of these models.)

The current fleet of satellites over Antarctica is measuring the continent, especially the ice.  These observations are documenting the status and changes of the continent, and how fast the ice is melting (pretty damn fast).  These are some of the most consequential scientific measurements ever made.

So, it is crucial that this satellite data is interpreted correctly.

This year NASA researchers have been collecting ground truth measurements in Antarctica [2].  (This team did similar ground truth measurements in Greenland.)  The project flew a helicopter with a very precise laser altimeter along the exact path of ICESat-2, measuring the height of the ice at the same time as the satellite pass.  I learn that this is known as an “underflight”. : – )

This sounds simple, but this is Antarctica, and the task is to fly along a path in the middle of a 300m swath, with weather, wind and other challenges.

Well done!

The same research group had to go out on the ice to rescue some of their instruments [1].  These instruments are collecting data on the movement and conditions of the sea ice—yet more ground truth to cross validate with satellite and aerial data.

The ice is moving, cracking and colliding.  Some of the instruments were in danger of being crushed, and lost forever.  So, researchers went out on the ice to dig out and relocate the instruments.  This was difficult  and  dangerous, and the instruments were offline during the move so this wasn’t optimal.  But they did preserve as many instruments as they could.

File under: “action nerds”

  1. Steven Fons, Instrument Rescue Operation, in NASA Earth Observatory – Notes from the Field, April 2, 2020.
  2. Steven Fons, MOSAiC Meets ICESat-2, in NASA Earth Observatory – Notes from the Field, April 7, 2020.

West Antarctic Ice Canyon Is Melting Fast

The ice is melting everywhere. The glaciers are disappearing,  Greenland will soon be melted, and Antarctica seems to be melting, too [2].

Antarctica is a large and complex continent, so the glaciers and ice caps are moving at different paces, some melting faster than others, and ice even accumulating in some places.

The places most likely to change rapidly are where ice meets the ocean.  In many places, warmer ocean waters (and, in this part of the world, “warm” is a degree or two above freezing) and changing currents are melting the ice from the bottom at the same time that warmer air and changed weather patterns are depositing less snow on the top.

This month researchers report on satellite measurements of the Denham Glacier in East Antarctica [3].  Using radar interferometry from 2017-1028, the research traced the grounding line of the glacier, and constructed a map of the sea bottom in the area.

The new grounding line is 5km inland from earlier measurements in 1996, suggesting a retreat at some 250m per year, though it probably has not been a steady linear retreat.

The study found evidence for a 3000 m trough under the glacier.  As warm sea water enters this area, the ice above will be melted and weakened.  This undersea canyon is likely to promote continued rapid retreat of the glacier.  Other measurements indicate that the glacier is thinning by 0.4 m/year, and moving toward the sea at more than 1km / year.   Altogether, this paints a picture of a glacier that may break up and decline rapidly, dumping ice and water into the ocean.

This finding is significant because this is a big glacier, holding a volume of ice equivalent to 1.5m of sea level.  If this area rapidly melts into the sea, it will add enough water to raise the average ocean up to your chest.  That’s a lot of ice, and it’s a catastrophically large rise in sea level.


And, by the way, West Antarctica is generally thought to be the stable, slow changing area, compared to East Antarctica.  So, look out about Antarctic generalizations.

  1. Jonathan Amos, Climate change: Earth’s deepest ice canyon vulnerable to melting, in BBC News – Science & Environment, March 23, 2020.
  2. Jonathan Amos, Greenland and Antarctica ice loss accelerating, in BBC News – Science & Environment, March 12, 2020.
  3. V. Brancato, E. Rignot, P. Milillo, M. Morlighem, J. Mouginot, L. An, B. Scheuchl, S. Jeong, P. Rizzoli, J. L. Bueso Bello, and P. Prats-Iraola, Grounding line retreat of Denman Glacier, East Antarctica, measured with COSMO-SkyMed radar interferometry data. Geophysical Research Letters, n/a (n/a):e2019GL086291, 2020/03/23 2020.


Measuring icebergs

The ice is melting everywhere, so there is really good reason to science the hell out of it.

One of the points of greatest interest is following the changes in the ice, which accumulates, melts, and flows down to the sea, where it breaks off into bergs that float out to sea.  This ever changing flow creates and destroys frozen ice, which conversely holds or releases liquid water into the oceans.  Depending on the total balance of this process, there could be large changes in the amount of water in the oceans, affecting average sea levels by many meters.  One of the factors to understand is how fast and where wandering icebergs deliver their meltwater.  I.e., where do they go and how fast do they melt.

This winter researchers at Northeastern University, Woods Hole, and other universities report on measuring the life of icebergs in the water [2].  As everyone knows, most of an iceberg is underwater where you can’t easily see it. They are also large, highly irregularly shaped, continuously melting—and moving unpredictably. (And, of course, floating ice is pretty similar to cold water, so it isn’t trivial to tell them apart with instruments.)

In short, it isn’t easy to measure the size and shape of an iceberg, let alone follow its evolution as it melts.

The basic idea is to measure the position and motion of the iceberg at the same time as measuring particular areas above and below the waterline.  Repeated measurements on all sides can then reconstruct the three-dimensional shape of the iceberg at that time.

The new technique combines data from sonar with images from a camera coupled to the sonar system (i.e., taking images from the point of view of the sonar instrument). The instrument is mounted on a remote operated robot kayak.

With a small ocean robot, Northeastern researchers produced high-resolution models of icebergs in Sermilik Fjord, Greenland. (Photo courtesy Hanumant Singh) From [1]
The sonar gives strips of measurements of the surface of the iceberg, the imagery is processed to reveal the “pose” of the object above the water,  i.e.the 3D position at the time of the measurement.  Repeating these measurements from all sides as the iceberg moves unpredictably yields a dataset of slices.

The researchers process these slices to reconstruct a detailed three dimensional mesh model of the iceberg.  The measurements require one circuit around the iceberg (in calm seas), so this is practical and relatively inexpensive.

The mathematics are actually pretty general, and could be used for other similar measurements, “[a]n apt example is that of mapping and motion estimation of asteroids and comets”. ([2], p. 471)

  1. Roberto Molar Candanosa, How to stop an iceberg in its tracks, in News@Northeastern, February 27, 2020.
  2. V. Shah, K. Schild, M. Lindeman, D. Duncan, D. Sutherland, C. Cenedese, F. Straneo, and H. Singh, Multi-Sensor Mapping for Low Contrast, Quasi-Dynamic, Large Objects. IEEE Robotics and Automation Letters, 5 (2):470-476, 2020.


Meanwhile Over at Pine Island…

It’s (literally) hot times in Antarctica.  Thwaites Glacier is calving, and next door Pine Island Glacier continues to retreat rapidly.

This winter NASA compiled a collection of satellite imagery from the last twenty years [1].   Basically, the glacier has been calving bergs faster than the ice is arriving from inland, with a result that the front is retreating.


So, this part of Antarctica seems to be pushing ice down to the ocean at a faster pace.

Now this is only a tiny amount of the total Antarctica icepack, and a short term trend isn’t necessarily going to continue for a long time.  On the other hand, this kind of  instability could signal wider changes that are harder to see.  We know that the oceans are warmer, and the icepack is changing in many parts of Antarctica, so these glaciers could be responding and contributing to overall melting. (See this, this, this, this)

There is good reason to science the bejesus out of this part of the world.  If nothing else, we may be able to witness our watery doom in more or less real time.

  1. Kathryn Hansen, Iceberg B-49 calved from the Antarctic glacier in February 2020, in NASA Earth Observatory, February 14, 2020.


Under the Antarctic Ice

The Thwaites Glacier in West Antarctica is changing rapidly.  If there is any doubt in your mind, NASA has a nice before and after pair of images, from 2001 and 2019 [3].  These images look like winter versus spring on a frozen pond.  But they are the same time of the year (summer), less than 20 years apart.  The glacier is breaking up over the water, and this is happening fast.

These changes could mean that the glacier will flow even more rapidly to the sea, moving more ice from the interior into the sea, where it will melt.  This is a big deal, if that happens.  So there is a major research campaign to measure the bejesus out of Thwaites.

One of the areas of interest is what is happening at the grounding line, where the glacier touches bedrock.  This is a major brake on the ice, halting or slowing the flow out onto the water.  There is evidence that the ocean water offshore is warming, and if that warmer water reaches the grounding line it could lubricate or otherwise change things, releasing the ice to rush on into the (warm) ocean.  Boom!

(The BBC tags this “the Doomsday Glacier” [4], which I think is a bit over the top.  But it’s certainly important.)

In addition to visiting, sensing, and drilling into the ice [4], the research mission included the first robot submarine visit to the actual grounding line [1]. <<link>>  This was a pretty heroic mission, drilling through 590 meters of ice, and remote operating the sub for 15 km round trips.  Wow!


The mission captured the first images of the important grounding line.  (The full results will be published soon I’m sure.)

This same team is contributing to the development of missions to explore under the ice on Europa (should we last that long.)

  1. Michelle Babcock, First look under Thwaites Glacier and Kamb Ice Stream, in Life Under the Ice – Blog, January 28, 2020.
  2. Ben Brumfield, Robotic Submarine Snaps First-Ever Images at Foundation of Notorious Antarctic Glacier, in Georgia Tech News, January 29, 2020.
  3. Kathryn Hansen, Thwaites Glacier Transformed, in NASA Earth Observatory, February 6, 2020.
  4. Justin Rowlatt, Antarctica melting: Climate change and the journey to the ‘doomsday glacier’, in BBC News – Science & Environment, January 28, 2020.


Robot Wednesday