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Vergent

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Re: Melt Ponds
« Reply #50 on: July 26, 2013, 05:05:34 AM »
lake e^x

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Vergent

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Re: Melt Ponds
« Reply #51 on: July 26, 2013, 05:11:45 AM »
sorry about the double post, its going to drain today.



too much water

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helorime

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Re: Melt Ponds
« Reply #52 on: July 26, 2013, 05:46:30 AM »
Clearly the ice has turned into ice-9 and is sinking....
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Re: Melt Ponds
« Reply #53 on: July 28, 2013, 05:56:20 PM »
An image showing "Extensive melt pond coverage... on the Alaskan side of the Arctic Ocean" from the NPEO web site:

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Re: Melt Ponds
« Reply #54 on: July 28, 2013, 06:36:23 PM »
An image showing "Extensive melt pond coverage... on the Alaskan side of the Arctic Ocean" from the NPEO web site:



Wow.  Now, if we imagine the effects of a cyclone, with wind and waves.....
Even if the floes had substantial thickness under those melt ponds, such surface irregularities will make the floes far more vulnerable to fracturing. Like when cutting glass, you just create a single deep scratch, apply pressure, and it fractures easily.  The irregularities concentrate the fracturing forces.

Since we've got more low-pressure cyclonic systems in the forecast, and since waves from them can travel great distances, this whole region may shortly resemble a vast slush field (I mean, even more than it already does).

Vergent

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Re: Melt Ponds
« Reply #55 on: July 28, 2013, 07:13:38 PM »

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Re: Melt Ponds
« Reply #56 on: July 28, 2013, 07:44:08 PM »
Back to square # 1:
Have a ice day!

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Re: Melt Ponds
« Reply #57 on: July 28, 2013, 08:08:41 PM »
Aral lake?

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Re: Melt Ponds
« Reply #58 on: July 28, 2013, 10:01:14 PM »
An image showing "Extensive melt pond coverage... on the Alaskan side of the Arctic Ocean" from the NPEO web site:



If you follow the cataracts of water closely, a large percentage of the "melt ponds" on these floes connect directly to open sea in one way or another.  To me, it looks a lot more like a floe that's reached a combination of irregularity in its surface smoothness (but what means, I'm not sure) and overall reduction in thickness that it is simply half-way under(sea)water.

This would certainly hash with the behavior of the "North Pole Lake Webcam" we've been tracking lately.  Instead of "draining", the ice could have indeed risen to "drain" a salt-water lake due to disintegration of nearby parts of the larger floe whose weight was holding that area down.  Too bad there isn't a salinity sensor on the part of the bouy that may eventually end-up in a "melt pond" :-)

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Re: Melt Ponds
« Reply #59 on: July 28, 2013, 10:45:31 PM »
An image showing "Extensive melt pond coverage... on the Alaskan side of the Arctic Ocean" from

That (and the comment from the NPEO site) is really scary looking, Jim.

Albedo?  What is this albedo you speak of?
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Nightvid Cole

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Re: Melt Ponds
« Reply #60 on: July 28, 2013, 10:46:27 PM »
An image showing "Extensive melt pond coverage... on the Alaskan side of the Arctic Ocean" from the NPEO web site:



If you follow the cataracts of water closely, a large percentage of the "melt ponds" on these floes connect directly to open sea in one way or another.  To me, it looks a lot more like a floe that's reached a combination of irregularity in its surface smoothness (but what means, I'm not sure) and overall reduction in thickness that it is simply half-way under(sea)water.

This would certainly hash with the behavior of the "North Pole Lake Webcam" we've been tracking lately.  Instead of "draining", the ice could have indeed risen to "drain" a salt-water lake due to disintegration of nearby parts of the larger floe whose weight was holding that area down.  Too bad there isn't a salinity sensor on the part of the bouy that may eventually end-up in a "melt pond" :-)

Cheers,

Gideon

I suspect they started out as melt ponds and expanded until they connected to each other and to the open sea.

Vergent

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Re: Melt Ponds
« Reply #61 on: July 29, 2013, 10:01:19 PM »


A second generation of melt ponds has begun.

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prokaryotes

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Re: Melt Ponds
« Reply #62 on: July 29, 2013, 10:12:10 PM »
Can anyone outline or link to some analysis how this year compares to last year and the years before? How unusual is this melt there?  Is this happening every year, maybe this year just earlier or was this previously considered stable? Although are there projections which saw this development coming? Thanks.
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Vergent

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Re: Melt Ponds
« Reply #63 on: July 29, 2013, 11:09:55 PM »
Can anyone outline or link to some analysis how this year compares to last year and the years before? How unusual is this melt there?  Is this happening every year, maybe this year just earlier or was this previously considered stable? Although are there projections which saw this development coming? Thanks.



The climate models have a poor record with regard to arctic ice.

https://sites.google.com/site/arcticseaicegraphs/longterm

Follow this link to the long term trends.

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Re: Melt Ponds
« Reply #64 on: July 30, 2013, 12:42:07 AM »
Can anyone outline or link to some analysis how this year compares to last year and the years before? How unusual is this melt there?  Is this happening every year, maybe this year just earlier or was this previously considered stable? Although are there projections which saw this development coming? Thanks.



The climate models have a poor record with regard to arctic ice.

Vergent


I think prokaryotes was asking more specifically about the pattern of melt ponding, and how much we know about its long term trends.  I'm also interested if anyone knows; for example here's James Morison of the North Pole Environmental Observatory quoted as saying that he had seen much more extensive melt ponds (in an article that still fails to point out the webcam isn't at the pole):
http://www.theatlantic.com/technology/archive/13/07/the-pond-at-the-north-pole/278093/

Your point about any predictions drawn from the large-scale climate models is of course well-taken.

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Re: Melt Ponds
« Reply #65 on: July 30, 2013, 01:34:51 AM »
The recent history of melt ponds seen by the pole-cams:

http://www.arctic.noaa.gov/detect/ice-npole.shtml

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Re: Melt Ponds
« Reply #66 on: July 30, 2013, 03:16:12 AM »
The recent history of melt ponds seen by the pole-cams:

http://www.arctic.noaa.gov/detect/ice-npole.shtml

Vergent

Look to me like 2013 is much more like 2012 than any of the others.
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Re: Melt Ponds
« Reply #67 on: July 30, 2013, 04:38:58 AM »
The recent history of melt ponds seen by the pole-cams:

http://www.arctic.noaa.gov/detect/ice-npole.shtml

Vergent

That's a nice summary.  Thanks!

-Dan

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Re: Melt Ponds
« Reply #68 on: July 30, 2013, 11:31:20 AM »
Can anyone outline or link to some analysis how this year compares to last year and the years before? How unusual is this melt there?  Is this happening every year, maybe this year just earlier or was this previously considered stable? Although are there projections which saw this development coming? Thanks.
The ICDC presents melting pond research for the years 2000-2011. The scientists used true color MODIS 8 day composites and trained a neural network to determine surface properties. The conclusion reads: ... The mean melt pond fraction per grid cell for the entire Arctic Ocean derived from MODIS satellite data of the last 12 years shows a strong increase in June. By the end of June
the maximum with a mean melt pond fraction above 15 % is reached, followed by a second maximum in end of July
. ...

There is somewhere another paper showing that melt ponds decrease albedo and increase energy flux into floes substantially. Combine this with the fact they form easier and drain later on (flat) first year ice and you'll recognize another important feedback effect. A reference these physics have been implemented in models is still to be found.

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Re: Melt Ponds
« Reply #69 on: July 30, 2013, 02:08:43 PM »
Quote
A reference these physics have been implemented in models is still to be found.

Holland, Marika M., David A. Bailey, Bruce P. Briegleb, Bonnie Light, Elizabeth Hunke, 2012: Improved Sea Ice Shortwave Radiation Physics in CCSM4: The Impact of Melt Ponds and Aerosols on Arctic Sea Ice*. J. Climate, 25, 1413–1430. doi: http://dx.doi.org/10.1175/JCLI-D-11-00078.1

The Los Alamos Sea Ice Model A CICE Update
http://www.oc.nps.edu/NAME/2012_RASM_Tucson_Hunke_Nov2012.pdf

Taylor, P. D., and D. L. Feltham (2004), A model of melt pond evolution on sea ice,
J. Geophys. Res., 109 , C12007, doi:10.1029/2004JC002361.
http://www.cpom.org/people/dlf/meltpondsin1D2004.pdf

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Re: Melt Ponds
« Reply #70 on: July 30, 2013, 02:48:32 PM »
Nice, thx, happens not often I change my mind that happily. The first link states: In simulations with no ponds or aerosols in sea ice, the Arctic ice is over 1 m thicker and retains more summer ice cover.

Quote
A reference these physics have been implemented in models is still to be found.
Holland, Marika M., David A. Bailey, Bruce P. Briegleb, Bonnie Light, Elizabeth Hunke, 2012: Improved Sea Ice Shortwave Radiation Physics in CCSM4: The Impact of Melt Ponds and Aerosols on Arctic Sea Ice*. J. Climate, 25, 1413–1430. doi: http://dx.doi.org/10.1175/JCLI-D-11-00078.1

The Los Alamos Sea Ice Model A CICE Update
http://www.oc.nps.edu/NAME/2012_RASM_Tucson_Hunke_Nov2012.pdf

Taylor, P. D., and D. L. Feltham (2004), A model of melt pond evolution on sea ice,
J. Geophys. Res., 109 , C12007, doi:10.1029/2004JC002361.
http://www.cpom.org/people/dlf/meltpondsin1D2004.pdf

Jim Hunt

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Re: Melt Ponds
« Reply #71 on: July 30, 2013, 03:29:32 PM »
A reference these physics have been implemented in models is still to be found.

There's more on this over on The Distributed Arctic Sea Ice Model thread.

See in particular "Incorporation of a physically based melt pond scheme into the sea ice component of a climate model" and more recent papers from Flocco and Feltham.
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Hans

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Re: Melt Ponds
« Reply #72 on: August 07, 2013, 07:52:26 AM »
Question: has webcam 1 been attacked by a polar bear?

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Re: Melt Ponds
« Reply #73 on: August 07, 2013, 12:03:24 PM »
I don't think so, Hans. The camera was there for a long time after the foot prints. But it's in the drink now, no matter how it got there.

http://psc.apl.washington.edu/northpole/NPEO2013/webcams1and2.html

Peter Ellis

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Re: Melt Ponds
« Reply #74 on: August 07, 2013, 01:11:43 PM »
Check the time stamps on the photos.  First one with the footprints + smudge on the lens is 19:59 on the 5th August.  Last one is 20:09 the same day.  After that, it fell over some time before 19:59 on the 6th - so we only really know that it stayed upright for at least 10 minutes after the first evidence of the bear being there.  Also note: it was distinctly askew from the moment the footprints appeared.  I'm guessing the bear knocked it a bit off balance, then it fell down properly a few hours later.

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Re: Melt Ponds
« Reply #75 on: August 07, 2013, 04:36:37 PM »
Check the time stamps on the photos.  First one with the footprints + smudge on the lens is 19:59 on the 5th August.  Last one is 20:09 the same day.  After that, it fell over some time before 19:59 on the 6th - so we only really know that it stayed upright for at least 10 minutes after the first evidence of the bear being there.  Also note: it was distinctly askew from the moment the footprints appeared.  I'm guessing the bear knocked it a bit off balance, then it fell down properly a few hours later.

Or perhaps the bear returned and knocked it over?

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Re: Melt Ponds
« Reply #76 on: August 07, 2013, 10:15:33 PM »
I'm guessing the bear knocked it a bit off balance, then it fell down properly a few hours later.

There you have it: we have passed the Arctic sea ice tipping point.  ;D

I think those buoys are designed to be self-righting. They easily weather gale force winds. It would take significant force to put one on it's side and make it stay that way. Ever see a Polar bear kill a 2-ton walrus?

I'm guessing the bear saw his selfie on facebook, and came back to destroy the evidence (sea bears are smarter than the average bear).  8)
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Freegrass

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Re: Melt Ponds
« Reply #77 on: September 03, 2020, 04:48:58 PM »
I'm so surprised there isn't a thread on melt ponds yet.
This is an interesting discussing from the melting thread.

mdoliner

"Melt ponds cannot drain. nine tenths of the floe is below sea level."

Imagine a floe 2 meters thick, 20 cm above water level. A melt pond forms in the middle of it, 40 cm deep, but not in contact with the ocean below. Then cracking allows it to drain. Previously the ice below the pond had the weight of 40 cm of water sitting on top of it. Now it only has 20 cm above it as the pond drains to sea level. It is essentially not balanced buoyantly. So it will try to rise.

As it rises, further water drains from the pond, until a new balance is reached. Since the remainder of the ice under the pond is 1.6 meters thick, that balance means the ex pond becomes 16 cm of ice above the water line, 1.44 meters below the water line.

If it is able to rise at all! But that requires that the connection to the ice around the pond adjusts and is put under strain. Thus possibly cracking. If the connections to the surrounding ice are strong enough to prevent the rise, then the ice is under tensile stresses at some points. Not good for a crystalline material where cracks can grow due to melting.

mdoliner

"Melt ponds cannot drain. nine tenths of the floe is below sea level."

Imagine a floe 2 meters thick, 20 cm above water level. A melt pond forms in the middle of it, 40 cm deep, but not in contact with the ocean below. Then cracking allows it to drain.
I'm not sure if that could happen. If the ice cracks, seawater from below will push it's way into the cracks until it reaches the meltpond, at which point the surface of the meltpond will fall down to sea level. The weight balance of the ice floe would change slighly, but the melt and cracking needed to connect the meltpond to the underlying seawater would probably involve a much greater disturbance.

But the water in the meltpond cannot "drain" down through 1.6m of ice to somehow pour out into the surrounding ocean at a depth of 1.8 meters (in your example) - what force would compel it to take on such a journey? Not gravity, that's for sure.

In fact, talking about meltponds "draining" is probably meaningless. If the ice that seperates the meltpond from the underlying seawater melts or cracks, the water level of the meltpond will change to match the level of the surrounding ocean by mixing with the intruding seawater. But this slight change in the weight balance of the floe is much smaller than the changes required to enable the pond to communicate with the underlying seawater.

Sorry for the tautological posting.
I wanted to comment on the bold part.

Wouldn't the fresh water drain until it reaches the level of the fresh water/salt water boundary under the ice?
« Last Edit: September 03, 2020, 05:13:51 PM by Freegrass »
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SteveMDFP

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Re: Melt Ponds
« Reply #78 on: September 03, 2020, 05:00:44 PM »
Wouldn't the fresh water drain until it reaches the level of the fresh water/salt water boundary?

Since the floe is floating, the drained melt pond will reach a level matching that of the surrounding sea.

Or, actually, very slightly higher, as the still-fresh water is slightly less dense than sea water.  The weight of a water column inside the floe must match the weight of a corresponding column outside the floe (down to the same arbitrary depth), to be in equilibrium.

Edit:  Ooops.  We already have a melt ponds thread, at least one other:

Melt Ponds!
https://forum.arctic-sea-ice.net/index.php/topic,427.0.html

This thread should be closed/locked.
« Last Edit: September 03, 2020, 05:11:42 PM by SteveMDFP »

oren

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Re: Melt Ponds
« Reply #79 on: September 03, 2020, 05:06:04 PM »
An old source but still interesting:
https://web.archive.org/web/20070817050130/http://www.crrel.usace.army.mil/sid/perovich/SHEBAice/meltpond.htm
Quote
Our pond studies are focused on understanding: (1) the temporal evolution of pond volume and distribution; (2) the partitioning of surface meltwater between storage in ponds and runoff into leads; and (3) the effect of ponds on the optical and structural properties of the underlying ice.
As the snow melted in June, melt ponds began to form on the surface. As melt progressed these ponds grew, both in areal extent and in depth. Throughout June and July the melt ponds deepened, in some cases completely melting through to the ocean. Once a pond had a salt water connection to the ocean, melting further accelerated. "In the land of ice, salt water is the ultimate corrosive." Average pond depths at the end of July were were roughly 0.5 m. By mid-August the pond surfaces were freezing.

We monitored pond extent and depth along the albedo line from mid-June through mid-August. Data are in the directory POND under filenames ALMPmmdd.csv. Profiles of pond depth were recorded every four days. During the course of the summer ponds along the albedo line grew about 0.5 m deeper and a few meters wider. The maximum pond fraction along the albedo line was 32% on August 8. Pond depths and widths were also measured for a "sea level" pond at Seattle and an "alpine" pond at the ridge.

The pond fraction and average pond depth along the albedo line from 20 June to 10 August 1998 are plotted to the right.

oren

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Re: Melt Ponds
« Reply #80 on: September 03, 2020, 05:12:07 PM »
https://seaice.uni-bremen.de/melt-ponds/

Quote
Melt ponds on the Arctic sea ice affect the albedo, mass balance and heat balance of the ice by translating the increase of air temperature into drastic and rapid surface type changes. They introduce a positive feedback within the sea ice albedo feedback loop, thus facilitating further ice melt. In the context of changing Arctic climate, knowledge of melt pond fraction, its spatial distribution and the length of the melt season is required to reflect and predict the role of the sea ice cover in the radiative balance of the region.

The temporal dynamics of melt can be subdivided into four stages (Eicken et al., 2002):

* Melt onset: widespread ponding and lateral melt water flow.
* Drainage: both the surface albedo and melt pond fraction decrease due to removal of snow cover and due to pond drainage.
* Melt evolution: the meltwater penetrates deeper into the ice, the pond coverage continues to evolve and melt pond fraction to grow.
* Freeze-up: surface albedo is still affected by the now over-frozen ponds.

The melt pond fraction during each of these stages, their duration and the date of their onset/end are specific to sea ice type and can provide a lot of information on the state of the sea ice and its change. A satellite retrieval of the melt pond fraction and albedo allows to observe the melt evolution and how it is reflected in the surface optical properties throughout the whole Arctic summer.

Freegrass

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Re: Melt Ponds
« Reply #81 on: September 03, 2020, 05:18:01 PM »
Wouldn't the fresh water drain until it reaches the level of the fresh water/salt water boundary?

Since the floe is floating, the drained melt pond will reach a level matching that of the surrounding sea.

Or, actually, very slightly higher, as the still-fresh water is slightly less dense than sea water.  The weight of a water column inside the floe must match the weight of a corresponding column outside the floe (down to the same arbitrary depth), to be in equilibrium.

Edit:  Ooops.  We already have a melt ponds thread, at least one other:

Melt Ponds!
https://forum.arctic-sea-ice.net/index.php/topic,427.0.html

This thread should be closed/locked.
I did a search and nothing came up.
I already moved my initial message to the old Melting Ponds Thread. So you can close this one Oren. Better to continue on the old thread with its last message from 2013?  ???
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oren

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Re: Melt Ponds
« Reply #82 on: September 03, 2020, 05:24:10 PM »
I merged both threads into one. Important subject, please go on.

oren

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Re: Melt Ponds
« Reply #83 on: September 03, 2020, 05:28:27 PM »
https://www.whoi.edu/fileserver.do?id=137327&pt=2&p=113029

Melt ponds: from understanding of controlling physics to climate model parameterization
Danny Feltham
Centre for Polar Observation and Modelling, UCL

It's a very long presentation, seems interesting.

oren

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Re: Melt Ponds
« Reply #84 on: September 03, 2020, 05:41:38 PM »
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL078077

Salinity Control of Thermal Evolution of Late Summer Melt Ponds on Arctic Sea Ice

Quote
Abstract
The thermal evolution of melt ponds on Arctic sea ice was investigated through a combination of autonomous observations and two‐dimensional high‐resolution fluid dynamics simulations. We observed one relatively fresh pond and one saline pond on the same ice floe, with similar depth. The comparison of observations and simulations indicates that thermal convection dominates in relatively fresh ponds, but conductive heat transfer dominates in salt‐stratified ponds. Using a parameterized surface energy balance, we estimate that the heat flux to the ice is larger under the saline pond than the freshwater pond when averaged over the observational period. The deviation is sensitive to assumed wind, varying between 3 and 14 W/m2 for winds from 0 to 5 m/s. If this effect persists as conditions evolve through the melt season, our results suggest that this imbalance potentially has a climatologically significant impact on sea‐ice evolution.

Plain Language Summary
Sea ice provides key feedbacks on polar and global climate, with melt ponds being particularly significant. Melt ponds darken the ice surface, thereby increasing the absorption of sunlight and accelerating ice melt. This study provides a new perspective on melt‐pond salinity, its previously unrecognized significance in controlling the thermal properties of ponds, and the potential impact on ice melting as we transition toward a younger sea ice cover. Many state‐of‐the‐art sea ice models represent melt ponds as a freshwater layer with a surface temperature of 0 °C, consistent with a past Arctic ocean dominated by desalinated perennial ice and relatively fresh ponds. However, perennial ice has diminished in recent decades, with increasing prevalence of young saline ice. This leads to ponds with a wider range of salinities and temperatures. We show that salinity strongly impacts pond temperatures, using observations of adjacent freshwater and saline melt ponds on Arctic sea ice. Combining this data with model simulations, we find that melt‐pond salinity impacts heat transfer to the ice below and the resulting melting rate. Our study reveals that melt‐pond salinity and salt stratification are key variables influencing heat transfer in melt ponds, which need to be considered in future model development.

wili

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Re: Melt Ponds
« Reply #85 on: September 03, 2020, 05:53:59 PM »
Couldn't the water in the melt pond dribble over the edge, rather than sinking down the middle, that is? I guess it depends on the depth of the ice floe.
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SteveMDFP

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Re: Melt Ponds
« Reply #86 on: September 03, 2020, 05:55:18 PM »
I did a search and nothing came up.
I already moved my initial message to the old Melting Ponds Thread. So you can close this one Oren. Better to continue on the old thread with its last message from 2013?  ???

The built-in search function is rubbish, I'm afraid.  For future reference, Google does a better job of finding threads. E.g.,
https://www.google.com/search?q=%22melt+pond%22+physics+site%3Bforum.arctic-sea-ice.net

On the search line, one would type:
"melt pond" physics site:forum.arctic-sea-ice.net

The "site:" part is incredibly useful for restricting to a domain or site.  You can also specify, e.g., "filetype:"  And more.

oren

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Re: Melt Ponds
« Reply #87 on: September 03, 2020, 05:56:10 PM »
VERY good advice Steve. Indeed the internal search function is terrible.

Freegrass

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Re: Melt Ponds
« Reply #88 on: September 03, 2020, 07:13:24 PM »
Insightful crosspost from the melting thread.

Glen Tamblyn re pond draining.

If there is a hole in the bottom of the pond the ice is the same as a floating doughnut. the water in the hole will rise to sea level. i agree that the water in the pond that is above sea level will drain, but that is only one tenth of the depth of the pond.  And yes the floe will be lighter by the amount that drains, but the pond, since it is draining, has the depth of the whole floe. nine-tenths of its depth will remain. Of course if the pond is very shallow and yet punches through in one deep place so that all the water is above sea level yes it will drain, but ponds warm faster than ice because of albedo, so why would that happen?
It's as simple as communicating vessels, isn't it? Once the vessels are connected, they level out.

The question is if the melt pond will mix with the salt water layer below. If the answer is yes, then the melting increases in the pond. But logic tells me that it would be reasonable to assume that as the floe melts out on the outside, that only fresh meltwater can get mixed in with the freshwater in the melt pond. Because the salty water would reside in a lower layer that can't reach the floe?

And then we get into evaporation and salt content of the icefloe. Does the meltwater in the pond contain salt? I assume that the simplistic answer is yes in FYI, and no in MYI?

And what happens to melt ponds when floes are disturbed by swells and wind? Does a storm add salt water to the melt ponds?

And if a melt pond has a hole, do we then still speak about melt ponds in a floe? Or do we then just start calling them circular doughnut floes?

And why is it spelled a Floe? And not a floating Floa?  ???
« Last Edit: September 03, 2020, 08:50:44 PM by Freegrass »
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Re: Melt Ponds
« Reply #89 on: September 03, 2020, 08:08:30 PM »
I addressed your last question on the other thread. It's probably from a Norwegian world 'flo' that means 'flat slab' from a root that ultimately also yields the 'flag' in 'flag-stone.' So it's the shape and not the act of floating that the term originally refers to...who'd have thunk it?
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Re: Melt Ponds
« Reply #90 on: September 03, 2020, 08:43:11 PM »
I addressed your last question on the other thread. It's probably from a Norwegian world 'flo' that means 'flat slab' from a root that ultimately also yields the 'flag' in 'flag-stone.' So it's the shape and not the act of floating that the term originally refers to...who'd have thunk it?
Did you get my reply there?
And now I better stop posting because it's whiskey coke day... 8)

https://forum.arctic-sea-ice.net/index.php/topic,3060.msg284889.html#msg284889
« Last Edit: September 03, 2020, 08:53:59 PM by Freegrass »
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Tor Bejnar

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Re: Melt Ponds
« Reply #91 on: September 03, 2020, 11:38:54 PM »
Melt pond links courtesy Tor Bejnar https://phys.org/news/2017-01-arctic-ponds-meltwater-clogs-ice.html       https://www.sciencedaily.com/releases/2017/01/170123145213.htm   
and gregcharles  https://www.nasa.gov/content/goddard/melt-ponds-shine-in-nasa-laser-altimeter-images/
I'll sort out the above images later, and there's a couple more links I'm looking for but where?

Early in the melt season, cracks beneath melt ponds heal, because the ice is colder at the bottom of the floe.
Arctic ice is healthy for children and other living things.

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Re: Melt Ponds
« Reply #92 on: September 04, 2020, 06:47:04 AM »
Fine to move the discussion here. But the discussion above is not the discussion I was having.

My point was about the verb "to drain" and my claim that a meltpond on floating ice cannot "drain" under realistic circumstances. But to recap, this discussion started when Glenn_Tamblyn posted this a few days back:

However, if a melt pond drains, could that trigger other issues. A while back scientists identified a mechanism they think is involved in the collapse of large ice shelves. Obviously they are fresh water ice and a couple of orders of magnitude thicker but might the same mechanism apply to sea ice?

- Melt pond forms, down to some depth.
- Melt pond drains away.
- The ice beneath the melt pond now needs to rise to rebalance buoyancy.
- But the ice surrounding the drained pond doesn't need to adjust.
- Thus leading to stresses in the ice around the edges of the empty pond as the empty pond tries to rise, and potentially cracking.
- Repeated occurrences of this is believed to lead to a cascading failure and collapse of ice shelves.

But mdoloner stated the obvious:

Melt ponds cannot drain. nine tenths of the floe is below sea level.

And I honestly thought that that was that. I'ts all about the word "drain" which implies that water disappears down an opening and flows away. The big meltponds on top of glaciers do exactly this.

But a water on top of a floating floe cannot "drain". If a crack were to appear, water would enter from below at the same time as the level of the meltpond would sink to meet the water level surrounding the floe. This is not "draining" unless the bottom of the meltpond is higher than the surrounding sea level.

Shared humanity weighed in with:

??? Once melt water has punched through the ice floe, it will seek its own level which would be sea level.

which begs the question - what forces allow melt water to "punch through" an ice floe? This phrasing doesn't explain anything, neither as a mechanism nor as a metaphor.

Finally Glenn_Tamblin answers mdoliner with the following example:

Imagine a floe 2 meters thick, 20 cm above water level. A melt pond forms in the middle of it, 40 cm deep, but not in contact with the ocean below. Then cracking allows it to drain.

Which is what triggered my posting.

This whole discussion is about the difference between a rigid but floating ice shelf possibly hundreds of meters thick, where meltponds form on the surface and when cracking occurs, the water in the meltpond obviously drains away (it flows down into the crack to meet upswelling sea water, and the water level in the crack seeks to match the sea level surrounding the ice). But here we are talking of a difference of tens of meters between the bottom of the meltpond and the sea level, and the water is able to drain down to sea level.

Floating sea ice is not rigid as an ice shelf, and it is vastly thinner.  And the only circumstances under which a melt pond on an ice floe can be said to "drain" is if the bottom of the meltpond is sufficiently above sea level when cracking occurs to enable the water to disappear from view. I find it hard to imagine such a circumstance, and it certainly does not apply to Glenn's example.

To recap: A melt pond can only be said to have "drained" if the water disappears. This can only happen if the bottom of the meltpond is above sea level when cracking occurs. Most meltponds seem to have bottoms that reach below sea level, hence cannot "drain". But a scenario of thicker ice with a meltpond that bottoms out above sea level is of course feasible, and if such a flow were to crack, the melpond would drain and the weight of the meltpond itself could be a contributing factor to the cracking itself (water being denser than ice and all that, although "punching" is not a good way to describe this). But this is extremely unlikely to be a significant factcor in arctic ice melt, which was what Glenn's original post was about.
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Re: Melt Ponds
« Reply #93 on: September 04, 2020, 10:14:53 AM »
The bulk of ice forms with vertical growing ice crystals this plus the exclusion of salt tends to create channels through the ice. If the ice is thicker than 2 meters it is likely stacked but that process has some gaps between layers. The freeze melt cycle will over seasons fill these channels. Freshwater ice is more solid and would not have channels to drain through.

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Re: Melt Ponds
« Reply #94 on: September 04, 2020, 10:34:11 AM »
Binntho, melt ponds can be said to "drain" even if it's a partial drain that just causes their horizontal extent to shrink significantly (rather than disappear entirely). They do do that, and in scientific literature this is called "draining". Which is why it's better to discuss it in a dedicated thread where one can throw links at the problem, rather than a comment in passing in the season thread.

From my post upthread:
Quote
The temporal dynamics of melt can be subdivided into four stages (Eicken et al., 2002):

* Melt onset: widespread ponding and lateral melt water flow.
* Drainage: both the surface albedo and melt pond fraction decrease due to removal of snow cover and due to pond drainage.
* Melt evolution: the meltwater penetrates deeper into the ice, the pond coverage continues to evolve and melt pond fraction to grow.
* Freeze-up: surface albedo is still affected by the now over-frozen ponds.

A couple of additional notes:
Melt ponds are created initially in the snow layer, which due to its light density would tend to be above the water line, thus enabling drainage to have a bigger effect.
The fresh water freezes in contact with the colder ice below, sealing the melt pond until the core of the ice warms.

binntho

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Re: Melt Ponds
« Reply #95 on: September 04, 2020, 11:14:07 AM »
Oren, acknowledged. And thanks for reminding me that when water from meltponds seeps into the underlying ice, it freezes and seals off the meltpond and increases the structural strength of the floe.

But this use of "drain" is not what the original poster (Glenn) had in mind.

So let's clarify that meltponds can indeed drain in the sense that "parts or all of the water moves down into the ice".

And of course, partial draining of a meltpond is also draining, and the sinking of surface water into porous ice could potentlially leave a "dry" meltpond with a bottom lower than the surrounding sea level.

But the thinking that meltponds can drain out through the bottom of the ice, even that they can somehow "punch" their way out, is clearly wrong.
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Re: Melt Ponds
« Reply #96 on: September 04, 2020, 06:45:59 PM »
Great to see this reinvigorated forum. Melt ponds have a lot of non-intuitive aspects. The article pair below is rather surprising for the late date of discovery within the century of melt pond study. With first year ice becoming ever more abundant and melt occurring perhaps earlier via Arctic Amplification, the intricate processes described below become ever more important.

Brine exclusion during FYI maturation ends up on the ice surface, in interior channels, and as non-buoyant water that sinks, affecting stratification and inhibiting later mixing. The Polarstern scientists are already skimming ice off the surface before lowering gear and seeing connecting currents.

In the North Pole region, with half the area in melt ponds, some measuring as deep as 1.5m, what fraction of the ice volume in December will be completely refrozen melt ponds rather than thermodynamic bottom ice? Some fraction will have drained and so have lower topography which might have consequences for re-formation via trapping in the following melt season.

Arctic melt ponds form when meltwater clogs ice pores
Pond formation mechanism previously unknown
https://unews.utah.edu/melt-ponds/ popular account

In 2014, Golden, along with study first author Chris Polashenski of the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory and colleagues traveled aboard the U.S. Coast Guard cutter Healy to the Chukchi Sea, between Alaska and Siberia, to investigate massive algae blooms below the ice, which had been first observed in 2011. As part of their study they needed to measure the permeability of the ice. Permeability is a measure of how well interconnected voids and channels within a material allow fluid to flow through.

Their first attempt involved drilling a hole in the ice down below the “freeboard level,” or water table, to see how quickly the water filled the hole back in.

“It filled up to the freeboard level in about a second and a half,” Golden says, indicating the ice was too permeable to make a measurement. Next, the team tried to add water to the hole to see how quickly the water level re-equilibrated to the freeboard level. They planned several attempts, and noticed that in the second attempt, the water level fell much more slowly than in the first attempt.

“And then the third time was the charm,” Golden says. The team poured water into the hole and the level didn’t go down at all. “We formed a melt pond!” he says.

Intrigued, the team tested different levels of water salinity in boreholes and used dyes to trace the progress of the water through the ice. The team used red and green food coloring from the Healy’s kitchen. All of their experimentation pointed to a clear mechanism for melt pond formation.

“The freezing point of the fresh meltwater from snow is zero Celsius,” Golden says. “But the ice itself is maybe -1 or -1.5. The freezing point of seawater is -1.8. So basically, you’re getting this infusion of fresh water and there’s enough cold there to clog up the pores. You’re lowering the permeability of the ice by this process of freezing freshwater plugs into the porous microstructure.” With lowered permeability, the meltwater can form a pool on top of the ice.

Percolation blockage: A process that enables melt pond formation on first year Arctic sea ice
Chris Polashenski  Kenneth M. Golden  Donald K. Perovich et al
16 January 2017
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016JC011994 journal account

Melt pond formation atop Arctic sea ice is a primary control of shortwave energy balance in the Arctic Ocean. During late spring and summer, the ponds determine sea ice albedo and how much solar radiation is transmitted into the upper ocean through the sea ice. The initial formation of ponds requires that melt water be retained above sea level on the ice surface.

Both theory and observations, however, show that first year sea ice is so highly porous prior to the formation of melt ponds that multi-day retention of water above hydraulic equilibrium should not be possible.

Here we present results of percolation experiments that identify and directly demonstrate a mechanism allowing melt pond formation. The infiltration of fresh water into the pore structure of sea ice is responsible for blocking percolation pathways with ice, sealing the ice against water percolation, and allowing water to pool above sea level.

We demonstrate that this mechanism is dependent on fresh water availability, known to be predominantly from snowmelt, and ice temperature at melt onset. We argue that the blockage process has the potential to exert significant control over inter-annual variability in ice albedo

While optical properties of individual ponds vary, the areal fraction of the surface that the ponds cover is by far the most important aspect of pond formation in determining spatially averaged albedo and solar partitioning.

On first year sea ice, early in the melt season, pond coverage is largely controlled by a hydraulic balance of meltwater inflows and outflows and the bathymetry of the depressions available for this water to pool in. Limited outflow pathways result in an accumulation of meltwater above sea level and large pond coverage on undeformed ice.

.Later in the melt season, pathways for water to pass between the ice surface and ocean become relatively unrestricted, first through the formation of large drainage holes, and later through the onset of permeability through the ice matrix [Polashenski et al., 2012]. After large levels of permeability are established, pond coverage is controlled by the fraction of the ice surface situated below sea level ...[many more pages of detail]
« Last Edit: September 04, 2020, 06:57:15 PM by A-Team »

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Re: Melt Ponds
« Reply #97 on: September 05, 2020, 01:43:45 AM »
The bulk of ice forms with vertical growing ice crystals this plus the exclusion of salt tends to create channels through the ice. If the ice is thicker than 2 meters it is likely stacked but that process has some gaps between layers. The freeze melt cycle will over seasons fill these channels. Freshwater ice is more solid and would not have channels to drain through.


freshwater ice most definitely can be porous and saturated with water, whether waterfall or glacier ice
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Re: Melt Ponds
« Reply #98 on: September 05, 2020, 02:50:30 PM »
Melt ponds are growing in importance as FYI increases its proportion yet it remains quite difficult to measure via remote sensing. The two papers below describe in great detail an effort to use multispectral sensors (RGB and beyond) from Sentinel-2AB for this purpose.
 
There's more to melt ponds than just surface area as that alone does not fully determine take-up of summer insolation because depth, volume, algae, pollutants, and salinity (ie freezing temperature) also have roles in the ever-evolving albedo.

Snow melt initiates pond formation but since there was so little during the Mosaic year and it so quickly blew into topographic lees, very little of summer melt pond volume arose from snow. The SWE (snow water equivalence) of dry cold snow after some abrasion is perhaps 10%, meaning a meter of snow drift could only furnish 10 cm of water.

To clarify, a melt pond forming on an extensive pressure ridge with containment topography could be a meter or two above sea level. If that developed a low drainage channel, the water would indeed drain out. However we are mostly concerned with flat first year ice with very modest freeboard so the doughnut model applies: incomplete pond drainage only to ambient sea level.

The substantial volume of water remaining will eventually freeze solid in winter modulo its brine exclusion, creating a massive inclusion within the hosting ice that will have various consequences for the following melt season, including more facile re-melt if fresher. Given less MYI and the sunny summer this year with extensive melt ponds even at the North Pole, this type of inclusion could be a goodly fraction of total ice volume.

The Bathymetry of Melt Ponds on Arctic Sea Ice Using Hyperspectral Imagery
M König,  G Birnbaum N Oppelt
https://www.mdpi.com/2072-4292/12/16/2623/htm#B65-remotesensing-12-02623

Melt pond coverage, i.e., areal fraction of melt ponds on sea ice, depends significantly on sea ice surface topography which is in turn strongly influenced by deformation and aging processes, snow cover and ice permeability. Undeformed first-year ice is characterized by a homogenous snow cover enabling lateral spreading of shallow ponds, with pond depth mostly < 50 cm, and cover up to 80% of the ice surface. Multi-year ice shows a preexistent hummocky topography that controls snow depth distribution and lateral pond spreading, and a low permeability that retains meltwater at the ice surface.

Application of Sentinel-2 MSI in Arctic research: evaluating the performance of atmospheric correction approaches over Arctic sea ice
M König, M Hieronymi, N Oppelt
https://www.frontiersin.org/articles/10.3389/feart.2019.00022/full

Multispectral remote sensing may be a powerful tool for areal retrieval of biogeophysical
parameters in the Arctic sea ice. The MultiSpectral Instrument on board the Sentinel-2
satellites of the European Space Agency offers new possibilities for Arctic research; S-2A
and S-2B provide 13 spectral bands between 443 and 2202 nm and spatial resolutions
between 10 and 60 m, which may enable the monitoring of large areas of Arctic sea ice. For
an accurate retrieval of parameters such as surface albedo, the elimination of atmospheric influences in the data is essential. We therefore provide an evaluation of five currently available atmospheric correction processors for S-2 (ACOLITE, ATCOR, iCOR, Polymer, and Sen2Cor).

Melt pond work at the Polarstern
https://www.meereisportal.de/en/mosaic/driftstories/driftstory-07-the-importance-of-the-first-snowball/

Gerit Birnbaum and her team were able to document the waxing and waning of the meltwater ponds down to the nearest square metre, since during the helicopter survey flights over the ice, cameras recorded the size and shape of the individual ponds. Furthermore, based on the camera data, the researchers were able to determine the size distribution of the meltwater ponds, whether the ponds were interconnected, and how deep each one was. The average albedo (reflectivity) of the sea ice was also measured, while a laser scanner mapped its surface topography.

Knowing how early in the year the first ponds form, how large they become, and when they drain is essential in terms of predicting when in the summer the Arctic is likely to be ice-free for the first time. As a dark, sunlight-absorbing area, the network of meltwater ponds is a major factor in the Arctic sea ice melting more rapidly and extensively in summer than it has in the past.

Consequently, Birnbaum’s meltwater pond data gathered during MOSAiC will be used to support numerous scientific analyses. Some researchers are investigating whether the ponds on the MOSAiC floe and in its immediate vicinity are representative of the sea ice in the Central Arctic. At the same time, others are using data from the helicopter flyovers to assess how accurately the various satellite-based measuring systems capture the Arctic’s meltwater ponds.

One of these systems is MODIS, the Moderate Resolution Imaging Spectroradiometer, aboard the United States’ Terra and Aqua satellites. This summer, AWI sea-ice physicists plan to use MODIS data to painstakingly monitor sea-ice melting across the Arctic. To do so, they will use the satellite system to record where and when sea ice was present, in which areas it was covered with meltwater ponds, and where areas of open water formed.

Freegrass

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Re: Melt Ponds
« Reply #99 on: September 05, 2020, 05:17:39 PM »
As always, great explanation A-team! Thank you!

Looking at the area vs extent numbers Gerontocrat just posted, I was curious as to why area is rising while extent is dropping. This also has to do with melt ponds, and I would love to learn more about that.
« Last Edit: September 05, 2020, 05:24:38 PM by Freegrass »
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