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Author Topic: The caa-greenland mega crack  (Read 15369 times)

SteveMDFP

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Re: The caa-greenland mega crack
« Reply #50 on: September 03, 2019, 03:38:01 PM »
Blumenkraft,

Every year in the freezing season, the volume of the Arctic sea surface expands by roughly 10 percent (due to the fact that density of sea ice is lover than that of sea water). If everything (including air pressure and sea level) remains constant, something will have to give in. . . .

I don't think that's how the physics works.  Certainly Nares and Fram surface currents are more robustly southward in winter than summer.  But not, I think, because sea water is freezing.  Sea ice displaces its *weight* and not its volume. 

Just as the water level in a glass of ice water doesn't change as the ice melts, neither does it change if ice forms in the glass.  Thus winter freezing of sea water into sea ice doesn't create any net change in forces of flow (all other changes being equal, which they never are in actuality).

I don't have an explanation for the observed seasonal flow patterns, but I'm pretty sure volume of ice formation isn't it.

longwalks1

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Re: The caa-greenland mega crack
« Reply #51 on: September 03, 2019, 04:35:12 PM »
For the Timothy McGeehan Wieslaw Maslowski
Evaluation and control mechanisms of volume and freshwater export through the Canadian Arctic Archipelago in a high‐resolution pan‐Arctic ice‐ocean model
 https://doi.org/10.1029/2011JC007261

Nice Find.  Here is a link to a pdf final copy.  I have too many pre-print papers myself that I have not updated on my computer

blumenkraft

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Re: The caa-greenland mega crack
« Reply #52 on: September 03, 2019, 05:57:27 PM »
@longwalks, @Steve, @aslan, @P-maker yeah, that's exactly the kind of discussion i wanted to kickstart! Thanks, guys for contributing.

That said, reading Longwalks linked paper, i realize i'm stupid. I looked for SST anomalies the whole time but only in the Arctic basin, never in Baffin bay. That's indeed a great hint.

Quote
Abstract
[1] This study examined the 1979–2004 volume and freshwater fluxes through the Canadian Arctic Archipelago (CAA) and into the Labrador Sea using a high resolution (∼9 km) coupled ice‐ocean model of the pan‐Arctic region to provide a reference, compare with limited observational estimates, and investigate control mechanisms of this exchange. The 26‐year mean volume and freshwater fluxes through Nares Strait were 0.77 Sv ± 0.17 Sv and 10.38 mSv ± 1.67 mSv respectively, while those through Lancaster Sound amounted to 0.76 Sv ± 0.12 Sv and 48.45 mSv ± 7.83 mSv respectively. The 26‐year mean volume and freshwater fluxes through Davis Strait were 1.55 Sv ± 0.29 Sv and 62.66 mSv ± 11.67 mSv while the modeled Fram Strait branch provided very little (∼2%) freshwater into the Labrador Sea compared to the total CAA input. Compared to available observations, the model provides reasonable volume and freshwater fluxes, as well as sea ice thickness and concentration in the CAA. In Nares Strait and Lancaster Sound, volume flux anomalies were controlled by the sea surface height (SSH) gradient anomalies along the straits and freshwater anomalies were highly correlated with the volume anomalies. At least half of the variance in the time series of SSH gradient anomaly was due to SSH anomalies in northern Baffin Bay. The West Greenland Current (WGC) exhibits seasonality, with cross shelf flow (into the Labrador Sea) peaking in January/February/March, while reducing the northward flow across eastern Davis Strait. We hypothesize that the eddy‐reduced northward flow of WGC results in the lower volume and SSH in Baffin Bay. This maximizes the SSH gradients between the Arctic Ocean and Baffin Bay, leading to maximum winter volume fluxes through Nares Strait and Lancaster Sound. Model limitations include the insufficient spatial resolution of atmospheric forcing (especially to account for the effects of local topography), the representation of river runoff into Hudson Bay and coastal buoyancy currents, low mobility of modeled ice, and incomplete depiction of ice arching. Many of these issues are expected to be resolved with increased model grid cell resolution, improved sea ice and ocean models and more realistic atmospheric forcing.
Refugees welcome

aslan

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Re: The caa-greenland mega crack
« Reply #53 on: September 03, 2019, 09:47:01 PM »
Yes thanks longwalks ;) If there is specfic interest for the Nare Strait, the work of A. Münchow is worth citing :

"The established flow of seawater from Pacific to Atlantic Oceans through the Arctic has been attributed to higher sea level in the Pacific (Wijffels et al. 1992), associated with the lower salinity of Pacific waters. Sea level in the Atlantic may be more than 0.5 m lower than in the Pacific and 0.1–0.3 m lower than in the Arctic (Muench 1971). More accurate estimates of steric forcing have yet to be determined, but it is probably safe to conclude that much of the drop in sea level between Arctic and Atlantic Ocean occurs along the 530-km length of Nares Strait, thereby providing the impetus for the fluxes that we have measured.'

https://journals.ametsoc.org/doi/full/10.1175/JPO2962.1

https://www.researchgate.net/publication/233704692_Ocean_current_observations_from_Nares_Strait_to_the_west_of_Greenland_Interannual_to_tidal_variability_and_forcing

Juan C. García

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Re: The caa-greenland mega crack
« Reply #54 on: October 08, 2019, 02:34:42 PM »
I am surprised that remnants of the caa-greenland mega crack are still there today. I wonder of the implications that it could have on the 2020 melting season. That is, could be possible to have more mobility of the older ice on 2020, if it is not strongly attached to land? It should be first-year ice what we will have on the mega crack.
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

kassy

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Re: The caa-greenland mega crack
« Reply #55 on: October 08, 2019, 03:43:36 PM »
The big question is if the mega crack will happen again next year and so on. The ice being young does not help but if the reason is changed currents (or weaknesses only recently showing) that will change the story for the future.

A much more mobile central ice pack can go anywhere in a bad year.
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

Juan C. García

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Re: The caa-greenland mega crack
« Reply #56 on: October 09, 2019, 06:12:13 AM »
The big question is if the mega crack will happen again next year and so on. The ice being young does not help but if the reason is changed currents (or weaknesses only recently showing) that will change the story for the future.

A much more mobile central ice pack can go anywhere in a bad year.
It also happened on 2018. Maybe not as big on CAA, but surely important north of Greenland.
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

uniquorn

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Re: The caa-greenland mega crack
« Reply #57 on: October 09, 2019, 01:06:57 PM »
Today's worldview viirs brightness temperature, band15, night with yesterday's amsr2-uhh inset.
https://go.nasa.gov/2MvVvvg
click for full resolution

Pmt111500

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Re: The caa-greenland mega crack
« Reply #58 on: October 10, 2019, 11:34:47 AM »
The big question is if the mega crack will happen again next year and so on. The ice being young does not help but if the reason is changed currents (or weaknesses only recently showing) that will change the story for the future.

A much more mobile central ice pack can go anywhere in a bad year.
It also happened on 2018. Maybe not as big on CAA, but surely important north of Greenland.

At this point in time for me it is not anymore a question of will it happen, but will it not happen on some years. This is essentially the same phenomenon that's common knowledge on other shores as well, the waves turn toward the shore by friction with the shore and the return current may take an unwary swimmer/diver pretty far out. As the ice is 90% underwater, somewhere near the shore the outbound forces exceed the cohesion of the ice and the crack develops. Strong winds and currents may counteract, of course, but I'd be surprised if this does not become a regular feature of the Arctic now.
Cooling the outside by heat pump.

philopek

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Re: The caa-greenland mega crack
« Reply #59 on: October 10, 2019, 04:40:51 PM »
<SNIPPED>unwary swimmer/diver pretty far out. As the ice is 90% underwater, somewhere near the shore the outbound forces exceed the cohesion of the ice and the crack develops. Strong winds and currents may counteract, of course, but I'd be surprised if this does not become a regular feature of the Arctic now.

Good point for consideration.

I assume you mean something of the linked kind.

https://en.wikipedia.org/wiki/Rip_current

Pmt111500

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Re: The caa-greenland mega crack
« Reply #60 on: October 10, 2019, 05:32:44 PM »
<SNIPPED>unwary swimmer/diver pretty far out. As the ice is 90% underwater, somewhere near the shore the outbound forces exceed the cohesion of the ice and the crack develops. Strong winds and currents may counteract, of course, but I'd be surprised if this does not become a regular feature of the Arctic now.

Good point for consideration.

I assume you mean something of the linked kind.

https://en.wikipedia.org/wiki/Rip_current

Yep, didn't have the english word for it.

With ice over water they're not strong but still there.
« Last Edit: October 11, 2019, 07:45:46 AM by Pmt111500 »
Cooling the outside by heat pump.

Shared Humanity

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Re: The caa-greenland mega crack
« Reply #61 on: October 11, 2019, 04:28:34 PM »
Local winds and shoreline wave behavior certainly could contribute to cracks along the CAA and the north coast of Greenland but far more important are the ocean currents that have always been in play. Arctic sea ice has always either migrated towards the Beaufort or towards the Fram. Ice east of the Lincoln Sea will eventually find its way through the Fram while ice west of the the Lincoln Sea is drawn into the Beaufort. When the ice in this area of the Arctic Ocean was made up of thick (5 to 10 meters) rafts of MYI, these currents struggled to cause the ice to lift off and move. This thick ice no linger exists here. We have a melange of small MYI ice flows no more than 4 meters thick and thin 1st year ice that is highly mobile. I see no process that will cause thick MYI ice to reform so we should expect this lifting off behavior to persist and worsen.

uniquorn

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Re: The caa-greenland mega crack
« Reply #62 on: October 31, 2019, 04:40:30 PM »
uni-hamburg amsr2-uhh update of the caa/cab crack, sep21-oct30

RoxTheGeologist

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Re: The caa-greenland mega crack
« Reply #63 on: October 31, 2019, 05:32:13 PM »
Blumenkraft,

Every year in the freezing season, the volume of the Arctic sea surface expands by roughly 10 percent (due to the fact that density of sea ice is lover than that of sea water). If everything (including air pressure and sea level) remains constant, something will have to give in. . . .

I don't think that's how the physics works.  Certainly Nares and Fram surface currents are more robustly southward in winter than summer.  But not, I think, because sea water is freezing.  Sea ice displaces its *weight* and not its volume. 

Just as the water level in a glass of ice water doesn't change as the ice melts, neither does it change if ice forms in the glass.  Thus winter freezing of sea water into sea ice doesn't create any net change in forces of flow (all other changes being equal, which they never are in actuality).

I don't have an explanation for the observed seasonal flow patterns, but I'm pretty sure volume of ice formation isn't it.

If you put a piece of ice in a glass of saltwater, the freshwater from the ice flows to cover the saltwater. Freshwater/ice from the arctic is less dense and therefore there is an elevation difference. Hydrostatic stress is the same but the diviatoric stress makes the water flow (as its incompressible). its a long time since I did any continuum mechanics so my explanation may be wonky. Water flows downhill?

uniquorn

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Re: The caa-greenland mega crack
« Reply #64 on: October 31, 2019, 08:42:21 PM »
Today's worldview viirs brightness temperature band15, night. 'Heat' escaping from the cracks at ~-2C. Cloud forming over the Lincoln sea at some distance from the Greenland coast. Click for full resolution.
https://go.nasa.gov/2WvntvO

uniquorn

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Re: The caa-greenland mega crack
« Reply #65 on: November 02, 2019, 08:48:39 PM »
Floes tearing across the PGAS, recently fast ice lifting off from Ellesmere.
https://go.nasa.gov/32a0hoj, oct31-nov2   click to run
« Last Edit: November 02, 2019, 08:59:30 PM by uniquorn »

HapHazard

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Re: The caa-greenland mega crack
« Reply #66 on: November 03, 2019, 01:57:41 AM »
So how "normal" is this? Or is "the crack" now a normal feature?

For a few years now, I've had a hunch that if the polar vortex breaks down enough (plus the "right" weather for a week or so), the entire pack may pull away from the CAA in the summer and thus accelerate melt > new record minimum by a fair margin. I find this quite concerning, as with [current?] preconditioning it could be quite abrupt.

?

uniquorn

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Re: The caa-greenland mega crack
« Reply #67 on: November 03, 2019, 03:08:41 PM »
uni-hamburg amsr2-uhh, north CAA/Greenland, 2012-2018 (some missing data)

HapHazard

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Re: The caa-greenland mega crack
« Reply #68 on: November 04, 2019, 08:31:50 PM »
So, it appears to have been "normal but intermittent" but this year it's has been more akin to a permanent feature.

uniquorn

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Re: The caa-greenland mega crack
« Reply #69 on: November 04, 2019, 11:22:56 PM »
Nares export and more lift off from the west greenland coast. Looks set to continue with the current forecast.
https://go.nasa.gov/2rd2Qcm , oct30-nov4, click to run

uniquorn

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Re: The caa-greenland mega crack
« Reply #70 on: November 07, 2019, 10:56:28 PM »
Ice north west of Ellesmere looking quite ragged today.
https://go.nasa.gov/2CkcoV8 , nov1-7 click to run

uniquorn

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Re: The caa-greenland mega crack
« Reply #71 on: November 12, 2019, 04:24:31 PM »
More lift off from ellesmere today and quite a big pull back in the Peary channel. Lincoln sea starting to look 'normal'.
https://go.nasa.gov/2KgFdGp , nov8-12 click to run
full moon?
« Last Edit: November 12, 2019, 04:34:08 PM by uniquorn »

blumenkraft

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Re: The caa-greenland mega crack
« Reply #72 on: November 12, 2019, 04:45:32 PM »
full moon?

I increasingly think this is a main variable.
Refugees welcome

uniquorn

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Re: The caa-greenland mega crack
« Reply #73 on: November 24, 2019, 10:50:30 AM »
Some lift off to feed the Beaufort arc

uniquorn

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Re: The caa-greenland mega crack
« Reply #74 on: November 26, 2019, 04:18:12 PM »
crack comparison, Peary-PGAS, nov26 2017-2019   https://go.nasa.gov/2DoNgwR
map courtesy of ossifrage
« Last Edit: November 26, 2019, 04:29:02 PM by uniquorn »

uniquorn

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Re: The caa-greenland mega crack
« Reply #75 on: December 06, 2019, 01:38:35 PM »
significant shear, https://go.nasa.gov/38eGIiQ   cffr

uniquorn

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Re: The caa-greenland mega crack
« Reply #76 on: December 06, 2019, 07:41:49 PM »
Fast ice still lifting off the mclure strait, https://go.nasa.gov/38fCYxy

uniquorn

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Re: The caa-greenland mega crack
« Reply #77 on: December 08, 2019, 11:31:22 AM »
Lincoln sea still mobile. Lift off again from NW Greenland coast.
https://go.nasa.gov/2PsDJe3  dec1-8 ctr