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Antarctica 2017

Re: Antarctica 2017

Unread postby Plantagenet » Thu 20 Apr 2017, 11:52:32

The physics and math involved here isn't very complicated.

Once you get lakes on the surface of the ice, the liquid water absorbs solar energy. Any small fracture in the ice below will tend to thaw and allow the surface water to penetrate deeper into the ice. If even a tiny amount of flow is established into the ice you get "thermal erosion" where the water flow progressively enlarges the tiny hole into what can eventually be a giant moulin.

Its really a function of the amount of surface melt. If there isn't much surface melt, then small streams will tend to run off over the surface of the ice. If there is a considerable amount of surface melt, there will be more of a tendency for ponds and then lakes to form, and that in turn results in greater likelihood of moulins developing.

So far there isn't much surface melt over most of Antarctica and in some areas today small amounts of water mainly runs off over the surface.

However, in other parts of Antarctica surface lakes have started to form. And, just like in Greenland, some of these lakes are draining down moulins into ice. The physics of glaciers is actually pretty simple, since the thermodynamic properties of ice are so well known. You put standing water on top of ice, add some solar energy, and the water will start to thaw the underlying ice. Its math 101. And its starting to happen in Antarctica.

global-warming-climate-change-langhovde-glacier-east-antarctica-glacial-lakes

In a new study, scientists who study the largest ice mass on Earth – East Antarctica – have found that it is showing a surprising feature reminiscent of the fastest melting one: Greenland.

More specifically, the satellite-based study found that atop the coastal Langhovde Glacier in East Antarctica’s Dronning Maud Land, large numbers of “supraglacial” or meltwater lakes have been forming – nearly 8,000 of them during summer months between the year 2000 and 2013. Moreover, in some cases, just as in Greenland, these lakes appear to have then been draining down into the floating parts of the glacier, potentially weakening it and making it more likely to fracture and break apart.

This is the first time that such a drainage phenomenon has been observed in East Antarctica, the researchers say – though it was previously spotted on the warmer Antarctic Peninsula and was likely part of what drove spectacular events there like the shattering of the Larsen B ice shelf in 2002.

When it comes to East Antarctica, however, “that’s the part of the continent where people have for quite a long time assumed that it’s relatively stable, there’s not a huge amount of change, it’s very, very cold, and so, it’s only very recently that the first supraglacial lakes, on top of the ice, were identified,” said Stewart Jamieson, a glaciologist at Durham University in the UK and one of the study’s authors.


Cheers!

Seasonal Supraglacial Lakes in Antarctica---Geophysical Research Letters
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Re: Antarctica 2017

Unread postby rockdoc123 » Thu 20 Apr 2017, 17:05:44

The physics and math involved here isn't very complicated.

Once you get lakes on the surface of the ice, the liquid water absorbs solar energy. Any small fracture in the ice below will tend to thaw and allow the surface water to penetrate deeper into the ice. If even a tiny amount of flow is established into the ice you get "thermal erosion" where the water flow progressively enlarges the tiny hole into what can eventually be a giant moulin.


No one is arguing about how moulins form, first year Geology or Geography topic. What has been pointed out by both Kingslake and Bell is that in all the ice shelves they investigated outside of the Pennisula there is evidence for long distance transport from surface meltwater. In fact the paper you reference:

Langley, E.S. et al, 2016. Seasonal evolution of supraglacial lakes on an East Antarctic outlet glacier. Geoph Res Lett, V 43, 16. Pp 8563-8571

recognizes the presence of these drainage channels and references Kingslake's previous paper of 2015.

Linear surface channels are observed every austral summer (Figure S4). The majority of channels are located on the grounded ice and tend to follow the same path each year, initiating from, and terminating at, the same point. They are found up to 15 km inland (630 m asl) and reach lengths of 3.5 km. Some initiate from lakes and form sinuous drainage networks, following the local topographic slope. Although these channels are fed by lakes, we never observe lakes fully emptying via a channel.


Surface channels have been observed elsewhere in East Antarctica, specifically the Nivlisen ice shelf [Kingslake et al., 2015], but they have rarely been documented on the grounded ice sheet. Sinuous channels that we observed instigating from lakes closely resemble those described by Kingslake et al. [2015], and we assume a similar initiation mechanism via the turbulent dissipation of heat [Tedesco and Steiner, 2011]. The delay in channel formation (Figures 2c and S1b) is probably related to the time it takes for a lake to fill and overspill its boundaries. We observe “stable drainage,” where channel incision, and lake water-level drawdown, does not exceed meltwater input and so does not entirely drain the lake. Because “unstable drainage” is considered a product of greater initial lake area and input [Kingslake et al., 2015], such events might be observed on Langhovde Glacier in the near future, should warming occur.


and it is worth noting that the Langhovde glacier that Langley et al reference is immediately adjacent the area investigated by Kinglake et al, 2017; Rio Baudoin ice shelf where they identified numerous channels.

And a relevant quote from Kingslake, 2017 with regard to surface melt ponds is:

We have shown that widespread and persistent surface drainage moves water great distances from grounded ablation areas, onto and across ice shelves, and into areas that otherwise would not experience meltwater accumulation. Large-scale drainage is likely to be a dominant factor in future ice-sheet stability. Improving the representation of ice-sheet surface hydrology in climate and ice-sheet models will be vital for improving predictions of ice-sheet mass balance and sea-level rise


And Bell et al pointed out that long distance surface melt drainage was also characteristic of Pederman glacier in Greenland. As I noted above Bell et al points out that surface channel drainage would be predicted to be the mechanism of drainage where there is sufficient surface topography. Once channels form they overtake any other mode of transport (tendency toward lowest free energy i.e. easiest path). And the other important point they make that where the topography is appropriate channels are expected as melt water increases.

Taking Bell et al in context and going back to the Langley et al paper they state:

The location of lakes on Langhovde Glacier is closely related to ice surface topography, with lake growth favoring low surface gradients.


Not at odds with what Bell et al is saying.

Neither Kingslake et al and Bell et al are claiming that wide spread long distance drainage is the only mechanism of meltwater transport, but what they are pointing out is it is a significant factor in all of the ice sheets they investigated.

Why is this important. Simply because to justify the DeConto and Pollard paper you need to have all of the meltwater produced trickling into cravasses and cause large scale ice sheet calving and eventual collapse. If a goodly portion of that meltwater is bypassing those crevasses and being deposited directly in the ocean and if there is reason to believe that transportation mechanism will increase in the future (as Bell and Kingslake both indicate) then the model of DeConto and Pollard as it stands is incorrect.

Note also that Bell et al and Kingslake et al point out these transportation mechanism has been going on in East Antarctica since the fifties. And in a large part of East Antarctica surface mass balance has been increasing and accelerating it's increase. This makes sense given that increasing SMB equates necessarily to an increased toppgraphic profile of moving ice sheets....that increased topography would favor the sort of long distance drainage that Bell et al and Kingslake et al have pointed to.

Of course I could have simply taken the tact you have several times in the past......Bell et al is a more recent paper and hence Langley et al needs to be updated with this new theory. :P :roll: But there is no need to do that.

Everything is consistent but certainly not with an Antarctic that is draining solely via subsurface drainage into moulins.
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Re: Antarctica 2017

Unread postby Plantagenet » Thu 20 Apr 2017, 18:33:34

rockdoc123 wrote: to justify the DeConto and Pollard paper you need to have all of the meltwater produced trickling into cravasses and cause large scale ice sheet calving and eventual collapse.


Thats not true.

Either you don't understand what you are reading or you are intentionally misrepresenting the facts.

The DeConto and Pollard paper (2016) does't have to" have all of the meltwater produced trickling into cravasses and cause large scale ice sheet calving" as you wrongly claim.

The principal mechanism driving calving in the DeConto and Pollard paper (2016) is different then what you are claiming. Lets go back and read their paper and see what they actually said, shall we? Now read slowly and try to understand all the words:

"a warming ocean has the potential to quickly erode ice shelves from below, at rates exceeding 10 m yr−1 °C−1 (ref. 14). Ice-shelf thinning and reduced backstress enhance seaward ice flow, grounding-zone thinning, and retreat (Fig. 2b). Because the flux of ice across the grounding line increases strongly as a function of its thickness15, initial retreat onto a reverse-sloping bed (where the bed deepens and the ice thickens upstream) can trigger a runaway Marine Ice Sheet Instability "

By a "runway Marine Ice Sheet instability" they mean rapid ice retreat back into the Ice Sheet due to continued calving at the unstable ice margin.

If you were a student in one of my seminars, I'd give you an "F" for your lack of understanding of this paper. You not only didn't understand the mechanism of ice retreat discussed in this paper, but you don't even understand that you don't understand what the paper is saying.

You are a bit of a thickie, aren't you?

Sheesh! :roll:

Cheers!
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Re: Antarctica 2017

Unread postby rockdoc123 » Thu 20 Apr 2017, 20:16:59

Thats not true.

Either you don't understand what you are reading or you are intentionally misrepresenting the facts.

If you were a student in one of my seminars, I'd give you an "F" for your lack of understanding of this paper. You not only didn't understand the mechanism of ice retreat discussed in this paper, but you don't even understand that you don't understand what the paper is saying. 


Well it is pretty apparent you don’t understand what the issue is so I pretty much pity anybody who sits in one of your seminars. And your comment is pretty rich coming from someone who actually didn’t even know what DeConto and Pollard had actually done, you simply were quoting from a press release. Maybe you teach your seminars from press release as well.

In fact the mechanism of retreat by ice shelf collapse has been captured and modeled in numerous papers previously, that is not what is new here. What is completely new in this paper is they include the impact of surface melt water and its impact on crevasse failure due to downward perculoation. Read the frigging paper
So far, the potential for MISI to cause ice-sheet retreat has focused on the role of ocean-driven melting of buttressing ice shelves from below1. However, it is often overlooked that the major ice shelves in the Ross and Weddell seas and the many smaller shelves and ice tongues buttressing outlet glaciers are also vulnerable to atmospheric warming. Today, summer temperatures approach or just exceed 0 °C on many shelves21, and their flat surfaces near sea level mean that little atmospheric warming would be needed to dramatically increase the areal extent of surface melting and summer rainfall.
Meltwater on ice-shelf surfaces causes thinning if it percolates through the shelf to the ocean. If refreezing occurs, the ice is warmed, reducing its viscosity and speeding its flow. The presence of rain and meltwater can also influence crevassing and calving rates (hydrofracturing) as witnessed on the Antarctic Peninsula’s Larson B ice shelf during its sudden break-up in 2002. Similar dynamics could have affected the ice sheet during ancient warm intervals, and given enough future warming, could eventually affect many ice shelves and ice tongues, including the major buttressing shelves in the Ross and Weddell seas.


and further on they explain what they did:

To capture the dynamics of MICI (Fig. 2d–f), new physical treatments of surface-melt and rainwater-enhanced calving (hydrofracturing) and grounding-line ice-cliff dynamics have been added25. Including these processes was found to increase the model’s contribution to Pliocene GMSL from +7 m (ref. 18) to +17 m (ref. 25).


and we can understand how important this was to their model from comments in the Methods section
The model is modified from ref. 25 to include a more physically based parameterization of the vertical flow of surface mobile liquid water (runoff and rainfall) through moulins and other fracture systems towards the base, which affects the vertical temperature profiles within the ice sheet. Vertical sub-grid-scale columns of liquid water are assumed to exist, through which the water freely drains while exchanging heat by conduction with the surrounding ambient ice that cools and can freeze some or all of the liquid water within the ice interior.


Because of the new ice-model physics that directly involve the atmosphere via meltwater enhancement of crevassing and calving, highly resolved atmospheric climatologies are needed at spatial resolutions beyond those of most GCMs. However, multi-century RCM simulations are computationally infeasible. To accommodate the need for long but high-resolution climatologies, the nested GCM–RCM is run to equilibrium with 1×PAL, 2×PAL, 4×PAL and 8×PAL CO2. I


So what do we have? You first claimed DeConto and Pollard was a paper measuring SMB (which it is not), you then suggested that papers which did measure recent and current SMB in Antartica should be updated based on the DeConto and Pollard paper (which is beyond comprehension how you update actual observations based on models) and then you suggested that papers which were submitted at the same time as DeConto and Pollard needed to be updated by D&M because it was newer (i.e. it failed to get out of review as quickly) and now you are suggesting that surface melt and percolation into fractures, moulins and crevasses has nothing to do with the D&M model (which also is very apparently wrong if you actually bother to read the paper, indeed it is one of the few changes that D&M have made to previous models).

I don’t need to attack you with adhominem comments….you just keep digging yourself deeper and deeper all on your own.
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Re: Antarctica 2017

Unread postby Plantagenet » Sun 23 Apr 2017, 16:47:07

Cool video of rivers and waterfalls forming in Antarctica

antarctica-rivers-waterfalls-discovered-

Take glacier ice...add heat....and you get meltwater.

Add more heat and you get more meltwater.

The math is pretty clear on that one.

Cheers!

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Re: Antarctica 2017

Unread postby rockdoc123 » Sun 23 Apr 2017, 22:14:50

Take glacier ice...add heat....and you get meltwater.

Add more heat and you get more meltwater.

The math is pretty clear on that one.


and apparently according to the papers just discussed they are sending all the melt into the ocean.
Given we know what current mass balance is, we know what the recent acceleration in mass balance (negative in the peninsula and positive in East Antarctica) and the recent papers are suggesting all that melt isn't going to create massive calving events I am not sure what the hand wringing is all about.
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Re: Antarctica 2017

Unread postby Plantagenet » Mon 24 Apr 2017, 00:04:10

rockdoc123 wrote:...according to the papers just discussed they are sending all the melt into the ocean.


Actually, no.

The GRL paper on the formation of thousands of lakes in East Antarctica says that some of the melt is draining into the ice sheet.

A news report on this paper says:

In a new study, scientists who study the largest ice mass on Earth – East Antarctica – have found that it is showing a surprising feature reminiscent of the fastest melting one: Greenland.

More specifically, the satellite-based study found that atop the coastal Langhovde Glacier in East Antarctica’s Dronning Maud Land, large numbers of “supraglacial” or meltwater lakes have been forming – nearly 8,000 of them during summer months between the year 2000 and 2013. Moreover, in some cases, just as in Greenland, these lakes appear to have then been draining down into the floating parts of the glacier, potentially weakening it and making it more likely to fracture and break apart.


Its the same thing again--- you don't understand what you are reading.

rockdoc123 wrote:I am not sure what .... is all about.


Thats not surprising considering you don't understand what you are reading.

Cheers!

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Re: Antarctica 2017

Unread postby rockdoc123 » Mon 24 Apr 2017, 12:05:36

The GRL paper on the formation of thousands of lakes in East Antarctica says that some of the melt is draining into the ice sheet.


Good God....you don't even know what it is you posted. The video you show was taken by the Kingslake et all and Bell et al research groups (Bell was a co-author with Kingslake). The video is not the ponded meltwater noted by Langley et al but rather the channels which Bell clearly points out transfers all of the water to the offshore. And if you bothered to read the Bell paper you would understand the connection between topography and channels and intensity of melt and connectivity of ponds.

Its the same thing again--- you don't understand what you are reading.


Do we really need to go back through the history of your inept understanding of the literature once again? From my post above:

So what do we have? You first claimed DeConto and Pollard was a paper measuring SMB (which it is not), you then suggested that papers which did measure recent and current SMB in Antartica should be updated based on the DeConto and Pollard paper (which is beyond comprehension how you update actual observations based on models) and then you suggested that papers which were submitted at the same time as DeConto and Pollard needed to be updated by D&M because it was newer (i.e. it failed to get out of review as quickly) and now you are suggesting that surface melt and percolation into fractures, moulins and crevasses has nothing to do with the D&M model (which also is very apparently wrong if you actually bother to read the paper, indeed it is one of the few changes that D&M have made to previous models).


So now we can add to that you think a video showing channels and waterfalls somehow relates to a paper by Langely et al in 2016 that discussed seasonal ponded meltwater. That video is demonstrating the point that Bell et al makes that the channels and related waterfalls are extremely efficient at vacating meltwater from the ice sheet to the ocean.

An important point Bell et al is making (and made in the Kingslake et al paper as well) is that with continued warming interconnection of ponds by channels is favored (as observed in the field) and that increased lateral shear on the edges of ice sheets will create long, connected meltwater channels favoring movement of meltwater into the ocean rather than contributing to hydraulic fracturing and calving.
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Re: Antarctica 2017

Unread postby chilyb » Tue 02 May 2017, 20:40:58

http://www.bbc.com/news/science-environment-39759329

A new study has found an atmospheric melting phenomenon in the region to be far more prevalent than anyone had realized.

This is the foehn winds that drop over the big mountains of the peninsula, raising the temperature of the air on the leeward side well above freezing.

-------

The effect on the ice that pushes east from the Peninsula out over the Weddell Sea is clear. It produces great ponds of brilliant blue melt water at the surface.

Such warm, downslope winds are well known across the Earth, of course; and they all have a local name. The chinook winds, for example, that drop over the Rockies and Cascades in North America are the exact same thing.

Foehn is just the title they garnered originally in Europe's Alps. And while their presence on the White Continent has also long been recognised, the BAS study is really the first effort to try to quantify their behavior.

Examining data from 2009 to 2012, Turton and colleagues identified over 200 foehn episodes a year. That makes them more frequent than anyone had thought previously. And the range is broader, too, with occurrences being recorded much further south on the Peninsula.

This all means their melting influence on the eastern shelf ice has very likely been underestimated. "In summer, we expect some melt, around 2mm per day. But in spring we’re having an equal amount of melt as we are in summer during the foehn winds," Ms Turton told BBC News.

"That's significant because it’s making the melt onset earlier. We kind of expect melt in January/February time; but we’re also seeing it sometimes in September/October, in particularly frequent foehn wind conditions."


apparently just a conference presentation, so we'll have to keep a lookout for a corresponding journal publication. I am talking to you, rockdoc123!
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Re: Antarctica

Unread postby Plantagenet » Fri 05 May 2017, 15:42:20

New crack develops in Larsen "C" Ice shelf

a-new-crack-in-one-of-antarcticas-biggest-ice-shelves-could-mean-a-major-break-is-near

This supports the claim that the Larsen "C" ice shelf is starting to break up, just as the Larsen "B" ice shelf did a few years ago.

Cheers!

Image
New Crack forms in Larsen "C" Ice Shelf and splits off towards the ocean

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Re: Antarctica

Unread postby sparky » Fri 05 May 2017, 16:19:42

.
Large slab of floating ice breaking from Antarctica mainland is the usual way it happen there
the county sized block then hang around , get refrozen , re-float around , re freeze again
until after a few years they finally float free and melt
that's nothing unusual per see

https://en.wikipedia.org/wiki/Iceberg_B-15
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Re: Antarctica

Unread postby Plantagenet » Fri 05 May 2017, 16:34:05

sparky wrote:.
Large slab of floating ice breaking from Antarctica mainland is the usual way it happen there
the county sized block then hang around , get refrozen , re-float around , re freeze again
until after a few years they finally float free and melt
that's nothing unusual per see


The ice shelves around Antarctica are temperature sensitive. The reason there are ice shelves surrounding Antarctica but not Greenland is that Antarctica is much colder then Greenland.

Conversely, as Antarctica warms up the ice shelves should be become unstable and disintegrate. This is exactly what seems to be happening now.

The Larsen "B" ice shelf disintegrated several years ago. As far as we can tell, this ice shelf had been stable for as long as human's had been visiting the Antarctic Peninsula and apparently stable for 10,000 years prior to breaking up.

Now the Larsen "C" ice shelf is developing huge cracks and showing signs of instability.

When something hasn't happened in the previous 10,000 years and suddenly its happening now, then that actually is "unusual per se." In fact, its highly unusual.

Cheers!

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Re: Antarctica 2017

Unread postby dohboi » Fri 05 May 2017, 21:49:11

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Re: Antarctica 2017

Unread postby rockdoc123 » Sat 06 May 2017, 10:48:19

When something hasn't happened in the previous 10,000 years and suddenly its happening now, then that actually is "unusual per se." In fact, its highly unusual.


Larsen B was stable throughout the Holocene but that wasn't the case for a number of it's neighbouring ice shelfs, several of which collapsed in the past 10,000 years.

Hodgson, D.A. et al, 2006. Examining Holocene stability of Antarctic Peninsula Ice Shelves. EOS, V. 87, pp 305-312.

Authors point to collapse of George IV ice shelf around 9000 ya, Prince Gustav Channel ice shelf around 5000 ya and several possible episodes of collapse at Larsen A shelf 1400, 2100 and 3800 ya.

While the geological record shows that recent retreat of the Larsen B Ice Shelf is unique in the Holocene, this is not a feature common to all of the other Antarctic Peninsula ice shelves so far studied. Specifically, there is evidence that ice shelves on the west and northeast of the Antarctic Peninsula have behaved differently, experiencing previous retreat events associated with warm periods in the middle and early Holocene.


Thus, according to this alternative hypothesis, the earlier deglaciation of the northern and western side may have made the glacial system more susceptible to advection of warmer ocean currents. This is consistent with the evidence that at least some ice shelves there retreated in periods of early and mid-Holocene atmospheric and ocean warmth, while the thicker ice shelves on the east, such as the Larsen B Ice Shelf, remained buttressed against these warm periods. Present-day ice shelf retreat therefore is not entirely unprecedented and has occurred previously in the Holocene, even south of the present-day climatic limit of ice shelf stability
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Re: Antarctica 2017

Unread postby kiwichick » Sat 06 May 2017, 11:39:27

as per your quote RD .....the Larsen shelves are on the eastern side of the peninsula
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Re: Antarctica 2017

Unread postby rockdoc123 » Sat 06 May 2017, 12:11:27

And your point would be?
Prince Gustave Channel ice shelf is on the east side as well and Larsen A is on the east side. Both experience collapse in the past 10,000 years.
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Re: Antarctica 2017

Unread postby dohboi » Sat 06 May 2017, 13:09:22

And then there's:

UAE plans to drag an ICEBERG from Antarctica to provide drinking water for millions


http://www.dailymail.co.uk/sciencetech/ ... rctic.html

8O :shock: :P :roll: :|
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Re: Antarctica 2017

Unread postby kiwichick » Sat 06 May 2017, 17:29:14

@ rd......you might want to check the map re Larsen A .....hint its just above Larsen B
and Gustav is just above ...or at least there was ice there ......Larsen A

Larsen A was in place for about 4000 years
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Re: Antarctica 2017

Unread postby rockdoc123 » Sat 06 May 2017, 17:43:54

@ rd......you might want to check the map re Larsen A .....hint its just above Larsen B
and Gustav is just above ...or at least there was ice there ......Larsen A

Larsen A was in place for about 4000 years


And you might want to quit being so cryptic. Exactly what is it you are trying to say? Are you suggesting Larsen A and Gustav are not on the east side of the peninsula?

My response was to plantaneget who suggested ice sheets in the area had been there for at least 10,000 years. The paper I referenced pointed out they had not. That includes ice sheets adjacent Larsen B (on the east side of the peninsula) and those on the west side of the peninsula.
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Re: Antarctica 2017

Unread postby kiwichick » Sat 06 May 2017, 20:47:12

@ rd.....and you should read the quote you provided , which talked about the ice shelves on the western side fluctuating .....not those on the eastern side.....according to the quote you provided
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