I noticed that when you look at the ice-sheets covering the globe during the last ice age, that from mid-Siberia up to Alaska appears icesheet-free.

Some explain this due to pole shifting, where the poles where at different locations than in their current status; the Northpole than being located at the Hudson Bay. If glaciation is centred on poles in general, then the pole-shift seems a sound explaination.

Yet, a pole shift seems so hard to comprehend, but is there another explaination why the sheets seem to cover the Atlantic part mainly?

(Note that a 2-D map is distorted compared with a real Earth-globe)

This map suggests the polar region was not ice free. Only that the spread of new glaciation started on land masses close to the pole and spread in both directions.

http://shiro.wustl.edu/210A/transpar...ssion/w103.jpg

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I didn't mean that polar regions were ice free, but the penetration of ice sheets on land masses. It just looked like the asian side had far less (up to none) of it as opposed to the Atlantic side. Massive glaciers cover parts of Europe, North America, but ice masses stand at the Asian coastline. On the part of Europe, ice masses would have reached up to Spain, and some mention even Marocco, although that would definitely raise doubts based on it's latitude.

Again, I am not sure about it, that's why I ask it here.

Hmm... I see what you mean. I don't know for sure. I'd be interested in hearing an alternative explanation too.

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Just guessing here.

Since Greenland is the northernmost land mass, I'd guess that the ice cap formed there first, and then had a cooling effect on weather patterns flowing over and to the adjacent land and water areas, namely North America and Europe, and the North Atlantic.

So assisted by this "cool boost", it was much easier for those land masses to accumulate their own ice packs, whereas Asia was much further away from any cooling effect.

My guess (as a meteorologist, but not one qualified to answer this question definitively) is that the average path of the jet stream was influenced by the oceans (which would have stayed warmer than the land, due to heat capacity issues), and that allowed the middle sections of the great land masses (Eurasia, North America) to glaciate. Since the Pacific is larger than the Atlantic, its influence would have been greater, causing the jet stream to "make up" for that elsewhere. Generally (at least now), the polar jet stream forms a curvy hexagon or pentagon shape in its path around the world. Seems reasonable that it would continue to form some polygon during an ice age.

Note, too, that coastal Alaska and British Columbia are mountainous, so glaciers are "normal" there.

Might be a good topic for a paleoclimatologist - if it hasn't already been done. A really quick Google search turned up nothing useful. I'll be interested to see other ideas....

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You have to remember that ice caps won't form just because it's cold. There also has to be precipitation - a lot of precipitation - to "feed" the growing caps. I'm guessing that eastern Siberia was cold but dry for various meteorological reasons. :-k

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Also, compare Greenland's thick ice sheet today with relatively ice-free Canada in the same latitude and just a few hundred kilometres away.

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(Emphasis mine)

That's not entirely true.... The South Pole averages a mere 0.1 inch (about 3 mm) of water-equivalent precipitation per year. At extremely cold temperatures, there is very little sublimation, so the ice remains. After enough time, well,....

As for Greenland vs Canada, I have no idea. 8-[

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"I am Meteora, supreme goddess of weather" - Meteora, in The Unchained Goddess

One nice thing about being a meteorologist who also likes astronomy is that the sky is always interesting!

Just a guess (with no expertise at all in the field) Greenland is an island and pretty much rock I think. Whereas Canada (aside from being warmed from the love we in the US have for our neighbor) has trees and dirt, cities, stuff which retains heat and thus, melts the potential permafrost. Hey, I don't know. I'll go with the love thing for now.

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Love... that's IT!

Actually, at the same latitude as Greenland, Canada is also rocky and nearly lifeless. Baffin Island has a few glaciers on it. If I remember correctly, the ground under the ice layers in Greenland is mostly below sea level, too.... I really have no clue why Greenland became an ice block. :-?

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"I am Meteora, supreme goddess of weather" - Meteora, in The Unchained Goddess

One nice thing about being a meteorologist who also likes astronomy is that the sky is always interesting!

patrick: You're correct in suggesting that we don't have to look to "pole shifting" to find an explanation for the distribution of ice in the northern hemisphere. Firstly, we understand very well the how the combined effect of cyclic variations in the eccentricity, obliquity, and precession of the Earth lead to the onset of glacial periods. What is less well understood are the processes that amplify these relatively small Milankovitch Factors. We have geophysical evidence for several glacial cycles over the last half million (or more) years, and it shows a periodicity that fits well with these variations in Earth-Sun geometry. There is no room in this explanation for a shift in the position of the poles.

Another thing to keep in mind is that patrick's map is a Mercator projection, which really stretches the apparent size of areas nearer the poles. Any attempt to find the center of the ice masses based on such a projection is confounded by this stretching. For example, the idea that Hudson Bay might be the center of that ice is severely challenged by the polar projection in Quartermain's link.

I think the explanation lies, as Meteora suggests, in ocean/continent geometry and the effects of heat transfer processes - winds and ocean currents. The Pacific ocean has effects on weather cycles over the entire globe, and those areas that remained ice-free are closer to the Pacific Ocean. Of course this doesn't explain the ice along the west coast of North America, but there I'd expect the accumulation of large winter snowfalls to more than offset the melts due to milder summer temperatures.

I'm also somewhat curious to the effects of topography during a glaciation. In modern times we see differences in precipitation on the windward versus lee sides of mountain ranges - rainshadow effects, and steep southerly slopes in the northern hemisphere are snowfree earlier in the summer. To what extent do these conditions continue during a glacial period? I'm sure they must continue, because we know there were refugia - places where vegetation survived and from which it was poised to expand into a deglaciating landscape. Anyway, that's another topic and the link to astronomy is getting tenuous. . . .

Except for the 100,000 year cycle, which is the strongest.

I think patrick's point is that the ice map doesn't center on the north pole, and that would need an argument other than the milankovitch cycles. Since there doesn't seem to be any evidence for a pole shift per se, we assume that it is meteorological--not that everything is already explained by the milankovitch cycles.

An interesting addition are the locations of found Mammoth, which appear everywhere (from a certain latitide) except around the Hudson area, Greenland and Northern Scandinavia.

Add my emphasis. Growing caps will certainly need more precipitation than maintaining a status quo, or even a very, very gradual buildup such as could account for Antarctica.

Also, in general, remember that any representation of the ice cap over the oceans has to be pretty much pure conjecture, based on the models that keep our current assumptions, such as the North Pole being in the same place. While I don't take this as strong evidence that it has changed location, if you are considering the possibility, you probably have to pretty much ignore what those diagrams show for how far south the ice went over the ocean.

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I am far from being an expert on this but judging from both of Patricks' maps, the point where the ice ends in Siberia is about where I'd expect the air to run out of water for percipitation. Since, world wide, winds average west to east, Alaska and Canada would get their moisture from the Pacific and arctic oceans. Eastern Siberia doesn't have anything west of it but western Siberia.

Thus speaketh the neophite.

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Right. I just meant that "lots" of precipitation wasn't absolutely necessary in a very cold environment. Near the edges of the growing ice cap, though, lots of precipitation in the frozen form would be needed.

I try to be concise, and look what happens!

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"I am Meteora, supreme goddess of weather" - Meteora, in The Unchained Goddess

One nice thing about being a meteorologist who also likes astronomy is that the sky is always interesting!

That's partly right, but weather doesn't always go west to east. East coasts of continents are usually rainy because of the effects of the oceans on the global circulation pattern. Actually, it's a lot more complicated even than that. Since this is an astronomy board, and not a meteorology board, I suppose I should leave it at that.

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"I am Meteora, supreme goddess of weather" - Meteora, in The Unchained Goddess

One nice thing about being a meteorologist who also likes astronomy is that the sky is always interesting!

Oh, trying to be concise again, eh? Won't you ever learn?!? :wink:

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No.

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"I am Meteora, supreme goddess of weather" - Meteora, in The Unchained Goddess

One nice thing about being a meteorologist who also likes astronomy is that the sky is always interesting!

During the ice-age, the Bering-strait was dry land (caused by glaciation, lowering the sea levels), so no stream could eventually pass through it. This obstruction caused waters not to reach the Pacific side, cut off from the circulation of any Atlantic currents.

If the Pacific side apparently enjoyed a 'milder' climate compared to the Atlantic, it might indicate that climatical conditions for gladiation around the North Pole stem from water-currents from lower Atlantic latitudes, and not from the present North Pole region itself. Such currents have less influence beyond the area of 'land-lock in' (Bering Strait).

Assuming a cooler Atlantic side would clarify lack of mammoths at lower (Atlantic) latitudes; from Hudson area up to Scandinavia, it is almost as if a polar shift-effect did occur, providing the reasoning I forwarded is correct.