New paper from Maslanik et al.

I'm going to try and regularly report on new scientific papers that discuss some aspect or other of Arctic sea ice. Creating a special segment on the blog that categorizes all important research papers (a bit like the AGW Observer blog) is still on my to-do list.

Following yesterday's blog post that referred to Chris R's blog where he devotes several posts to multiyear ice, I now call attention to a new paper by Maslanik, Stroeve, Fowler and Emery called Distribution and trends in Arctic sea ice age through spring 2011, which was published in Geophysical Research Letters on July 14th.

From the abstract:

Analysis of a satellite-derived record of sea ice age for 1980 through March 2011 shows continued net decrease in multiyear ice coverage in the Arctic Ocean, with particularly extensive loss of the oldest ice types. The fraction of total ice extent made up of multiyear sea ice in March decreased from about 75% in the mid 1980s to 45% in 2011, while the proportion of the oldest ice declined from 50% of the multiyear ice pack to 10%. These losses in the oldest ice now extend into the central Arctic Ocean and adjacent to the Canadian Archipelago; areas where the ice cover was relatively stable prior to 2007 and where long-term survival of sea ice through summer is considered to be most likely. Following record-minimum multiyear ice coverage in summer 2008, the total multiyear ice extent has increased to amounts consistent with the negative trend from 2001–2006, with an increasing proportion of older ice types. This implies some ability for the ice pack to recover from extreme conditions. This recovery has been weakest in the Beaufort Sea and Canada Basin though, with multiyear ice coverage decreasing by 83% from 2002 to 2009 in the Canada Basin, and with more multiyear ice extent now lost in the Pacific sector than elsewhere in the Arctic Ocean.

One thing I find interesting, because I didn't know about it until I read Chris R's recent work, is the description at the start of the paper of how age is assigned to ice:

Ice age is estimated by treating each grid cell that contains ice as a discrete, independent Lagrangian parcel, and then transporting the parcels at weekly time steps. In cases where particles of different ages fall within a single grid cell, the cell’s age is assigned that of the oldest particle.

(...)

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.

This graph nicely shows how multi-year ice has recovered from the 2007/2008 massacre:

They go on to explain how much multiyear ice extent has declined in the last 30 years in specific regions. These graphs show the extents of multiyear ice and 5+ ice for the third week of March and at the September minimum for (a) Canada Basin, (b) Beaufort Sea, (c) East Siberian Sea, (d) Nansen Basin, and (e) north of Canadian Archipelago (regions 1, 2, 4, 6, and 7 in the map at the top of this post):

Maslanik et al. explain that the recent recovery of multiyear ice is the result mainly of unusual SLP patterns:

Strong and sustained negative AO periods during winter [Stroeve et al., 2011] not seen since the late 1960s were present in 2010, with an annual meanAOindex of −1.04. This was the lowest annual mean from 1950 through 2010, over two standard deviations from the mean of −0.14, and one of only three years with a negative AO in 11 of the 12 months. The year 2010 was also unusual as the only year over the same period with a negative North Atlantic Oscillation (NAO) in all months, with an annual mean NAO index of −1.30; the lowest observed over the 61‐year period and more than three standard deviations less than the long‐term mean of −0.10. As a result, while mean ice transport was cyclonic in 2009 (see http://www.arctic.noaa.gov/reportcard), transport was more anticyclonic in 2010.

Perhaps that the extreme compaction in 2007 also had to do something with it, by making much of the remaining ice thicker than usual. A small negative feedback, I guess.

In the final part of the paper the authors show how most of summertime reduction of multiyear ice has occured on the Pacific side of the Arctic, ie within the Beaufort Sea and Canada Basin (regions 1 and 2; red), versus loss elsewhere in the Arctic Ocean (regions 3 through 8; blue) for (a) multiyear ice, and (b) 5+ ice:

Multiyear ice extent in the area North of the Canadian Archipelago (region 7 on the map at the top of the post) was relatively stable until 2006. Above normal transport observed during the winter of 2009/2010 to the Beaufort Sea and increased export through the Nares Strait in recent years contributed to this. But little of this transported ice has made it through the summer in recent years:

The mean survival rate of multiyear ice extent in the Beaufort Sea as a whole declined from 93% over 1981–2005 to 73% during 2006–2010, with most of the surviving ice located in the eastern portion of the region (e.g., Figure 1). Regions 1 and 2 now account for the majority of summertime reductions in multiyear ice extent, exceeding the losses elsewhere in the Arctic Ocean.

(..)

While convergence and deformation or transport to adjacent regions between mid May and the September minimum contribute to some of the loss in extent, the short time period  and the directions of transport in the regions suggest that nearly all of the loss is due to melt. This changing significance of the Pacific sector is particularly apparent for the oldest ice types. Most of the reduction in coverage of the 5+ ice over summer now occurs within the Arctic Basin itself, with relatively little loss through the Fram Strait.

So to conclude: multiyear ice has recovered somewhat from the 2007/2008 cryocide due to unusual SLP patterns, which could point to a capacity for the Arctic sea ice to bounce back after extreme ice loss. At the same time we see that most of the multiyear ice is now being lost on the Pacific side of the Arctic. This could have something to with an increase of warm water transport through Bering Strait, with open water areas absorbing more solar heat, with a negative Arctic Dipole, or a combination of all three.

The paper ends with the relevant question:

A key question then is whether the increases in the extent and age of the multiyear ice seen over the last three years can be sustained ‐ continuing the recovery observed since the 2007/2008 record minima and thickening enough to become less vulnerable to another extreme melt season [e.g., Lindsay et al., 2009].

We might find out this melting season, as it has been pretty extreme so far.

I'd like to thank Dr. Julienne Stroeve for allowing me to cite from this concise, but very instructive paper. I actually understood all of it.

 

Comments

[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.