Mechanical erosion of ice sheets

[Gray-Wolf]

Sorry to bang on about this but on the 30 day run of the sea ice melt (cryosphere today) from Antarctica then you can plainly see a flow off the Ross ice shelf (or under???) driving the ablation of the sea ice here. The colder, denser flow would tend to run lower in the ocean until the geography (an intercepting mid-oceanic ridge) forced it to rise. The cold water anoms. seem to have deepened off NZ this week also.

The above image (courtesy NASA) shows both topography and ice flow movements and you can work out for yourselves how any meltwater surges could end up in the position of the increased sea ice melt.

Edited January 8, 2007 by Gray-Wolf

[Gray-Wolf]

http://www.nsidc.org/data/iceshelves_images/ross_east.html Show the East Ross Ice shelf at the start of DEC. and if you Zoom in you'll see some VERY LARGE cracks developing on the ice shelf front (many tens of miles long over 7.5 degrees of Lat.)

'S'not a double post honest, just couldn't post the image yesterday!

To download a high def image just scroll down and select 'East ross modis images' and select 'show images' when you get to it.

Edited January 9, 2007 by Gray-Wolf

[parmenides3]

Looks interesting, G-W; why not contact someone at the BAS & find out if it's a matter of concern to them? If you can't I know someone I can get in touch with.

:)P

[AtlanticFlamethrower]

Gray-Wolf

The cold anomalies off new zealand may be explained as upwelling, such as here, from early Jan, two years ago. Exactly the same pattern, NZ sandwiched between purple anomalies - however this time to the south is a warm anomaly.

Compared to now

I suspect you are right about the cold anomalies being caused by summer melt ice water.

I wouldn't message BAS unless you have a specific question to ask them. They must know the SST situation and the theories of shelf collapse and there is nothing they can do about it even if you're right.

Edited January 10, 2007 by AtlanticFlamethrower

[Gray-Wolf]

Hi P3. As you'll no doubt be aware McMurdo is on the western side of this shelf and anything I'm suggesting would be happening right in front of their eyes ( any massive cold water outflow would be behind the 'channel' in the sea ice, right by their base) and seeing as we are not getting any rumblings of major changes/incidents then it is either not happening or not yet ready for public consumption.

The folk out there in NWeather land may not all fully understand my concerns about the rapid deglaciation of the West Antarctic Ice Sheet (WAIS) so I'll lay out what I believe we know. Most of the WAIS is many hundreds/thousands of feet below sea level (some isostatic depression, most landscape) and so it is possible to have this particular ice mass mass 'float' and be denuded by wind ,wave and temperature (as the blocks drift North) The only thing supposedly keeping things as they are is the Ross Ice shelf which effectively 'seals out' the ocean. If the Ross ice shelf goes (the much smaller Larson B took just 35 days to break off and dissappear) then the sea may get under WAIS and float it off. Current estimates vary over the sea level rise it would generate (16 to 50ft) but this is not the slow steady rises we are promised. The final phase may well be a 1 season event so the majority of the inundation would happen over our late winter /early spring (not a nice time to face such an event.....if there is a 'good time' that is).

Studies from both Greenland and Antartica are slowly unlocking some of the 'mysteries' of the ice sheets and most of their findings on the subject just seem to add more concerns to the issue. WAIS's lower levels may already be floating and it is thought that only a small inundation would 'destabilise' large areas of the sheet. From other ice shelf collapses we know what happens to the remaining ice field.

I will post The British Antarctic Survey with my concerns and I will post any reply here.

Hi A.F , Just seen your post. I will E-mail regarding the MODIS image as I'm intrigued to know if it has a history, I'm sure it'll get to someones inbox.

Edited January 10, 2007 by Gray-Wolf

[AtlanticFlamethrower]

I still think the majority of that cold pool is caused by upwelling. Did you notice how the warm upwelling to the east of it has grown at the same time?

[parmenides3]

G-W; this is the place you need to be looking, methinks: http://polar.ncep.noaa.gov/seaice/Ross.html The links provide explanation of the MMAB metric and archive data, too. If you want to know about the ice shelf situation, Bob Grumbine will almost certainly reply to an email enquiry: try him.

Let us know what you find out.

:)P

[Gray-Wolf]

G-W; this is the place you need to be looking, methinks: http://polar.ncep.noaa.gov/seaice/Ross.html The links provide explanation of the MMAB metric and archive data, too. If you want to know about the ice shelf situation, Bob Grumbine will almost certainly reply to an email enquiry: try him.

Let us know what you find out.

:)P

Cheers P3, will do!

[Gray-Wolf]

G-W; this is the place you need to be looking, methinks: http://polar.ncep.noaa.gov/seaice/Ross.html The links provide explanation of the MMAB metric and archive data, too. If you want to know about the ice shelf situation, Bob Grumbine will almost certainly reply to an email enquiry: try him.

Let us know what you find out.

:)P

Cheers P3, will do!

[Gray-Wolf]

Boy he was quick!

Ian wrote:

> Hi Mr Grumbine,

> I've been a keen observer of both the

> Actic and Antarctic melt seasons for a number of years now and have

> witnessed some of the major 'highlights' (?) of both sea ice retreat and

> ice shelf collapse since 1995.

>

> At the moment I am interested in finding out more about the potential

> for catastrophic collapse of the Ross ice shelf (and the destabilisation

> of the WAIS behind) and have noted some intersting 'cracks?' at the

> seaward edge of the east Ross Ice Shelf. Do you have any history for the

> large linear feature shown on this MODIS image from 6th Dec 2006?

> Thank you for your time,

>

> Ian Ballantine-Gray

I can't help you on the cracks; my work is on the sea ice rather than

the ice shelves. To my non-expert eye, the linear feature further left

of the ice island and intersecting the edge of the ice sheet looks

somewhat like the feature that eventually calved iceberg B-9 in the

1980s. But it'll take knowing the history of the feature and probably

some seismological study to know whether it's really a crack capable of

doing a major calving event. The one that eventually gave rise to B-9

was there for, if I remember rightly, decades.

The little I mention here are some incidentals of having been a

graduate student of Doug MacAyeal's back then --

http://geosci.uchicago.edu/people/faculty/macayeal.shtml

Doug is working on icebergs and ice shelf breakup, so is a knowledgeable

person to ask.

More focused on the remote sensing is the National Snow and Ice Data

Center http://nsidc.org/ Several good people are there.

Good luck, and thanks for the image,

Robert Grumbine

I of course will follow his advice!

Edited January 11, 2007 by Gray-Wolf

[Gray-Wolf]

Hi P3, probably a better place to reply than the other thread. 'Hunch' sounds so dismissive in my ears! :lol:

The B.A.S's site reassures us that the IPCC say "the likelihood of major sea level rise by 2100 due to a collapse of the West Arctic ice sheet is considered low" but it was last updated (according to the web page) 8 May 2000.

Since then B15 calved off the Ross Ice shelf and the Larson Ice shelf has collapsed. The glaciers held back by the Larson shelf have accelerated seaward at an alarming rate leading to B.A.S.'s Chris Rapley saying "Scientists used to view Antarctica as a slumbering giant but now he sees it as an awakening giant "

Since the 'reassurance' deep penetration radar has discovered 'deceleration folding' within the WAIS suggesting a much faster basal flow rate before the ice shelves once again restricted flow.

The 'old' reassurance was before NASA released to 'ice stream' images from the WAIS and so before a time we understood better the extensive nature of both the streams and there function.

The reassurance from B.A.S., via the IPCC is also before the release of the findings Mr D. R. MacAyeal (university of Chicago) regarding the rapid break up of Ice sheet/shelves and the mechanisms at play.

Mr Grumbine (of the NOAA , sea ice, Mcmurdo sound) also pointed me towards Mr MacAyeal and I consider that it is his 'findings' that translate pretty much into my 'hunch' and the mechanisms behind it.

Of course their isn't a peer reviewed paper out there at present declaring imminent Antarctic collapse but then their wasn't for the acceleration of the glaciers on the peninsula before the event was there?

So if B15a could be smashed by a storm swell generated 13,5000km away in the Arctic basin then what are these current storms doing to the ice up around Svalbard?, or for that matter in the southern oceans. Teleconnections between tropical and opposite hemisphere oceans with the southern oceans was obviously just not thought through as ,when revealed you think "of course it would...."

If a modest temperature rise can facilitate stormier oceans then the mechanical erosion of the ice shelves and large areas of ice sheets is assured in a 'Hienrich event' type timescale (if we can truely associate the rapid, synchrinous pulses of iceberg calvings on widely separated margins of the north atlantic ice sheets during Heinrich events to increased storminess driven by atmospheric climate change).

And in the "Will this winter change your opinion......." thread. Well in the light of what increased storminess can facilitate in a warming world, then maybe the winter will change a lot of folks opinions regarding climate change! :lol:

[parmenides3]

Morning, G-W: As far as 'hunch' is concerned; I was deliberately making a point that, in the absence of clear evidence to support our suspicions, all we have left to work on is our own sense of what 'feels' right. It isn't wrong to think this way, but it is important to be aware that one is thinking 'non-rationally'. Like you, I worry about the WAIS, but mainly becuase there really is, in scientific terms, so little hard data to work on. We are only just entering the era of detailed observation, in particular of ice-shelf dynamics, and every paper seems to bring new knowledge or awareness of the processes involved.

There have been papers recently on different aspects of the WAIS, in particular, a 2005 one which estimated the probability of a collapse formally. There is also good material on this in the Hadley Centre's 'Avoiding Dangerous Climate Change' brochure, produced last year, which reflects current understanding well.

On the speed of glaciers, there has been some good material produced this year, which indicates, for the Arctic examples, that flow rates are as much as double the previous estimates. But the speed of the glaciers only comes into play if (and only if) there is first a collapse of the Ross Ice Shelf. Since Larsen B, this has been monitored constantly, in particular during the Austral Summer (now). As conditions in the Antarctic haven't changed a great deal, yet, in terms of warming, and no other causal mechanism has been defined, the current feeling is that this is okay for the time being.

For the oceans to destabilise the Ross Shelf, they would have to be driven right into the bay by Northerlies, though you may be right, that undermining the shelf 'attachment' to the sea bed is a big issue; the idea being that the entire shelf could just 'come adrift'. This scenario is one of the least understood, though, and is very hard to test in practical terms.

Realclimate has new material on the Arctic, on http://www.realclimate.org/ and a good section on the cryosphere, including Benestad's 2006 paper on Greenland.

I don't think there's enough similarity between scenarios to postulate 'Heinrich-style' calvings, especially as these would have occurred inopen ocean, whereas the Ross shelf is an enclosed structure.

:)P

[Gray-Wolf]

I can't quite see how the Ross Ice shelf is enclosed, If you look at the above graphic you will note that the shelf is within a 'funnel' inlet compresing and deflecting storm swells (causing positive and negative interference of waves)

The more B15 type calving events that occur (remember the crack images?) the more pronounced the funneling becomes on the remaining shelf. The shelf is being attacked from inland as well putting great dynamic pressures on the rear of the sheet from the (accellerating) ice streams and so is more like a 'cork in a bottle' than Larson ice shelf ever was. It has been mooted that the final portion of Ross would be shoved into ocean water by the ice behind (the 'ruck /subsurface folding') within the WAIS can be viewed as 'tied up movement' in the way friction in fault planes can 'tie up' movement for many years. The potential energy of this ice 'spring' is immense.

Edited January 13, 2007 by Gray-Wolf

[parmenides3]

After a bit of digging, I found the slide show for Chris Rapley's speech on the WAIS, but not the accompanying text, on the BritainUsa site, British consulate, Denver, site; there's a straight link to it, but it is a large file.

More peculiarly, I was surprised to find this : http://www.wbgu.de/wbgu_sn2006_voll_en.html

Which is a very large (German-based) summary of CC. Chapter 3 contains some interesting thoughts on sea level & the WAIS. I say surprised, because it looks like a pretty decent summary, but I've seen no press or comment about it so far. It makes rather more dramatic reading than the stuff we are used to on UK or US sites. recommended.

:)P

[Gray-Wolf]

Well, Mr Mr D.R. MacAyeal got back to me;

Hi Ian,

Probably the best people to talk to about forecasting crack propagation are the people on the cc list. The honest answer is that we don't know that much about how or when cracks propagate (we've got an instrumented site out at the tip of the crack that's near the ice front in the upper left hand side of your image... that's a site we call "nascent iceberg"). Ian Joughin and Helen Fricker have done various image analyses on some of the cracks, not necessarily the one you're referring to (the "next" B15 crack--which is a perfect name). Ian has done InSAR analysis on the crack that led to the calving of C19.

My off the cuff view is that the cracks in the Ross Ice Shelf are not subject to a "catastrophic" collapse of the ice shelf at this present stage, as these cracks are "normal" and part of the system....

However, that's assuming the present climate regime and that the processes of crack propagation will remain in "slow mode" in spite of any potential for global warming effects, etc.

Your problem is interesting, keep me posted and stay in touch... say "Hello" to Bob Grumbine for me...

Doug

On Jan 13, 2007, at 12:55 PM, Ian wrote:

Hi Mr MacAyeal,

I was pointed in your direction by one of you ex-students (Robert Grumbine) as he feels my query is more in your sphere of expertise. I am trying to track down the history of some cracks/crevasses behind where the b15 berg calved in 2000.

The attached image shows the dec6 image from the MODIS overflight and clearly shows an extensive crack to the side of Roosevelt island heading off towards McMurdo. Could you possibly give this crack a history and forcast for me as I am increasingly concerned about the potential for rapid calving in the Ross Ice shelf region.

Thank you for your time,

Ian Ballantine-Gray

<rosse_2006340_1950_modis_ch02.png>

I suppose this means 1 of 2 things;

1/ There isn't a concern over the large crack (or he'd know more about it)

2/ It is as I suspected and show a new crevace forming (of immense proportions)

I shall now contact the other guys he mentioned and see what they have to say.

Maybe I should be the founding member of the "Horses mouth Society" (H.M.S. for short!)

[Gray-Wolf]

Double post!

Just spotted ITV's coverage this week on Antartica. May be of interest? They seem to angling at the scientist down there seeing something 'different' this melt.

[Gray-Wolf]

Well I'm interested!!!

Ted Scanbos has now got back to me with more links/reading

Hello Ian --

Have a look at this website:

http://www-nsidc.colorado.edu/data/iceshel.../ross_east.html

You'll see images here that go back to the early 1990's. The crack

you see in the recent image has been there for some time, since at

least the period of record for this site; it is not visible in the

USGS AVHRR mosaic of Antarctica image (for this area, the mosaic image

came from 1983), but as you'll see, the crack is sometimes visible and

sometimes invisible at this 'moderate-resolution' scale. Landsat images

from the late 1980-s appear to show that it formed sometime in 1988.

A sketch map of the Ross from 1971 shows no rift in the region. A

recent compilation of very early satellite photos from 1962-1963

(from Ken Jezek, Ohio State) shows two shorter rifts in the same area.

(clearly an earlier generation).

Three papers you could read:

Lazzarra et al., 1999, On the Recent Calving of Icebergs from the Ross..

Polar Geography, vol 23,no.3, p. 201-212. (Describes the year-2000

calvings, despite the journal date)

Joughin and MacAyeal, 2005, Calving of Large Tabular Icebergs from Ice

Shelf Rift Systems, Geophysical Res. Letters, vol. 32, L02501,

doi:10.1029/2004GL020978.

Jacobs et al., 1986. The recent advance of the Ross Ice Shelf, Antarctica

Journal of Glaciology vol 32. no 112, p. 464-474.

These describe the B-15 and associated calvings in detail, and develop

a model for how cracks propagate (slowly and steadily until an abrupt

final 'release' break).

The Ross seems stable. The recent spate of calvings merely returned the

ice front to a range in keeping with historical measurements from the

1950s and 1960s. Moreover, the characteristics of rapid calving and

retreat -- extensive summer melting, surface melt ponds, mean summer

air temperatures of ~-1.5 C, embayment calving past historical minimum

extents -- none of those features have appeared.

Thanks for prompting a nice review of the images and old files.

Ted

Again it would all seem to hinge on temps in the area increasing (only by 1 to 1.5c on this years temps) so we shall wait and see how increased sea temps affect the coastal strips.

I must say that none of the 'experts' thus far have seemed very confident in the 'status quo' being maintained.

Off to check out some images!

[parmenides3]

So am I; keep it going, G-W! Small point to anyone who wants to find out about stuff: every time I email someone 'important', I get a reply. Try it. Remember, 'experts' are people, too.

Have you found Rapley's presentation/ speech about the WAIS, yet?

:)P

[AtlanticFlamethrower]

Gray-Wolf, wonderful example how to use contacts to further research. Really interesting reading and well worth the effort. Thanks!

I thought this was particularly interesting though -

The Ross seems stable. The recent spate of calvings merely returned the

ice front to a range in keeping with historical measurements from the

1950s and 1960s. Moreover, the characteristics of rapid calving and

retreat -- extensive summer melting, surface melt ponds, mean summer

air temperatures of ~-1.5 C, embayment calving past historical minimum

extents -- none of those features have appeared.

[Gray-Wolf]

Gray-Wolf, wonderful example how to use contacts to further research. Really interesting reading and well worth the effort. Thanks!

I thought this was particularly interesting though -

But as Doug said "that's assuming the present climate regime and crack propagation mechanisms remain in 'slow mode' " and though temps in the region haven't broken 1c this summer I'm sure the sea has!

This is a sketch of how I think the mechanism works. To the East the bay closes in so it is only the western side that would fall foul to this type of breakup. The compression on the ice as it is forced around the island is released on the lee side and ,depending on how far the ice edge is, you can see how some force will be applied to the areas of the crevasses I point out.

Edited January 17, 2007 by Gray-Wolf

[The Penguin]

I don't get this GW. You say the situation down there is black. The expert says it's white. Then you say, "ah, but if it was darker it would be black". Well, yes it would, but The Man says it's not. So, until things actually change, whenever that might be, the situation is white and "stable". No?

[Gray-Wolf]

I don't get this GW. You say the situation down there is black. The expert says it's white. Then you say, "ah, but if it was darker it would be black". Well, yes it would, but The Man says it's not. So, until things actually change, whenever that might be, the situation is white and "stable". No?

If you feel that our environment is 'stable' then yes it is white. But that was on the proviso that 'if things stay the same'. My eyes and ears tell me something is different in our climate over the past 5 years (a step change in rate of change). Though singing the 'there ,there,' song they have also highlighted the delacacy of the balence in the Ross sea/shelf region and nobody is disputing the catastrophy of the coninent housing 90% of global freshwater going into meltdown either.

[parmenides3]

Just an aside: http://www.eurekalert.org/pub_releases/200...s-wai021406.php

:)P

[The Penguin]

GW, I know I’m a sad old pedant, and I fully respect your hard earned position as n-w expert on Antarctic ice shelves (no sarcasm intended), but “stable” was taken from your quote and was not my imposed interpretation.

3P, I know I’m a sad old cynic, but all I take from that piece is that Professor Rapley had applied for further funding; and a year later, has likely now secured it I would think.

[Gray-Wolf]

GW, I know I’m a sad old pedant, and I fully respect your hard earned position as n-w expert on Antarctic ice shelves (no sarcasm intended), but “stable” was taken from your quote and was not my imposed interpretation.

I know penguin, tis I who's the pedant!

It has only been the discussions on here that have peaked my interest in the Antarctic continent. It is yet another area where I feel 5 years will either allay or confirm fears about the processes down there and whether or not change is occurring that could affect us globally.

Because of the remoteness of the area remote sensing is a valuable tool to the people studying there. As such we can all become 'mini-experts' of a sort by helping monitor ice sheet/shelf changes over the melt season and amassing our own 'catalogue' of images that will enable us to track any change.

Until enough evidence is amassed to change our scientists current estimation of the state of the Antarctic continent as 'stable' then everyone must follow that line but we must be aware that the caveat always is that this state may alter if the climate there changes to a warmer one.

The fact of rapid deglaciation cannot be ignored as once it starts to occur then it will be just that, rapid, and so scrabbling to assess whether we have arrived close to this point is of importance and worthy of funding.