MadSci Network: Earth Sciences

Re: How do icecaps form? Just precipitation, or also distillation of seawater?

Date: Sun Feb 24 15:54:04 2002
Posted By: David Scarboro, Faculty, Earth Sciences, The Open University
Area of science: Earth Sciences
ID: 1013311281.Es

Dear Isaac,

The answer to your question depends on whether the icecap is on land or 
sea.  The North Pole is surrounded entirely by the Arctic Ocean.  The 
icecap there is formed by the freezing of the ocean surface.  
Precipitation (snow) will add a little to it each year, but the amount 
derived from snow is inconsequential compared to the thickness of sea 
ice.  When seawater freezes, the salt that it contains is not frozen with 
it, but concentrated in the unfrozen water below the ice.  Therefore, 
paradoxical as it may seem, sea ice is frozen fresh water.  At the same 
time, the seawater below the ice is more saline than normal seawater.

Do not confuse sea ice frozen from seawater such as at the North Pole with 
icebergs.  Ice bergs form where a mountain glacier or ice sheet reaches 
the sea.  Fragments of the glacier or ice sheet break off and float away 
as icebergs.  Icebergs, being originally part of a land-based glacier or 
ice sheet, are made of ice that was deposited on land as snow.

The South Pole lies within the Antarctic Continent, so the southern icecap 
formed on land.  In fact, the southern icecap is really two separate ice 
sheets, the East Antarctic ice sheet and the West Antarctic ice sheet.  
These ice sheets were formed entirely by precipitation.  In the interior 
of Antarctica precipitation is as low as 50 mm per year, while in coastal 
regions it can be as high as 250 mm per year.  With such low rates of 
precipitation in the interior, the Antarctic ice sheets continue to exist 
because they move very slowly and lose only a small portion of their 
volume each year as icebergs.

I hope this answers your question.

Best wishes,

David Scarboro

Current Queue | Current Queue for Earth Sciences | Earth Sciences archives

Try the links in the MadSci Library for more information on Earth Sciences.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2002. All rights reserved.