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William Crump

Does the paper have any information on whether there has been a decline or expansion of first year ice and whether the thickness of first year ice is declining at a rate that will cause the Arctic to be "virtually ice free" by 2020 or sooner?

Arcticio

The school of ice is demanding, not everybody makes it into next year. Most Pacific students leave during first year. School will close in Summer soon.

Neven

Will, as far as I could tell there was nothing about FYI.

One other question that popped up for me, was whether MYI has fixed thicknesses related to age. I know for instance that first year ice can get 2 meters thick at the most. But what about second or third year ice? Put in other words: can MYI get thinner, even though it is labeled MYI?

L. Hamilton

MYI might be thicker on average, but as it melts the thickness must drop toward zero.

Greg Wellman

Multiyear ice has a higher probability of being involved in "slabbing" which is how really thick ice happens. Other than that, multiyear ice would tend to be around the thickness of the thickest first year ice, or a little thicker. It's harder to melt because it's fresher (brine rejection) but it can still melt in situ if enough heat is delivered to it.

On a separate note

Because the grid cell is assigned the age of the oldest ice present, a cell with a total concentration as low as 15% at the end of the melt period is coded as multiyear ice even though the majority of ice present after freeze‐up is first‐year ice.
One wonders if something like that is going on with the Cryosat thicknesses.

Artful Dodger

Greg, Neven, the "sea ice >15% MYI is MYI" definition also means that the average thickness of MYI must be decreasing, even if each individual particle of MYI remained the same thickness. This is a consequence of the definition.

We are also losing MYI by average thickness, not just by loss of extent.

Lord Soth

I have noticed that the 4th and 5th year ice combined has been shrinking every year since 2007, and is now around 500,000 sq km total.

This goes to show, that there is no guarantee that younger ice will survive the melt season, to become older ice the following year. It can either melt in situ or be pushed out of Fran or Nares strait.

Artful Dodger

Quite right, Lord Soth. It's a double-whammy when MYI is lost to advection, because meltwater freshens the Arctic surface layer. Instead this fresh water is transported to the North Atlantic.

So the Arctic loses both the latent heat of fusion of the ice, and the fresh water which insulates the sea ice. Bamm bamm.

Mike Constable

I have been surprised at the satellite estimates of sea-ice thickness, which seem much higher than surface-made measurements(?), or the state of the ice from satellite images.
Could this be that the ice is more porous and therefore the surface floats higher than would be expected for solid ice? Or is it that the density of the water is higher (more salt content) than would be expected in the calculations, making the ice float higher?
Comments, anyone?

AmbiValent

Isn't the reason for "recovery" of 2-year MYI after 2007 that this surviving ice ended up in safe areas in the central Arctic and the reason it tends to melt anyway in the 4th or 5th year that it's transported out of these (shrinking) areas?

cynicus

Mike, regarding satellites showing thicker ice then there is, does this help?

Chris Reynolds

Greg Wellman,

The Cryosat system measures freeboard, the height of the ice above the sea level, it does so much more accurately than ICESat (the system behind Kwok's earlier findings of thining). Basically the early release of Cryosat was done before full validation was completed (NSIDC Sea Ice News June), so for example the Wegener (AWI) findings of thickness dropping from 1.7 to 1.4metres in the last 3 years (May findings) don't appear to have been taken into account, see here.

If you take June's extent from NSIDC and thickness from PIOMAS then the ice pack would appear to be about 1.4m thick, see here. This on the face of it tallies with AWI's findings. But the AWI fights were mainly over the Canadian Arctic Archipelago, where the ice should be thickest. And as we know there are regional variations in thickness the brute force of calculating from NSIDC/PIOMAS arguably overstates thickness for most of the pack, if PIOMAS is to be accepted as reasonably accurate.

For what it's worth I think the initial Cryosat thickness retrievals are likely to be significant overstatements of thickness. If they're right then Kwok was substantially wrong, which implies PIOMAS is wrong, and a whole load of small scale / anecdotal observations are wrong. Using Occam's Razor - the simplest solution is that Cryosat is overstating.

Cynicus,

The findings of Dr Barber show one of the perils of using extent, with a threshold of 15%, as Maslanik et al do. Whilst the result is statistically robust and can be used with confidence it may understate the situation on the ground. As Neven outlines, an area of ice may have as little as 15% multi year ice, the rest can be thinner first year ice, but such an area is still classed as multi-year using Maslanik's approach. Furthermore as the ice isn't in the sort of massive pack it once was it's possible that the mechanical compression that ridges MY ice to make it thicker won't work as it did in the past. Put a load of marbles in a tray and with a ruler you can ridge them up by compression. Put the marbles in layers of foam (like the less robust first year ice) and the marbles don't ridge up, the foam compresses.

Greg Wellman

Chris,
Thanks for that detail on thickness. I agree that even after the revision of PIOMAS it clearly implies lower average thicknesses than Cryosat, and most other data we have agrees more with PIOMAS than the initial results from Cryosat. Does anyone know in what timeframe we might see recalibrated Cryosat results?

Espen

I have done some rough estimates of the fast/ shore ice north of Ellesmere Island and Northern Greenland, my result is there is less than 300km of ice, and at least half of that is probably gone by mid September. So we are down at some 100 - 150 km of fast / shore ice by then. The fast /shore ice in North East Greenland will probably disappear as well by mid September, so only about max. 150 + some few kms around some Russian Islands and maybe Svalbard is all thats left of fast ice in the whole arctic sea???. Pretty dramatic!!!

Chris Reynolds

Neven,

Thanks for your precis of this paper. It's a very important addition to the research on the state of the Arctic ice pack, which I personally see as key to understanding 2007 and it's implications. I'll blog at the weekend.

I'll leave you with my favourite quote from the paper.
"The recovery in multiyear ice extent through March 2011 from the extreme reductions in 2007 and 2008 along
with the continued aging of the surviving ice through multiple melt seasons is consistent with an ice pack that has not passed a tipping point across the Arctic Ocean as a whole, and reflects favorable large‐scale ice transport patterns conducive to retaining multiyear ice."

Mike Constable


The "recovery " of MY ice in the graph is caused by increases of 2nd year ice at the bottom of the picture! That is the product of the huge production of 1st yr ice each winter to cover the summer melt-out. You have to go back to '97 before you get more 2nd yr ice than in last 3 yrs.
5+ yr ice has continued to decline since'07 and cannot get back even to pre '09 levels this winter.
4+ yr ice figures 'might' recover next year 'if' 1/2 of this years 3yr ice survives.
As for "retaining multiyear ice", Petermann ice island escaped last year. But I notice the western part of the Ayles ice island is drifting through the NW Passage http://sailwx.info/shiptrack/shipposition.phtml?call=47554

Artful Dodger

According to this method of accounting for MYI, the Titanic should be pulling into New York Harbour by 2016, +/- 3 years... ;^)

Chris Reynolds

Mike Constable,

The second graphic is figure 2 from the original paper. In that figure it is clear that there has been an increase in 3rd year ice. I suspect that the main reason we've not seen an increase in 4th year is that we've had only 3 full seasons since 2007. If, in the longer run, it turns out that 4th and 5th year don't increase markedly this would imply that typical survival times really are as short as 3 years. That would be another strand of evidence for us having transitioned from a mainly MY ice pack to a mainly FY.

Ian earlier paper Maslanik states that in the central Arctic pack: "25% of this [multi year] ice at least 9 years old. By 2007 however, the coverage of ice 5+ years old decreased to 7%, and no very old ice (9 + years old) has survived."

I think this is a real increase in older ice, that it supports the statement I quote above (July 21 2011 22:10). However I suspect that we won't see ice as old as 9 years making a come back due to reduced sea ice survival rates.

Seke Rob

[quote]I know for instance that first year ice can get 2 meters thick at the most.[/quote]

http://www.jpl.nasa.gov/news/news.cfm?release=2009-107

Here they speak of 'usually' 2 meters FYI and a loss of 17cm per annum on MYI. Think to have read of topping at 2.40, but can't find it again. Elsewhere: http://nsidc.org/sotc/sea_ice.html it shows to vary year on year... 1.40 meter this time as measured by AWI... no wonder wheels are falling off even when there's no extreme / optimal insolation. Anyway, the concentration dropped to 70% last few days.

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