QUESTION:
What studies have you made concerning the age of the ice?   Do
you count the layers of ice and snow like you would count the
rings on a tree trunk?  What has been discovered about the
environment by looking at the dust in the snow?  How old is
the oldest snow?  How do you know?
        
        Fifth Graders in Mr. Scott Petersen's Class
        Jeffereson Elementary School
        Mason City, Iowa


ANSWER from Julie M. Palais, Antarctic Glaciology Program
            Office of Polar Programs
            National Science Foundation
            Thu, 20 Feb 1997 11:16:16 -0500

Dear Fifth Graders and Mr. Petersen,

First it should be noted that most of the studies of the ice and ice cores
do not take place at Palmer Station. Most of the work that takes place at
Palmer deals with Oceanography and Marine Biology.  The ice core studies
generally take place at remote stations on the ice sheet such as South Pole,
Vostok, Byrd Station and other small temporary field camps.

What studies have you made concerning the age of the ice?   

Reply: Scientists study ice cores to learn something about the climate and
atmospheric conditions in the past. Ice cores are ideal for these studies
since they preserve a very detailed record of dust, gases, temperature and
accumulation (among other things) in the past.  Ice cores are dated by
counting annual layers (actually winter/summer variations in different
components in the ice)(like tree rings) and by comparison with other
information from deep sea cores.  In addition, scientists can make models of
the accumulation and ice flow in order to estimate the age of the ice at
depth.  Finally, scientists who study volcanic eruptions of known age can
look in ice cores to see if there is volcanic ash and gas residues from
certain known eruptions in order to date the age of the ice (see also the
Jan./Feb. 1997 issue of Dragonfly Magazine-National Science Teachers Assoc.
Pub for an article by Julie Palais called "Fire and Ice: Searching for
Volcanic Eruptions in Glacial Ice").

Do you count the layers of ice and snow like you would count the
rings on a tree trunk?  

Reply: Yes, layers of snow and ice can be recognized as having formed in the
winter or summer by their chemistry and also by their appearance (light vs.
dark due to the size of the ice crystals).  Alternations of light and dark
layers and high and low concentration of dust (more dust in Spring and
Summer/less in Fall and Winter) enable glaciologists to count annual layers
back in ice cores.

What has been discovered about the environment by looking at the dust in the
snow?

Reply:It has been discovered that there were periods of time in the past
where there was alot more dust in the atmosphere than there is now.  Ice
that formed during the last glaciation had 20 times more dust than todays
atmosphere.
  
How old is the oldest snow?  How do you know?

The oldest ice in Antarctica is probably about a half million years old.
This is known because we have dated the ice near the bottom (by comparison
with deep sea cores) and it is at least 400,000 years old.  The oldest ice
is estimted to have formed about 500,000 years ago.  We compare our cores
with cores of sediment from the ocean bottom where there are shells of small
animals called forams.  Scientists studying ocean sediments can date their
samples with radioactive methods.  When we compare our cores with theirs we
can see similarities that enable us to say that our cores are similar in
age.  Their cores go back much further in time (millions of years) but they
are less detailed because of the lower accumulation of sediment on the
seafloor (compared to the accumulation of snow which forms ice cores).

Thanks for your very fine questions!
Julie