Ask A Scientist© Environmental Earth Science Archive

name         T.J. Bucholz
status       educator
age          30s

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?

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
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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
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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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