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Name: T.J. Bucholz
Status: Educator
Age: 30s
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Question:
Are oceanic icebergs comprised of salt or fresh water?
If they are made of fresh water, why are icebergs fresh water completely surrounded by salt water?



Replies:
For the most part icebergs are fresh water. The reason is that when ice freezes slowly enough to not trap salt water inclusions, the complex crystal structure of ice does not provide any space for the salt to become incorporated into the crystal structure.

You can demonstrate this for yourself by PARTIALLY freezing a solution of salt water, say about 5% in your frig freezer. Freeze about 1/4 of the water. Remove the frozen ice and carefully rinse it in cold fresh water, say just above 0 C. so you don't melt the ice very much. Rinse it several times with new fresh cold water then taste the ice cube and compare that taste to the taste of the original salt solution.

Vince Calder


T. J. ,

Icebergs are huge pieces of ice calved (broken off of) from glaciers (common in Alaska) or another, land-based, continental ice sheet (Antarctica, Greenland, etc.). These are fresh water, as the ice from which they come accumulated on land as snowfall piled on year after year.

Sea ice (often called ice floes) is more or less flat pieces of ice that resulted from Spring ice breakup of the polar (Arctic or Antarctic) ice caps (frozen sea water) that were frozen during the long winter.

The iceberg is extremely dense ice, sometimes with snow on top. The salt sea water does not mix with the fresh water ice that the iceberg is made of.

You can find more information on icebergs and sea ice at

www.antarctic.com.au/encyclopaedia/physical/IbergSI.html

David R. Cook
Atmospheric Section
Environmental Research Division
Argonne National Laboratory


True icebergs are galcier fragments that have fallen into the sea. Glaciers are made of compacted smow, which is fresh water.

Additionally, "sea ice" that forms from the freezing of sea water is also basically fresh water as well. This is because when saltwater freezes, it excludes salt from the ice crystal lattice. You can test this out yourself in your freezer. Put some saltwater in a pan and place it in your freezer. When some of the water is frozen, skim it out , rinse it with cold water to remove any liquid saltwater on it, and let it melt. Taste both the melted ice and the remaining unfrozen saltwater, and see if one is saltier than the other.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois



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