Thursday 10 January 2008 à 11:08

A hole in the ozone layer

Par Sophie Mouge. Correspondent aboard the Aurora Australis

Big areas of pack ice are surrounding the ship… For those of us present on the bridge this morning, this allows us to spot the first emperor penguins of the voyage!

Emperor penguin stranded on an ice floe.

This is the largest species of penguin, reaching 1.2 m in height. These birds are able to dive as deep as 560 meters for up to 20 minutes, and they have been shown to sometime feed on the bottom at depth under 400m. They eat mainly fish and sometimes squid. After mating, the males spend most of the winter in the rookerie on the fast ice, incubating their eggs. Male and female then alternate duties of brooding the chick and travels at sea to feed and bring food to the chicks.

The same emperor penguin in a horizontal position.

To keep from losing too much time breaking through the ice, the Voyage Leader and scientists decided to move the CASO program’s CTD sampling areas. So we are traveling alongside the pieces of sea ice.

Pack ice around the Aurora Australis.

Scattered sea ice around the Aurora Australis with an iceberg in the background.

We often spend time on the helideck, which is close to our working rooms an dallows us to enjoy the permanent show of the Antarctic landscape around us, without straying away from our work for too long!

Scattered sea ice around the Aurora Australis.

Move around the ship we frequently spot Mark (researcher) and Emily (student) working in their prefab: because there is so little space for all the equipment, their laboratory is situated in a prefab on the deck where they can get the 110 v electrical current. Both of them work at the University of Washington at Seattle, in the US.

Emily inside the laboratory on the helideck.

Inside, Mark and Emily also use the samples brought up by the CTDs and are busy measuring the amount of CFCs in the ocean.

CFCs: Chlorofluorocarbons are gases that were created by humans for refrigeration! They include, for example, freon, the gas that used to be the cooling fluid in refrigerators and air conditioners. The 1987 Montreal Protocol banned production of CFCs. Since the CFC were banned in 1987 the initial volume has been decreasing by just 1% per year…

Why are Mark and Emily interested in CFCs?
Because of the discovery in 1985 of a hole in the ozone layer over Antarctica, caused precisely by CFCs, which act by breaking two ozone molecules (O3) into three molecule of oxygen (O2). CFCs were emitted into the atmosphere in industrialized countries, then transported over the South Pole by atmospheric currents. During the southern winter, an enormous eddy, called the polar vortex, forms and concentrates the CFCs in the stratosphere (10 to 50 km above the Earth’s surface).
Ozone at that altitude is a gas that is very useful to all living creatures because it absorbs UV rays, protecting organisms from their damaging effects (genetic mutations, for example, causing skin cancer in some of the most southerly countries of the world). Harvey Marchant mentioned yesterday that many planktonic organisms were dying because of the impact of UV in surface waters.

Why are Mark and Emily interested in CFCs in the Southern Ocean?
Gases are exchanged between the atmosphere and the ocean surface. That is how CFCs enter the water.

Experimental method:
Gases are dissolved in water. To separate them out, Mark and Emily inject the water into a machine that extracts the CFCs from the water.

Mark holds a syringe of sea water.

Sea water is injected into a machine with a syringe.

We are measuring three kinds of CFCs:
- CFC-11: CCl3F
- CFC-12: CCl2F2
- CFC-113 : CCl2FCClF2
They are apportioned using gas chromatography, which measures the amount of each CFC. Chromatography is a method of chemical analysis by which the components of a mixture are separated.

Here is an example of a graph of the data after they are processed:
Change in CFC-11 as a function of depth - CLIVAR data - X access: quantity of CFC in picomoles/kg. Y axis: depth in meters.

What does it show? The quantity of CFC is greater in surface waters then diminishes significantly starting at 200 meters down. Below 3,000 m, the quantity of CFC rises again.

What can we deduce? Agitation on the ocean surface lets the CFCs penetrate and dissolve in the water. That is why they are found mainly in the ocean surface.

Schematic of the concentration of CFC-12 as a function of pressure (hence depth) – CLIVAR data – The schematic groups data from the Southern Ocean along a profile and shows the existence of two zones that are rich in CFCs: the surface and the depths close to the bottom.

So what explains the presence of CFCs in deep waters that have no a priori connection with the surface?
Mark explains that Antarctic water plunges from the surface to abyssal depths, taking the CFCs with them. This current is well known to oceanographers as Antarctic Bottom Water.

Nice view from the CFC lab!

Humans created CFCs that created the disaggregating of the stratospheric ozone that protects us from UV. Cases of skin cancer have been established as fact in the most southern countries of the world. Since CFC production was stopped in 1987, the initial volume has diminished by only one percent a year.

But as the proverb says, “Every cloud has a silver lining.” CFCs now serve as markers for oceanographers to track the movement of water masses in the ocean.



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