Cracks and the mobility of ice in the Beaufort

As mentioned in the post on last week's weird winter weather, a large blocking high over the Beaufort Sea also caused a cracking that was a minor repeat of last year's spectacular and extensive cracking event. Although this one wasn't as notable (Jan. 1st image on the right was posted by Jim Hunt on the ASIF),
I'd like to share with you this article Chris Reynolds posted on his Dosbat blog a couple of days ago,
in which he discusses the effect thinning ice will probably have on the amount of cracking events occuring in the future:

Thinner Ice in Beaufort and Beaufort Breakups

Last February I posted about a break up of sea ice that occurred in the Beaufort Sea, now another break up has happened over the last week. It demands a post, but one looking at the bigger picture, indeed were I to try to go over what has happened in the last week the result would read surprisingly similar to my post of February 2013.

I'm still not totally convinced this is unusual, but there is reason from the scientific literature to expect more sea ice break ups in the Beaufort Sea.

First it's worth looking at the ice state as seen in polar orbiting infra red satellite images, source Environment Canada:

The Beaufort Sea is centre left of the image, fracturing is seen throughout the image, however Beaufort has been left heavily fractured, with fractures running along the coast of the Canadian Arctic Archipelago (towards the rose of compass points overlayed around the pole). As with last year this is because winds have set up a general clockwise motion of the pack placing ice under tension and giving rise to rapid parallel cracking.

Last year there was clear termination of cracks as they reached the thicker multi year ice, which could be identified from ASCAT, see first link of this post for details. That is less evident this year however it provided a clue that ice state in Beaufort (in 2013 virtually all first year ice following the 2012 record minimum) was playing a pivotal role in allowing the development of the fracturing.

Given the difficulty of ascertaining whether one, or even both of these events are unusual (I gave my opinion on that last year), perhaps a more fruitful question is this: Is there any reason to suspect that winter sea ice cracking might be becoming more intense than in the past?

Read the rest here.

Comments

[Wipneus]

I have posted an animation of ASI AMSR2 ice concentration (from Uni Hamburg data) on the forum (registration required):
https://forum.arctic-sea-ice.net/index.php/topic,382.msg18817/topicseen.html#msg18817

[I Ballantinegray1]

I've also noted the Kara/Barentsz sectors coming in for a bit of 'slippage' as synoptics dictate? there seems to be a large slab pulled away from the main ice field in early Jan?

Also the ice out of Fram appears far smaller, in floe size, as it rounds Greenland and breaks free of the pack?( with a lot of open water around the floes?).

[Jim Hunt]

Thanks Neven and Chris.

Some additional information. The current Beaufort "cracks" are (just about!) visible in the Arctic sea ice surface temperature plots on the new Danish Polar Portal. Here's an extract from January 11:

The fractures certainly look to me to be crossing large areas of multi-year ice.

For more references on fracturing and mobility of sea ice (and more thickness graphs from Chris!) see also "Drift, Deformation and Fracture of Sea Ice" on the ASIF.

[Chris Reynolds]

Thanks Neven,

In the comments at my blog Anonymous makes a good point about the importance of pressure gradients.

While the wind puts the ice in tension and separates the floes after the fracture, I don't think it is the critical factor in the breakup. Both events were caused by very strong high pressure systems and the weakest mode for a large flate plate is a force, or pressure gradient, that is directed along the axis that passes through the thin height of the plate.

It's difficult to pull apart a glass plate along the plane of the plate, but easy to break it perpendicular to the plane.

It's the high pressure gradient in these systems that fractures the ice, not the wind.

There has been a lot of focus on the fracture in February last year but not much recognition of the compressive flows in March/April that ridged those regions of thinner ice into thick masses.

My reply is in the comments over at my blog, but I thought this comment worth people considering. Essentially I think the point with regards pressure gradients is reasonable but without the wind pushing ice away from Banks Island the parallel fracturing that is so distinctive wouldn't happen.

The final part of anon's comment has got me thinking: We have a lot of data on the ice, but one thing that is missing are map plots of strain on the ice, compression or tension.

How hard would it be to work out such plots from NCEP/NCAR pressure/wind data? I ask because I haven't a clue. But I suspect a plot showing tension in (for example) red scales, and compression in blue would be very informative.

[Chris Reynolds]

Actually, you can get a reasonable idea from PIPS/HYCOM ice movement, so it's probably not worth the work.
http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticicespddrfnowcast.gif

[Blaine]

Exactly, Chris. Both the HYCOM and PIOMAS models calculate the the stress and strain in the ice as a very important model parameter. They don't currently release this data, but could release it in a form accessible to casual users without a lot of additional effort. Clearly they think there isn't a whole lot of interest, and I'm not they're wrong in general.

What makes modeling difficult is that there is a large hysteresis with breaking the ice. Either the ice breaks or it doesn't, and later releasing the stress won't unbreak the ice. They're now incorporating ice concentration data, but aren't incorporating data on whether the ice is fast or broken.

I don't find it terribly surprising that the Beaufort is cracking up again this year. The ice thickness is still rather low and the wind stress is large at the moment.

I'm wondering about the depth of the thick ice region as well. Prince Gustaf Adolf Sea fast ice broke up last year and a large amount of ice drifted south through it. You can see it just rapidly clearing out the thick ice in the HYCOM model. I'm not sure that breakup has ever happened before. I'd very much like to see a year-to-year Cryosat-2 data comparison for September and not October, so it wouldn't be skewed by snow.

[jdallen_wa]

Nosing around through old arctic science articles, I came across this:

http://www.jpl.nasa.gov/m/news/news.php?release=2010-056#.UthHKH-9KSM

The short summary is, post-Mortem, folks at NASA saw a correlation between the lack of ice arches (I.e. Nares strait) and ice loss/ extent crash in 2007. The *cause* obviously lies elsewhere, but might it be a signal?

[TenneyNaumer]

This business of the breakup of ice in the eastern Beaufort is rather new. It did not happen before the big melt of 2007, to the best of my knowledge, because the ice in general north of Alaska and Canada was thick enough to withstand the stresses.

In 2006, the Nares Strait took forever to melt enough to permit ice to flow through.

Next, the ice arches went, and they have never been the same again. This year they are having a hard time freezing up, as is the strait.

After 2007, the land fast ice really began to disappear from the archipelago, and that meant that the winter freeze up was more susceptible to stresses. Nothing to put a break on it whether it wanted to go clockwise or counter-clockwise.

And so, in 2013, the multi-year ice became so thin it just went south through the channels:

http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticictn/nowcast/ictn2013092118_2013092200_153_arcticictn.001.gif

It has not been replaced, and will be yet one more weaker point in 2014.

And as you know, the AO is letting a lot of warmer water and air into the Arctic via the North Atlantic, setting things up for yet another big melt.

I would venture to say that the warmer waters are again going to be a problem for the ice around the archipelago.

[TenneyNaumer]

Should have said 'during the winter':

This business of the breakup of ice in the eastern Beaufort, during the winter, is rather new.

[John Christensen]

Thanks Jim Hunt for the link to the DMI sea surface temp, which is a great addition to other maps available.

As can be seen from todays image (http://ocean.dmi.dk/arctic/ice_temp/index.uk.php), a number of interesting features are visible:
- Cracks in the Beafort ice, probably due to the clockwise winds of the central Arctic high currently in place
- Apparently landlocked ice in Laptev towards Kara, where offshore winds are nearly creating a gap between landlocked and floating ice. This should be a primary spot of ice formation right now.
- Nice views of the Nares Strait ice arches to the North splitting cold from very cold ice, and to the South splitting cold from significantly less cold ice. The ice temperatures would seem to indicate the arches are very solid at this point, but let's see when spring arrives.

[Jim Hunt]

My pleasure John. You need to leave more white space around the link though:

http://ocean.dmi.dk/arctic/ice_temp/index.uk.php

Many of the features you refer to are also now starting to become visible in MODIS/WorldView once again. See e.g.

[John Christensen]

Thanks Jim, yes the , got in the way..

The position of the high pressure seems condusive for getting the Beaufort gyre in gear, which will push/pull the ice towards the ESS side of the Arctic.

However, with -15 to -25C in the area, cracks should fill up quickly in the ice that is 1.7-3 meters thick. With later changes in wind or current, new ice will easily get compacted against the thicker surrounding pack, so uncertain whether the cracking would be overall negative (higher mobility) or positive (net volume gain)..

[Jim Hunt]

The current high's forecast to have departed by the weekend. The buoys in the Beaufort (that started on thin ice) are currently up to around 1.5 meters ice thickness. See e.g.

http://imb.crrel.usace.army.mil/2013F.htm

Lots of uncertainties!

[John Christensen]

Hmmm, HYCOM indicates we should have just above 2 meters of ice in that area..

http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticictn_nowcast_anim30d.gif

Makes you wonder if the difference is between model and measurement, or if the HYCOM tends to include snow cover also?