The break-up of (Ward Hunt and Ayles) ice shelves on the north shore of Ellesmere island gets in the news from time to time (google “Ward Hunt ice shelf”) and has been mentioned by posters here. The issue as framed by Steve Bloom is:
However, if [the Ward Hunt Ice Shelf] is ~3000 year old as cited in the Mueller [et al 2003 ] paper, Ward Hunt Ice Shelf did survive the MWP, and it has now broken up.
This is a fair enough question. Indeed, we don’t hear much of Mannian multiproxy studies these days, but we do hear about ice shelves in both the Arctic and Antarctic, which are being adduced as evidence of “unprecedented” change. Anyone interested in relative medieval-modern levels has to fairly consider this evidence. (Although I will add that if such evidence were to show conclusively that there was no MWP, I would not agree that this vindicated MBH any more than alternative proofs of evolution vindicated the Piltdown Mann.)
My view of relative medieval-modern levels in the Arctic is very much influenced by (what I believe to be) irrefutable evidence of significantly more northerly treelines in Russia (e.g. Yamal) and of warmth in Greenland and the north Atlantic. If the ice shelf information at the north shore of Ellesmere Island yields a different story, then that needs to be factored into one’s view – maybe it says something about ocean currents. Bur before reflecting on such possibilities, let’s see exactly what the evidence is for and against the Ward Hunt Ice Shelf in the MWP. This will take a few posts, as the answer, as so often, leads into interesting by-ways and sidetracks.
Ayles Ice Shelf
Let’s start, not with the Ward Hunt Ice Shelf, but with the nearby Ayles Shelf. In December 2005, the Ayles Ice Shelf was in the news as follows:
Dec 29, 2006 The Ayles Ice Shelf “€? all 41 square miles (105 km2) of it “€? broke clear 16 months ago from the coast of Ellesmere Island, about 500 miles south of the North Pole in the Canadian Arctic. … The ice shelf was one of six major shelves remaining in Canada’s Arctic. They are packed with ancient ice that is more than 3,000 years old. They float on the sea but are connected to land.. Some scientists say it is the largest event of its kind in Canada in 30 years and that climate change was a major element.
Indulge me for a moment. We’ve seen that the 2005 hurricane season was unprecented for sevennnnn-ty years. Now we learn that the Ayles Ice Shelf was unprecedented for over thirrrrrr-ty years.
Ellesmere Island ice shelves have been breaking up throughout the 20th century – well before the recent warming from the 1970s on. Jeffries [Arctic 1986] stated:
The historical evidence of Aldrich and Peary who traveled along the north coast of Ellesmere Island in 1875-76 and 1906 respectively leaves little doubt that a once extensive ice shelf fringed the coast from Point Moss to Nansen Sound . During the present century the Ellesmere Ice Shelf has disintegrated creating many ice islands that circulate in the Arctic Ocean, leaving only smaller, individual ice shelves. The largest observed ice island calving occurred at Ward Hunt Ice Shelf where almost 600 km2 of ice broke away at some time between August 1961 and April 1963,
So the break-up size at Ayles Ice Shelf in 2005 (105 km2) was quite a bit less than the 1961-63 breakup at Ward Hunt ice shelf (600 km2). Presumably if the present ice shelves are only 10% of ice shelves at the end of the 19th century, presumably there have been a number of other such events throughout the 20th century (precedents). In addition, to the 1961-63 Ward Hunt break-up, Jeffries 1986 reported that 48 km2 of calving between 1959 and 1974 at Ayles and Milne Ice Shelves.
Reports of ongoing break-up through the 20th century are in many locations. Braun et al 2004 (coauthor Bradley) stated:
The entire northern coastline of the island [Ellesmere] appears to have been fringed by a continuous ice shelf 500 km in length as late as the turn of the century [Vincent et al., 2001]. This large Ellesmere Ice Shelf progressively disintegrated over the course of the twentieth century, and today only 10% remains [Vincent et al., 2001], the largest remnant being the Ward Hunt Ice Shelf (Figure 2). The ice shelf fractured into two distinct pieces south of Ward Hunt Island between 2000 and 2002, after experiencing some 20 years of relative stability [Mueller et al., 2003]. The causes behind the disintegration of the Ellesmere and Ward Hunt Ice Shelves over the last 100 years are still a subject of debate but are likely a combination of several mechanisms, including wind, wave, and tidal action, pressure by Arctic Ocean pack ice, and recent climate change [Vincent et al., 2001; Mueller et al., 2003].
There is even similar summary in wikipedia:
The northwest coast of Ellesmere Island was covered by a massive, 500 km long ice shelf until the twentieth century. The Ellesmere ice shelf reduced by 90 percent in the twentieth century due to global warming, leaving the separate Alfred Ernest, Ayles, Milne, Ward Hunt, and Markham Ice Shelves.[8] A 1986 survey of Canadian ice shelves found that 48 square km (3.3 cubic kilometers) of ice calved from the Milne and Ayles ice shelves between 1959 and 1974.[9] The Ward Hunt Ice Shelf, the largest remaining section of thick (>10 m) landfast sea ice along the northern coastline of Ellesmere Island, lost 600 square km of ice in a massive calving in 1961-1962.[10] It further decreased by 27% in thickness (13 m) between 1967 and 1999.[11]
So whatever significance is placed on Ellesmere Island ice shelf calving, this is not something that started with warming in the past 30 years, but is something that has been going on for over a century.
A Crack in the Ward Hunt Ice Shelf
Steve Bloom referred to the “break-up” of the Ward Hunt ice shelf. While it’s quite possible and even probably that the Ward Hunt Ice Shelf will break up, the actual news to date is not about its break-up but about a crack in the ice – perhaps a prelude to a break-up, but not itself a break-up. Here’s an excerpt from a 2003 news report:
The Ward Hunt Ice Shelf, which is 443 square kilometres in size, now has a major crack that runs right through it from north to south. The scientists say the fracturing – which has been developing since the spring of 2000 – is the end result of a three-decade-long decline. “We’re now seeing some very extensive fractures in it that extend many kilometres horizontally across the ice-shelf; and they extend all the way through from the top to the bottom, many tens of metres through the ice shelf. And we’ve never seen fractures like this,” Dr Jeffries told the BBC.
Here is a picture of the crack in the Ward Hunt Ice Shelf from contemporary stories:
Original Caption: This Canadian RADARSAT image, acquired in August 2002, shows the central crack in the Ward Hunt Ice Shelf running down the center of the image. (Image courtesy of the Alaska Satellite Facility, Geophysical Institute, University of Alaska Fairbanks)
Disraeli Fjord
Now interesting as the crack in the Ward Hunt Ice Shelf may be, I fail to see how this, in itself, sheds much light on relative medieval-modern temperatures. I haven’t seen any evidence or argument showing that a similar crack in the ice shelf could not have existed in the MWP. Is it possible that the Ward Hunt Ice Shelf reached a situation rather like the present one at the end of (say) the 12th century and then reformed. I don’t see how air and satellite photos, interesting as they may be, can shed much light on the matter.
Now there’s a little more to the Ward Hunt crack than this. The Ward Hunt Ice Shelf acted as a type of dam in the Disraeli Fjord, resulting in something called an “epishelf lake” in Disaraeli Fjord. The initiation of the crack led to the draining of the epishelf lake. From the same news story
…The immediate consequence of the rupture has been the loss of almost all of the freshwater from the Northern Hemisphere’s largest epishelf lake (a body of mostly freshwater trapped behind an ice shelf). The freshwater lay in the 30-kilometre- [20-mile] long Disraeli Fiord. At its deepest, the freshwater measured 43 metres [140 feet], and sat atop 360 metres [1,200 feet] of denser ocean water.
Another contemporary report said that the information “hinted” that the ice shelf was 3000 years old:
Disraeli Fiord now has a direct connection to the ocean for the first time in thousands of years. Before the fracture appeared, researchers found ancient driftwood from the Mackenzie River and Eurasia in the lake; no wood samples were younger than 3,000 years, hinting that the Ward Hunt Ice Shelf has sealed the fiord off from the Arctic Ocean for at least that long.
A 2004 article in Geophysical Institute Quarterly somewhat upgraded the “hint” to a “suggestion” as follows:
Disraeli Fiord now has a direct surface connection to the ocean for the first time in thousands of years. Before the fracture appeared, researchers found ancient driftwood, probably from the Mackenzie River and Eurasia, stranded on the shores of the fiord. None of the wood samples were less than 3,000 years old, suggesting that the Ward Hunt Ice Shelf sealed the fiord off from the Arctic Ocean at least that long ago.
NASA expressed the situation more strongly (see also here and here )
by August 29, the ice in the fiord had broken up for the first time in recorded history. This and later images also distinctly show the crack running from the fiord across the shelf to the ocean.
A simple check of information on Disraeli Fjord shows that the fjord is connected to salt water below the ice shelf.
The mouth of Disraeli Fiord in northern Ellesmere Island is dammed by the Ward Hunt Ice Shelf from the surface to a depth of 44 metres. The fiord contains virtually fresh water to this depth overlying cold salt water. A perennial ice cover precludes any wind induced mixing. Fresh water enters the fiord in the form of melt streams which flow down to the pycnocline. This water flows out beneath the shelf, carrying some of the underlying salt water with it. Heat flows downward across the pycnocline causing formation of frazil ice in the lower part of the fresh layer. This ice floats up to adhere to the fiord ice. Salt water flowing out under the ice shelf is replaced by water of Atlantic origin entering at the bottom.
Given this interconnection, I don’t see how you can conclude from the information presently in the record that the salt water in the epishelf lake had been there for over 3,000 years; indeed, the evidence seems to be that it is circulated. The attribution of a date of 3000 years for the Ward Hunt Ice Shelf thus rests entirely on the driftwood evidence.
Vincent et al Polar Record 2001 stated:
The original extent and age of Ellesmere Ice Shelf are also subjects of conjecture, although on the basis of driftwood analysis, it appears that ice shelfs along this section of the coastline began to develop during a period of cooling in the mid-Holocene about 4000 years ago (Evans and England 1992).
Braun et al 2004 stated:
The ice shelves along Ellesmere Island’s north coast formed initially some 3000″€œ4000 years ago [Evans and England, 1992; Jeffries, 1994] as climatic conditions in the High Arctic deteriorated from the early-middle Holocene warm phase [Bradley, 1990].
However, Braun et al 2004 also says that Ward Hunt Ice Rise formed within the last 1500 years as follows:
The Ward Hunt Ice Rise (Figure 2) is between 40 and 100 m thick and formed within the last 1500 years when the ice shelf thickened and grounded on the isostatically uplifted seafloor north of Ward Hunt Island [Lyons et al., 1972]
Thus, the only evidence on the dating of the Ward Hunt Ice Shelf comes from the driftwood, which has many points of interest and which I’ll discuss in my next post on this topic.
Climate Audit 
55 Comments
More scaremongering publicity. Most ice shelves calve off from the main glacier if they grow too big (long) and stress fractures occur due to tidal action which cause them to eventually break off – structural properties of ice is similar to concrete – great strength in compression and very poor strength in tension. Calving of ice shelves is a natural process.
Richard, the Canadian ice shelves are not ‘glacial.’
IIRC, they are formed from consolidation of sea ice and snow into grounded shelves along the coastal margin.
Ayles broke off from the shore, and floated away into an ice iceberg island – something like 30 miles offshore in the first few days – among the seasonal sea ice.
If there was 3000 yo ice on the Ayles shelf, that means the shelf has been there for 3000 years, without breaking up and floating away.
SteveM – Is that my quote up there, or Bloom’s? I’m not Steve Bloom. Although it is certainly possible that I said something very similar to what Bloom said – he is a smart guy. Grin.
Could you link it for context?
#2. They are “neoglacial” in the sense that they formed after the Holocene Optimum i.e. at most, the Ayles calving would be unprecendented in three thousannnnnnnnnn-d years. In a subsequent post, I will consider the evidence for dating these ice shelves.
SteveM, no one is claiming otherwise – drop the damned snark.
Re: #2
It still doesn’t change the structural properties of ice. Tidal action places great stress on ice shelves and they eventually crack.
Just a quick note that of course the thirty year reference was to the sat record. You knew that, but couldn’t pass up the chance for a cheap snark. Or would it be better to call it a McGuffin in this context?
6: And of course, the larger they get, the more torque the tide puts on them, and the more likely they are to crack. This all could show that the shelf has been growing in size and finally got too large ??
jae, uh.. what? Are you claiming that vertical tidal movement at the outer edge of an ice shelf translates to ‘torque’ at the inner edge? ie, that ice is suffiently rigid over a span of 10s of kilometers?
Richard – sure. And this one survived, apparently, for 3000 years without that happening, and has just done so now, in a context of receding sea ice and widespread collapse of the canadian ice shelves, with apparently two ice shelves predating the MWP collapsing within a couple years of each other, and in close synchrony with the collapse of old ice shelves in the antarctic at the other end of the world.
And with Canadian ice core from nearby indicating ‘unprecedented’ (I know its hard, SteveM, but see if you can resist. I have faith in you) warming on the context of the last few thousand years.
#7. I thought that the 30 years referred to the time since a prior large breakup. What makes you think that it has anything to do with the satellite record?
9: Yes, as the moment arm gets longer, the moment gets larger. Even though the ice is somewhat elastic, I think there could be some effect here. Especially if the ice was getting thicker. Also, one very large wave or tide could cause cracking, I should think. (I am just speculating, though…).
Re #11
Can we checked the earthquake records at the time of breakup? How close can we date/time the breakup? Could a small tsunami wave, resulting from an earth quake somewhere else due the heavy lifting? Any ideas were to check earthquakes records for this area?
Russ,
The USGS has a site, check them out they show all EQs globally. I would provide the link but don’t know how.
Re #10: There’s no reference to any specific similar event in the mid-’70s. Considering that this one wasn’t spotted in the year it actually happened, it seems obvious enough that it wouldn’t be prudent to make such a sweeping statement for any prior period.
Dane,
Here is the link to the latest Earthquakes
SteveM, there are excellent pictures on this page :visible earthtop/middle of the page, blue jpeg links
Look how small it looks in perspective: Picture of Ward Hunt Ice Shelf
Doesn’t it look like two places smashing into each other?
There was a reported ‘earthquake’ when at least one of the ice shelves fractured off – it apparetnly looks like the ice breaking up caused the shaking.
The Ellesmere Ice Shelf has been breaking up for a century – so much for jae’s ‘maybe it broke because it was getting bigger.” The remaining inshore parts seem to have been several thousand years old, and are now breaking up. There are multiple fracturing events at different times – are we now getting multiple ice-fracturing earthquakes for the first time in 3000 years?
The amount of straining toward invented unsupported causes for this kind of evidence is something I find astonishing. This is even better than the “volcanoes did it” handwaving after Larsen B.
How do we know which came first, the breakup, or the earth quake? Who was there to observe? Are all iceshelf breakups indicated by an earth quake signature? This is interesting. Earth quakes are stored energy, suddenly released. What was the stored energy in the ice that was large enough to trigger earth quake sensors?
More interesting quotes from Jeffries [Arctic 1986] :
Keep in mind this report was written in 1984. Without invoking global warming he expected the instability of these ice shelves.
Also of interest the report notes that the “Ayles Ice Shelf moved about 5 km out of Ayles Fiord.” It is unclear how to reconcile that with the comment about 3,000 year old ice in this article (referenced above).
re: #18 Lee,
No offence to anyone but I see straining on both sides here. If the iceshelf hs been breaking up for a century, then obviously it’s not possible to blame it on AGW, just on GW. One thing we tend to forget about is that a lot of the ice from the last glacial has hung around albeit with back and forth activity. As it works itself down to an interglacial minimum, it makes it easier for new events to occur, at least within the perview of the present interglacial. Thus, if there’s a number of landed glaciers near a bay, this may keep an ice shelf from totally disintigrating during a warm period. But if a very warm period occurs and melts the glaciers, then even when a new cold period occurs which recreates the glaciers on a smaller scale, it won’t take as long or as much warmth to melt them the next time. I don’t know if that sort of thing is in play here, but it’s one thing to look at. Another would be, as I think’s been hinted at, is to do some analysis of the old sections of the shelf and see if they’re solid and continuous or if they show signs of past break-up and reformation.
Finally one point on the drift-wood. From what I could get from Steve M’s original post, this drift-wood would have come from far away. Merely because there’s now a narrow break between two sections doesn’t necessarily mean that younger driftwood can now get to the shore. For that matter it doesn’t necessarily mean that there is driftwood TO get to the shore. It might be useful to see what ages of driftwood there are on other sections of shore which are now ice-free.
18, Lee:
you don’t have any better explanation than I do. LOL. It is all speculation.
Dardinger –
These are not glacial ice shelves. We don’t know how old the outer parts of the shelf were, the parts already gone. If these inshore parts were 3,000 yo, that does not mean the outer parts were. If the outer parts were younger, those losses do nto tell us much. But if the inner parts are 3,000 yo, and are now being lost, that is strongly indicative – not definitive – that something is different now than during the time they existed.
Given clear indications of increasing temperature, and nearby ice cores indicating l20th century temps are higher than in the last several thousand years, temperature seems an obvious reason. Given that the ice shelves have been thinning, and that is not attributable to precipitation changes, temp seems an even stronger possibility.
Couple that with antarctic losses of old ice shelves, also due to temp, on the other end of the planet, at nearly the same time, and this is oen more pretty strong piece of evidence that high latitude temps (ntegrated over some period of time) are moving to levels higher than during the history of those ice shelves.
This is not definitive – I consider it (if the ages seem reasonably solid) to be strongly indicative. And it doesn’t rely on invented earthquakes or vertical levers of several feet lifting across many kilometers of somehow-rigid ice to ‘torque’ the shelf off, somehow uniquely now rather than during the last 3000 years.
Lee, you say (emphasis mine):
Citation, please.
Also, you say:
Correct me if I’m wrong, but it seems to me that the tide operates under the entire shelf, not just the outer edge. Because of this, the vertical force on the shelf is proportional to how far it sticks out into the water. The point of maximum strain would occur somewhere near the shore. That’s why they break off in big chunks.
All of that, however, neglects two facts:
1) The breakup of the shelf has been going on since at least the ’50s, and quite possibly before. Temperature seems the obvious cause.
2) We don’t know how long the Ward Hunt ice shelf has been there. Even if we can date the Ayles ice shelf, that doesn’t tell us the age of the Ward Hunt.
I find this comment particularly telling:
One thing to remember about ice shelves is that, like glaciers, they collect snow. Because of this, they are not permanent features of the landscape. Even if the temperature does not rise, they will eventually break off.
My guess? The shelves achieved a much larger size during the Little Ice Age (remember that glaciers all over the world were advancing at that time), and have been retreating ever since.
w.
Where does the driftwood come from?
Lee keeps saying the ice shelves are not glacial, but the Braun paper states:
“The surface balance of the ice rise and ice shelf follows the temporal pattern seen on other measured High Arctic glaciers.”
“ice shelf” is the part of a glacier that enters or floats on the sea is in not?
Here’s a slide show of the area:
link hope it works!
Also found this paper: link
During the period 23 April to 5 June 1983 a successful program of ice shelf studies was completed on the north coast of Ellesmere Island. Asin 1982, the emphasis was on ice coring;
a total of 55 m of 7.6 cm diameter ice core obtained by SIPRE hand corer will be the subject of chemical, isotopic and crystallographic investigations. The longest core, 3 1.79 m, was composed of ice-firn/superimposed ice to a depth of 10 m, below which the salinity values show the ice to be old sea ice.
The ImSt nxent massive calving of ice from Ward Hunt Ice Shelf (Hattersley-Smith, 1963) has been discussed in terms of the near coincidence of tidal and seismic events creating conditions in the ice shelf leading to fracture (Holdsworth, 1971). Undoubtedly this influenced the calving not only at Ward Hunt Ice Shelf but also at Milne and Ayles fiords. The calving might also have been related to vibrations within the ice. Strainmeter measurements revealed vibrations or oscillating strains with 35- to 40-second cycles, 5- to 6-minute cycles and 20-minute cycles. All these oscillations will exist in the water adjacent to and beneath the ice shelf
re:26
The slideshow direct link doesn’t work, sorry. You have to access it from this page:link
willis,
If SteveM would cite the quote of mine (I’m pretty sure its mine – if not, its from Bloom in the same place as mine ) as I requested when he first quoted it, it would lead directly to my cite for the Canadian ice core.
Ice shelves collect snow. They also sublimate, and melt if temps increase enough. The reports are that these ice shelves have been thinning over the last decades, as I said above.
And yes,it is almost certain that the Ellesmere Ice Shelf got bigger during the LIA, and is getting smaller now. If the inner ice is 3,000 yo, then this strongly implies that growth and diminution happens along the outer margin, and this inner part has been stable. Now it isn’t, it seems.
I am supposed to be taking a break from posting here due to personal obligations, but given the hype around this, the “all AGW all the time” content of my FT daily and a scaremongering story I heard on ABC (radio) news this morning, I cannot stand aside …
RE: “The entire northern coastline of the island [Ellesmere] appears to have been fringed by a continuous ice shelf 500 km in length as late as the turn of the century [Vincent et al., 2001]. This large Ellesmere Ice Shelf progressively disintegrated over the course of the twentieth century, and today only 10% remains [Vincent et al., 2001]”
Right off the bat, I question this. Anyone who has faith in claimed arreal calculations of shorefast ice be it of local or glacial origin, prior to 1960, well, I’d love to face you across a gambling table (snicker). These so called “ice shelves” come and go, and are still quite poorly understood. To make a claim “only 10% remains” would require a highly reliable, properly archived, peer reviewed, quality controlled data set and even with that, without satellite images, nagging suspicions would remain. So the fact is, our reliable base line for any claims regarding changes in area of so called “ice shelves” would have to be about 1960.
RE: “This Canadian RADARSAT image, acquired in August 2002, shows the central crack in the Ward Hunt Ice Shelf running down the center of the image. ”
Here the frustrated rheologist in me asserts itself. The crack appears to propagate from a stress riser at the sharp corner of that little island offshore of the main landmass of Ellesmere. And what is the origin of that stress? If you look to the North of that little island, there is major berg, impinging on, heck, enveloping, the entire northern shore and then some, of the islet. It appears to have come from the NE (which I would expect, given prevailing winds), of course during a previous late summer, early fall. To the SW of the islet, you can see where conjugate sheer fractures in the shelf from the initial compressive event were created then later healed. The eastern lobe of the berg snagged on the islet (and I would also imagine the overall mass simply ran aground overall). You can see that lead to the West of the islet – that is also a clue that the berg wedged into the shelf, then snagged, and has since even counterrotated clockwise since snagging. The big crack to the SE of the islet was probably initially created due to the resulting tensile strain as the shelf on the W side of the islet was pushed toward the SW. Since then, the counterrotation of the berg has further compressed the ice in the shelf to the east of the islet (look at all the active conjugate sheer fractures on that side) and of course, opened up the crack a bit by pushing ice on the the NE side of the crack toward the SE. What a fascinating image.
Obviously, any ice breakup event (indeed, any event) will have proximate causes.
The question is, though, why did this set of proximate causes break the ice now, and not at some time during the last 3000 years, assuming that the shelves are in fact 3000 yo. Why now? Why now for both northern and southern hemispheres? Pointing at the specific proximate causes is not sufficient to get at those underlying questions.
There is something very odd about the Aug 7 image in “rocks'” link in #17. If that berg wedged into the shelf, then how is it that “shelf ice” managed to “cover the tracks” of the berg? Or is it even shelf ice? Perhaps what was believed to be shelf ice was in fact sea ice. So, what broke off may not have been shelf ice at all, but instead, sea ice which had formed in the gap made as the berg initially impinged on the shelf, just the NE of the islet. A forensic approach is needed here.
Shelf ice vs sea ice …. if you look to the NW of the islet, you can see where the inpingine berg wedged part of the shelf NNW-ward. The shelf ice is recognizable as having a slightly lighter “color” (I realize it’s a radar image) than the “shorefast” (more properly, shelf fast) ice just to the NW of the proper shelf ice. That is an expected place for shorefast ice to have formed during the winter of 2001 – 2002. It is in the lee of the islet and also is slightly protected by the “headland” of shelf ice that was pushed northward by the berg.
RE: #30 – ask yourself the question, how often would a berg that large just happen to impinge on the shelf, right where there is a little islet like that? Is that a 1 in 30 year, 1 in 300 year, 1 in 3000 year or even more rare event?
re 33 – the answer is, I don’t know any more than you do – but this isn’t the only shelf.
And it vibrates too.
A scab on the pinky toe of Earth? She’s not a whiner.
RE: #34 – How do we know whether or not the current rate of fracturing events on ice shelfs is abnormal? The reason I ask is, we’ve only had satellites since the late 1950s, and the real explosion in satellite imagery for earth sciences use started during the 1970s, only coming to fruition with the internet (allowing more eyes to look at them). It may well be that there were many major shelf events that were missed previously. This reminds me of the TC debate.
Re #36: Steve S., the estimate of extent of the ice shelf 100 years ago is from careful ground observations by the Peary expedition. Those are discussed in one of the cited papers. A necessary implication of those observations is that the bulk of the shelf broke up unobserved between then and 1960. Of course this has meaning for past climate only if the work done to date the remnant shelves is valid. I look forward to Steve M.’s post on that.
RE: “careful ground observations by the Peary expedition. ”
I would love to see you (or anyone else) try to distinguish between ice shelf and sea ice using ground observations, especially if there was blowing snow. Good luck.
Even with air photos it is very tricky to try and tell the difference between true ice shelf and shore fast (or more properly, shelf fast) sea ice. Especially when there is a lot of snow cover. Another problem is trying to compare ground reports and air images that were not taken during roughly the same time of year and with roughly the same amount of snow cover. I am quite concerned that some of the earlier assessments labeled sea ice as ice shelf. Back to my proposed baseline of satellite imagery. All other methods are suspect.
Another comment. Let’s face it. Prior to the 1980s (and all the debate about AGW on politicization of climatology and cryology) things like studying ice were a real backwater. For someone masochistic enough to do Arctic studies back in the first 60 – 80 years of the 20th Century, it was not like you’d get into lots of trouble for making erroneous measurements / observations or being somewhat sloppy about quality. In defense of the scientists doing it, it was underfunded and you basically had to travel like a hunter or trapper (dog sled, seasonal boat, bush planes, etc) so it was not very inviting for having large teams and lots of equipment. Things being what they are, anything done in this field prior to the 60s needs to be taken with a major grain of salt. Anything done from the 60s to about the 90s was in the midst of a huge learning curve. Caveat emptor and all that.
Re #38: The shelf ice has some peculiar characteristics that you would know about had you actually read the paper that quotes Peary’s material.
I didn’t realize it when looking at the picture of the Ward Hunt ice shelf, but on looking at Mueller, ea 2003, Ward Hunt Island is the small stony island at the top of the picture, and the denser white mass above it is grounded ice. The larger land mass to the south is a peninsula from Ellesmere Island. The picture above is right from Mueller’s Figure 1. From Mueller Figure 1, Ward Hunt Island is about 5 km by 3 km.
The discussion here got me thinking about alternative ways (other than shelf-melting) that old driftwood might get beached above an ice-shelf. I wondered about ablative and especially sublimation losses from a shelf. The arctic ice-shelves are not glacier-fed. Instead, as Steve M. pointed out, they accrete drifting ice-floes at their seaward edge. They also collect snow.
Looking at the picture above, and Figure 1 of Mueller 2003, notice the landward side of the grounded ice has a large chasm that follows the shape of the north shore of Ward Hunt Island. This chasm is present in the 1999 picture of the shelf also shown in Mueller’s Figure 1. 1999 is prior to the crack formation. Strong grounding to the island occurs only on the west side.
The chasm following the north coast of Ward Hunt Island is what one might expect if the stony surface of the island was warmed more by the sun than was the adjoining ice. A bit of ice shelf softening and wind-assisted sublimation would occur as a consequence. I’d wonder whether this process is typical of all Arctic ice-shelves. If the ice-pressure leading to grounding comes from the accretion zone at the sea-side, then continued grounding of the ice must mean that ice lost to sublimation and ablation on the shore-side is replaced by ice from seaward. The mechanism would be pressure-induced ice-flow.
The north shore of Ellesmere Island peninsula also seems to support a dark space between the stony shore and the ice-shelf, following the Ward Island pattern. It’s interesting to see that the ice on the west side of the Disraeli Fjord pushes up against Ellesmere the way the west-side ice does on Ward Hunt Island. It’s as though the greatest ice-pressure were from the west.
Now consider what would happen to a bit of driftwood caught in the ice. If the “shore-sublimation and ablation followed by seaward-replacement” mechanism is correct, a bit of wood trapped in the ice would migrate showly shoreward from the pressure-flow of the ice. Eventually, it would reach the shore with its surrounding ice. That bit of wood should then get dropped on the stony beach when its surrounding ice ablated/sublimed away, as it would do if the mechanism operates.
If that were possible, then one could get driftwood on the shore above an ice-shelf even if the shelf never melted at all.
It should be possible to measure the rate of pressure-induced ice-flow in an Arctic ice shelf. This would constitute a severe test of the above mechanism. It the mechanism passed the test, one would have a good idea of how long it would take for a given piece of wood to get to shore after the ice floe accretion event. No driftwood on a stony shore above an ice shelf should be younger than this migration time, unless the shelf were far smaller, or gone completely, more recently than the current pressure-drift rate allows.
That would mean one could only use the age of currently beached driftwood to judge the last time an ice shelf melted away iff the wood is younger than the current pressure-induced flow rate allows. Older wood would tell you nothing about when the shelf last melted.
#42
I raised a similar counterintuitive diffusion mechanism in the driftwood thread [# 16]. I’d imagine that floating ice couldn’t exert pressure on neighboring ice, in the way that glacial ice could, absent some outside force – such as ocean currents. Unlike glacial ice, which has an uphill and downhill side, all the ice in the shelf is at sea level. If depositing currents are what you mean by ‘ice-pressure’, maybe so.
I was wondering if maybe tidal forces in play, however. Tidal forces travel in a wavefront from east to west, of course. Could that explain why a North-South crack formed ? Is there a directional preference for ice shelf cracks ? Is there a higher incidence of cracking during the new Moon or when the Moon is closer to Earth in its orbit ? Like Sgt. Schultz, I know nothing, I only raise questions.
If a diffusion mechanism for getting wood through the shelf exists, and if it is either a quick process with wood gathered by humans on the shoreline or a 2500-year mechanism with low deposition rate, we should expect to find some pieces of wood somewhere within the shelf ice – if we took the time to look for it.
The Ward Hunt Ice Shelf is back in the news again:
BBC Link
There is no mention of the “unprecedented cracks” in 2000. Being a BBC reporter must be a lot like being senile: every day is full of unprecedented phenomena.
When I hear about ice shelves collapsing I always look for their age:
“The Ward Hunt shelf’s characteristic corrugated surface, described by Mueller “like a giant Ruffles potato chip,” is now fractured by dozens of deep cracks in the 3,000-year-old, 40-metre thick ice.”
Hmmm
Only 3000 years? That means it must has grown since the last ice age. Perhaps this is not the first time it has broken a part. A quick looky at the Greenland ice core reveals a distinct warm period about 3500 years ago. Hmm. Unprecedented breakup? I don’t think so.
The Holocene thermal optimum.
Re: bender (#46),
Actually, no. That was more that 5000 years ago. Here is a temperature plot from the ice cores:
(source http://mclean.ch/climate/Eye_opening.htm)
Any ideas on what caused those temperature spikes?
I just got here so maybe this has been covered elsewhere already. If so, my apologies for repeating.
But hasn’t there been a lot of seismic and volcanic activity in the sub-ocean regions of the Arctic lately? I’m not a scientist. I just want to know why all the climate change arguments are blinkered on atmospherics when the hottest heat source for the planet is swirling beneath our oceans doing all sorts of things we haven’t even begun to study.
Are there any “hockey stick” graphs of the earth’s core temperatures over the past 30 years, 100 years, 3,000 years, to prove or disprove the now Biblical Gor-aph?
Could changes in the earth’s core, its expected shift in magnetic poles, its increasing(?) seismic and volcanic activity, possibly have anything to do with increasing atmospheric temperatures and our changing atmostphere in general? Is there data that rules any of this out? Is there data? Has the IPCC studied this data? Is the data not worth “correlating” to?
Or are we assuming the earth’s core is an irrevocable constant because assuming otherwise would be too inconvenient to the truth our preachers prefer to preach? Do we know? Does Father Gore know?
And even if we, or He, does know, is the mass-hysteria response of “OMG, we killed Ellesmere Island!” either reasonable or helpful, never mind a viable means to a solution?
Folks
I hope that this is not too far off topic but here goes. There is precious little data around from the early NASA remote sensing spacecraft (Nimbus) I am working on a project to digitize Lunar Orbiter Images and have recently found out that the early Nimbus data was archived on the same type of machines (Ampex FR-900 series). Does anyone know if this data still exists? If it does, we can digitize it now with the working machines that we have just brought back into service. This would help take polar data back into the 1960’s. If anyone knows anything about this please contact me at:
wingod at Earthlink dot net
Raven, you are correct that that comment #46 was mistaken by couple thousand years. Do you want me to guess? Do you know the answer? If it’s Greenland is it geothermal related? I think I know where you’re going with this, and that’s cool with me.
Re: bender (#50)
It it was a rhetorical question. I can only guess. But the data is telling me that breakups of the artic ice cap have occurred naturally in the recent past so I don’t find the ‘tipping point’ argument to be very compelling. The quasi periodic nature has been noted by others.
Re: bender (#50)
I don’t know the answer. But you can look up Bond Events (spam filter eats the links). In any case, I think the data and the age of the ice shelves collapsing suggests that the claims of an artic ice tipping point are likely over stated.
#51/52 That seems to be a relevant observation. I wonder how that squares up with the primary literature. I won’t comment just yet about the role of time lagged responses. Too much confusion over OHC. I’m too likely to get myself in trouble making unsupportable/incorrect statements.
Ellesmere island ice shelf has 10,000 people fooled!!
Ellesmere island’s ice shelf is the huges thing on Earth!!! I actualy went there and it was huge!!!
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