"Smart" and "Stupid" Questions About Antarctica - Feel Free To Ask

[Gray-Wolf]

With the startling drop in sea ice around Antarctica we might need a thread like this as more and more folk take an interest?

So , for starters;

Will the loss of the Larsen's impact the ice cover in Weddell over the years to come? I ask as I could see Ronne suffering if facing open water and swells from storms. I can see the Ross end of the channel ( that makes West Antarctica an Island at our Temp/GHG forcings?) opening up but found it harder to see similar happening in Weddell due to the perennial ice there?

[Tigertown]

If the Sea Ice around Antarctica reaches an early low or just ends with a very extreme low, will this throw the whole system further  off kilter and even affect the Arctic's 2017 melt season? In a more stable system, I would answer; Hardly! Now,though, I am not so sure.

[Tealight]

Will the loss of the Larsen's impact the ice cover in Weddell over the years to come? I ask as I could see Ronne suffering if facing open water and swells from storms. I can see the Ross end of the channel ( that makes West Antarctica an Island at our Temp/GHG forcings?) opening up but found it harder to see similar happening in Weddell due to the perennial ice there?

The Weddel Sea is still shelterd by the Antarctic Peninsula so I don't expect the loss of Larsen to have any significant impact.

For Pine Island glacier its a different story. Its is directly connected over channels to the Filchner-Ronne ice shelf. The bedrock is pretty much everywhere below -1000m. In a few hundred years the Antarctic Peninsula could become an actual island.

I just downloaded Bedmap2 for Antarctica and will try to analyze some interesting features.

Attached is Westantarctica as a bedrockmap and surface map. For Bedrock black means above sea level and bright pink below -1000m.

[Gray-Wolf]

Do full moon tides impact the ice shelfs more than normal tides?

[AbruptSLR]

In a few hundred years the Antarctic Peninsula could become an actual island.

While your timing might be correct, in Reply #23 of the following linked thread entitled: "Potential Collapse Scenario for the WAIS", I indicate that if we continue on our BAU pathway for a few more decades the Antarctic Peninsula could become an island sometime between 2090 and 2100:

http://forum.arctic-sea-ice.net/index.php/topic,31.0.html

[AbruptSLR]

Do full moon tides impact the ice shelfs more than normal tides?

Yes, ice shelves response directly with the magnitude of the tides, so a full moon tide cases more bending stress in the ice shelves than do normal tides.

[Gray-Wolf]

Thanks for that AbruptSLR!

I kinda figured it must ! With most shelfs now free of sea ice the coming 'Full moon wiggle' is probably and 'extra' that the majority of the last 30 years didn't get due to the attachment of the Sea ice to the shelf front?

[dingojoe]

So, what exactly is the baseline when determining extent and minimum of sea ice in Antarctica?  I assume ice shelves are not included when computing sea ice extent.  Unlike the Arctic, there is quite a bit of sea covered with ice shelves.  Looking at NASA's Worldview, they provide boundaries for the land and for ice shelves.  Sometimes the boundaries seem to have been updated (like for Larsen A and B), others seem to not quite match (not an ice shelf but the boundary for the PIIG is outdated).  Was the area covered by Larsen A and B not considered sea ice covered when they were ice shelves but now that the shelves have collapsed the area is counted?  If the large area of Larsen C were to break off but not immediately move out, does that instantly increase the area covered by sea ice? 

I know these examples are relatively small in the scheme of things, but they do add up.

[Tigertown]

The shelves are considered permanent and not counted in sea ice extent. Permanent is a word used a lot more loosely now days. I will leave the rest for others to comment on.

[dingojoe]

The shelves are considered permanent and not counted in sea ice extent. Permanent is a word used a lot more loosely now days. I will leave the rest for others to comment on.

So, just to clarify, prior to the breakup of Larsen B, that area was not considered part of sea ice extent, but this year the area that was formerly Larsen B and is currently covered by fast ice is considered part of the sea ice extent calculation.  Correct?

[Tigertown]

That fast ice and any other fast ice around Antarctica other than shelf ice would be sea ice. Shelf ice comes from glaciers pushing out past a grounding line into the ocean and are usually much taller than simple fast ice.

Ice shelf in background.

[Tealight]

The shelves are considered permanent and not counted in sea ice extent. Permanent is a word used a lot more loosely now days. I will leave the rest for others to comment on.

So, just to clarify, prior to the breakup of Larsen B, that area was not considered part of sea ice extent, but this year the area that was formerly Larsen B and is currently covered by fast ice is considered part of the sea ice extent calculation.  Correct?

The NSIDC uses land masks and coastal masks for their extent calculations. These prevent false sea ice detection from continents, islands, ice shelfs and coastlines. I'm pretty sure that they never change these masks to keep data consistent with previous years.

When you look at the latest Antarctica map Larsen A and B are still masked out.
http://nsidc.org/arcticseaicenews/files/1999/12/s_anom_hires.png

Nasa Worldview uses coastlines from different sources and they can update their data as they please.

[Tealight]

I found a strange ice area next to the Thwaites Glacier Tongue. It is a semi-permanent feature and looks different than the normal sea ice around it. In Sentinel1 images it darker than normal sea ice. Does anyone know why this ice is so different?

Link to Worldview: http://go.nasa.gov/2gIuO4R

[johnm33]

I'm no expert but when sentinel catches tidal surges they show up much whiter than normal, so maybe this is just thin new ice with a dusting of snow, thus a very smooth surface[?] and not very reflective.

[Tigertown]

It stayed attached to the fast ice(or tongue, not sure which) while everything broke up around it, for what that's worth.

EDIT: Last melt season some ice north of this location broke off as the season was ending and then came together at this location and froze together and attached to the ice there, and stayed.

[Tealight]

From the answers I assume that it is quite unknown and no one has named it yet. I believe it is caused by the Iceberg B22 (the big block to the right of my mentioned area), which calved off in 2002 and a large portion of it is still stuck there. The ocean depth varies between 800m and 300-250m  so the iceberg should disrupt or completly block ocean currents. My mentioned strange ice area  could be caused by this blockage. However is the different color and longevity solely a result of little ice movement or does the iceberg melt and create an area of (fresher)water ice?

Click on the image to start animation.

[CalamityCountdown]

In reporting on the loss on sea ice extent on a daily basis, is it meaningful to report the loss in terms of the reduction in percent of total extent loss?. Is a 300,000 km loss of SIE in a day more  startling when there is 10,000,000 km of Antarctic SIE versus when there is just 6,000,000 km (which could be the extent at some point even before this month ends)?

[Tigertown]

@Tealight        You probably were right about that being old tongue ice. I think it may have been there a long time and had old hard frozen snow on it, perhaps giving it the visual difference; maybe or maybe not.
Whatever the case, I think it's days are numbered now.
Also, thanks for spotting it when you did, as it has been interesting to watch.

[Paddy]

What data sources give updates on the size of the Antarctic ice cap itself, and changes therein?

[oren]

There was some good site mentioned on the forum recently which shows ice mass balance for Antarctica, even with a breakdown by region. I have it bookmarked at home, will post later if no one can recall.

[Tealight]

@Tealight        You probably were right about that being old tongue ice. I think it may have been there a long time and had old hard frozen snow on it, perhaps giving it the visual difference; maybe or maybe not.
Whatever the case, I think it's days are numbered now.
Also, thanks for spotting it when you did, as it has been interesting to watch.

I closely followed the area everyday. On radar it now looks more similar to sea ice ice. Maybe the snow has melted away and exposed the regular sea ice. It will be interesting to see it melt away completely.

[Red]

Concerning the Halloween Crack and other new found surprises is there any evidence that any of this could be related to lessening gravitational pull due to ice mass loss? The rate of thinning is increasing like mad everywhere it would seem. At some point would this not show up as a weakening of the pull at the periphery? If so, would it not cause some lowering of the MSL translating into slightly lower low tides giving added stress to points closer to the coastline? There has to be a critical threshold for the formation of stress cracks that could probably be measured in centimetres.

[oren]

Concerning the Halloween Crack and other new found surprises is there any evidence that any of this could be related to lessening gravitational pull due to ice mass loss? The rate of thinning is increasing like mad everywhere it would seem. At some point would this not show up as a weakening of the pull at the periphery? If so, would it not cause some lowering of the MSL translating into slightly lower low tides giving added stress to points closer to the coastline? There has to be a critical threshold for the formation of stress cracks that could probably be measured in centimetres.

The WAIS is at 2.2 million Gt, and the whole AIS is around 25 million Gt.
Mass loss is around 150 Gt/year, which I believe is still quite negligible at this point though I haven't done any math. But if anyone can find measurements of MSL around Antarctica showing a slight lowering this can resolve the question directly.

[CalamityCountdown]

I just did a Google search for "albedo sea ice". All the 1st page News articles were focused on the Arctic. Given that it looks like a new satellite era record low for Antarctic SIE will be set within the next few weeks, is there a good reason why so much less attention is being paid to the albedo effect in Antarctica? And the lack of attention gets even more pronounced with a Google search for "albedo effect antarctica". The first listing is a 2015 article that discusses the increase in SIE in the Antarctic

[magnamentis]

I just did a Google search for "albedo sea ice". All the 1st page News articles were focused on the Arctic. Given that it looks like a new satellite era record low for Antarctic SIE will be set within the next few weeks, is there a good reason why so much less attention is being paid to the albedo effect in Antarctica? And the lack of attention gets even more pronounced with a Google search for "albedo effect antarctica". The first listing is a 2015 article that discusses the increase in SIE in the Antarctic

i share your general opinion and after a short back and forth discussion after i posted a similar post like yours a few months ago things got a bit more active on the global and antarctic side.

nevertheless i have an idea, must not be correct, but at least an idea as to why this is so. i think the main reason is that the arctic, at least the surrounding land, has been populated for a long time, hence there is a history, more know how and probably people were doing science there even before the existence of the antarctic was even known.

since this is still the case, i mean that the arctic and it's periphery are well populated compared to the antarctic which is basically "not populated" except a few stations, the interest in and knowledge about the arctic is many times greater. perhaps someone else has a better idea/explanation, let's see :-)

EDIT: as to albedo, the impact depending on surface conditions (water, ice, rock etc. ) and latitude (sun angle) should be the same, at least mathematically, again there are pros around here and there is certainly more details to tell but as a general rule of thumb that should be similar like in the arctic. one thing that obviously differs is that the part which is ocean in the north is land in the south and the part which is often land in the north (periphery) is 99% ocean in the south.

[Red]

Concerning the Halloween Crack and other new found surprises is there any evidence that any of this could be related to lessening gravitational pull due to ice mass loss? The rate of thinning is increasing like mad everywhere it would seem. At some point would this not show up as a weakening of the pull at the periphery? If so, would it not cause some lowering of the MSL translating into slightly lower low tides giving added stress to points closer to the coastline? There has to be a critical threshold for the formation of stress cracks that could probably be measured in centimetres.

The WAIS is at 2.2 million Gt, and the whole AIS is around 25 million Gt.
Mass loss is around 150 Gt/year, which I believe is still quite negligible at this point though I haven't done any math. But if anyone can find measurements of MSL around Antarctica showing a slight lowering this can resolve the question directly.

Oren that math is way over my pay grade. I'm just curious if there is anything to that thought. The forces in play have a maximum that at some point will be weakened by mass loss. At a certain point it becomes " the straw that broke the camels back". 

[FredBear]

I just did a Google search for "albedo sea ice". All the 1st page News articles were focused on the Arctic.

Perhaps the albedo of sea ice is much less important in the southern hemisphere
The differences between North and South poles are:-
1. Apart from Greenland, the land areas in the north loses most of the snow cover, leading to low albedo each year. In the south the land keeps the snow cover each year so that has relatively high albedo.
2. The sea ice in the north used to protect the dark ocean below over vast areas but that albedo is being reduced. In the south, most of the sea ice normally melts out so the albedo effects are changing relatively little (up till now?).
3. Black carbon deposits are more prevalent in the north because of the surrounding land, and organic growth can come up from the underlying sea. (Darkening of the ice is particularly important for reducing albedo in the Greenland Ice Sheet.) In the south the snow cover is relatively pristine until it falls off the edge of the continent.
I have ignored the changes in albedo that occur as snow starts melting as these are also more significant in the north.

[Paddy]

Stupid, open-ended question here: do we expect sea ice extent around Antarctica to go back to something vaguely in line with the previous trend next year or to stay low following this year's drop?

[Darvince]

CFS, which is trash at predicting Arctic sea ice, does a decent job with Antarctic sea ice, and predicts an even lower maximum for 2017 with the Weddell polynya developing and lasting all winter.

[kassy]

Stephan's analysis now shows it is just about certain that the maximum was reached on the 30th August at 18.72 million km2. This day's data adds to that likelihood. This maximum is 10 days earlier than the earliest date this century and 3 weeks earlier than the average date of the last 10 years.

So lots of extent this year but an early end. This does fit in with the freshening surface waters near Antarctica elevating extent while the early end is caused by ongoing AGW?

[gerontocrat]

Stephan's analysis now shows it is just about certain that the maximum was reached on the 30th August at 18.72 million km2. This day's data adds to that likelihood. This maximum is 10 days earlier than the earliest date this century and 3 weeks earlier than the average date of the last 10 years.

So lots of extent this year but an early end. This does fit in with the freshening surface waters near Antarctica elevating extent while the early end is caused by ongoing AGW?

There is a poleward shift in warmer surface waters while farther south it is more about deeper waters warming and attcking ice shelves and marine-terminating glaciers from underneath.

This year may be a demonstration of the consequences, especially if we see correspondingly high Antarctic mass loss from GRACE-FO data. But one year in this very variable year by year data is no proof,

https://www.science.org/doi/10.1126/sciadv.abf8755
INTRODUCTION
In recent decades, the Southern Ocean has undergone widespread but spatially heterogeneous warming. In the northern part of the Antarctic Circumpolar Current (ACC; 45° to 55°S), the temperature of the upper 1000 m has increased rapidly (0.1° to 0.2°C per decade), partly due to enhanced surface heat uptake (1). In contrast, multidecadal warming in the southern part of the ACC (55° to 65°S, subpolar zone) is confined to a deeper layer (below 200 m) and is relatively gradual (~0.1°C per decade) (1–5). Upwelling of subsurface cold water (<0°C), reinforced by intensified westerlies, has cooled the subpolar ocean surface (6). Deep warm salty water (below 200 m, temperature > 0°C, salinity > 34.85 g kg−1), known as Circumpolar Deep Water (CDW), compensates volumetrically for the near-surface divergence, and subsequent enhancement of poleward CDW upwelling may lead to warming below 200 m. CDW primarily supplies heat to the Antarctic continental shelves. Thus, multidecadal warming of the subpolar CDW layer has enormous implications for Antarctic ice shelves (7), global overturning circulation (, and marine ecosystems (9).

[kassy]

NSIDC ANTARCTIC SEA ICE AREA  (5 day trailing average):  13,454,120 KM2 as at 08-Oct-2021


The projection above should be taken as an additional indicator of the oddness of this years melt season to date (rather than as an expectation of the minimum), to which can be added that Antarctic sea ice area has been lowest in the satellite record for the last 3 days after being at 2nd highest at the end of August.

I am going to claim the progression outlined above as a hint (not proof, for that we should see it in the next years).

[Mr. Ä]

Once Antartic ice sheet melts a bit and isostatic rebound really starts will the volcanos there become highly active? Or just a bit more active? Or less active?

[gerontocrat]

Once Antartic ice sheet melts a bit and isostatic rebound really starts will the volcanos there become highly active? Or just a bit more active? Or less active?

Have a read of this from AbruptSLR

https://forum.arctic-sea-ice.net/index.php/topic,1053.msg130380.html#msg130380

[AbruptSLR]

Once Antartic ice sheet melts a bit and isostatic rebound really starts will the volcanos there become highly active? Or just a bit more active? Or less active?

Many of the posts in the Antarctic Tectonics thread (see link below) discuss this question further.

https://forum.arctic-sea-ice.net/index.php/topic,393.100.html

[FredBear]

I have been noticing a dark mark in Worldview images to the north (left) of the Pine Island Glacier with a slight grey streak "blowing" westward (down) across the ice. The feature is near the top left of the first image and I wondered if it has volcanic activity? (It is a persistent feature for many years in Worldview images so I could not post in "What's new in Antarctica?"!). The snow to the west also has slightly more of a blue tint (indicating more melting this year).
I also include a link to a map, the feature would be about the position of the smudge above the "H" of HUDSON MOUNTAINS (above WALGREEN) at the top of the map.

https://data.pgc.umn.edu/maps/antarctica/pgc/17/preview/Map%2011%20Amundsen%20Sea%20Ed%204.jpg

[Carex]

Anywhere in the Forum, or referenced in non-paywalled articles, is there a discussion of the breakup of Ninnis Ice Tongue and the smaller shelves and tongues east toward the Cook Ice Shelf?  (always good to keep the questions thread on the 1st page).

[SteveMDFP]

Anywhere in the Forum, or referenced in non-paywalled articles, is there a discussion of the breakup of Ninnis Ice Tongue and the smaller shelves and tongues east toward the Cook Ice Shelf?  (always good to keep the questions thread on the 1st page).

See, for example,
https://forum.arctic-sea-ice.net/index.php/topic,3218.msg277437.html#msg277437

Finding related posts is a non-trivial task. The forum's built-in search is highly unsatisfactory.  Google search works much better, but you have to know how to limit to a particular site.  I found the above with a Google Search string of:

Ninnis site:forum.arctic-sea-ice.net

You can use this example to search for anything on the forum.  Just substitute your choice of words in place of "Ninnis" above.

As for literature beyond this forum, Google Scholar is excellent.  Just go to scholar.google.com and enter your words of interest.

[Tor Bejnar]

What happens to pixel counting after an ice shelf breaks up? 

The mask showing the "edge" of Antarctica needs to be changed.  This only happens once in a while (years?), certainly not every month (to account for shelf growth or breakup around the continent).

The area of, for example, the Land Glacier tongue, that was "permanent landfast ice" is now "floating icebergs" with little open water, so, I presume, is "greater than 15% ice covered sea".  When/if the area where there was ice shelf becomes open water, how is this counted?  Maybe: still part of the mask, so not counted at all? 

Does this matter at all since the area of most ice shelf breakages is too tiny to make a dent in the overall picture?

[paolo]

Tor Bejnar,
1) The mask has not been updated for several years (just look at the PIG mask)
2) A simple mélange of icebergs and fast ice is not taken into account in the mask (besides, the mask is often useful to differentiate a real calving from a release of icebergs that had already calved)

[gerontocrat]

My understanding is
- Fast ice is sea ice (i.e frozen seawater) and is included in the mask for sea ice extent and area data
- ice shelves are freshwater, i.e. orginating from snowfall, and are excluded from the mask for sea ice extent and area data

So when fast ice melts and becomes openwater then no problem - the data changes.

But when the shelves break up the area that was permanent shelf ice is replaced by seasonal sea ice growth and loss. If the mask does not change this will not be picked up in the data. But if the mask is changed  then this messes up comparisons with previous years. Maybe this does matter for the Arctic that has lost most of its shelves during the 44 years of the satellite record.

I am going to ask NSIDC for enlightenment.

[paolo]

Gerontocrat,
I don't know if the mask displayed by Polar View in the S1 images is the same as the one used for the sea ice extent/area calculations

[oren]

I believe calved icebergs that drift beyond the masked shelf area are counted as sea ice. OTOH their total area is relatively tiny.

[FredBear]

Tor Bejnar,
1) The mask has not been updated for several years (just look at the PIG mask)
2) A simple mélange of icebergs and fast ice is not taken into account in the mask (besides, the mask is often useful to differentiate a real calving from a release of icebergs that had already calved)

I take 2010 as the approximate date for the coastal/ice shelf masks - if you run back through the years on any day in Worldview it is usually quite close.
Individual areas may be difficult to get an exact fit - e.g. the Land Glacier for example. In 2010 this was surrounded by fast ice with the main marked glacier tongue basically filling the mask. Until recently there was a spray of icebergs reinforcing the fast ice outside the mask but now the whole lot seems to be breaking away (& even taking part of the glacier tongue).
The areas of Larsens A & B exclude the old ice shelves which shattered (prior to 2010) whereas the Larsen C mask extends over the area vacated by A68 (c.2018).
The Thwaites Glacier Ice Tongue illustrates the problem of choosing boundaries - originally (circa 2000) it extended a long way outside the marked area, then B22 formed and has been slowly drifting away. In the meantime the tongue (consisting of an accumulation of blocks of ice) has continued alternately to break away and reform to different extents    .   .    .

[paolo]

FreadBear,
Beware, there are several masks that have been created!
Tor Bejnar was referring to the mask used by PolarView and not the one used by Worldview.
PolarView's is much more recent than Worldview's, just look at the PIG.

[gerontocrat]

Gerontocrat,
I don't know if the mask displayed by Polar View in the S1 images is the same as the one used for the sea ice extent/area calculations

My interest is in the NSIDC (and JAXA) masks as they are the ones that define the most commonly used historical record of sea ice extent and area.

The multiplicity of masks used obviously makes difficulties in comparisons between data produced by different products.

[paolo]

I looked through the masks I had available and found that the WorldView mask seems to match the MEaSURE mask and the PolarView mask seems to match the SCAR Antarctic Digital Database (ADD) Version 7.0 mask.
See the attached image relating to the PIG, I have also added the two latest versions of the latter mask (as you can see they are quite recent).

Click to enlarge

[Phil.]

Just a simple question: what is the difference between the blue and beige areas on the images in the animations shown of the glaciers? 

[paolo]

The blue is precisely the mask visualizing the historical coastline (the front line: land/glacier/ice shelf)

[gerontocrat]

Below is what the people at NSIDC have to say about masks and ice shelves breaking up.
It seems the scientists themselves discuss about whether to change or not change masks as shelves break up.

Thank you for your patience. Here is the response I received:

"It’s actually a really good question and something we’ve been thinking about.

Currently, the sea ice products use a static land mask - i.e., it is the same land always in all fields over the full time series. The land mask includes land and ice shelves because ice shelves are ice that originate on land, not sea ice. So it is intended to remove all areas where sea ice is not possible.

The issue, as the user notes, is that the ice shelves change - they can expand outward or they can retreat, e.g., through calving of ice bergs. Of particular note was the Larsen-B ice shelf, which broke up in 2002. Generally, when an ice shelf breaks up or calves off, that area will be replaced by sea ice, at least during winter.

So, if one is interested in detecting sea ice wherever and whenever it may occur, then one wants a “land” mask that is as accurate and up-to-date as possible. However, if one wants a consistent time series of sea ice conditions over time, then a consistent land mask is needed and you don’t want to map specific changes in ice shelves. For example, when the Larsen-B ice shelf broke up, the resulting embayment froze over with sea ice. So before the break-up there was no sea ice there because it couldn’t occur there because the ice shelf was there. But after the ice shelf break-up, there is “new” area for sea ice. So you end up with kind of an artificial jump in sea ice, not due to changing climate conditions, but due to a new area where sea ice was not previous possible.

It actually can become counter-intuitive in a way. You have the Larsen-B ice shelf. Warming causes that that to break-up. Then sea ice forms, which adds to the total sea ice, so you have an increase in sea due to warming!

This has been discussed among scientists. One avenue is to provide two land masks: (1) a changing land mask, e.g., that is updated regularly (maybe every year) to reflect the changing ice shelves and allow people to track sea ice wherever it may occur at a given time, and (2) a “climate” land mask that does not change and is “conservative” - i.e., anywhere that was land or ice shelf at any time during the period of record (e.g., since 1979) is masked as “land”; this prevents any “artificial” increase (or decrease) in sea ice due to changes in ice shelves.

A couple notes:

This is mainly an issue for the Antarctic. There are some small ice shelves in the Arctic and some have broken up. But they are a very small area compared to the overall Arctic sea ice area, even during summer. So they don’t really affect the totals - they are in the “noise”.

Overall, the Antarctic ice shelves are bigger and the changes are bigger, but still relatively small overall. For example, the Larsen-B break-up was ~3250 sq km. So, compared to the minimum sea ice extent of ~2,000,000 sq km, it is at most 0.16%. The biggest iceberg calvings on the order of 5000 sq km, which is 0.25% of the minimum extent. Of course, there have been various break-ups and calvings, so the small numbers can add up. But then the ice shelves also advance, especially after a calving even, so the ice shelf will “fill in” over time. So in the large-scale time series, it is not a major issue, but I think something that could be improved.

After an ice berg calves, it will drift amid the sea ice for a period of time - for the big Antarctic icebergs, it can be years. Those ice bergs are not masked out, so they are detected as sea ice. During winter, this is a minor detail because sea ice would fill in where the berg was anyway. During summer, the iceberg will remain in areas where sea ice melts away, so you can get “artificial” sea ice - icebergs posing as sea ice - that increase the extent. But again, these are quite small compared to the overall extent."

Please let me know if you have any additional questions.