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Antarctica 2017

Re: Antarctica 2017

Unread postby Plantagenet » Wed 19 Apr 2017, 13:19:30

vox_mundi wrote:Water is streaming across Antarctica: New survey finds liquid flow more widespread than thought

Image
A 400-foot-wide waterfall drains off the Nansen Ice Shelf into the ocean

Video - In the first such continent-wide survey, scientists have found extensive drainages of meltwater flowing over parts of Antarctica's ice during the brief summer. Researchers already knew such features existed, but assumed they were confined mainly to Antarctica's fastest-warming, most northerly reaches. Many of the newly mapped drainages are not new, but the fact they exist at all is significant; they appear to proliferate with small upswings in temperature, so warming projected for this century could quickly magnify their influence on sea level. An accompanying study looks at how such systems might influence the great ice shelves ringing the continent, which some researchers fear could collapse, bringing catastrophic sea-level rises. Both studies appear this week in the leading scientific journal Nature.

Explorers and scientists have documented a few Antarctic melt streams starting in the early 20th century, but no one knew how extensive they were. The authors found out by systematically cataloging images of surface water in photos taken from military aircraft from 1947 onward, and satellite imagery from 1973 on. They found nearly 700 seasonal systems of interconnected ponds, channels and braided streams fringing the continent on all sides. Some run as far as 75 miles, with ponds up to several miles wide. They start as close as 375 miles from the South Pole, and at 4,300 feet above sea level, where liquid water was generally thought to be rare to impossible.

"This is not in the future—this is widespread now, and has been for decades," said lead author Jonathan Kingslake, a glaciologist at Columbia University's Lamont-Doherty Earth Observatory. "I think most polar scientists have considered water moving across the surface of Antarctica to be extremely rare. But we found a lot of it, over very large areas." The data are too sparse in many locations for the researchers to tell whether the extent or number of drainages have increased over the seven decades covered by the study. "We have no reason to think they have," said Kingslake. "But without further work, we can't tell. Now, looking forward, it will be really important to work out how these systems will change in response to warming, and how this will affect the ice sheets."

Image
Each red 'X' represents a separate drainage. Up to now, such features were thought to exist mainly on the far northerly Antarctic Peninsula (upper left). Their widespread presence signals that the ice may be more vulnerable to melting than previously thought. Credit: Adapted from Kingslake et al., Nature 2017

The most dramatic example is the Antarctic Peninsula, which juts far north from the main ice sheet, and where average temperatures have soared 7 degrees Fahrenheit in the last 50 years. In 1995 and 2002, large chunks of the peninsula's Larsen Ice Shelf suddenly disintegrated into the ocean within days. Scientists now suspect that pooling water was at work; liquid tends to burrow down, fracturing the ice with heat or pressure, or both, until a shattering point is reached. Today, another giant piece of the Larsen is cracking, and could come apart at any time.

Further south, temperatures have remained more or less stable, but many of the newly spotted streams there already make their way from the interior out onto ice shelves, or originate on the shelves themselves. That raises the specter that such collapses could happen across much vaster reaches of Antarctica this century, should warming proceed as expected, said Kingslake.

Antarctica's visible drainages may be the tip of the proverbial iceberg. Another study by a separate team published in January revealed that East Antarctica's Roi Baudouin Ice Shelf harbors a largely invisible liquid drainage just under the snow. The team, led by Utrecht University polar scientist Jan Lenaerts, detected it using radar images and drilling. They suspect that such features lurk in many places. And unlike surface streams, these ones are insulated, so may stay liquid year-round.

Until recently, icebergs discharged from glaciers were Greenland's main contributor to sea-level rise. But between 2011 and 2014, 70 percent of the 269 million tons of Greenland's ice and snow lost to the ocean came directly from meltwater, not icebergs.

Image


Widespread movement of meltwater onto and across Antarctic ice shelves - Image1, Image2, Image3, Image4, Image5, Image6


This is exactly the kind of thing that is now implicated in speeding up the rate of movement of the Greenland Ice Sheet, taking more ice more rapidly to the sea where it calves and contributes to sea level rise.

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Re: Antarctica 2017

Unread postby rockdoc123 » Wed 19 Apr 2017, 14:42:59

The paper referred to is:

Kingslake, J. et al, 2017. Widespread movement of meltwater onto and across Antarctic ice shelves. Nature, 544, pp 349-352. doi:10.1038/nature22049

They look at aerial photos for a period of years on various spots on Antarctica but have not done any work (at least not presented in this paper) to determine whether there is anymore melt now versus 30 years ago, in fact nothing was done to quantify melt. What is weird to me is they suggest in their abstract:

To understand the impact of water moving across the ice surface a broad quantification of surface meltwater and its drainage is needed. Yet, despite extensive research in Greenland7–10 and observations of individual drainage systems in Antarctica10–17, we have little understanding of Antarctic-wide surface hydrology or how it will evolve


But in fact a recent paper:

Trusel, L.D. et al, 2013. Satellite-based estimates of Antarctic surface meltwater fluxes. Geoph, Res Letters, V40, pp 6148-6153.

Actually did look at satellite imagery over a decade period and then linked that to a climate model. What was discovered is that surface melt as a whole was decreasing somewhat, not increasing.

here a diagram from their work illustrating measured meltwater and comparison with Racmo.

Image

But what is most surprising is that one of the Kingslake et al co-authors published another paper in the same issue of Nature:

Bell, R.E. et al, 2017. Antarctic ice shelf potentially stabilized by export of meltwater in surface river. Nature Letters, 544, pp 344-348. doi:10.1038/nature22048

Meltwater stored in ponds and crevasses can weaken and fracture ice shelves, triggering their rapid disintegration. This ice-shelf collapse results in an increased flux of ice from adjacent glaciers and ice streams, thereby raising sea level globally4. However, surface rivers forming on ice shelves could potentially export stored meltwater and prevent its destructive effects. Here we present evidence for persistent active drainage networks—interconnected streams, ponds and rivers—on the Nansen Ice Shelf in Antarctica that export a large fraction of the ice shelf’s meltwater into the ocean. We find that active drainage has exported water off the ice surface through waterfalls and dolines for more than a century. The surface river terminates in a 130-metre-wide waterfall that can export the entire annual surface melt over the course of seven days. During warmer melt seasons, these drainage networks adapt to changing environmental conditions by remaining active for longer and exporting more water. Similar networks are present on the ice shelf in front of Petermann Glacier, Greenland, but other systems, such as on the Larsen C and Amery Ice Shelves, retain surface water at present. The underlying reasons for export versus retention remain unclear. Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica—contrary to present Antarctic ice-sheet models, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.



so there appear to be problems portraying this as 1. Unusual, 2 getting worse or 3. A bad thing.

More importantly the Bell et al paper has the potential to completely throw into question the modeling of DeConto and Pollard.
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Re: Antarctica 2017

Unread postby dohboi » Wed 19 Apr 2017, 14:52:24

Some nice pictures here of earlier calving events off PIG:

https://earthobservatory.nasa.gov/IOTD/ ... p?id=89638
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Re: Antarctica 2017

Unread postby Plantagenet » Wed 19 Apr 2017, 15:14:34

rockdoc123 wrote:Bell, R.E. et al, 2017. Antarctic ice shelf potentially stabilized by export of meltwater in surface river. Nature Letters, 544, pp 344-348. doi:10.1038/nature22048

.... our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica—contrary to present Antarctic ice-sheet models, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.[/b]


...the Bell et al paper has the potential to completely throw into question the modeling of DeConto and Pollard.


We've got a reality check on the models in the Greenland Ice Sheet.

As I indicated above, very similar surface meltwater flows have been observed increasing over time on the Greenland Ice Sheet in response to global warming. In Greenland changes in surface hydrology associated with global warming have resulted in huge amounts of surface meltwater. This water collects in ponds and lakes that grow until the surface drainage forms huge moulins that drain the lakes and connect surface melt directly to the subsurface. Adding more water to the glacier bed has resulted in an acceleration of glacier flow, and the concomitant delivery of more Greenland ice to the sea. There are now hundreds of observations of this phenomenon.

Its seems probable to me that similar things will happen in the future in Antarctica as the climate continues to warm, i.e. the development of more surface lakes and more surface drainage culminating in connections between the surface meltwater and the glacier base.

Image
As temperatures rise and melting increases, surface meltwater in Greenland increasingly is captured in giant moulins that take the meltwater directly to the glacier bed. IMHO it seems likely that rising temps in Antarctic will eventually produce similar processes in Antarctica

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Re: Antarctica 2017

Unread postby rockdoc123 » Wed 19 Apr 2017, 15:19:24

I
ts seems probable to me that similar things will happen in the future in Antarctica as the climate continues to warm, i.e. the development of more surface lakes and more surface drainage culminating in connections between the surface meltwater and the glacier base.


you should read both the Kingslake et al and the Bell et al papers. The point made is the meltwater is not accumulating in moulins in Antarctica...it is draining to the ocean which is the rationale behind Bell et al pointing out it is more likely a stabilizing factor than one which would contribute to meltwater penetrating crevasses and increasing calving.
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Re: Antarctica 2017

Unread postby Plantagenet » Wed 19 Apr 2017, 15:42:21

rockdoc123 wrote:... meltwater is not accumulating in moulins in Antarctica...it is draining to the ocean


Thats how the limited surface hydrologic system in Antarctica operates now, yes. It used to operate that way in Greenland as well. But as Greenland warmed the amount of surface melt grew dramatically, and the hydrologic system totally changed.

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Re: Antarctica 2017

Unread postby rockdoc123 » Wed 19 Apr 2017, 16:10:42

Thats how the limited surface hydrologic system in Antarctica operates now, yes. It used to operate that way in Greenland as well. But as Greenland warmed the amount of surface melt grew dramatically, and the hydrologic system totally changed.


Well that isn’t the situation at all according to Bell et al

With the exception of the ice shelves on the Antarctic Peninsula, the surface melt rates on Antarctic ice shelves are presently relatively low. With surface melt rates projected to increase, a key question is whether Nansen-style drainage systems will develop elsewhere and export water off the ice shelves. Using surface digital elevation models (DEMs)26, we analysed possible surface drainage networks of four large ice shelves—Amery, FilchnerRonne, Larsen C and Ross—using a simple routing algorithm (Fig. 4; Methods). Some ice-sheet models project that these ice shelves will disintegrate quickly after the surface melt exceeds 1.5m yr−1 within the next century. Our analysis, however, suggests that drainage networks aligned along troughs could form where ice-flow units of variable thickness and velocity meet at shear margins, similar to the shear-margin river on Nansen Ice Shelf. As surface melt increases, shear-margin rivers may develop on these other ice shelves, extending up to hundreds of kilometres inland (for example, 80km inland on Amery, 65km on Larsen B, 350km on Ross and 440km on Filchner).





The large-scale morphology of future drainage networks will depend on surface and basal mass balance as well as ice-shelf strain rates. Our results show (for the first time, to our knowledge) that surface meltwater on an ice shelf can be exported off the ice shelf through a hydrologic system that evolves as melt increases. We suggest that river networks that facilitate meltwater export will develop on other ice shelves as melt rates increase. Ice-shelf rivers are presently active in northern Greenland (on Petermann Glacier; Extended Data Fig.). These rivers, which reduce the stored surface water, will form when the ice-surface slope is sufficiently steep and the storage capacity in firn aquifers, ponds and crevasses is limited. The slope of an ice shelf ’s surface is strongly controlled by the thickness of incoming ice and by the basal melt rate, which is driven by ocean temperatures. The ice-surface mass balance is controlled by surface accumulation, the persistence of katabatic winds and run-off. Comparing the atmosphere and oceanographic conditions for ice shelves with surface rivers (Nansen, Petermann, and possibly 79N in Greenland) with ice shelves on which water is retained at present (Larsen C and Amery) will advance our understanding of the role of surface river export in a warming world. At present, surface meltwater is being produced and transported onto ice shelves around Antarctica and is expected to increase in the future.
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Re: Antarctica 2017

Unread postby dohboi » Wed 19 Apr 2017, 16:27:44

https://www.nature.com/nature/journal/v ... 22048.html

But since "The underlying reasons for export versus retention remain unclear," we can't really have any idea whether export will dominate in a warming world.
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Re: Antarctica 2017

Unread postby rockdoc123 » Wed 19 Apr 2017, 16:36:59

you missed the following sentence in the abstract

Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica—contrary to present Antarctic ice-sheet models1, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.


my quotes are from the actual Bell et al paper, not the abstract which is a generalized summary. In science nothing is a certainty but the authors do have a model:

We suggest that river networks that facilitate meltwater export will develop on other ice shelves as melt rates increase. Ice-shelf rivers are presently active in northern Greenland (on Petermann Glacier; Extended Data Fig.). These rivers, which reduce the stored surface water, will form when the ice-surface slope is sufficiently steep and the storage capacity in firn aquifers, ponds and crevasses is limited. The slope of an ice shelf ’s surface is strongly controlled by the thickness of incoming ice and by the basal melt rate, which is driven by ocean temperatures. The ice-surface mass balance is controlled by surface accumulation, the persistence of katabatic winds and run-off.


and the comment in the last paragraph of the Conclusions is telling:

At present, surface meltwater is being produced and transported onto ice shelves around Antarctica and is expected to increase in the future.


And if you want to go with the "we can't forecast what will happen with surface melt" argument then by default you have to throw out the DeConto and Pollard paper because that is exactly what they were attempting to do.
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Re: Antarctica 2017

Unread postby dohboi » Wed 19 Apr 2017, 17:20:30

"...rivers could export melt..."

Exactly. Thanks for making my point for me so well! :) :) :)
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Re: Antarctica 2017

Unread postby rockdoc123 » Wed 19 Apr 2017, 19:41:30

Exactly. Thanks for making my point for me so well! :) :) :)


Well I guess we now know that you are throwing out all future projections by anyone including Alley, DeConto etc for Antarctica.
Thanks for coming out, you won't be missed. :roll:

Now maybe the adults can have an intelligent discussion.
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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.


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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:

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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.

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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!

"Its a brave new world"
---President Obama, 4/25/16
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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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