275 replies to this topic

[Gray-Wolf]

BLAST FROM THE PAST, on 27 Apr 2008, 11:58 AM, said:

GW
It is whilst record ice levels are being recorded


BFTP

As you know the degradation of the ice sheets in Antarctica is not dependant on sea ice levels, in fact more sea ice exerts greater leverage on shelf edges when sea swells are icreased (due to a faster circumpolar wind) leading to an increase in shelf failure. We all know from the Peninsula what happens to the glaciers behind when you take away the fringing coastal shelf ice and just how busy things are below both East and West Antarctic ice sheets.

[ghrud]

Gray-Wolf, on 27 Apr 2008, 12:05 PM, said:

As you know the degradation of the ice sheets in Antarctica is not dependant on sea ice levels, in fact more sea ice exerts greater leverage on shelf edges when sea swells are icreased (due to a faster circumpolar wind) leading to an increase in shelf failure. We all know from the Peninsula what happens to the glaciers behind when you take away the fringing coastal shelf ice and just how busy things are below both East and West Antarctic ice sheets.

Too much ice, too little ice; you can't have your cake and eat it!

[Gray-Wolf]

ghrud, on 27 Apr 2008, 12:56 PM, said:

Too much ice, too little ice; you can't have your cake and eat it!

Without wanting to sound too British Rail you need be mindful of the type of ice you are talking about.

Which would you rather be facing ,ghrud , if it were flowing towards you 1m of sea ice or 3km of glacial ice in the form of an ice sheet????

You see they may be frozen water but they are oh such different beasties.


Which do you imagine has more to fear from gravity? 1m of ice or 3km of ice? Which ice type would keep supercooled water fluid and under immense pressures ? 1m of ice or 3km of ice? Which type of ice poses the biggest threat to mankind on it's ablation? 1m sea ice or 3km of continental ice sheet.......

Be careful of words that only wish to illuminate our facile sides ghrud.....

Ho Hum.

[Iceberg]

I missed this article from March.Sorry if it's already been posted.
http://nsidc.org/new...25_Wilkins.html

Antarctic Ice Shelf Disintegration caused by melting trigger.

And this in a season which was described as very good for sea ice. Hope we don't get a bad one.

[Gray-Wolf]

Though I'm struggling to find the article research into glacier movement have recently recently declared that they move in a different way to what we once thought. Seismometers on the ice (in both Greenland and Antarctica) have been showing many 'glacier Quakes' since the study started in 03'. Initially this was put down to calving at the snout but recent triangulation work has shown that the focus of the quakes is from within the glacier itself. It would appear that instead of a steady 'creep' the whole glacier has snaps where it moves a distance in one catastrophic failure and then 'freezes back to the base (the source of the quakes.....some which dwarf most 'normal ' earthquakes giving a 7 on the Richter scale and easily measurable from stations in Australia).

The acceleration of glaciers would seem to involve more and greater 'steps' with each jolt and obviously, if the momentum is great enough, has the ability to drain huge quantities of glacial ice in a very short 'event'.

With the upland melt noted on the EAIS lubricating the glaciers feeding Ross Embayment the fear now is that the glacial movement itself could push/fracture the embayment itself releasing the upland ice into the arctic ocean and is not reliant upon the shelf ablating prior to any draining of the upland ice.

The Wilkins breakup may have been this type of event with the shelf still trapped in winter sea ice when it failed.

[Gray-Wolf]

http://www.scienceda...80604141005.htm

I've found another appraisal of the paper mentioned above.

[BLAST FROM THE PAST]

Gray-Wolf, on 9 Jun 2008, 09:44 AM, said:

http://www.scienceda...80604141005.htm

I've found another appraisal of the paper mentioned above.

GW
Ta and very interesting. This next quote concerns me and for a different reason

Seismic waves from what are loosely called "glacial earthquakes," mainly near Greenland, were originally reported in 2003, and the numbers have been increasing in recent years.

Within the magnetic field system from 'heavenly' bodies [sun/planets] and the Milankovitch cycles an increase of seismic activity is believed to experienced. Are we on precipice of a major cooldown...are the signs beginning to show? That is my fear.

BFTP


Just to add the real reason for the movements are not really known but they are occurring. A very interesting article though and a good post

BFTP

[Gray-Wolf]

Ta Blast.

I can only guess from the geology I know that the movements may be similar to fault plane movements where the forces eventually overcome the inertia along the fault plane resulting in slippage. Of course here we have this occurring many times daily in the glacier and also instead of it being a rock on rock surface it is ice on rock at the movement surface. Because of the pressures on the ice it is able to both plastically deform and freeze/thaw (almost like the partial melt that occurs in metamorphic rocks with tiny areas melting whilst the matrix remains solid.

With the increased snowfall occurring on the peninsula the 'pressures' on the glaciers must surely be increasing forcing more 'slips' and transporting ever more ice to the oceans.

I would imagine that, in a 'melting' scenario like Greenland there is a great increase in basal water flow further lubricating the movement surface and so allowing for bigger slips to occur each failure at the movement surface that occurs.

[jethro]

Given the regular 12 hour spacing, I suspect Lunar or tidal influences at play here; it would be interesting if the magnitude varied along with the different tides.

[Chris Knight]

jethro, on 9 Jun 2008, 10:56 AM, said:

Given the regular 12 hour spacing, I suspect Lunar or tidal influences at play here; it would be interesting if the magnitude varied along with the different tides.

The Antarctic has rather a unique tidal signature. The solar tidal influence cycles over the year, with little contribution to the monthly and diurnal cycle tidal heights. Here is the tide forecast for Ross Island over the next week:



The Antarctic tidal range is comparable to the swell experienced in the open oceans, rather than the large ranges we see around the UK and other parts of the northern hemisphere where the land and ocean topographies focus the tides over shallow continental shelves into narrowing inlets. The limits are +1.2m and -0.1m compared with the astronomical low tide datum. These limits are encountered at spring tides which occur near the lunar perigee or apogee, but in the Antarctic, bear no relationship to the phase of the moon!

In September, the full moon nearly coincides with the Antarctic neap tide:



In both charts, the little wiggles near the neap tides with the least tidal range are due to the solar component of the Antarctic ocean tide. The reason it does not produce two high tides a day as is experienced on most northern hemisphere coasts, is because there is no continent to impede the tidal race following the moon's gravitational pull on the southern oceans around the Antarctic continent.

So, I am not surprised that there is diurnal seismic signal on the southern continent, and as you surmise, Jethro, it is likely to have a lunar connection.

If anyone cares to look at Google Earth, the volcanic submarine arc that comprises the South Sandwich Is. follows the lunar tidal drag, shaping both Antarctica, & South America over the last few million years, as do most younger volcanic arcs, e.g. Monsarrat, evolving in an eastern direction. The more northerly,older Pacific arcs have a south-eastern orientation, and just a few old arcs, like Fiji, in the central Pacific, tend to the west, following the inertial rotation of the earth.

(The tidal charts were generated using Wxtide4.7 from http://wxtide32.com

[bluecon]

The Arctic also has small tides which is why in the winter they can build roads on top of it and drive huge loads over the ice.

[Gray-Wolf]

Jethro, I seem to remember (though I have the memory of a goldfish) a paper on the tidal influence on the Glaciers on Antarctica with the calvings at the snout being strongly influenced by the gravitational pull of the moon.

Though less measurable the earths crust also swells/is pulled up when the moon is overhead (just as the oceans are pulled up/bulge when the moon is overhead)

Bluecon, due to the spec. grav. of ice being less than continental crust I would expect it to bulge more than the land surface when the moon is overhead and so the 'ice truckers' to whom you refer do drive over this dynamic event once a month. I think you'll find ice thickness has more to do with the negating of ocean tidal surges. This of course is important as the 'new' thinner single year ice can, and will, be ruptured by tidal action in a way that the Perennial ice could not which in turn leads to faster ablation as a greater surface area of ice surface is presented to the warm (relatively) waters below

[jethro]

GW: It was the regular 12 hour spacing which made me think of Lunar, glad I'm not completely bonkers.

Came across these pics - no not mine - on-line.

Apparently,

"Blue stripes are often created when a crevice in the ice sheet
fills up with meltwater and freezes so quickly that no bubbles form.

When an iceberg falls into the sea, a layer of salty seawater can
freeze to the underside. If this is rich in algae, it can form a
green stripe.

Brown, black and yellow lines are caused by sediment, picked up
when the ice sheet grinds downhill towards the sea".

Attached Thumbnails

• 
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• 
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[bluecon]

Gray-Wolf, on 10 Jun 2008, 08:48 AM, said:

Jethro, I seem to remember (though I have the memory of a goldfish) a paper on the tidal influence on the Glaciers on Antarctica with the calvings at the snout being strongly influenced by the gravitational pull of the moon.

Though less measurable the earths crust also swells/is pulled up when the moon is overhead (just as the oceans are pulled up/bulge when the moon is overhead)

Bluecon, due to the spec. grav. of ice being less than continental crust I would expect it to bulge more than the land surface when the moon is overhead and so the 'ice truckers' to whom you refer do drive over this dynamic event once a month. I think you'll find ice thickness has more to do with the negating of ocean tidal surges. This of course is important as the 'new' thinner single year ice can, and will, be ruptured by tidal action in a way that the Perennial ice could not which in turn leads to faster ablation as a greater surface area of ice surface is presented to the warm (relatively) waters below

The full moon causes larger tides that tend to crack the ice.
They still manage to have little problem running huge semi trucks(do you call them lorries?) with huge loads over hundreds of miles of ice roads to supply the oil drilling, etc., sites on the ice.

[Gray-Wolf]

bluecon, on 10 Jun 2008, 03:00 PM, said:

The full moon causes larger tides that tend to crack the ice.
They still manage to have little problem running huge semi trucks(do you call them lorries?) with huge loads over hundreds of miles of ice roads to supply the oil drilling, etc., sites on the ice.

And most of the gear for D'Day trundled over small ,wooden barges.......I'm sure you have a point somewhere bluecon but I'm struggling to find it .

Again we seem to be having a similar type of confusion here to that up north with ice mins remaining constant regardless of what single year ice forms whilst ,meanwhile, the continent and shelves shed mass year on year. Most models explain how we will see the decline in antarctic ice with increased circumpolar winds and more rapid deep water upwelling (and all the short term impacts this brings) yet some still whitter about a bit of sea ice whilst all around is warming.



Ho Hum.

[BLAST FROM THE PAST]

Gray-Wolf, on 11 Jun 2008, 01:24 PM, said:

And most of the gear for D'Day trundled over small ,wooden barges.......I'm sure you have a point somewhere bluecon but I'm struggling to find it .

Again we seem to be having a similar type of confusion here to that up north with ice mins remaining constant regardless of what single year ice forms whilst ,meanwhile, the continent and shelves shed mass year on year. Most models explain how we will see the decline in antarctic ice with increased circumpolar winds and more rapid deep water upwelling (and all the short term impacts this brings) yet some still whitter about a bit of sea ice whilst all around is warming.



Ho Hum.

Sorry GW you are obviously not looking at the overall ice cover/anomaly. It continues to rise and even after the recent Wilkins collapse we are still ahead of even last year! And no we are not currently warming...like it or not there has been no warming for 10 years and ALL the signs are of a downturn in global temps....that is current not projection.

BFTP,

[Gray-Wolf]

http://www.scienceda...80612141015.htm

funny old world eh?

[BLAST FROM THE PAST]

Gray-Wolf, on 13 Jun 2008, 08:56 AM, said:

http://www.scienceda...80612141015.htm

funny old world eh?

Yes it is...and as that report clearly shows IPCC are certainly not be all and end all and in all honesty they haven't a clue how the planet will respond. It may warm it may not. That to me underlines the whole problem with full AGW..it demonstrates the fact that global climate change is an 'unknown'. For now we cool.


BFTP

[pottyprof]

Gray-Wolf, on 13 Jun 2008, 08:56 AM, said:

http://www.scienceda...80612141015.htm

funny old world eh?

Very much so..

Interesting read GW..

[Gray-Wolf]

It's another " Clean Air Act" is it not??? Back then we 'cleaned up our act to preserve surface air quality only to exacerbate global warming and it seems we are doing the same again. When we note something that we have caused that will directly impact 'human life' we act without thinking about what it has shielded us from.....silly old humans eh?