Tracing Water Masses

By Carmen Rodriguez and Patrick Mears

 

Next up for our analyses onboard is the CFCs group.  CFCs (chlorofluorocarbons) are a group of man-made compounds that were introduced as spray aerosols and refrigerants since the mid-1900s.  It was later discovered that they react with ozone in the atmosphere, which depletes the ozone layer at the poles.  Not good.  Fortunately, these gases were eventually banned from production.  But the historical emissions still linger in our atmosphere.

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There are, however, some upsides to CFCs.  1^st - there’s almost no natural concentration in the ocean, 2^nd - they are relatively inert (non-reactive) in the ocean, 3^rd - they have a well-documented emissions history.  This makes CFCs an excellent candidate for “tracing” the movement of water masses in the ocean.  This is done by correlating the concentration measured at any given depth in the ocean to the atmospheric concentration from the past.  Then we can estimate the age of that water mass, which is the time since it was last at the surface. 

The concentration of CFCs in the oceans is small, though, so oceanographers must be very careful with their measurements.  CFCs need to be analyzed with a very high precision and any potential atmospheric contamination should be avoided. 



[Molly Martin and Eugene Gorman running CFCs in the Main Lab.  Picture credit Patrick Mears.]

On this cruise, Molly Martin, Eugene Gorman, and Ben Hickman measure the tracer gases CFCs and SF₆ (sulfur hexafluoride) onboard.  They’re surrounded by various overhead lines which supply gases or electrical cables to operate the system.  This is a complicated analysis.  However these “tracers” enable us to determine the age of a water mass, and from this, we can better picture the biogeochemical processes and circulation occurring in the global ocean.