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Antarctica 2017

Re: Antarctica 2017

Unread postby Rod_Cloutier » Fri 17 Feb 2017, 18:22:07

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Re: Antarctica 2017

Unread postby Tanada » Sat 18 Feb 2017, 09:30:20

I am always interested in these tabular icebergs, they are so much larger in scale than the ones that ususally form in the Arctic. The key factor is, how long until the current sweeps it out into the ice pack where it will circulate and melt? Many times when these break loose they ground within a few weeks, even a few days. Once grounded they are essentially in the same environment they were when attached to the shelf and can persist for up too a decade before melting away completely. On the other side of the coin if they get swept far out to sea they usually melt within a year because even a very large tabular berg in the warmer waters doesn't last long. Some pictures at link below quote.

17 February 2017 • 12:38am
Glacial 'aftershock' spawns Antarctic iceberg the size of Manhattan

Antarctica's rapidly melting Pine Island Glacier has shed an iceberg the size of Manhattan, the latest evidence of the ice shelf’s fragility.

Nasa released photographs showing the block of ice separating from the southwest coast of the continent taken between January 26 and January 31.

The sequence, taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) on Nasa’s Terra satellite, shows the berg when it first broke and then as it drifts in the bay.

According to Ian Howat, a glaciologist at Ohio State University, the event was about 10 times smaller than in July 2015, when a 30-kilometre-long (20-mile) rift developed below the ice surface, then broke through and calved an iceberg spanning 583 square kilometers (225 square miles).

“I think this event is the calving equivalent of an ‘aftershock’ following the much bigger event,” Mr Howat said. “Apparently, there are weaknesses in the ice shelf - just inland of the rift that caused the 2015 calving - that are resulting in these smaller breaks.”

Scientists have observed other small rifts in the glacier which are predicted to bring more calving in the near future.

“Such ‘rapid fire’ calving does appear to be unusual for this glacier,” Mr Howat said. But the phenomenon “fits into the larger picture of basal crevasses in the centre of the ice shelf being eroded by warm ocean water, causing the ice shelf to break from the inside out.”

Scientists have been closely monitoring Pine Island, one of the main glaciers responsible for moving ice from the interior of the West Antarctic Ice Sheet to the ocean, and its connection to rising sea levels.

They have observed an increase in the speed of the loss of ice which ultimately would contribute to sea level rise.


http://www.telegraph.co.uk/science/2017 ... manhattan/
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Re: Antarctica 2017

Unread postby dohboi » Wed 01 Mar 2017, 16:38:38

Antarctica hits ... balmy 17.5°C (63.5°F)

http://www.timeslive.co.za/scitech/2017 ... 3.5%C2%B0F
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Re: Antarctica 2017

Unread postby dohboi » Sun 05 Mar 2017, 22:53:00

https://www.skepticalscience.com/2017-S ... st_09.html

Antarctic Sea Ice Sets Record Low, Providing Another Mystery for Scientists

(One wonders why Arctic sea ice gets a sticky, but somehow Antarctica doesn't rate!?)
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Re: Antarctica 2017

Unread postby dohboi » Sun 19 Mar 2017, 13:20:31

http://www.climatecodered.org/2017/01/a ... multi.html

The Amundsen Sea sector of the West Antarctic Ice Sheet has most likely been destabilized and ice retreat is unstoppable for the current conditions.

No further acceleration in climate change is necessary to trigger the collapse of the rest of the West Antarctic Ice Sheet, with loss of a significant fraction on a decadal to century time scale.

Antarctica has the potential to contribute more than a metre of sea-level rise by 2100.

A large fraction of West Antarctic basin ice could be gone within two centuries, causing a 3–5 metre sea level rise.
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Re: Antarctica 2017

Unread postby Subjectivist » Sun 19 Mar 2017, 15:18:39

dohboi wrote:http://www.climatecodered.org/2017/01/antarctic-tipping-points-for-multi.html

The Amundsen Sea sector of the West Antarctic Ice Sheet has most likely been destabilized and ice retreat is unstoppable for the current conditions.

No further acceleration in climate change is necessary to trigger the collapse of the rest of the West Antarctic Ice Sheet, with loss of a significant fraction on a decadal to century time scale.

Antarctica has the potential to contribute more than a metre of sea-level rise by 2100.

A large fraction of West Antarctic basin ice could be gone within two centuries, causing a 3–5 metre sea level rise.


If Dr. Alley is right about Thwaites destabilizing it will be a whole lot more than a meter by 2100.
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Re: Antarctica 2017

Unread postby dohboi » Sun 19 Mar 2017, 21:47:25

Yeah, these reports always underplay the actual alarm that the latest science point toward. I'm not sure anyone really looking at the best current understanding of the latest science is thinking of anything much less than two meters by century end any more.

But remember that this is talking about the Antarctic alone.
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Re: Antarctica 2017

Unread postby dohboi » Thu 23 Mar 2017, 22:52:10

Not the latest, but worth keeping in mind:

Here is Richard Alley, the glaciologist who the MIT atmospheric physicist Kerry Emanuel described as the world’s foremost expert on the relationship of ice and climate, discussing recent ice sheet model results in 2016. At Thwaites Glacier, West Antarctica:

...once you get off of the stabilizing sill, whenever that is in West Antarctica, the time scale of getting rid of the West Antarctic [3.3m GMSLR, 4m in the Northern Hemisphere], it’s not centuries, it’s multi-decadal.

This is not maybe the best case, it’s not the worst case.


At 31:40 in this presentation https://www.youtube.com/watch?v=a7MNA44RMNA

And when might Thwaites get off its stabilizing sill?

From the NY Times recently https://www.nytimes.com/2015/11/15/maga ... .html?_r=0 :

When I asked Richard Alley, almost certainly the most respected glaciologist in the United States, whether he would be surprised to see Thwaites collapse in his lifetime, he drew a breath. Alley is 58.

‘‘Up until very recently, I would have said, ‘Yes, I’d be surprised,’ ’’ he told me. ‘‘Right now, I’m not sure. I’m still cautiously optimistic that in my life, Thwaites has got enough stability on the ridge where it now sits that I will die before it does. But I’m not confident about that for my kids. And if someday I have grandkids, I’m not at all confident for them.’’


(thanks to Erik at rs blog for links and text)
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Re: Antarctica 2017

Unread postby chilyb » Fri 24 Mar 2017, 07:49:16

according to rockdoc123, predicting the collapse of Thwaites is all just guesswork at this point. And, fortunately, we will all be safely dead by the time it happens anyway. So I don't know why we are even discussing this!

post1338117.html#p1338117
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Re: Antarctica 2017

Unread postby Plantagenet » Fri 24 Mar 2017, 13:34:55

chilyb wrote:according to rockdoc123, predicting the collapse of Thwaites is all just guesswork at this point. And, fortunately, we will all be safely dead by the time it happens anyway. So I don't know why we are even discussing this!


Thwaites is just one of many glaciers in Antarctica and Greenland that are being destabilized by global warming.

When you add up all the meltwater from all the sources, its inevitable that we are going to see significant sea level rise in coming decades.

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Re: Antarctica 2017

Unread postby dissident » Fri 24 Mar 2017, 15:11:19

chilyb wrote:according to rockdoc123, predicting the collapse of Thwaites is all just guesswork at this point. And, fortunately, we will all be safely dead by the time it happens anyway. So I don't know why we are even discussing this!

post1338117.html#p1338117


The shill likely does not even have an actual degree.

What Alley presented was vastly more than guess work. The question is when the warmed North Atlantic Deep waters finally hit the Antarctic coasts (because that is where they come to the surface). Any model that gets the THC flow rate correct can give us a good idea.

I would not get too smug about "not in our lifetimes" notion unless everyone here is in their 70s.
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Re: Antarctica 2017

Unread postby rockdoc123 » Fri 24 Mar 2017, 17:13:17

The shill likely does not even have an actual degree.

given your research and cognitive skills recently displayed I suspect I'm not the one whose educational background is in question. :roll:

And as to my comments on Thwaite there are several things that are important
- snowfall is predicted to increase in all of the computer models that look at warming and surface mass balance. Looking only at melt from the glaciers is not instructive as to future SMB without taking into account increased precipitation due to heating
- Thwaites and its neighbours sit above an area of elevated mantle heat flow as has been attested to in recent publications and makes sense given it is close to a former convergent boundary and observable volcanic activity. If the heat from below is causing glaciers in the area to increase in velocity due to basal melt there is really no way of predicting what the future might bring given such heating can increase, be intermittent, or completely cease at some point.
-surface temperatures have only been rising in a small part of Antarctica, for the most part they have either remained relatively flat or been decreasing over the instrumental record. A 2 C increase in temperature (RCP 8.5 by 2100) across the continent would still leave the vast majority well below freezing for the entire year.

As to timing of any of this I already posted reference to the following paper:

Sun, S. et al, 2016. Impact of ocean forcing on the Aurora Basin in the 21st and 22nd centuries. Annals of Glaciology, doi: 10.1017/aog.2016.27

Their analysis is based on a combined ice sheet/ocean model which takes into account ocean heating but doesn't address additional precipitation from atmospheric heating.

From the discussion:

DISCUSSION In this section, we discuss the evolution of the Aurora Basins major outlets: Totten, Dalton and Vanderford glaciers, over the 21st century and 22nd century, and the impact of ocean warming and basal friction to this evolution. The limitations of our method are also discussed. Ice mass loss of Aurora basin is sensitive to ice shelves thinning by ocean warming. The ice-sheet model produces 6000–14 000 km3 loss of ice or a SLR of 15–35 mm over 2 centuries. This is about half the mass loss from West Antarctica when forced by temperature anomalies produced by the FESOM ocean model (Cornford and others, 2015). The basin is potentially unstable under ocean warming. However, in our simulation, the influence of ocean warming to ice-sheet retreat would be limited to ∼3 centuries in our experiment; grounding line retreat and ice mass loss stop after that


It seems to me that a 15 - 35 mm sealevel rise contribution in a couple of centuries is a far cry from the 3 m by 2100 that individuals here seem to have no problem with.

And I would once again point out that comments I make on this thread (as in it's predecessors) are based on published literature for which I provide reference. It is not based on my opinions other than that gained from reading of these publications. IF you have a problem with what I have pointed out then you need to take issue with the referenced literature rather than attack me personally.
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Re: Antarctica 2017

Unread postby dohboi » Fri 24 Mar 2017, 21:24:09

Dis...yes...

Just in case anyone missed it...

baby rock was absolutely sure that there was not way that there could be warmer waters in lower depths than colder waters in polar regions.

The guy constantly spouts utterly and total idiocy on these threads constantly, occasionally cloaked in out-of-context, unlinked quotes that seem vaguely to support his bs positions but that inevitably turn out upon inspection to be again utter and total bs.

In any other well moderated forum such an obvious shill and troll would be banned.

But we seem to embrace such utter crap and bullshit artists on this forum as if they were the gods' gift to humanity here....

Such is the burden under which we labor in these increasingly fallow fields here...
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Re: Antarctica 2017

Unread postby chilyb » Fri 24 Mar 2017, 22:32:57

I think the glacier scientists have ruled out the effect of undersea volcanos at this point. Rockdoc123 you are a true minister of doubt! LOL
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Re: Antarctica 2017

Unread postby dissident » Fri 24 Mar 2017, 23:32:16

chilyb wrote:I think the glacier scientists have ruled out the effect of undersea volcanos at this point. Rockdoc123 you are a true minister of doubt! LOL


http://www.livescience.com/46194-volcan ... ciers.html

Volcanoes have been pumping geothermal energy into the Thwaites glacier system for a very long time. Yet we are seeing destabilization only when atmospheric CO2 levels exceed 400 ppmv unlike during the whole of the period going back 4 million years to the closing of the Panama channel and seabed changes around Indonesia that changed the global ocean circulation.

This tells us that volcanoes are one of the biggest denier crocks.
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Re: Antarctica 2017

Unread postby rockdoc123 » Sat 25 Mar 2017, 11:59:14

I think the glacier scientists have ruled out the effect of undersea volcanos at this point.


well you better send some emails to a whole bunch of scientists who have been looking at this issue for a considerable time. There are many papers, I won't post the entire abstract for each as it will make up way to large of a post. I'll just post the relevant comments but you can go to the abstract and paper for the full story

we can go back to the time when climate change was just starting to get a lot of attention:

Blankenship, D., et al, 1993. Active volcanism beneath the West Antarctic ice-sheet and implications for ice sheet stability. Nature 361, pp 526-529

Because its bed is grounded well below sea level, the stability of the WAIS may depend on geologically controlled conditions at the base which are independent of climate. In particular, heat supplied to the base of the ice sheet could increase basal melting and thereby trigger ice streaming, by providing the water for a lubricating basal layer of till on which ice streams are thought to slide.

Here we present aerogeophysical evidence for active volcanism and associated elevated heat flow beneath the WAIS near the critical region where ice streaming begins.


and the relatively recent:

Behrendt, J.C., 2012. The aeromagnetic method as a tool to identify Cenozoic magmatism in the West Antarctic Rift System beneath the West Antarctic Ice Sheet – a review; Thiel sublacial volcano as a possible source of the ash layer in the WAISCORE.. Tectonophysics, v 585, pp 124-136. http://dx.doi.org/10.1016/j.tecto.2012.06.035

Exposed volcanoes in the WARS are < 34 Ma, but at least four are active. If a few buried volcanic centers are active, subglacial volcanism may well affect the WAIS regime. Aerogeophysical data (Blankenship et al., 1993, Mt. Casertz; Corr and Vaughan, 2008, near Hudson Mts.) indicated active subglacial volcanism. Magnetic data indicate a caldera and a surrounding “low” in the WAISCORE vicinity possibly the result of a shallow Curie isotherm. High heat flow reported from temperature logging in the WAISCORE (Conway et al., 2011; Clow, personal commun.) and a volcanic ash layer (Dunbar, 2012) are consistent with this interpretation. A subaerially erupted subglacial volcano, (Mt Thiel), about 100 km distant, may be the ash source.
The present rapid changes resulting from global warming, could be accelerated by subglacial volcanism.


Schroeder, D. M, et al, 2014. Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet. PNAS. V 111, pp 9070-9072

Heterogeneous hydrologic, lithologic, and geologic basal boundary conditions can exert strong control on the evolution, stability, and sea level contribution of marine ice sheets. Geothermal flux is one of the most dynamically critical ice sheet boundary conditions but is extremely difficult to constrain at the scale required to understand and predict the behavior of rapidly changing glaciers. This lack of observational constraint on geothermal flux is particularly problematic for the glacier catchments of the West Antarctic Ice Sheet within the low topography of the West Antarctic Rift System where geothermal fluxes are expected to be high, heterogeneous, and possibly transient. We use airborne radar sounding data with a subglacial water routing model to estimate the distribution of basal melting and geothermal flux beneath Thwaites Glacier, West Antarctica. We show that the Thwaites Glacier catchment has a minimum average geothermal flux of ∼114 ± 10 mW/m2 with areas of high flux exceeding 200 mW/m2 consistent with hypothesized rift-associated magmatic migration and volcanism. These areas of highest geothermal flux include the westernmost tributary of Thwaites Glacier adjacent to the subaerial Mount Takahe volcano and the upper reaches of the central tributary near the West Antarctic Ice Sheet Divide ice core drilling site


Damiani, T.M., et al, 2014. Variable crustal thickness beneath Thwaites Glacier revealed from airborne gravimetry, possible implications for geothermal heat flux in West Antarctica., Earth and Planetary Science Letters, V 407, pp 109-122]/i]

The thin continental crust we reveal beneath Thwaites Glacier supports the hypothesis that the West Antarctic Rift System underlies the region and is expressed topographically as the Byrd Subglacial Basin. This rifted crust is of similar thickness to that calculated from airborne gravity data beneath neighboring Pine Island Glacier, and is more extended than crust in the adjacent Siple Coast sector of the Ross Sea Embayment. A zone of thinner crust is also identified near the area's subaerial volcanoes lending support to a recent interpretation predicting that this part of Marie Byrd Land is a major volcanic dome, likely within the West Antarctic Rift System itself. Near-zero Bouguer gravity disturbances for the subglacial highlands and subaerial volcanoes indicate the absence of supporting crustal roots, suggesting either (1) thermal support from a warm lithosphere or alternatively, and arguably less likely; (2) flexural support of the topography by a cool and rigid lithosphere, or (3) Pratt-like compensation. Although forward modeling of gravity data is non-unique in respect to these alternative possibilities, we prefer the hypothesis that Marie Byrd Land volcanoes are thermally-supported by warmer upper mantle. The presence of such inferred warm upper mantle also suggests regionally elevated geothermal heat flux in this sector of the West Antarctic Rift System and consequently the potential for enhanced meltwater production beneath parts of Thwaites Glacier itself


[i]Carson, C.J. et al, 2014. Hot rocks in a cold place: high sub-glacial heat flow in East Antarctica. Jour Geol Soc, 171, doi: 10.1144/jgs2013-030


We show that variations in abundance and distribution of heat-producing elements within the Antarctic continental crust result in greater and more variable regional sub-glacial heat flows than currently assumed in ice modelling studies. Such elevated heat flows would have a fundamental effect on ice sheet behaviour and highlight that geological controls on heat flow must be considered to obtain more accurate and refined predictions of ice mass balance and sea-level change.


Pittard, M.L. 2016. Organization of ice flow by localized regions of elevated geothermal heat flux. Geoph Res Lett, v43,7, pp 3342-3350. DOI: 10.1002/2016GL068436

We find that high heat flux regions have a significant effect across areas of slow-moving ice with the influence extending both upstream and downstream of the geothermal anomaly, while fast-moving ice is relatively unaffected. Our results suggest that localized regions of elevated geothermal heat flux may play an important role in the organization of ice sheet flow


Fisher, A.T., et al, 2015. High geothermal heat flux measured below the West Antarctic Ice Sheet. Science Advances, v1,6, DOI: 10.1126/sciadv.1500093

The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow, and mass balance of ice sheets, but measurements of this parameter are difficult to make in ice-covered regions. We report the first direct measurement of geothermal heat flux into the base of the West Antarctic Ice Sheet (WAIS), below Subglacial Lake Whillans, determined from the thermal gradient and the thermal conductivity of sediment under the lake. The heat flux at this site is 285 ± 80 mW/m2, significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m2. The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region.


So, no I'm afraid no one has ruled out a contribution to basal heating from mantle derived elevated high heat flow.

Volcanoes have been pumping geothermal energy into the Thwaites glacier system for a very long time. Yet we are seeing destabilization only when atmospheric CO2 levels exceed 400 ppmv unlike during the whole of the period going back 4 million years to the closing of the Panama channel and seabed changes around Indonesia that changed the global ocean circulation.


well first off the current ice sheet in Antarctica began to form about 34 Mya when CO2 was around 600 ppm, so arguing a correlation is basically stupid at best. Also you infer that glaciers in WAIS have only been retreating which is as far from the truth as you can get. They have a considerable history of repeated advance and retreat since the ice sheet formed.

Graham, A.G.C. et al, 2016. Submarine glacial-landform distribution across the West Antarctic margin, from grounding line to slope: the Pine Island – Thwaites ice-stream system. Jour of Geol Soc, v 46 pp 493 – 500. doi: 10.1144/M46.173

The outer-shelf seismic stratigraphy shows cycles of erosion and deposition by ice streams that maintained a broadly consistent flow path through time (Gohl et al, 2013). The overall geological context is, therefore, one of repeated glaciation and degalciation since at least the Miocene.


Pollard, D and De Conto RM.2009. Modelling West Antarctic ice sheet growth and collapse through the past five million years. Nature, pp 329 – 332. doi: 10.1038/nature07809

The West Antarctic ice sheet (WAIS), with ice volume equivalent to approximately 5 m of sea level, has long been considered capable of past and future catastrophic collapse. Today, the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams. Grounding lines are several hundred metres below sea level and the bed deepens upstream, raising the prospect of runaway retreat. Projections of future WAIS behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms. Its variation since the Last Glacial Maximum is best known, with grounding lines advancing to the continental-shelf edges around approximately 15 kyr ago before retreating to near-modern locations by approximately 3 kyr ago. Prior collapses during the warmth of the early Pliocene epoch and some Pleistocene interglacials have been suggested indirectly from records of sea level and deep-sea-core isotopes, and by the discovery of open-ocean diatoms in subglacial sediments. Until now, however, little direct evidence of such behaviour has been available. Here we use a combined ice sheet/ice shelf model capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing to simulate Antarctic ice sheet variations over the past five million years. Modelled WAIS variations range from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands. Transitions between glacial, intermediate and collapsed states are relatively rapid, taking one to several thousand years. Our simulation is in good agreement with a new sediment record (ANDRILL AND-1B) recovered from the western Ross Sea, indicating a long-term trend from more frequently collapsed to more glaciated states, dominant 40-kyr cyclicity in the Pliocene, and major retreats at marine isotope stage 31 ( approximately 1.07 Myr ago) and other super-interglacials


The bottom line is that given all of predictions around WAIS are based on models they are completely at the mercy of inputs for which there is a huge amount of uncertainty. Inputting a low value for basal heat flow will result in a result not driven by heat from below, putting in a higher number results in the opposite. A number of boundary conditions have to be in place for glaciers to speed up or slow down including increased snow accumulation, basal pressure melting due to overburden and slip, basal perturbations, surface warming, ocean warming in some cases and yes basal heating from geothermal sources. When various variables are left out or poorly estimated the result is nothing more than a possible scenario, one that is no more valid than any other.
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Re: Antarctica 2017

Unread postby chilyb » Sun 26 Mar 2017, 00:39:16

Study finds surprisingly high geothermal heating beneath West Antarctic Ice Sheet


http://news.ucsc.edu/2015/07/antarctic-heating.html

The amount of heat flowing toward the base of the West Antarctic ice sheet from geothermal sources deep within the Earth is surprisingly high, according to a new study led by UC Santa Cruz researchers. The results, published July 10 in Science Advances, provide important data for researchers trying to predict the fate of the ice sheet, which has experienced rapid melting over the past decade.

Lead author Andrew Fisher, professor of Earth and planetary sciences at UC Santa Cruz, emphasized that the geothermal heating reported in this study does not explain the alarming loss of ice from West Antarctica that has been documented by other researchers. "The ice sheet developed and evolved with the geothermal heat flux coming up from below--it's part of the system. But this could help explain why the ice sheet is so unstable. When you add the effects of global warming, things can start to change quickly," he said.

High heat flow below the West Antarctic ice sheet may also help explain the presence of lakes beneath it and why parts of the ice sheet flow rapidly as ice streams. Water at the base of the ice streams is thought to provide the lubrication that speeds their motion, carrying large volumes of ice out onto the floating ice shelves at the edges of the ice sheet. Fisher noted that the geothermal measurement was from only one location, and heat flux is likely to vary from place to place beneath the ice sheet.
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Re: Antarctica 2017

Unread postby rockdoc123 » Sun 26 Mar 2017, 10:40:39

Once again rather than referencing grey journalism why is it people can't just go to the actual published research. I already posted the reference for the work conducted by Fisher in the above post.

Fisher, A.T., et al, 2015. High geothermal heat flux measured below the West Antarctic Ice Sheet. Science Advances, v1,6, DOI: 10.1126/sciadv.1500093

this from the Discussion in that paper:

The spatial extent of elevated geothermal heat flux below the WAIS is not indicated by our data, although the alignment of areas having rapid ice movement, subglacial lakes, and/or high heat flux (Fig. 4C) may indicate a causal link. Much of the negative mass balance of continental ice sheets is driven by the rapid flow of ice streams that terminate at ice shelves and outlet glaciers. Basal boundary conditions, including bed topography and interactions with warm ocean water , are important in controlling the rates of ice stream discharge. Geothermal heat flux remains a critical but poorly constrained variable in many models of dynamic ice sheets, and it may help to determine ice stream locations and discharge rates and the associated development of subglacial hydrologic systems

Meltwater production from the grounded part of the entire Antarctic Ice Sheet is thought to be ~65 giga–metric tons/year on the basis of continental-scale estimates of the geothermal heat flux. Every additional 100 mW/m2 of excess geothermal heat applied to the base of the WAIS (about half of that inferred in this study of SLW based on the difference between geothermal and basal ice heat fluxes) would be equivalent to an increase in meltwater of ~19 giga–metric tons/year.


The paper describes one site which was visited within the tectonically complex WAIS. The drill site corresponds to an area of high heat flow identified by previous researchers. Fisher et al is explicit in this paper that they are neither suggesting that high basal heat flow is responsible for rapid flow of glaciers in WAIS nor are they suggesting it has nothing to do with it. Basically they point out it is an important element that needs to be considered in understanding glacial flow in this region.

And that was my original point. You can't have reliable forecasts for collapse of glaciers in WAIS without a proper understanding of basal heat flow. The studies I pointed to above draw attention to the notion that geothermal gradients as measured at the basement ice interface are much higher locally throughout WAIS and in certain parts of EAIS as well. The fact that volcanic activity is well known in this area aligns well with the idea of localized areas of higher heat flow and thinned crust.
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Re: Antarctica 2017

Unread postby Plantagenet » Sun 26 Mar 2017, 11:39:07

Fisher et al is explicit in this paper that they are neither suggesting that high basal heat flow is responsible for rapid flow of glaciers in WAIS nor are they suggesting it has nothing to do with it. Basically they point out it is an important element that needs to be considered in understanding glacial flow in this region.

And that was my original point. You can't have reliable forecasts for collapse of glaciers in WAIS without a proper understanding of basal heat flow.


Of course.

But thats true of every parameter involved in glacier flow. To have a truly reliable forecast you need better data on ocean and air temperatures, precipitation, cloudiness, basal topography, wind and lateral snow transport, internal temperature profiles, basal sediments, basal water content, etc. etc.

However, when you do the math, the amount of "extra" melt you get from elevated basal heat flow in local areas isn't very large. A far more important factor is the destabilization going on due to accelerated melt and calving at the termini due to warmer oceans---and this factor points to acceleration of ice loss from the Antarctic glaciers in coming years.

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Re: Antarctica 2017

Unread postby rockdoc123 » Sun 26 Mar 2017, 13:26:26

However, when you do the math, the amount of "extra" melt you get from elevated basal heat flow in local areas isn't very large.


several of the papers I posted above disagree with that

As an example the Fisher et al paper makes the statement:

Meltwater production from the grounded part of the entire Antarctic Ice Sheet is thought to be ~65 giga–metric tons/year on the basis of continental-scale estimates of the geothermal heat flux (34). Every additional 100 mW/m2 of excess geothermal heat applied to the base of the WAIS (about half of that inferred in this study of SLW based on the difference between geothermal and basal ice heat fluxes) would be equivalent to an increase in meltwater of ~19 giga–metric tons/year.


essentially that is a 30% increase in melt over areas with elevated geothermal heating.

And the paper I referenced above:

Pittard, M.L. 2016. Organization of ice flow by localized regions of elevated geothermal heat flux. Geoph Res Lett, v43,7, pp 3342-3350. DOI: 10.1002/2016GL068436

from the body of the paper:

Elevated sub-glacial heat flow can: (1) affect ice rheology and viscosity; (2) facilitate local pressure melting of the basal ice resulting in mechanical decoupling of the basal ice–rock interface, the formation of sub-glacial meltwater, basal hydrological networks and sub-glacial lakes; (3) promote development of easily deformed water-saturated basal till and other unconsolidated sediments (e.g. Greve & Hutter 1995; Siegert 2000). These factors can facilitate ice surging and ice stream flow (e.g. Greve 2005; Pollard et al. 2005; Llubes et al. 2006)

In regions of low ice velocity, the addition of localized high GHF leads to a change in flow behavior, with the increase in ice velocity delineated from the surrounding ice flow into a stream-like flow. The increased velocity is seen up to 100 km upstream and hundreds of kilometers downstream from the HHFR. The increase in velocity slows downstream to control values as the elevated ice temperature is diffused with distance. In the case of Exp_3, the diffusion continued approximately 300 km downstream of the 50 km wide HHFR
.

and the conclusion:

6. Conclusion The inclusion of high heat flow regions caused by synthetic but plausible estimates of localized radiogenic crustal heat production caused local variation in ice velocity and consequently ice thickness. The largest influence was in regions of low ice velocity, with the impact seen 100 km upstream and 300 km downstream of the high heat flow region with a change in the flow behavior of the region. The flow changes from sheet flow to stream flow, with slight decreases in velocity seen adjacent to the region of stream-like flow. The increased local ice velocities will influence the organization of ice flow, which will affect long-period model runs. The direct influence on regions of fast flow is minimal, with heat generated by the fast flow dominating the local high heat flow, with no change in ice flow behavior. The existence of high heat flow regions may impact basal inversions for the initiation of ice sheet models by influencing the ice temperature and local viscosity of the ice. Further techniques to estimate or measure geothermal heat flux are required to fully assess possible impacts on ice dynamics and mass budget estimates.


and the major point that Pittard et al make is if you don't get the heat flow contribution to basal melt correctly then the rest of your model overcompensates with one or more variables in order to match the observed surface flow rates. Using that same model to project into the future will almost certainly give an incorrect answer.

Note that a lot of the previous work modeling basal melt in glaciers has used heat flow at the basement interface in the order of 20 - 40 mW/m2. Many of those studies found little contribution to melt compared to pressure melting. But what is different here is the Fisher paper has identified an area with heat flow of 285 mW/m2. That is a substantive difference and the geophysical work referenced above suggests similar elevated heat flows are present in the area around Thwaites.

And as I've pointed out previously the Thwaites models that were predicting rapid collapse are ice/ocean models and did not include the view that as temperatures rise precipitation increases. Increased precipitation has two affects 1. it contributes to glacial speed as a consequence of internal deformation flow and 2. it negates a portion of sea level rise due to melting of ice sheets at their margins (i.e. surface mass balance).
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