Chukchi Borderland Project
 
 
 

Daily Updates from

our Teacher at Sea

 
 

September 3
 

CFC Sampling:  How Old Is That Water?
   by Sarah Zimmermann
 
 
 
{Sarah is substituting for Ms. Grimes today.  Ms. Grimes is feeling under the weather but is well-cared for and will be back on the job of reporting her experiences at sea to you.}

 
 
 
 
 
 

  Our group is the first to sample each Niskin bottle because we are measuring a gas in the water.

  Once the bottle is opened, gas from the water can escape and gas from the air can mix into the water, both of these processes will ruin our samples.  Great care is taken to keep air from the lab from getting into our syringes.  If you were to put 5 drops of the chemical we're measuring into a swimming pool our instruments would be able to detect its presence.

Setup:  getting syringes ready for the next station.

 
 
 

Drawing our sample from the Niskin bottle.
 What are we measuring?

  We measure chemicals called chloro-fluoro-carbons, called CFCs for short.  These chemicals do not occur naturally.

So how did they get there?

  People started using these chemicals in the 1930s mostly as refrigerants and solvents.
 

  Refrigerant is the material in the refrigerator coils that changes between fluid and gas as it works to cool the refrigerator.  Solvents are used to dissolve other materials, just like water is a solvent for salt. 

 
 
 
  The CFC gas mixes into the atmosphere.  Once it is in the atmosphere it travels all over the world.  Breaking waves in the ocean incorporate air into the water and, by this process, the CFCs in the atmosphere eventually get mixed into the surface water.

Waves breaking in open ocean.

 
 
 

Bringing the samples back to our lab, which is set up in
a standard 20 foot container.
 Why do we measure CFCs?

The key to understanding this tracer is that when the surface water cools in winter and becomes denser it sinks to greater depths and takes the CFCs with it.

These chemicals are conserved- meaning they are stable and do not break down in the water or are removed by some process like growing phytoplankton.  So when we measure CFCs in subsurface water, we can tell how much CFCs were in the atmosphere when the water was last at the surface.

Because the level of atmospheric CFC has been constantly increasing each year we can use the level like a ruler and  pinpoint which year the water was at the surface.  If the water has no CFCs, like the water here deeper than 1800 meters (about one mile), we know it has not been near the surface in 75 years.  If the water has lots of CFC then it must have been near the surface recently.  This information helps us understand the circulation pattern of the Arctic Ocean  (both horizontally and vertically!).

 
 
 
The CFC clock:

The amount of CFCs in the atmosphere has been changing from the 1930s to the present.

First as CFCs became popular, more and more were made,
increasing the concentration in the atmosphere.  Then, in the 1980s it was realized that the CFCs were reacting with the ozone in the atmosphere helping to produce the ozone holes that are responsible for letting so much of the strong ultraviolet light of the sun reach the earth.

CFCs were banned from being used because of this.  Still, the levels have not dropped but the concentration in the atmosphere isn't rising as quickly.

Running the sample.

 
 
 

Looking over the results.
 This concentration curve makes each year unique.  In fact there are a few different types of CFCs, each with their own concentration curve.

Using multiple curves lets us determine the water's age even if it mixes with water of a different age. 

Oceanographers didn't make CFCs but we're certainly taking advantage of their presence.