A new paper has been published which examines the factors involved in the 2002 collapse of the Larsen B ice shelf in Antarctica.
The lead author, Professor Neil Glasser of Aberystwyth University (Wales, UK) was interviewed about the findings in the Western Mail on 7th February:
‘Antarctic ice shelf did not just melt away’
Excerpt: Prof Glasser told the Western Mail, “Climate change may have been the last straw, but it was not the only straw.”
“Ice shelf collapse is not as simple as we first thought,” said Prof Glasser, lead author of the paper.”
“Because large amounts of meltwater appeared on the ice shelf just before it collapsed, we had always assumed that air temperature increases were to blame.”
“But our new study shows that ice-shelf break-up is not controlled simply by climate. A number of other atmospheric, oceanic and glaciological factors are involved.”
“The location and spacing of fractures on the ice shelf such as crevasses and rifts are very important too, because they determine how strong or weak the ice shelf is.”
Prof Glasser pointed out that he is not a climate change sceptic.
The full paper entitled, ‘A structural glaciological analysis of the 2002 Larsen B ice shelf collapse’ is currently available for free download from the Journal of Glaciology.
The Abstract reads:
This study provides a detailed structural glaciological analysis of changes in surface structures on the Larsen B ice shelf on the Antarctic Peninsula prior to its collapse in February–March 2002. Mapped features include the ice-shelf front, rifts, crevasses, longitudinal linear surface structures and meltwater features. We define domains on the ice shelf related to glacier source areas and demonstrate that, prior to collapse, the central Larsen B ice shelf consisted of four sutured flow units fed by Crane, Jorum, Punchbowl and Hektoria/Green/Evans glaciers. Between these flow units were ‘suture zones’ of thinner ice where the feeder glaciers merged. Prior to collapse, large open-rift systems were present offshore of Foyn Point and Cape Disappointment. These rifts became more pronounced in the years preceding break-up, and ice blocks in the rifts rotated because of the strong lateral shear in this zone. Velocity mapping of the suture zones indicates that the major rifts were not present more than about 20 years ago. We suggest that the ice shelf was preconditioned to collapse by partial rupturing of the sutures between flow units. This, we believe, was the result of ice-shelf front retreat during 1998–2000, reducing the lateral resistive stress on the upstream parts of the shelf and glacier flow units, ice-shelf thinning and pre-shelf-break-up glacier acceleration.
While we are on the subject of the Larsen B (and A) ice shelf, I am reminded of a paper from 2006, published in QUATERNARY SCIENCE REVIEWS, entitled: ‘Ice shelf history from petrographic and foraminiferal evidence, Northeast Antarctic Peninsula’
This paper suggests that there was “widespread ice shelf breakup in the mid-Holocene.” This finding is harmonious with the earlier finding of Pudsey and Evans (2001) that the adjacent Prince Gustav Channel ice shelf also retreated in mid-Holocene time, but that subsequent colder conditions, in their words, “allowed the ice shelf to reform.” It is also in harmony with the finding of Vaughan et al. (2001) that from 6000 to 1900 years ago the Prince Gustav Channel ice shelf, as they describe it, “was absent and climate was as warm as it has been recently.” Consequently, and most recently, Pudsey et al. concluded that “the maximum ice shelf limit may date only from the Little Ice Age,” which they report is “widely recognized” to have held sway in that part of the world between 700 and 150 years ago.
A large body of data makes it pretty clear that the greatest extent of the Larsen ice shelf during the current interglacial likely occurred only a few hundred years ago, and that the portions of it that recently disintegrated (Larsen-A and Larsen-B) were probably created about that same time. In addition, it would appear that some 2000 years ago the Larsen-A and B ice shelves likely were altogether absent, and that temperatures of that time were likely as warm as, or even warmer than, they have been recently. Furthermore, there was approximately 100 ppm less CO2 in the air of that time than there is in the air of today; and this fact suggests that something other than anthropogenic CO2 emissions was the cause of the earlier “balmy” conditions of northeast Antarctica, which implies that that same something else, or something different yet, could well be responsible for the current warmth of the region.
(CO2Science.org, December 2006)
The Abstract reads:
A detailed record of late Pleistocene deglaciation followed by mid-Holocene ice shelf breakup and late Holocene re-growth is contained in continental shelf sediments in the northern Larsen area, northeast Antarctic Peninsula. The zero age of core tops is confirmed by new and published 210Pb profiles, and 70 accelerator mass spectrometer (AMS) 14C dates on bulk organic carbon define sedimentation rates of 7.6–92 cm/ka. The varied geology in the local ice drainage basins facilitates the use of ice-rafted debris (IRD) provenance in determining the presence or absence of ice shelves. All inshore cores contain an interval of non-local IRD in the post-glacial section, demonstrating widespread ice shelf breakup in the mid-Holocene. Both breakup and re-growth may have taken centuries and there are no widespread debris layers associated with breakup. Cores beyond and up to 30 km inside the historical ice shelf limit exhibit a varied IRD provenance throughout the Holocene, suggesting the maximum ice shelf limit may date only from the Little Ice Age. Benthic foraminiferal assemblages are related to water masses and position on the continental shelf and have been modified by taphonomic processes. Nevertheless we discern a deglaciation signal in Prince Gustav Channel of a calcareous spike in predominantly agglutinated assemblages, and this is repeated at the time of mid-Holocene ice shelf breakup. The inferred mid-Holocene warm period occurred later in the northern Larsen area than on the west coast of the Antarctic Peninsula.
The above papers suggest that the collapse of the Larsen B ice shelf in 2002 wasn’t simple or unprecedented.
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
And indeed Paul you should have also reminded us of Robin Bell’s interesting article in Feb 2008 Scientific American on ice sheet “unequilibria”. Dr Bell being the chair of the Polar Research Board of the National Academies.
Our ice sheets – not so steady, not so frozen, on slippery slopes and some even lose their buttress. Sub-glacial and ice sheet plumbing is pretty interesting stuff and as mentioned prior ice sheet disintegration or collapse is more a concern than direct melting – direct melting being almost a ruse argument for denialists.
But that extra bit of meltwater sloshing down those moulins can be a big factor is helping those sheets slide.
http://www.sciam.com/article.cfm?id=the-unquiet-ice
As I believe neither I nor science understand what is going on, I have been reading for months perhaps years. A site at last has informed me of the basics, it is also in english, which helps comprehension.
So much info led me to give up, and then along came this.
http://nsidc.org/seaice/characteristics/difference.html
fluff
Luke, you say “But that extra bit of meltwater sloshing down those moulins can be a big factor is helping those sheets slide.”
Does that lubrication via meltwater apply to sheets that are already projecting out to sea?
Sliding ice sheets can be held by floating ice shelves – warmer sea temperatures can affect buttress stability Dr Robin Bell reports. If the floating buttress shelf is unstable it won’t hold back the sheets as much.
I commend the Sci Am review (link above) to you. From what I have read the notion of Antarctica melting away is not what is likely to happen. Disintegration and instability are the mechanisms. But clearly there is a lot we don’t understand and decadal influences to consider.
Increasing snowfall can also compound the problem of additional weight.
Recent science has also found all manner of sub-glacial lakes and interesting plumbing phenomena. Sometimes they burst to the surface – sometimes they link up.
Hydraulics under ice sheets seems more like engineering than “climate” science.
Hey; we will probably be discussing melt water “pulses” and that pesky MWP in relation to late Holocene sea levels after all.
The BBC actually reported this one:
Experts challenge ice shelf claim
http://news.bbc.co.uk/1/hi/wales/mid/7231372.stm
“It’s likely that melting from higher ocean temperatures, or even a gradual decline in the ice mass of the peninsula over the centuries, was pushing the Larsen to the brink”
Paul: Isn’t that a case for global warming?
These boffins don’t say much about their alternative ice engineering
Gavin,
“over the centuries”
Where did all the CO2 come from centuries ago, then?
JW: “over the centuries”
When was it we discovered fire?
Johnathan – this blog has been talking up a warmer MWP and other “natural” warming periods for some time. So simply shows warmer conditions can destabilise the ice sheets. Basic? Doesn’t have to be CO2. Exclusivity is not a good strategy.
when will all you Reality Deniers end your pointless posts and get back to studying “SCIENCE”? You all have a lot to learn!
Cheers….theoldhogger
Like what Hoggsy? Are you an oracle?
It’s global warming. All over the globe, it’s going to be one more factor in all the events that it influences. It might only be a bit here and there, but when you consider it is going to be happening everywhere on the planet, that all adds up to something collectively very significant.
Still not a word on “Medieval” to “Little Ice Age” sea level change ???
Could be the Seal Nunataks (volcanoes) in the ice field…just a small overlooked detail. But the British Antarctic Survey found somethign interesting.
http://wattsupwiththat.wordpress.com/2008/01/22/surprise-theres-an-active-volcano-under-antarctic-ice/
Keep watching that blog as I have more on Anarctic volcanoes coming. There’s another surprise related to the Ross ice shelf.
Very interesting Anthony but you need much more than the satellite surface temperature trend map. You need to have demonstrated significant volcanic activity – e.g. the new volcano mound found in the Antarctic Sound hardly registered when a thermal probe was dragged over it. Nevertheless your comments are very interesting developments.
Luke: It’s definitely all that extra snow falling in the middle thats creating the ground pressure.
Luke,
“shows warmer conditions can destabilise ‘sic’ the ice sheets. Doesn’t have to be CO2. Exclusivity is not a good strategy.”
Glad we agree, will you remember that, next time CO2 and AGW comes up?
Ender,
Now the cooking fires are the cause of AGW?
I think fires were around a lot longer than humans, we may use it but hardly discovered it?
“I think fires were around a lot longer than humans, we may use it but hardly discovered it”
Ahh johnathan but we took it inside overnight then kept it going virtually for ever as some would have it.
Luke, yes it is interesting.
The burden of proof is not mine, nor could it be since I’m not an antarctic surveyor. I’ll leave that to additional investigations by the British Antarctic Survey and others that are on site.
My job is as reporter and blogger.
There has been some mention that the Seal Nunataks may have produced some subsea hot mud flow, much like the one recently uncorked in Indonesia. I don’t think such eruptions are particularly loud, much like undersea hot vents near plate boundaries…they just keep flowing and flowing.
If you’ll have a look at this map, you’ll see that the Larsen ice shelf is on an extension of the Pacific ring of fire, that traces down through South America and the Andes.
http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/Maps/map_plate_tectonics_world.html
Given such placement, it is reasonable to expect active volcanism. Curiously, there is no mention of volcanism in the Wikipedia entry describing the Antarctic peninsula.
http://en.wikipedia.org/wiki/Antarctic_Peninsula
There are volcanoes next to the Larsen ice shelves A&B (16 of them) and volcanoes directly in the middle of the Ross ice shelf, Mt. Erebus, active, and Mt. Terror (said to be extinct).
Yet this is never mentioned by press reports. What is mentioned is that AGW driven global warming is likely the cause of ice shelf collapse.
When you have ice fields and volcanoes together, its seems like a perfect Occam’s Razor scenario to me.
Anthony I didn’t mean that literally you have to prove it. I’m simply saying it’s plausible but unproven. I encourage you to keep digging though. (“Does volcanism cause El Nino?” is the other one that comes up here on Jen’s from time to time).
Antarctica is way under-reported in general with major changes in southern hemisphere circulation possibly related to SAM also occurring in recent times. A possible mechanism for persistence of Australian drought in non-El Nino (SOI neutral) years.
The overall pattern of Antarctic temperature changes is consistent with global atmospheric circulation changes in the latter part of the twentieth century. Specifically, the atmospheric pattern known as the Southern Annular Mode (SAM) has strengthened in recent decades. This has been associated with the strong warming in the Peninsula and the tendency to cooling elsewhere across the continent. Thompson and Solomon (2002) linked this strengthened SAM with stratospheric ozone loss.
http://www.sciencemag.org/cgi/content/abstract/296/5569/895
with a major SAM workshop just last year http://web.archive.org/web/20070219035455/http://www.amos.org.au/conf2007/AMOS07_ABSTRACTS.pdf starts at page 147
There’s also a very signficant warming of the winter mid-troposphere over Antarctica.
http://scienceblogs.com/stoat/2006/03/science_significant_warming_of.php RC also blogged cautiously on this.
Perhaps Occam has a few razors. Nothing wrong with a few things going on at once?
Macquarie Island also showing a warming trend. Slide 28 here.
http://www.bom.gov.au/bmrc/clfor/cfstaff/nnn/RMSconf.ppt
and
data.aad.gov.au/aadc/soe/display_indicator.cfm?soe_id=2
and also from
http://www.environment.gov.au/soe/2006/publications/commentaries/antarctic/climate.html
Brown Glacier changes, Heard Island:-
All glaciers on Heard Island have retreated in extent since 1947. The total land area covered by glaciers has decreased from 288 km² in 1947 to 253 km² in 2000, that is, by 12 per cent (Ruddell 2006). The retreating ice has exposed 35 km² of new terrain, including several large lagoons, representing nearly 10 per cent of the total area of the island.
Brown Glacier showed surface elevation decreases of 5.9 to 11.7 metres between 2000 and 2003 (Thost and Truffer submitted). The glacier has decreased in area by about 35 per cent and thinned by 30.3 m, or around 0.5 m per year, in the period 1947–2004 (Thost and Truffer submitted). Ice loss in this period was more than twice the 1947–2004 average.
Changes in Heard Island glaciers correlate with underlying climate change in the southern Indian Ocean—temperature observations in the area show a warming of 0.9 °C over the same period (Thost and Allison 2005).
(And of course our local Green-Camouflaged Brown Davey Gam knew about the volcanism all along).
Anthony I didn’t mean that literally you have to prove it. I’m simply saying it’s plausible but unproven. I encourage you to keep digging though. (“Does volcanism cause El Nino?” is the other one that comes up here on Jen’s from time to time).
Antarctica is way under-reported in general with major changes in southern hemisphere circulation possibly related to SAM also occurring in recent times. A possible mechanism for persistence of Australian drought in non-El Nino (SOI neutral) years.
The overall pattern of Antarctic temperature changes is consistent with global atmospheric circulation changes in the latter part of the twentieth century. Specifically, the atmospheric pattern known as the Southern Annular Mode (SAM) has strengthened in recent decades. This has been associated with the strong warming in the Peninsula and the tendency to cooling elsewhere across the continent. Thompson and Solomon (2002) linked this strengthened SAM with stratospheric ozone loss.
http://www.sciencemag.org/cgi/content/abstract/296/5569/895
with a major SAM workshop just last year http://web.archive.org/web/20070219035455/http://www.amos.org.au/conf2007/AMOS07_ABSTRACTS.pdf starts at page 147
There’s also a very signficant warming of the winter mid-troposphere over Antarctica.
http://scienceblogs.com/stoat/2006/03/science_significant_warming_of.php RC also blogged cautiously on this.
Perhaps Occam has a few razors. Nothing wrong with a few things going on at once?
Macquarie Island also showing a warming trend. Slide 28 here.
http://www.bom.gov.au/bmrc/clfor/cfstaff/nnn/RMSconf.ppt
and
data.aad.gov.au/aadc/soe/display_indicator.cfm?soe_id=2
and also from
http://www.environment.gov.au/soe/2006/publications/commentaries/antarctic/climate.html
Brown Glacier changes, Heard Island:-
All glaciers on Heard Island have retreated in extent since 1947. The total land area covered by glaciers has decreased from 288 km² in 1947 to 253 km² in 2000, that is, by 12 per cent (Ruddell 2006). The retreating ice has exposed 35 km² of new terrain, including several large lagoons, representing nearly 10 per cent of the total area of the island.
Brown Glacier showed surface elevation decreases of 5.9 to 11.7 metres between 2000 and 2003 (Thost and Truffer submitted). The glacier has decreased in area by about 35 per cent and thinned by 30.3 m, or around 0.5 m per year, in the period 1947–2004 (Thost and Truffer submitted). Ice loss in this period was more than twice the 1947–2004 average.
Changes in Heard Island glaciers correlate with underlying climate change in the southern Indian Ocean—temperature observations in the area show a warming of 0.9 °C over the same period (Thost and Allison 2005).
(And of course our local Green-Camouflaged Brown Davey Gam knew about the volcanism all along).
Anthony, given that the ice loss seems to be a recent phenomena, wouldn’t the volcanism also have to be recent? Otherwise the heat from the volcanism would have already melted the ice. Those volcanoes would have been there at least 30 million years (or from when the Straits of Magellan opened).
If the heat flow is more or less constant it can’t be the cause of recent changes.
This would be the reason it is never mentioned, because it’s irrelevant.
A somewhat different Antarctica trend temperature map perhaps?
http://en.wikipedia.org/wiki/Image:Antarctic_Temperature_Trend_1981-2007.jpg
from http://en.wikipedia.org/wiki/Climate_of_Antarctica
Luke has zero understanding of Antartic Ice dynamics.
The presence of that enormous mass of ice which has depressed the earth’s crust under it, makes his, other, explanations of liquids (melted ice) facilitating ice movement towards the sea, UPHILL, seem somewhat strained.
But then from the safety of his computerised reality, Luke could imagine anything.
I might add that if polar ice depresses the earth’s crust, and the density of ice is 1.0 gm/cm^3, then one could also infer that the crust under the oceans are even more depressed, in a topographical se.se.
Think on it
Perhaps you should write to the chair of the Polar Research Board and suggest where she’s going wrong. If you had done the most MINIMAL amount of reading on the issue in Antarctica you should be ashamed of yourself. Louis after your recent outing here on matters geological I think we’ll be bothered with any explanations from youself from now on. You are a total ninny and silly old codger. Good day.