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. 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. 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. It further decreased by 27% in thickness (13 m) between 1967 and 1999.
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)
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.
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.