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Author Topic: Melt water in Antarctica  (Read 7994 times)

Tealight

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Melt water in Antarctica
« on: December 23, 2016, 03:07:16 PM »
Most of Antarctica is far too cold for surface melting in summer, but with global warming more and more regions go periodically above the freezing point. Regions which already experience surface melt will have longer melting periods.

Its time to keep track of these early changes and document if the melt water can form melt lakes like on Greenland or if it flows towards the coast. For the start I attach four images from East Antarctica. Three are upstream of the Amery ice shelf and one is at Cape Ann.


Iceismylife

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Re: Melt water in Antarctica
« Reply #1 on: December 23, 2016, 05:16:57 PM »
http://go.nasa.gov/2hQglIh

My contribution. Resolution sucks but if you can see it with this then it is big.

frankendoodle

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Re: Melt water in Antarctica
« Reply #2 on: December 28, 2016, 12:11:34 AM »
Wow, those polynyas make the ones in Greenland look like puddles.

CraigsIsland

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Re: Melt water in Antarctica
« Reply #3 on: December 28, 2016, 06:57:37 PM »
unreal.

I know the arctic has been the big indicator (seriously wacky up there) but - for antarctica - this is stunning and remarkably "dangerous".


Combined Arctic atmospheric/oceanic changes with greenland ice sheet and antarctica ice sheet changes, we're past the "tipping points". Further de-stabilization of the methane deposits will only accelerate the pace.

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Re: Melt water in Antarctica
« Reply #4 on: December 28, 2016, 07:06:50 PM »
I know the arctic has been the big indicator (seriously wacky up there) but - for antarctica - this is stunning and remarkably "dangerous".

Especially for sea level rise....That will be the next headline risk in the next few years.  It already looks as though the sea level rise is on a steeper slope UP since 2011.  And I guess most of us expected this....but maybe not this soon.
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Darvince

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Re: Melt water in Antarctica
« Reply #5 on: December 28, 2016, 07:20:23 PM »
Speaking of sea level rise, I think it will be telling when and how fast it starts to rise again after this La Nada, because that will most likely be the general rate of rise during this new sea level rise regime before it accelerates again.

Tealight

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Re: Melt water in Antarctica
« Reply #6 on: December 30, 2016, 12:53:27 PM »
Thanks for all the interest and contributions.

Now most of the inland ice of the Amery ice shelf is melting. The area is too huge for high-res images so I just provide the link to NASA Worldview
http://go.nasa.gov/2ikzfFc

JMP

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Re: Melt water in Antarctica
« Reply #7 on: January 05, 2017, 01:54:19 AM »
Nature article about wind causing meltwater.  And, wind exposing blue ice and firn increasing albedo, which in turn, also increases melting.

http://www.nature.com/nclimate/journal/v7/n1/full/nclimate3180.html


Abstract: "Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves causing grounded glaciers to accelerate and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line, which in the recent past has led to the disintegration of the most northerly ice shelves. Here, we provide observational and model evidence that this process also occurs over an East Antarctic ice shelf, where meltwater-induced firn air depletion is found in the grounding zone. Unlike the Antarctic Peninsula, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal East Antarctica high temperatures are caused by persistent katabatic winds originating from the ice sheet’s interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining >3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared with its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in situ observation of supraglacial flow and englacial storage of meltwater suggests that ice-shelf grounding zones in East Antarctica, like their Antarctic Peninsula counterparts, are vulnerable to hydrofracturing."

Carex

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Re: Melt water in Antarctica
« Reply #8 on: January 09, 2017, 04:06:10 PM »
After seeing this post my quick perusal of World View showed the areas effected to be much greater than shown in these few images.  Although I find time to read, I don't seem to be able to find the time to research, especially the time to climb the steep learning curve required.  So I was wondering if anyone knows of anyone who is, or has, searched the satellite record to tease out the extent and location of Antarctic melt ponding over the satellite period.

Tealight

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Re: Melt water in Antarctica
« Reply #9 on: January 10, 2017, 08:14:59 PM »
I'm only aware of a map by NASA which shows the first year of surface melt in an area, but not the melt area per year. The affected area is small in comparison to Antarctica, but probably similar to the melt area in Greenland.



Maybe the NSIDC can release a version of Greenland-Today for Antarctica. The sensor and algorithm to derive melt area should be very similar. All they have to do is create a new webpage and database for it.


Red

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Re: Melt water in Antarctica
« Reply #10 on: January 17, 2017, 05:52:59 PM »
 Long time lurker first time poster. Astonishing isn't it. I have been watching this since November. In particular the Amery shelf and the Shirase glacier. Haven't been able to see the Shirase very well for the past two weeks. However a small glimpse today and the leading sea ward face isn't looking very stable to me. There has been what looks like upwelling to the right against the land mass growing bigger since November with what appears to be under cutting by current all the way to open ocean. If I'm right thats a lot of movement from somewhere. the images I use are from NASA's EOSDIS Worldview. The last good view on November 4th:
https://worldview.earthdata.nasa.gov/?p=antarctic&l=MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2017-01-04&z=3&v=1333758.506606413,1673440.4053282563,1599742.506606413,1844960.4053282563

Today's view shows some of what looks like separating of the lead edge of the glacier as well as the shelf ice in increasingly bad shape.
https://worldview.earthdata.nasa.gov/?p=antarctic&l=MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2017-01-17&z=3&v=1316094.506606413,1656544.4053282563,1582078.506606413,1828064.4053282563

RoxTheGeologist

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Re: Melt water in Antarctica
« Reply #11 on: January 17, 2017, 09:29:46 PM »
Long time lurker first time poster. Astonishing isn't it. I have been watching this since November. In particular the Amery shelf and the Shirase glacier. Haven't been able to see the Shirase very well for the past two weeks. However a small glimpse today and the leading sea ward face isn't looking very stable to me. There has been what looks like upwelling to the right against the land mass growing bigger since November with what appears to be under cutting by current all the way to open ocean. If I'm right thats a lot of movement from somewhere. the images I use are from NASA's EOSDIS Worldview. The last good view on November 4th:
https://worldview.earthdata.nasa.gov/?p=antarctic&l=MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2017-01-04&z=3&v=1333758.506606413,1673440.4053282563,1599742.506606413,1844960.4053282563

Today's view shows some of what looks like separating of the lead edge of the glacier as well as the shelf ice in increasingly bad shape.
https://worldview.earthdata.nasa.gov/?p=antarctic&l=MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2017-01-17&z=3&v=1316094.506606413,1656544.4053282563,1582078.506606413,1828064.4053282563

Nice observation! For comparison for previous years, there are good images on Feb 12th 2014 through 2016. The large area of open water is not present in the those years, and the fast ice in the whole of the bay looks grey and in very bad shape this year.

Red

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Re: Melt water in Antarctica
« Reply #12 on: January 17, 2017, 11:21:33 PM »
Staring back in November when I first noticed it I started searching past history. There was no precedent for that. Last year there was some sign of softening at the land face to the right. However it was small and at the end of melt season, and possibly shadowing. The rate a which this whole area has collapsed is stunning. My question is, does this represent out flow of fresh water off the continent? The way it presents I'm thinking it might. Not a good sign and I would be quite happy to be proven wrong. The following image is the one that started my daily checking of this area in particular and the coast of the continent in general.
https://worldview.earthdata.nasa.gov/?p=antarctic&l=MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2016-11-08&z=3&v=1353927.9473384276,1689211.178337908,1619911.9473384276,1860731.178337908&ab=off&as=2014-02-12&ae=2014-02-19&av=3&al=false

solartim27

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Re: Melt water in Antarctica
« Reply #13 on: January 18, 2017, 12:01:29 AM »
Staring back in November when I first noticed it I started searching past history. There was no precedent for that.

Look at the dates 2016 Apr 1, and 2014 Jan 17, then 2014 later in April for how fast it can recover.   I was very alarmed by Thwaites this year, but noticed that 2013 was much worse.  My impression is that the antarctic sea ice is getting weaker, but stormy conditions breaking it up can't be ruled out yet.
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Red

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Re: Melt water in Antarctica
« Reply #14 on: January 18, 2017, 12:20:14 PM »
Staring back in November when I first noticed it I started searching past history. There was no precedent for that.

Look at the dates 2016 Apr 1, and 2014 Jan 17, then 2014 later in April for how fast it can recover.   I was very alarmed by Thwaites this year, but noticed that 2013 was much worse.  My impression is that the antarctic sea ice is getting weaker, but stormy conditions breaking it up can't be ruled out yet.

Sorry I should have stated that "precedent" :) was for the area in front of the Shirase. It is good to know however that an area can get its act back together after a seemingly disastrous season. :)

iwantatr8

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Re: Melt water in Antarctica
« Reply #15 on: January 18, 2017, 02:00:52 PM »
These folks have some historic data on this looking at daily melt but nothing for last year and this.

http://lgge.osug.fr/personnels/PICARD_Ghislain/melting/

logicmanPatrick

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Re: Melt water in Antarctica
« Reply #16 on: January 19, 2017, 05:54:47 AM »
Some calving of the Amery ice shelf in Prydz Bay, near the 'loose tooth'.

Images are from the Antarctica mosaic recent images, e.g.

https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?subset=Antarctica_r04c06.2017015.aqua.250m

1st image is enhanced to show tabular icebergs from the ice tongue.

2nd image is animated to highlight some of the cracks in the Amery ice shelf.

3 and 4 are the images I used to make the animation.
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logicmanPatrick

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Re: Melt water in Antarctica
« Reply #17 on: January 19, 2017, 05:59:32 AM »
Tabular iceberg image loaded as a thumbnail.

Here's the correct image (I hope!)

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Red

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Re: Melt water in Antarctica
« Reply #18 on: January 19, 2017, 12:16:51 PM »
Some calving of the Amery ice shelf in Prydz Bay, near the 'loose tooth'.

Images are from the Antarctica mosaic recent images, e.g.

https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?subset=Antarctica_r04c06.2017015.aqua.250m

1st image is enhanced to show tabular icebergs from the ice tongue.

2nd image is animated to highlight some of the cracks in the Amery ice shelf.

3 and 4 are the images I used to make the animation.
Nice images, impressive piece of ice.

Tealight

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Re: Melt water in Antarctica
« Reply #19 on: January 19, 2017, 07:08:26 PM »
These folks have some historic data on this looking at daily melt but nothing for last year and this.

http://lgge.osug.fr/personnels/PICARD_Ghislain/melting/


Thanks for the link :)

Maybe I can create some graphs from their data.

Darvince

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Re: Melt water in Antarctica
« Reply #20 on: January 23, 2017, 06:16:48 PM »
This striking melt pond across the center of the Amery Ice Shelf has had explosive growth the last ten days

http://go.nasa.gov/2iWj5W2

steve s

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Re: Melt water in Antarctica
« Reply #21 on: January 23, 2017, 07:33:15 PM »
This striking melt pond across the center of the Amery Ice Shelf has had explosive growth the last ten days

http://go.nasa.gov/2iWj5W2


All those melt ponds and no sign any have formed moulins yet. Can anyone here estimate when we could expect those ponds to drain?

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Re: Melt water in Antarctica
« Reply #22 on: January 23, 2017, 07:40:58 PM »
The linked reference indicates that East Antarctic ice shelves are more vulnerable, due to surface meltwater, than previously thought, with continued anthropogenic global warming:
 
Martin Siegert (2017), "Glaciology: Vulnerable Antarctic ice shelves", Nature Climate Change, Volume: 7, Pages: 11–12, doi:10.1038/nclimate3189

http://www.nature.com/nclimate/journal/v7/n1/full/nclimate3189.html

Summary: "The decay of floating ice shelves around Antarctica speeds up ice flow from the continent and contributes to increased sea-level rise. Now, meltwater attributed to warm winds has been discovered on an East Antarctic ice shelf, suggesting greater vulnerability than previously thought."
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AbruptSLR

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Re: Melt water in Antarctica
« Reply #23 on: January 24, 2017, 06:25:51 PM »
The linked article is entitled: "Abnormal Antarctic Heat, Surface Melt, Giant Cracks in Ice Shelves — More Troubling Signs of a World Tipping Toward Climate Chaos".

https://robertscribbler.com/2017/01/23/abnormal-antarctic-heat-surface-melt-giant-cracks-in-ice-shelves-more-troubling-signs-of-a-world-tipping-toward-climate-chaos/

Extract: "Around its edge zone, and from glacier top to ice shelf bottom, Antarctica is melting. Above-freezing surface temperatures during the austral summer of 2016-2017 have resulted in the formation of numerous surface-melt ponds around the Antarctic perimeter. Large cracks grow through Antarctic ice shelves as warmer ocean currents melt the towering glaciers from below. The overall picture is of a critical frozen region undergoing rapid change due to the human-forced heating of our world — a warming that has brought Antarctica to a tipping point, for such fundamental alterations to Antarctic ice are now likely to bring about a quickening rate of sea-level rise the world over."
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Tealight

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Re: Melt water in Antarctica
« Reply #24 on: January 28, 2017, 02:07:46 AM »
It's time for a few more high resolution images. This time from the McMurdo Dry Valleys and the surrounding areas. The terrain is generally very steep and meltwater or rain just runs down the glacier. Some ice-free slopes dump all their precipitation on the ice.

All images are at 10m resolution
1st image: Meltwater running off the glacier onto sea ice
2nd image: Edit: Probably slush (snow saturated with meltwater) The big blue area is 18km2
3rd image: Partially melted Lake Vida
4th image: More water run-off from slopes
« Last Edit: January 30, 2017, 12:22:57 AM by Tealight »

logicmanPatrick

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Re: Melt water in Antarctica
« Reply #25 on: January 28, 2017, 03:54:39 AM »
Tealight,

your image 2 shows wind shadow and scour.  The wind shadow effect occurs where air blowing over an obstruction induces turbulence to leeward which picks up the snow and carries it away leaving the blue ice surface showing.

The same effect occurs where the wind blows around an obstruction and becomes turbulent.

Generally speaking, in satellite images, pale blue is water, dark blue is ice.
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Red

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Re: Melt water in Antarctica
« Reply #26 on: January 28, 2017, 11:45:25 AM »
Thanks for these pics Tealight. These are indicative of what seems to be happening along the entire coast of the continent. Hopefully this is an anomaly and not the beginnings of the disaster that is the GIS.

DrTskoul

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Re: Melt water in Antarctica
« Reply #27 on: January 28, 2017, 03:10:28 PM »
Both causing albedo reduction....
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Tealight

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Re: Melt water in Antarctica
« Reply #28 on: January 29, 2017, 07:20:38 PM »
Tealight,

your image 2 shows wind shadow and scour.  The wind shadow effect occurs where air blowing over an obstruction induces turbulence to leeward which picks up the snow and carries it away leaving the blue ice surface showing.

The same effect occurs where the wind blows around an obstruction and becomes turbulent.

Generally speaking, in satellite images, pale blue is water, dark blue is ice.

Actually melt lakes are dark blue and blue ice is pale. The parts you have labeled melt ponds are just some melt/rain water channels, probably dried out and left light blue ice behind. The big deep blue area has almost the same shade as true melt ponds on the amery ice shelf or the partially melted lake Vida. For a simple wind shadow it is also too finely structured. There has to be some presence of liquid water even if it's not a real melt lake. Perhaps it is some frozen rain that fell on the glacier and the ice free slopes and just accumulated in this area.

« Last Edit: January 30, 2017, 12:21:21 AM by Tealight »

P-maker

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Re: Melt water in Antarctica
« Reply #29 on: January 29, 2017, 10:41:56 PM »
Patrick and Tealight

Please allow me a fact-based intervention after spending six summers in these kinds of environments.

a)   Wind-scoured bare ice surfaces are extremely rare in the Arctic and are only identified very few places in the Antarctic
b)   Pale blue areas this time of the year in the Antarctic are most likely slush areas – meaning snow fields (even on slopes) saturated with meltwater from slopes above
c)   Darker blue areas are most likely melt water lakes with elongated or irregular forms and a considerable depth

Areas close to nunataks are quite often low-lying - due to wind scour - and are thus prone to slush ice formation during the summer

You will see all four surface types in the fourth image provided by Tealight here: S2A_McMurdo_valleys_20161219.png

I would still like to reserve the phrase "melt pond" to something related to the surface of of sea ice (as long as we have it)

Tealight

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Re: Melt water in Antarctica
« Reply #30 on: January 30, 2017, 12:35:43 AM »
P-maker, thanks for clarifiying these surface types. Could you re-post an image with your interpretation? Like most here this is my first season looking at high resolution images of Antarctica. It's time for us to learn the different melt features and your expert knowledge from being in these enviroments is invaluable. 10m resolution isn't always enough and a top down view makes it even harder to identify the correct surface type.

PS: You list three types a,b and c, but two sentences later you mention four surface types.

Red

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Re: Melt water in Antarctica
« Reply #31 on: January 31, 2017, 01:02:27 AM »
This shot is about 300kms inland from the ocean in Queen Maud Land. This looks like melt to me if so this is a long way in and up from where you'd expect, I think. Please tell me I'm wrong.

https://worldview.earthdata.nasa.gov/?p=antarctic&l=MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2017-01-30&z=3&v=-204503.14945721978,1705201.9298067347,-71511.14945721978,1790961.9298067347

RoxTheGeologist

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Re: Melt water in Antarctica
« Reply #32 on: January 31, 2017, 07:13:24 PM »

The melt water in the Amery ice shelf looks to be moving rapidly to the ocean along its Western edge. It seems to have made it further towards the ocean than previous years.

For a few days earlier in January it was flowing at a few KMs a day! Its pretty wide too, at least a few hundred meters. For the last couple of days it has being pooling at its current terminus. Today's image:

http://go.nasa.gov/2knZb60

It's been nice and sunny too, the northern part of the shelf is darkening rapidly, as are the glaciers that feed it.

RoxTheGeologist

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Re: Melt water in Antarctica
« Reply #33 on: February 03, 2017, 07:12:42 PM »
Looking at the Amery ice sheet again.. I noticed these persistent plumes.

Could these be melt water, fresh water, flowing along under the ice shelf and then coming to the open ocean? The ocean at the edge of the ice shelf is probably cold enough to freeze some of the fresh water, hence the plume.

http://go.nasa.gov/2kamy2m is the EODIS link.

It fits in with the model of eroding the ice sheet that has been proposed: that fresh melt water flows along under the sheet and cause warm salty water to be drawn under the sheet by convection.

All that blue has to go somewhere, right?
« Last Edit: February 03, 2017, 07:18:16 PM by RoxTheGeologist »

Tealight

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Re: Melt water in Antarctica
« Reply #34 on: February 03, 2017, 11:38:09 PM »
Looking at the Amery ice sheet again.. I noticed these persistent plumes.

Could these be melt water, fresh water, flowing along under the ice shelf and then coming to the open ocean? The ocean at the edge of the ice shelf is probably cold enough to freeze some of the fresh water, hence the plume.

http://go.nasa.gov/2kamy2m is the EODIS link.

It fits in with the model of eroding the ice sheet that has been proposed: that fresh melt water flows along under the sheet and cause warm salty water to be drawn under the sheet by convection.

All that blue has to go somewhere, right?


Great observation! These plumes look nothing like sea ice or calved ice debri. They are also quite beautiful on Sentinel 2 images.

Very far inland I found two possible locations where meltwater goes beneath the ice. The first image shows a medium sized river (100m wide) ending apruptly. At the end are a few dark spots which should be holes draining all of the water.

The second image shows a mostly dried up meltwater lake featuring three big dark spots. They appear to be 30-40 meters wide, but it's hard to tell with a 10m resolution. To me 30-40m holes sound resonable compared to observations in Greeland.

Note: The red band (B4) is too sensitive on the Amery ice shelf and screws the colours in an RGB image. 

The third image is the plume Rox mentioned at 10m resolution.

RoxTheGeologist

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Re: Melt water in Antarctica
« Reply #35 on: February 04, 2017, 07:25:00 AM »

The third image is the plume Rox mentioned at 10m resolution.

You are right! that is very beautiful!

steve s

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Re: Melt water in Antarctica
« Reply #36 on: February 04, 2017, 08:44:35 AM »
A hypothesis about plume's visibility and shape -- no ice needed:

The third image shows an apparent outflow jet from the squared-off section of glacier. Rock flour scoured from underneath the glacier provides the visible silt. Then eddies and currents have spread the silt.

iwantatr8

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Re: Melt water in Antarctica
« Reply #37 on: February 04, 2017, 09:40:42 AM »
Here's a quick animation from worldview
It certainly looks like it may start as sediment clouded water but it soon forms ice on top before being drawn away in the current.

P-maker

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Re: Melt water in Antarctica
« Reply #38 on: February 04, 2017, 11:24:07 AM »
Regarding plumes in the water.

I think a mechanism related to wind-blown snow coming off the shelf edge is more likely. Remember, Coriolis force is reversed in the Southern Hemisphere. The rapid disappearance of the sea ice in the top of the image also points to strong winds blowing off-shore.

SteveMDFP

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Re: Melt water in Antarctica
« Reply #39 on: February 04, 2017, 12:33:02 PM »
Regarding plumes in the water.

I think a mechanism related to wind-blown snow coming off the shelf edge is more likely. Remember, Coriolis force is reversed in the Southern Hemisphere. The rapid disappearance of the sea ice in the top of the image also points to strong winds blowing off-shore.

I agree the plumes look wind-borne.  They move far faster than the floes.  In the very first image of these posted here, you can see that there's clearing of the mist on the leeward side of the floes.  I'd favor fog.  Cold air coming off the ice shelf, flowing over slightly warmer ocean.

DrTskoul

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Re: Melt water in Antarctica
« Reply #40 on: February 04, 2017, 01:54:59 PM »
How do we know it's on the water?
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Tealight

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Re: Melt water in Antarctica
« Reply #41 on: February 04, 2017, 02:09:52 PM »
Regarding plumes in the water.

I think a mechanism related to wind-blown snow coming off the shelf edge is more likely. Remember, Coriolis force is reversed in the Southern Hemisphere. The rapid disappearance of the sea ice in the top of the image also points to strong winds blowing off-shore.

I agree the plumes look wind-borne.  They move far faster than the floes.  In the very first image of these posted here, you can see that there's clearing of the mist on the leeward side of the floes.  I'd favor fog.  Cold air coming off the ice shelf, flowing over slightly warmer ocean.

Have you guys looked at the 3rd image in full resolution? It can't be snow because the ice sheet surface is too clear to indicate any kind of snow drift. The fine pattern in the water (meter scale) also can't be created by winds blowing over a smooth and uniform surface like the ocean. The coriolis force is on the scale of a few hundred kilometer. I must admit the contrast isn't great and the patterns could be invisible on TN monitors at a bad viewing angle.

The plume is right at the edge of the ice shelf and very locally restrained, just 5km wide. The crevassed surface right at the plume shows that there is a weak point in the ice shelf where meltwater can exit.

Winds blow over the whole ice shelf which is 200km wide. If they were responsible for the plumes we would see them over a wider area.

How do we know it's on the water?

The plume is influenced by icebergs.

DrTskoul

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Re: Melt water in Antarctica
« Reply #42 on: February 04, 2017, 02:46:00 PM »
It pays to watch carefully  :o
“You can know the name of a bird in all the languages of the world, but when you're finished, you'll know absolutely nothing whatever about the bird... So let's look at the bird and see what it's doing -- that's what counts.”
― Richard P. Feynman

maga

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Re: Melt water in Antarctica
« Reply #43 on: February 04, 2017, 03:11:44 PM »
I'm rather sure that the plume is some kind of ice. At the Amery Ice Shelf warm water enters from the east side, goes down to the grounding line and exits on the west side. The ice at the grounding line is extremely thick, 2 or 3km and the pressure melting point at this depth is a bit below the melting point at the surface. So, if the warm water loses all its energy to melt at depth, it will be below the freezing point at the surface when it exits from the cavity. The summer sunshine rapidly melts the ice again. The ice can also freeze to the bottom of the ice shelf and heal cracks which explains why the cracks are mostly on the east side of the ice shelf. We can observe the same feature ot the west side of the Ronne Ice Shelf.

Tealight

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Re: Melt water in Antarctica
« Reply #44 on: February 07, 2017, 08:34:12 PM »
These folks have some historic data on this looking at daily melt but nothing for last year and this.

http://lgge.osug.fr/personnels/PICARD_Ghislain/melting/


I did create two graphs from their cumulative data, one for corrected data and one for uncorrected data. Both datasets show very high annual variability and the uncorrected data shows a very small downward trend.

The Cumulative Melting Surface (CMS) for the different regions have been corrected from changes in acquisition hours due to satellite replacements with the method developed by Picard and Fily, 2006... To our opinion, the correction efficiently reduces errors for some regions (Peninsula, DML, Amery, Wilkes, MBL), but is less efficient or may add new errors for other regions (Filchner, Ross). In the latter regions, we recommend to use both the corrected and uncorrected CMS.

oren

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Re: Melt water in Antarctica
« Reply #45 on: February 08, 2017, 07:36:45 AM »
Tealight, your analysis of the plume is impressive and spot on. Thanks.

Tealight

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Re: Melt water in Antarctica
« Reply #46 on: February 27, 2017, 09:21:34 PM »
All of the melt lakes on the Amery Ice Shelf have frozen over, but blue water is still visible through the thin ice cover. Maybe some of them won't drain over the winter and will appear again next year.