Challenge Questions

"This should be obvious to you; you are a farmer."

It's the difference in land mass and its arrangement that makes ice at the poles so different. Antarctica has a central land mass surrounded by water; the Arctic has water surrounded by land.

Nicely explained here: http://nsidc.org/seaice/characteristics/difference.html

GA

This answers a different question - about why there is less sea ice in the Antarctic than in the Arctic. Post #3 gives a partial answer to the challenge as written: why there is more ice covering the land mass of Antarctica than in total around the North Pole.

One thing farmers worry about is rain/precipitation. There is very little precipitation in the Arctic but there is precipitation in the Antarctic. The Arctic is mostly sea and therefore at sea level. However, the Antarctic is a land mass with mountains. Moist air coming from the seas turns to precipitation as it rises over the mountains.

Thanks,

Jim

GA.

However, I think that two more features (one somewhat associated with the effect you describe) are needed before we have a sufficient explanation.

The low precipitation at the Arctic pole is also explained by the fact it is in a (mostly) frozen ocean surrounded by land: there's not much water available to be turned into precip. The Antarctic pole is on land surrounded by water, where sea ice that forms in winter breaks off and drifts north freely, so that there is plenty of water available to be turned into precipitation and dropped onto the land mass, as Jim rightly said. That precipitation falls as snow, so I assume that the summer warming/melting is enough to contribute to ice formation on the land, but insufficient to cause it to mostly run off before freezing.

Because the Arctic pole is in the ocean, the ice extending from the pole is always in contact with free water at some point: the corrosive effect of salt water on the ice would tend to keep it from building up year over year in the way that ice on land can do at the Antarctic pole. Being in the ocean, also means the effect of currents must be taken into account: warm currents that flow into the Arctic from the East contribute to the melting of ice in that ocean and reduce the opportunity for Arctic polar ice to build up.

GA.

We have for the Antarctic (so far): cooling moist air (due to surrounding sea and height), lack of salt and basal insulation (both due to the continent underneath).
However, in reality the precipitation over the thickest regions of the ice is rather small; this thickness is in some places so great that one more factor is needed.

Albedo is another factor - a very important one when it comes to the different ice buildup potential when in contact with water vs insulated by the land.

Ice and snow are highly reflective: the high albedo means that little energy is absorbed, thus keeping surface temperature of the ice to a minimum and reducing the chance of melting. This principle would apply equally to the actual North pole, since I believe there is little melting of snow or ice at the pole itself. But the free water in the Arctic ocean has a low albedo. The water is dark, absorbs energy readily, thus accelerating the tendency for ice to reach melting temperatures.

Indeed, the more open water is available to absorb energy, the faster melting goes. I believe this was a factor that was not considered in the early "climate change" models, and the reason why polar ice is now known to be melting at a much faster rate than previously estimated.

Yes, it's important - but it's much the same at the North Pole; so it's not directly a factor in creating the differences between North and South.

to add to your point....ice forming at the antarctic isn't going to slide into the water, other then by slow glacial drift. Precipitation is free rain falling from the sky - in that sense, both areas are as much desert as the Sahara. (willing to humbly stand corrected if it actually rains in either place). Antarctic ice isn't (for the most part) going to simply subside into the water because it's sat upon land. You expressed it well - GA to you, sir.

The land mass itself acts as insulator holding the ice up off the warmer water into the cold air.

Back to the farmers, that clue must meant something. I suppose it could have been a red herring.

To protect fruit trees from frost (and presumably some other crops as well) some farmers will place pails of water around the trees. Water stores heat better than rocks (or any other solid) so as the water freezes (phase change) it gives off 80 calories per gram. This is heat that protects the trees.

That is why a farmer should understand why there is more ice in the Antarctic. There is no place in the Arctic that is more than a few feet from water, and then only straight up, so almost all of the heat lost by the seawater is going directly into the ice above. In the Antarctic, precipitation that settles on land (which, by the way, is fresh water and freezes at a higher temperature) may be hundreds of miles from the ocean so does not benefit from the energy of the phase change.

The North polar ice, as a floating mass, is subject to tidal forces, and has continuous currents of saline ocean water flowing under it. Additionally, the rotational force acting on a mass a hundred meters thick and spanning hundreds of square kilometers, spinning at 1 revolution per day, with no anchorage, develops a pretty fair amount of tensile force even if the mass was centered over the pole.

The southern ice mass is land-based, mostly on mountains kilometers above sea level. There is no tensile force to be resolved in the ice, it is transferred to the land mass. As a result, the tens to hundreds of thousands of years of accumulated ice slowly drifts downhill to the sea, where it shelves, and then calves from the tidal actions, and then the slough bergs drift toward the equator, melting along the way.

This is the same principle as Greenland which, due to it's land base and in spite of its position several degrees farther south than the pole, has several magnitudes more ice than the north pole.

richh

The arctic ice floats on water - which cannot support tension and therefore conforms quite well to an equipotential surface (give or take second-order effects of circulation). Even if the ice did not naturally follow such an equipotential surface, the few metres separation between the surfaces of the ice and the "natural" surfaces of the water would not be enough to generate significant tensile forces.

I'll wait for the question to appear.

Give it 10 years and we'll all be asking or clarification - which first.

Anyway, the antarctic is heavier - it's bound to be in the South

Hi,

I doubt that the amount of rain or snow matters very much.

Antarctica has lower temperatures so any snow will be accumulated for long until evaporating or reaching the ocean by glaciers and break off.

Green land -a s mentioned above - has some km of ice-thickness.

Arctic floating ice is insulating the sea below from loosing heat by evaporation and radiation, acting like a blanket (the farmers know about the greenhouse effects of blankets ). So the sea stays warm and lick at the ice from below. (Plus the other actions described above).

<To combat global warming: remove any clouds and water vapor from the atmosphere>

RHABE

<To combat global warming: remove any clouds and water vapor from the atmosphere>

these are the smallest factors to the global warming! other - invisible- parts are much more important!

Actually, clouds have a major impact - much greater than CO2, for example. But change to cloud cover is unlikely to be driven cumulatively by man's production of steam, because the oceans provide a large source/sink of water and vapour that will stabilise the cover. Whether global warming itself will cause significant changes in cloud cover, and whether this will increase or reduce the warming are quite other matters.

Arctic ice is also effected by the gulf stream in the Atlantic to add to the warmth of the Arctic Ocean waters.

Jon

I always understood that Antarctica was classified as a desert. Secondly it was the coldest place on earth. So my thought would be that what little bit of precipitation it receives it holds onto therefore it doesn't evaporate as quick as it accumulates and over thousands of years of accumulation and compression glaciers continue to develop ice. Is this the answer we are looking for? Well maybe but trying to think like a farmer (as a person with farming background) this is what I have come up with.

http://en.wikipedia.org/wiki/Antarctica

GA

But why is this:-

"The temperature in the ice would rise at an approximate rate of 1^OC/200m due to gravity."

Now you point it out, it is probably incorrect - I'm not sure.

If correct, the origin would be an equivalent of the temperature gradient in the atmosphere. It is certainly a feature of transport (or diffusion) in liquids as well as gases. So if diffusion in the solid is significant we will certainly see some effect.

The reason I assumed this intrinsic distribution is that the ice is continually settling - and this would be the gravitational heating due to such movement. I've no idea whether such a distribution would be expected in a stationary solid, nor if it were what the magnitude would be.

A final note, I think that the fact that discounting such an effect would predict the "correct" depth for the ice would be more of a coincidence than a demonstration either way.

a little help?

the temperature in the earth rises with depth under the ssurface, the highest temperature on earth are in the core! Why s this - the pressure?

Wilhelm,

Heat from the sun and frictive pressures caused by the gravitaional effects of the sun and moon distorting the mass. Some heat can be attributed to nuclear decay.

Jon

The problem with the arctic ice mass is that the whole of it is an unanchored floating berg, except in the worst of winters, it can lock up to some of the northern islands of Canada, Russia, and Sweden. It usually reached the shores of Alaska in the past, according to Inuit lore/history. My recollection is that the 10" figure is water equivelant, building to perhaps a meter or 2 for the new ice, all of which melts in the spring/summer. The salt water flowing beneath this mass has a substantial melt contribution. The thinner annual ice is always up to about -2 C, the freezing point of the salt water beneath, with the exception of the wind chill and radiation loss. The older perennial ice melts and refreezes or flows down through melt channels to the sea, but at a lower rate than the annual snowfall compacts to.

In the winter, the radiation loss (either pole) is substantial due to the 6 month dark cycle, and reverses in the summer's 6 month daylight cycle.

The tidal and centripetal stresses in the ice cap cause substantial calving, even of the core polar mass. That is the source of the larger bergs large enough to sink ships in the event of a collision.

Most of the south polar ice bergs result from calving of glacial fronts often greater than one hundred meters of floating ice.

Then there is the Larsen shelf "B" berg.

richh

Thank you, that is interesting. But the situation could be far more complex than that, which stimulated me to do some sums.

To illustrate: a 20^OC temperature difference through 1.5-m thickness (estimated effective averages through the winter period) of ice would result in heat flow of 27-W/sq.m. This would be enough to freeze about 60-mg of stationary sea water every second - which amounts to a thickness contribution of 90-cm.
This is probably a gross overestimate of any contribution, given that the water is moving; indeed, at the other extreme the water could continue to melt the base of the ice, requiring significantly larger snowfalls than above.

What I'm trying to say is that, given the interaction of the ice with the sea, the precipitation figures are rather close to being a good match to the actual thickness build-up - and such matches always ring alarm bells that maybe the measure was the "easy" result rather than the actual amount of snow that fell. (BTW, my suspicion was primarily aroused by the fact that the nearest measurement station that I know of is in Greenland - but I could just be out of date)

Hi Physicist,

good explanation, GA.

Only one doubt: "gravitational heating" should be friction loss by bending by tidal forces.

This is cracking plus repeated plastic bending.

Cracking if brittle: low pressure, low temperature: at the surface,

bending if ductile, at depths where the flow velocity by pressure gradient will be sufficient to close any open cracks within suitable time.

So I assume this will change the vertical temperature profile by convection if there are open cracks going deep down.

Glaciers have these cracks but if significant in heat transfer I have no idea.

I also would suggest to adjust the heat flow estimate to the overall 75mW/m² as I do not see any mechanism where this energy will escape, originating deep down by radioactive decay and going nearly straight up - a little bit changed in direction by local variations of thermal conductivity.

RHABE

The main mechanism for heat originating under the Arctic seabed to escape is via the movement of the sea water ("the conveyor"). So everything relating to heat flow and/or freezing/melting at the base of the ice sheet can be derived from the temperature difference between the surface and the base of the ice sheet and the water temperature (my estimated 20-degC).

As ice floats rather low down, and the water is inevitably warmer than the surface air, the effect of the crack would almost certainly be to warm the top surface of the ice somewhat, which would tend to reduce the edge thickness. The top surface of the water, on the other hand, would tend to freeze, thus trying to fill the gap. But I doubt either effect is significant in the winter except towards the edges of the ice-pack - as I believe that cracks of significant size are relatively well-spaced.

Hi,

I did not think about arctic floating ice but about your estimates of antarctic ice-thickness by results of heat transfer and accompanying temperature difference.

RHABE

pressure heat occurs in a compressible fluid. At the depths of perhaps 5 kilometers, my wag of maximum antarctic ice depth, the pressure would be 4,000 psi, the compression of the ice is too small to have any thermal effect. The entrapped air, which may warm on it's way down, carries it's own heat upward as it is forced through the pores of the ice, and cools equally on it's way up as expansive cooling. A minuscule amount of air stays entrained and does offer some heat, but very little.

The arctic ice mass is afloat, with some edge binding, so I suppose you could call that flat. Antarctica is a mountainous continent, with several peaks at nearing 20 kilometers elevation. The flow rate of some parts of the glaciers running down to the sea is 80 m/day. At 140 kips, there is substantial frictional heating resulting in high pressure lakes that lubricate the flow, reducing the friction at under a fair percentage of the field. Any surface flow downward in the glaciers through cracks at these depths will freeze at the reduced pressure/increased freezing point in the pressure free cracks at lower depths, preventing air exchange through to the ice.

The antarctic is basically on the Rings of Fire, and it's areas of volcanism are a substantial threat to the planet. The last volcano to erupt under the ice blew away and vaporized several cubic miles of ice. Additionally, several geothermal geysers maintain a delicate balance between their melt and the refreeze that occurs most often in lubricated (water borne) areas.

Richh

the compression of the ice is too small to have any thermal effect

Hi,

yes, naturally you are right, as I posted just above this is (very likely) thought to be of tidal origin and thus pressure/gravity will have a big influence. (In thick ice sheet only).

If cracking this may help to enhance convection in the open cracks.

If bending a viscous mass and any cracks rapidly closing again this is only producing heat.

Unfortunately I have no idea about the viscous properties of ice in order to do an estimate if significant.

RHABE

with several peaks at nearing 20 kilometers elevation.

That's a new record, i thought till tody the highest mountain on earth was the Mount Everrest!

Wilhelm,

Where did you get the 20Km?

The highest Antarctic elevation is Vinson Massif 4,897 meters (16066 ft). Not even 5 km.

Jon

at post 83

Wilhelm,

Thanks.

Jon

My first thought was that it came from the thickness of the crust - but that is apparently more than 40-km in places. I'm reduced to the explanation that the thickness was found in an old Nasa report.

Fyz,

Good explanation.

Reminds me of the Gimli Glider incident of 1983. Same problem.

Jon

NoSciFi,

Antarctica is a mountainous continent, with several peaks at nearing 20 kilometers elevation.

The highest point in Antarctica is Vinson Massif 4,897meters. That is less than 4.9km.

The highest point in the world is only 8,850 meters. That is less than 9km.

Jon

arctic means "land of bears"

antarctic means "land with no bears"

Any farmer knows that a large animal such as a bear has to eat a lot. So my guess is that the bears are eating the ice in the north. and there are only penguins in the south. Bears eat more than penguins... ergo. More ice in the south than in the north. QED

Ah, now we know! All those penguins jump in the water, and when they come back, it drips to the ground and freezes into ice. Like children tracking in mud for thousands of years.

Less land mass below the equator to melt ice by transfering heat. Landmass-to water-to Antarctica.

There are ~186 days from the March to September equinox and ~179 days from September back to March, due to the velocity of the Earth in its elliptical orbit. In effect, this corresponds to a longer summer/shorter winter in the N. hemisphere and shorter summer/longer winter in the S. hemisphere, which likely contributes to a lower temperature in Antarctica. Historically, the growing season has been determined by the spring equinox as the time for planting until the autumn equinox as the time for harvest (as any self-respecting farmer should know), so it shouldn't be too much of a stretch to realize that the shorter summer (growing season) in the SH means a longer and colder winter, and thus more ice formation.

That is an interesting observation.

But there could be two aspects to this. I think that the longer winter comes after a shorter but hotter summer. Indeed, once we take the reduced distance into account it looks as if the total annual insolation into the Antarctic could be higher than into the Arctic.
Detail: first armwaving suggests that the angular velocity at aphelion and perihelion should be proportional to 1/R^3/2, whereas the insolation is proportional to 1/R². If that holds up through the period (and I don't know whether it does) that would make the total heat input in the antarctic summer greater than that in the arctic summer.

I have no idea whether that would correspond to a colder end to the winter, nor indeed whether if that is the case the increased summer melt would over-compensate. It's just too complex (and possibly not significant given the effects of altitude and insulating ground).

dac1267,

Due to its eliptical orbit the earth is closer to the sun during the part of the year that corresponds to the warm season in the southern hemisphere and cancels the effect of the shorter warm season.

Jon

dac,

Liked your answer, but the picture of your avatar creeps me out

the lowest temperature on earth is in siberia - on the northside of earth where the winterperiod is a week shorter!

Wilhelm,

Siberia? Are you thinking of Vostok research station?

Jon

Wilhelm,

You said the the lowest temperature on earth is in siberia - on the northside of earth where the winterperiod is a week shorter!

The coldest inhabited place on earth is in Siberia. It is not the coldest place on earth.

Of all inhabited areas, one of the coldest places in the world is Siberia. Although global warming has taken a toll on Siberian winters over the past decade, it's normal for temperatures to reach -60F (-51.1°C) in January. Oymyakon, Sakha Republic of the Russian Federation, in Eastern Siberia, has an average winter temperature of -96F (−71.2°C). The little village is home to 900 permanent residents, who endure winter for nine months out of the year, and considered -30°F (−71.2 °C) "balmy." The area is so cold that empty plastic bags taken outside will freeze within minutes and then crack like glass.

Jon

Earth is on an elliptical orbit around the Sun. An Ellipse has two focal points, each offset from the center. The tilt of the Earth is 23 degrees. In the Northern Hemisphere our summer (when we are tilted toward the Sun) we are actually on the long stroke of Earths elliptical orbit (farther from the Sun). The Northern Winters are on the Short stroke of the ellipse. So, the Southern Hemispheres Winter is on the Long stroke (with our Summer) and hence they have a colder Winters and also Warmer summers. Not sure why a farmer would know this?

Jazzed

the arctic ice shield is melting away from the water under it while the antarctic ice shield is laying on the ground (its an ice-farmer) and could not melting and flow away

WilhelmHKoen,

the antarctic ice shield is laying on the ground (its an ice-farmer) and could not melting and flow away

Guess again.

http://www.usatoday.com/weather/climate/globalwarming/2009-02-25-warming_N.htm

Jon

melting from the surfasce lets flow the glacierwater away, this happens to the arct5ic and the antarctic glaciers.

the arcit glaciers are melting from the underground - this could not happen to the antarctic glaciers because they are laying on the ground (there are local lakes and flows under the antarctic fglaciers but they do not flow directly into the ocean) while the arctic glaciers are swimming on the water.

antarctic glaciers are like mountain glaciers and they melting by the pressure of the glacier wall while arctic glaciers are like normal water and melting by the temperature of the polar water.

Wilhelm,

You are right but there are active volcanoes under some areas of the Antarctic ice shelf causing increased melting and glacial flow and creation of huge lakes under the ice. The volcanic activity stays under the thick ice and spreads intead of burning a hole through to the surface.

The sea shelf ice around Antarctica is also melting and breaking off at a higher rate and that allows a greater velocity of the glacial movement from land toward the sea.

There is a major glacier there that has increased its velocity by about 83 percent.

Jon

the volcanic activitie under the antarctic ice shield is only a temporary event and it happens in the north polar region too (iceland).

This in principally because the arctic ice is sea based while the antarctic ice is land based. The thermal capacity of land is much greater than sea water, so requires more solar energy to heat up. This is also why the arctic sea ice is extremely seasonal, fluctuating is area from season to season and year to year, where as the antarctic ice is almost constant. The same also applies to the Greenland ice sheets, which are decreasing in size, but to a much lesser degree than the arctic sea ice.

Seanan

The thermal capacity of land is much greater than sea water.

Eh?

Check the table about half way down this article.

this is only the specific melting heat - for water the melting point is nearly 0°C, for solids up to some thousand degrees!

Huh?

The articles title is "Specific heat capacity"

The table I'm referring to has the title

"Table of specific heat capacities at 25 °C unless otherwise noted Notable minima and maxima are shown in maroon"

No body mentioned latent heat.

I'm not refering to a table, i'm refering to my head/brain/ or what else you may call it!

I think the polar bears answer was on the right lines, but looking at the wrong end. Forget what the few bears put in their mouths. 40 trillion penguins put fish in, and out comes ... the Antarctic land mass. That's what livestock farmers understand.

shit happens - on land and on sea side!

every farmer (in the southern areas anyway) knows that ice is an insulator. When there is freeze warning the farmers in Florida will turn the sprinklers on to coat the oranges and strawberries with a layer of ice. This keeps them warmer than the surrounding air. So the fruit doesnt freeze even though they are covered in ice. A similar effect occurs in the north where the ice traps warmer temps in the water. Because the water is warmer it melts more of the ice. In Antartica the ice sets on top of the ground. The ground becomes a permafrost and is esentially just more ice, so no heat can be trapped there. The only place you will see a heat exchange in Antartica is around the coastal areas, where heat can be trapped under the ice in the water. There was a great video on the web that demonstred this when the larson ice shelf broke up last spring. This same permafrost/ice build up effect can be seen in the north in Greenland where the ice covers nearly the whole country and sets on top of the ground, not the water. Greenland is a mini-Antartica for the most part. It's less-polar location is the only thing that allows it to have habitable land area, and most of that is to it most southern tip.

Anyway the answer is because the ice heats the water in the north. it however does not heat the ground in the south. Farmers know this. If the ground temp falls below freezing you loose your crop. If the friut is sheilded from the freezing air it will stay warm.

This has to be something that an ordinary farmer would be aware of. Most don't know about the higher altitude in anartica or even about the effect of land surrounded by water vs water surrounded by land.

But, many farmers understand the effect of sun angle since they often build coldframes oriented toward the winter sun in order to get an early start on seedlings.

Where I live the climate is marginal for agriculture - the growing season is short and the weather is highly variable to say the least. Nonetheless people must eat and so some of us are farmers - my grandfather was a farmer here before electricity, fertilizer, cold frames, etc etc. But you're right that aspect - whether or what hours your slope faces the sun - is important for farming, if not for antarctic ice. This is microclimate stuff, maybe not so useful for the general question about polar ice.

What I know as a farmer about altitude is contrary to the point of "high altitude antarctica means colder". What is important to me vis a vis altitude is air drainage. I happen to live at the foot of some relatively higher hills. The risk of frost on cold clear calm nights is much greater in low lying areas, because cold air sinks. A hilltop, or somewhere up the slope, is a better site for a farm here. Obviously that doesn't hold true for very high altitude peaks, where it is colder all the time. Farmers in very mountainous places might have a different point of view.

The warming effect of water is very important for farmers in marginal cold climates. The earliest and longest developed farmland here was along the coast, for reasons that are obvious when I compare my father's garden to mine. Five minutes drive, but the weather is often very different, and the risk of frost is negligible next to the water when compared with a place inland and tucked below hills. Maybe water effects are the most relevant for farmers overall, since this is universally known and used in very different climates.

All the 'survival' farms of former days here were sited next to ponds or the ocean if at lower elevation, or else on a ridge or upper slopes of high ground inland, because of air drainage effects, and with less concern about altitude-cooling effects.

Yes. Just to the north of us is a very fertile, very cold valley. They put up with the cold temperature (typically 6-8 °F below the area average) in trade for soil that is rich to a depth of almost two feet. My father, after he retired, had a small farm up at about 4000 foot elevation that had good soil and sun, but a short season.

higher altitudes at the poles collect more sunlight

Antarctica has high elevation, no direct sunlight and the land underneath insulates.

The Artic has no significant elevation and direct sunlight and the ice is bathed in water that comes from rivers and the warm Atlantic stream and the cold meltwater drops into the Artic abyssal plane.

The Arctic Ocean is mostly covered by ice and surrounded by land, precipitation is relatively rare. Snowfall tends to be low, except near the ice edge.

Antarctica is entirely surrounded by ocean, so moisture is more readily available.

A farmer prefers direct sunlight and low elevations.

Jon

"Antarctica has <snip>, no direct sunlight"

Please explain, I thought that it got the same sunlight, give or take, as the Arctic.

They both have no direct sunlight.

The sun above the Artic and below the Antarctic circles is not considered as direct sunlight because of its oblique angle.

Jon

Funny, I live in the Arctic and I see the Sun almost overhead during the Summer Solstace. We even play a midnight golf tournment!

Guest,

That's Funny. I live near Seattle and the sun is never overhead here.

When I lived 75 miles south of the Arctic Circle by Russia it only went in a circle never really getting very high in the sky.

How do you define "live in the Arctic"?

Jon

Alternatively, "which way is up"?