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Author Topic: Aquifer under Greenland ice  (Read 6795 times)

Rick Aster

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Aquifer under Greenland ice
« on: December 23, 2013, 02:21:13 AM »
BBC News story today: 'Massive' reservoir of melt water found under Greenland ice http://www.bbc.co.uk/news/science-environment-25463647
Refers to Nature Geoscience article: Extensive liquid meltwater storage in firn within the Greenland ice sheet http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2043.html

The aquifer is estimated to be 70,000 square kilometers and is described as delaying the flow of melt water to the sea.

Rick Aster

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Re: Aquifer under Greenland ice
« Reply #1 on: December 23, 2013, 02:28:07 AM »
Several comments on this at Arctic Sea Ice Blog, with Colorado Bob suggesting that at some point in the future, “this could all just flow right into the ocean”: http://neven1.typepad.com/blog/2013/12/cryosat-arctic-sea-ice-up-from-record-low.html

Pmt111500

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Re: Aquifer under Greenland ice
« Reply #2 on: December 23, 2013, 06:48:40 AM »
Thanks. It's nice they've finally found it. This has been suggested for a long time, f.e. based on messy ice layers from the Eemian times, but there's been no publications that I know of before this one.
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Lennart van der Linde

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Re: Aquifer under Greenland ice
« Reply #3 on: December 23, 2013, 08:21:50 AM »
Also see this press release by Utrecht University:
http://press.uu.nl/a-large-body-of-liquid-water-layer-in-greenland-snow/

SCYetti

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Re: Aquifer under Greenland ice
« Reply #4 on: December 29, 2013, 06:30:03 PM »
This new information raises a great many questions in my mind about the stability of the Greenland Ice Sheet. This aquifer is said to be about 72,000 square kilometers in area and located 5 meters deep in some places and 50 meters deep in others. What are the vertical dimensions if the aquifer itself? More important what does this mean for the stability of the GIS? My thoughts are that this makes a sudden partial and yet catastrophic collapse more likely and sooner than we may have thought. I am curious as to the thoughts of others.

Stephen

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Re: Aquifer under Greenland ice
« Reply #5 on: February 13, 2014, 12:27:54 PM »
So when they say aquifer, they mean in the ice as opposed to separate from it, like Lake Vostok in Antarctica?
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Pmt111500

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Re: Aquifer under Greenland ice
« Reply #6 on: February 14, 2014, 08:28:45 AM »
I guess the aquifer is pretty much like slush, fe. in spring when a south facing bank melts a bit and the water flows to the flat ground under the snow, in the night (or winter, in the case of Greenland) the upper layer freezes solid but the slush is still there, as maybe found when stepping on the location. Happens only rarely nowadays here since we do not usually have enough snow for this to happen but the couple of times I had, after stepping on this, to walk back the rest of the way from school drew a vivid memory. It's sort of an ice equivalent of permafrost melting. Or, if you want a more dramatic example, a weak layer in deep alpine snow, that make an avalanche much more probable. Not that there are very steep gradients in Greenland interior.
« Last Edit: February 14, 2014, 09:02:48 AM by Pmt111500 »
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MOwens

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Re: Aquifer under Greenland ice
« Reply #7 on: February 14, 2014, 08:49:44 PM »
Regarding even deeper aquifers in ice sheets:

"Jarvis and Clarke [1974] observed significantly elevated temperatures extending over a 10 to 100m depth range on Steele Glacier, a cold-based glacier in Yukon Territory, Canada. The warmest ice temperatures, within 1C of the pressure melting point, were approximately 7C greater than the ice temperatures expected based on the geothermal gradient and mean annual air temperature. Thermodynamic modeling suggested that these elevated temperatures were due to the presence of a nearby crevasse that had filled with meltwater during a surge 7 years earlier and had not yet completely refrozen. Clarke and Jarvis [1976] suggested that liquid water could persist without refreezing in these crevasses for two to three decades. These observations and modeling results confirmed the ability of a single meltwater pulse to significantly elevate ice temperature for several years in a natural setting."

Phillips et al., 2013 - “Evaluation of cryo-hydrologic warming as an explanation for increased ice velocities in the wet snow zone, Sermeq Avannarleq, West Greenland;” J. Geophysical Research: Earth Surface; doi: 10.1002/jgrf.20079.

MOwens

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Re: Aquifer under Greenland ice
« Reply #8 on: February 24, 2014, 11:54:41 PM »
Here's a new article I've written based on talking to glaciologist William Colgan who studies hydrology of the Greenland ice sheet: http://www.fairfaxclimatewatch.com/blog/2014/02/liquid-water-inside-greenlands-ice-sheet.html

I also asked Colgan if water might start accumulating at the base of the ice sheet in the "bowl" of Greenland, instead of all routing out into the ocean, as is generally assumed with conventional thinking. He basically said that's valid hypothesis, but he wouldn't expect it to be the main issue this century, at least compared to the other issues with Greenland.

My thinking is this:

The water at the base of the sheet will go where pressure and gravity direct it, so there is a tendency for the water to get pushed towards areas of thinner ice where there is less overhead pressure, which is why - if one thinks on very large scale terms - it seems reasonable that the subglacial water will all get pushed towards the perimeter of the ice sheet where the ice is thinner. However, when one considers the fine-scale variations of the bed topography and the ice thickness overhead, it's clear that the pressure gradients in the center of the ice sheet (the "bowl" area) are quite varied. So for example, ice that reaches the ice sheet's base in the center might migrate upslope along the bedrock-ice interface, but then reach the top of a hill-like feature and stop migrating. Thus, a new subglacial lake would be born in that spot. As a consequence of having a new subglacial lake there, the ice overhead experiences less friction, and so it slides faster, thinning overhead of the lake area, thus reinforcing the tendency for water to migrate to the subglacial lake and expanding the capacity of the subglacial lake. Likewise, at the top of the ice sheet, the slight dip in surface elevation from the accelerated local ice flow will cause surface meltwater to preferentially pool in that spot, thus increasing the tendency for future rapid supraglacial lake drainage events in the location, thereby delivering more water to the subglacial lake and its "subglacial watershed."


sidd

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Re: Aquifer under Greenland ice
« Reply #9 on: February 25, 2014, 07:09:05 AM »
I just posted in another thread, but here is some bedrock maps for Greenland, based on the new Bamber results

http://membrane.com/sidd/greenland-2013/

You can see the subglacial hydrology

sidd

Pmt111500

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Re: Aquifer under Greenland ice
« Reply #10 on: February 26, 2014, 02:59:23 AM »
tangentially related is also the viscosity of ice as a function of temperature http://scitechdaily.com/new-research-explains-acceleration-of-greenlands-inland-ice/
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Shared Humanity

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Re: Aquifer under Greenland ice
« Reply #11 on: February 26, 2014, 02:52:51 PM »
I just posted in another thread, but here is some bedrock maps for Greenland, based on the new Bamber results

http://membrane.com/sidd/greenland-2013/

You can see the subglacial hydrology

sidd


Looking at the topology of Greenland, I have always suspected the fastest moving Greenland  glaciers are located near areas where low altitude (underwater) topology reaches from the interior of Greenland to the coast. Is this the case? If so, I believe the subglacial hydrology of  Greenland is already having a dramatic impact on mass loss.

Shared Humanity

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Re: Aquifer under Greenland ice
« Reply #12 on: February 26, 2014, 03:01:55 PM »
Here is what I mean.

https://skitch-img.s3.amazonaws.com/20101023-n88hgsw35x8i7bw7qkw3u1dd4b.jpg

Aren't these 4 locations already sites for fast moving Greenland glaciers?

Shared Humanity

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Re: Aquifer under Greenland ice
« Reply #13 on: February 26, 2014, 03:18:28 PM »
Article on Humboldt Glacier which streams over a relatively low topology feature of Greenland. What is particularly interesting to me is the volume of silt that flows into the sea here. It suggests to me a soft, easy to scour surface at the grounding line.

http://glacierchange.wordpress.com/2010/09/04/humboldt-glacier-retreat-greenland/

sidd

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Re: Aquifer under Greenland ice
« Reply #14 on: February 26, 2014, 11:01:32 PM »
Of the 4 indicated, Humboldt (as Prof. Pelto points out) does not have retrograde slope, and is not connected to the interior. The other 3 are. If you look at the net bedrock maps, you will see that the three (other than Humboldt) are all confined to narrower channels (again as Prof Pelto points out), this increases velocity. To me things that stand out in the subglacial topo:

a)how long the "grand canyon" leading to Peterman is
b) the remarkable "tributary system" (best seen in the view from the west) feeding Jacobshawn

sidd

solartim27

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Re: Aquifer under Greenland ice
« Reply #15 on: February 09, 2017, 06:14:10 PM »
Saw this on Kristin Poinar's twitter feed

http://journal.frontiersin.org/article/10.3389/feart.2017.00005/full
A firn aquifer in the Helheim Glacier catchment of Southeast Greenland lies directly upstream of a crevasse field. Previous measurements show that a 3.5-km long segment of the aquifer lost a large volume of water (26,000–65,000 m2 in cross section) between spring 2012 and spring 2013, compared to annual meltwater accumulation of 6000–15,000 m2. The water is thought to have entered the crevasses, but whether the water reached the bed or refroze within the ice sheet is unknown. ............ The effect of the basal water on the sliding velocity remains unknown. Were the firn aquifer not present to concentrate surface meltwater into crevasses, we find that no surface melt would reach the bed; instead, it would refreeze annually in crevasses at depths <500 m. The crevasse field downstream of the firn aquifer likely allows a large fraction of the aquifer water in our study area to reach the bed. Thus, future studies should consider the aquifer and crevasses as part of a common system. This system may uniquely affect ice-sheet dynamics by routing a large volume of water to the bed outside of the typical runoff period.

FNORD

Rick Aster

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Re: Aquifer under Greenland ice
« Reply #16 on: February 16, 2017, 04:13:16 PM »
From NASA: NASA Study Identifies New Pathway for Greenland Meltwater to Reach Ocean
https://www.nasa.gov/feature/goddard/2017/new-pathway-for-greenland-meltwater-to-reach-ocean

Cracks in the Greenland Ice Sheet let one of its aquifers drain to the ocean . . .

Gray-Wolf

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Re: Aquifer under Greenland ice
« Reply #17 on: February 16, 2017, 05:19:12 PM »
Thanks for that rick A!
I think some folk put things in boxes and 'Greenland' seems to be such? The current goings on in the Arctic Basin has also had impact on Greenland with some pretty big snowfalls on the eastern side/South ( impacted by the storms that went on into the basin?) so chances of some high melt totals flowing into the Sheet as summer progresses?

Each year must put more crevasses/gullys/channels/tunnels through the fabric of the ice sheet and each year must be slowly raising the temps inside the sheet from the bottom up?

When do we see the structural integrity of ice sheet begin to be compromised?

I also worry about this aquifer forming a layer where failure can occur? A big enough load on top and might we see some pretty spectacular movements down the slopes?
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RoxTheGeologist

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Re: Aquifer under Greenland ice
« Reply #18 on: February 16, 2017, 06:48:23 PM »

I also worry about this aquifer forming a layer where failure can occur? A big enough load on top and might we see some pretty spectacular movements down the slopes?

That's my worry too; A well lubricated point of failure causing a catastrophic collapse.

Red

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Re: Aquifer under Greenland ice
« Reply #19 on: February 17, 2017, 06:22:17 PM »
Looking at the coastline as the sun gets higher I've noticed what seems to be a lot of melt water for the time of year in the SW. Going back over the sat/pics to 2014 there isn't visual evidence for this amount of fresh water in these spots. I had to go forward to April 3rd 2014 to see a plume as big +/-. The area seems to produce fresh water year round but in the past it didn't push so far off shore at this time. This would indicate to me higher flow rates. In 2015 it's April 18th before I see a comparable plume and in 2016 it appears to be going strong in late January, cloud cover cause some dating issues for me. Point is, it would seem there has been a large increase in fresh water flow in these two areas apparent in the shafts below. There is some worry about sub glacial lakes suddenly emptying in the SE maybe there's a back door!

http://www.arctic.io/explorer/4Xa5A//4-N90-E0

Adam Ash

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Re: Aquifer under Greenland ice
« Reply #20 on: February 20, 2017, 08:11:40 AM »

I also worry about this aquifer forming a layer where failure can occur? A big enough load on top and might we see some pretty spectacular movements down the slopes?

That's my worry too; A well lubricated point of failure causing a catastrophic collapse.

While the idea of the ice sheet sliding sideways on these subglacial lakes is at first glance worrying, remember that a 1000 metre thick slab of ice needs 900 m of water to float it.  So these subglacial lakes have to be strongly confined hydraulically to create that uplift.  As soon as any disintegration starts this water pressure will probably bleed out the'sides' of the chaotic mess, and all the ice above the lake will just go thump onto bedrock. 

For example, Antarctica's Lake Vostok 250 km long by 50 km wide by around 400 m deep must be providing buoyancy for the 4000 metres of ice above it with a pore pressure of about 3600 m - so in a borehole drilled into it water must rise to within 400 m of the ice surface as clearly the ice must be supported hydraulically - even 4000 m thick ice could not span 50 km.

Certainly water at the bedrock interface will lubricate ice movement, but a float-away of the high ice sheet seems most unlikely.  (Not saying some catastrophic failure mode is not possible, just that mechanism seems unlikely.)
« Last Edit: February 20, 2017, 11:59:55 AM by Adam Ash »

Tony Mcleod

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Re: Aquifer under Greenland ice
« Reply #21 on: February 20, 2017, 11:27:41 AM »
Probably wont see slabs sliding into the ocean causing massive tsunamis but if 10, 20% of it is sitting on trapped water then there is that much less friction.

Gray-Wolf

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Re: Aquifer under Greenland ice
« Reply #22 on: February 20, 2017, 01:56:52 PM »
I was thinking more of a start point for an avalanche to begin with high over loading of new snow on a slippery shear zone?

I imagine the slopes are currently stable but the force of an avalanche might then prove irresistible for the snow/ice lower down slope and so build even larger forcings as the avalanche moves on? 

Like pushing over ever larger domino's a small initial push can build into a much bigger forcing due to the potential energy of the mass under gravity?
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