Antarctic Ice Discussion

[Gray-Wolf]

Didn't they put the reason for Larsen B's collapse at the door of storms over in Bering?

 

I'm sure I'd read something ,way back then, explaining the importance of swells generated on the other end of the planet in the final collapse and breakup of that section of shelf?

 

I'll have a dig around and get back to you.

 

Here we go;

 

MacAyeal and his colleagues discovered the effect of these waves after an iceberg they were studying, named B-15A, abruptly shattered on October 27, 2005. B-15A was a large iceberg, about the size of Luxembourg, which had run aground off of the coast of Antarctica. It broke up on a calm day with locally mild weather, puzzling observers. MacAyeal and his colleagues retrieved a seismometer that they had previously installed on the iceberg and analyzed the data. They discovered that just before the breakup, the seismometer recorded long, low swells that had rocked the iceberg and pounded it against the coast. MacAyeal traced the swells back to a surprising source--a giant winter storm off the coast of Alaska five thousand kilometers (eight thousand miles) away.

 

from here;

 

http://earthdata.nasa.gov/featured-stories/featured-research/after-larsen-b

 

If you imagine the process that is occuring to allow these fractures to form across the shelf then that 'undercut' can  become a very big hydrolic pump when a swell enters it at the wide end, compressing the water closer to the grounding line. Any weakness in the ice above will be impacted by this compression.

 

EDIT: The loss of Pine Island is another example of the 'retreat' of glaciers 'grounding lines' as warmer waters impact the bases of these ice shelfs. We now know that these waters, perculating through the submarine canyons and so flowing under the strengthened circumpolar current, have reached the Ross Embayment ( fed by most of the major outlet glaciers from the East Antarctic Ice Sheet). As P.I.G. retreats the outflow accelerates due to the loss of the friction that the old 'grounded section' used to provide ( removal of the butress) and so the draining of the West Antarctic ice sheet Accelerates impacting global sea level rises. Again these events are far in advance of the current models used to predict future sea level hikes which is why so many eyes were on P.I.G. to see just how quickly this change is occuring.

 

If I am reading things correctly then even without the slowing of the circumpolar current ( driven by the circumpolar winds alledgedly strenthened by the Ozone hole) Ross Embayment is now seen to be in as much danger as the Ice shelfs around the W.A.I.S. and so the E.A.I.S. could also begin to impact sea levels hundreds of years before we expected it to?

 

The other thing is 'climate matching'. when we look at past epochs with 400ppm CO2 we see a West Antarctic island with no ice at all.....is this where we are now headed?

 

But then someone will point out to interior snowfall and increases in precipitation.....when you consider just how much freshly fallen snow goes into making 1cm of glacial ice you'll quickly realise just how much we would need to see AGW increase snowfall to balance the scales?

Edited July 10, 2013 by Gray-Wolf

[knocker]

The last time

 

Watching the birth of an iceberg

PUNTA ARENAS, CHILE – After discovering an emerging crack that cuts across the floating ice shelf of Pine Island Glacier in Antarctica, NASA's Operation IceBridge has flown a follow-up mission and made the first-ever detailed airborne measurements of a major iceberg calving in progress.

 

 

http://www.eurekalert.org/pub_releases/2011-11/nsfc-wtb110211.php

 

Also of interest

 

Ocean currents speed melting of Antarctic ice A major glacier is undermined from below

Stronger ocean currents beneath West Antarctica's Pine Island Glacier Ice Shelf are eroding the ice from below, speeding the melting of the glacier as a whole, according to a new study in Nature Geoscience. A growing cavity beneath the ice shelf has allowed more warm water to melt the ice, the researchers say—a process that feeds back into the ongoing rise in global sea levels. The glacier is currently sliding into the sea at a clip of four kilometers (2.5 miles) a year, while its ice shelf is melting at about 80 cubic kilometers a year - 50 percent faster than it was in the early 1990s - the paper estimates.

 

 

http://www.eurekalert.org/pub_releases/2011-06/teia-ocs062311.php

[4wd]

a process that feeds back into the ongoing rise in global sea levels

 

I'm struggling with the idea of rising sea level feedbacks caused by a glacier which is already floating on the sea or at least displacing sea water.
As usual a normal event being mis-interpreted, and played for all it is worth.

[songster]

While the floating ice sheet itself doesn't add to sea level when it breaks off, while it's attached, its sheer mass acts as a kind of "plug" slowing down the flow of the land-based glaciers feeding the sheet. Now that the PIG has calved, look for the flow rate of the PIG to increase. This is where the feedback increase in sea level rise comes from (bearing in mind the fact that any individual glacier's contribution is very small).

[knocker]

a process that feeds back into the ongoing rise in global sea levels

 

I'm struggling with the idea of rising sea level feedbacks caused by a glacier which is already floating on the sea or at least displacing sea water.

As usual a normal event being mis-interpreted, and played for all it is worth.

 

I'm sorry, the glacier isn't floating on the sea but is grounded. It;s the massive lumps that calve, (icebergs) that break off when parts move seaward, that are then floating and add to sea level rise.

 

http://nora.nerc.ac.uk/259453/1/Jenkins_preprint.pdf

 

Thinning ice in West Antarctica, resulting from acceleration in the flow of outlet glaciers, is currently contributing about 10% of the

observed rise in global sea level. Pine Island Glacier (PIG) in particular has shown nearly continuous acceleration and thinning

throughout the short observational record. Rapid thinning of the floating ice shelf that forms where the glacier reaches the coast,

driven by changes in ocean heat transport beneath it, and the consequent inland retreat of the line separating grounded and floating ice

has been postulated to be the cause

 

Edited July 10, 2013 by knocker

[Methuselah]

a process that feeds back into the ongoing rise in global sea levels

 

I'm struggling with the idea of rising sea level feedbacks caused by a glacier which is already floating on the sea or at least displacing sea water.

As usual a normal event being mis-interpreted, and played for all it is worth.

But, whichever way you look at it, water is moving from land to sea...And that equates to a rise in sea level...

[jethro]

But, whichever way you look at it, water is moving from land to sea...And that equates to a rise in sea level...

 

Depends on whether or not that additional water is evaporating and being transferred elsewhere. Greenland is melting around the edges, but the interior has seen a rise in precipitation, leading to greater snow depths.

 

As always, it's difficult to tell much, without looking at all the variables.

[Methuselah]

Depends on whether or not that additional water is evaporating and being transferred elsewhere. Greenland is melting around the edges, but the interior has seen a rise in precipitation, leading to greater snow depths.

 

As always, it's difficult to tell much, without looking at all the variables.

 

That's all true, J...But it's not what I was disputing...I was merely pointing out that adding mass to an existing body of water raises the surface of the water...

[jethro]

That's all true, J...But it's not what I was disputing...I was merely pointing out that adding mass to an existing body of water raises the surface of the water...

True enough, but still depends if that rise is being countered by greater precipitation in the interior. If it's warming around Antarctica, there will be greater evaporation from the oceans.

[knocker]

Depends on whether or not that additional water is evaporating and being transferred elsewhere. Greenland is melting around the edges, but the interior has seen a rise in precipitation, leading to greater snow depths.

 

As always, it's difficult to tell much, without looking at all the variables.

 Quite true. The average annual loss of mass from the Greenland ice sheet during 2003-2012 has been approximately 234 km3 of water,- or approximately 0,65 mm in average annual contribution to global sea level. Barletta et al. 2012

 

http://polarportal.org/en/greenland-ice-shelf/nbsp/total-mass-change/

[Gray-Wolf]

Glacial ice begins as snow, which has high porosity and low density (.07 - .18 g/cc). Snow that survives the summer season undergoes a progressive transformation into more compact granules and finally into ice crystals. As the snow becomes buried under successive seasons of new snow it compacts and the crystals melt at grain-grain contacts. Melt pore water flows into empty spaces and re-freezes. The material near the surface of a glacier has a density from .4 to .8 g/cc and is known as firn or neve. This transformation can take from days to years, depending on the frequency and severity of freeze-thaw cycles. With further compaction and recrystallization the firn reaches a density of .8 - .9 g/cc and becomes ice. This final process can take years in temperate glaciers or hundreds to thousands of years in polar glaciers.

 

From here;

 

http://people.hofstra.edu/j_b_bennington/33notes/glaciers.html

 

So how warm are this polar waters to become to evaporate enough water to 'replenish' the mas loss we see? How much more to 'grow' the glaciers? By the time we have achieved this what will those temps be doing to the ice sheet behind?

 

To me it appears a non-sense that any kind of 'balancing act is going on when we look at the mega tonnage of ice that we shed from Greenland/antarctica in a post noughties 'average year' ?

 

We know precipitation rates increase as we warm the atmosphere and it is able to hold onto more moisture but can anyone get their heads around the amount of 'increase' we need to see to produce an extra tonne of ice and how long it would take for the snow to go through the stages needed to turn it into ice? We may 'raise' the land surface by adding snow on top of it but is that really comparable with the decompression of an ice sheet due to acceleration of the drain glaciers ( as the data on snow and ice density above shows )??? To me it's like the folk who claim Arctic 'recovery' when a sub 2m slab of ice regrows where once a multimetre floe of paleocryistic once stood. Sure , from above it might look white and cover the same piece of ocean but really??? Recovery???

 

Let us say the ice sheet deflates , through ablation and drainage, 20m and that shortfall is made up by 21m of snow is anyone really ,seriously, going to see this a a 'fair exchange'????

 

By using 'the average' time it takes snow to change into glacial ice and replenish the snout losses what levels will global temps be at? What levels will CO2 be at?

 

Anyone care to guess how much rain a 1mm skim off the global oceans would produce? Hmmmm, now that's an awful lot of extra rain dontchathink?

Edited July 10, 2013 by Gray-Wolf

[knocker]

Antarctic Glacier Calves Iceberg One-Fourth Size of Rhode Island

 

 

This week a European Earth-observing satellite confirmed that a large iceberg broke off of Pine Island Glacier, one of Antarctica's largest and fastest moving ice streams. The rift that led to the new iceberg was discovered in October 2011 during NASA's Operation IceBridge flights over the continent. The rift soon became the focus of international scientific attention. Seeing the rift grow and eventually form a 280-square-mile ice island gave researchers an opportunity to gather data that promises to improve our understanding of how glaciers calve.

 

http://www.nasa.gov/content/antarctic-glacier-calves-iceberg-one-fourth-size-of-rhode-island/#.Ud8mbqxNapD

Edited July 11, 2013 by knocker

[BornFromTheVoid]

Just to be clear, both Greenland and Antarctica having been losing mass at an accelerating rate in recent years, despite regional variation. This is contributing to global sea level rises.

 

 

 

[keithlucky]

Antarctic sea ice at the second highest level ever recorded http://arctic.atmos.uiuc.edu/cryosphere/timeseries.south.anom.1979-2008

 

Edited July 18, 2013 by keithlucky

[BornFromTheVoid]

Fixed your post for you.

 

As of July 13th, Antarctic sea ice area at the second highest level ever recorded for the time of yearhttp://arctic.atmos.uiuc.edu/cryosphere/timeseries.south.anom.1979-2008

 

If you cared to check now, instead of copying from Goddard, you'd find that it's currently the highest on record for the time of year!

[knocker]

A reminder.

 

Why Antarctic sea ice cover has increased under the effects of climate change

NASA and British Antarctic Survey scientists have reported the first direct evidence that marked changes to Antarctic sea ice drift caused by changing winds are responsible for observed increases in Antarctic sea ice cover in the past two decades. The results help explain why, unlike the dramatic sea ice losses being reported in the Arctic, Antarctic sea ice cover has increased under the effects of climate change.

 

 

http://www.jpl.nasa.gov/news/news.php?release=2012-355

Edited July 18, 2013 by knocker

[Methuselah]

A reminder.

 

Why Antarctic sea ice cover has increased under the effects of climate change

 

http://www.jpl.nasa.gov/news/news.php?release=2012-355

Which was precisely what climatologists were predicting - 40 years ago!

[knocker]

Quite an interesting site.

 

http://www.antarcticglaciers.org/

[keithlucky]

Antarctic ice approaches new record

 

[be cause]

Antarctic ice approaches new record

disinformation approaches a new record !  Antarctic sea ice has broken daily records on each of the last 4 days  The anomaly graph shown does not help in revealing  this .. instead it shows a falling anomaly reflecting 3 days of falling sea ice area .. thus failing in any way to support your erroneous statement .

[loafer]

disinformation approaches a new record !  Antarctic sea ice has broken daily records on each of the last 4 days  The anomaly graph shown does not help in revealing  this .. instead it shows a falling anomaly reflecting 3 days of falling sea ice area .. thus failing in any way to support your erroneous statement .

Your post doesn't make any sense.

First you say that there has been record sea ice on each of the last 4 days, then that the anomaly falling over the last three days shows falling sea ice extent.

Clearly the second of these two statements is false simply on a logical basis (I can win a record for todays date, even if my margin of winning is less than yesterday if the comparator is also increasing between the two days).

Perhaps this graph is a better illustration, though;

http://nsidc.org/data/seaice_index/images/daily_images/S_stddev_timeseries.png

[Gray-Wolf]

It appears that the massive east Antarctic Ice sheet is far less stable than was previously thought? Recent studies have shown that it partially melted over the last period we saw global temps/co2 levels similar to todays. We already knew that Greenland and West Antarctica melted over this period ( 3 -5 million years ago) but had thought EAIS 'stable' from around 14 million years ago.

 

It looks like over 60ft of extra sea level rise that we had not accounted for...... now i can better understand why the IPCC are loathe to start looking at the possible impacts of sea level rises over the coming century!

[4wd]

 

 

It looks like over 60ft of extra sea level rise that we had not accounted for...... now i can better understand why the IPCC are loathe to start looking at the possible impacts of sea level rises over the coming century!

A tad alarmist as usual. 

[be cause]

Your post doesn't make any sense.

First you say that there has been record sea ice on each of the last 4 days, then that the anomaly falling over the last three days shows falling sea ice extent.

Clearly the second of these two statements is false simply on a logical basis (I can win a record for todays date, even if my margin of winning is less than yesterday if the comparator is also increasing between the two days).

Perhaps this graph is a better illustration, though;

http://nsidc.org/data/seaice_index/images/daily_images/S_stddev_timeseries.png

Sorry Loafer but both my statements are factually accurate and true .. can be confirmed by going to Cryosphere Today and checking the records .. more useful than supplying unrelated extent information   It was the unusual being true that caused me to reply to Keithlucky's disinformation in the first place ..

[keithlucky]

Antarctic ice only 0.21 short of record.

http://arctic-roos.org/observations/satellite-data/sea-ice/ice-area-and-extent-in-arctic