20 March, 2001

Fire and Ice March 20 2001

-063 25 Lat / 52 11 long

No, not the perfume. It is just the name by which our lab is known. But let us start from the beginning.

My name is Tzvetie. I am from Bulgaria, but now I go to school in the US - Stanford University in California. I am a junior majoring in geology and my main interest for right now is glacial geology. There are two other Stanford students on this cruise - Melanie Hopkins and Lauren Rogers. We all work in Professor Dunbar's biogeochemistry lab. We look at the changes in the physical properties of seawater with depth. We use the CTD rosette to obtain our samples from the bottom of the ocean. After the CTD comes back on board Lauren, Melanie and I are responsible for sampling it and for processing the samples.

We start by filtering the seawater through a filter, which lets water through, but retains parcticulate organic matter (ex. phytoplankton). We will take these samples with us back to Stanford. We will use a machine called a Mass Spectrometer to determine the amounts of organic carbon and nitrogen.

After the water has warmed up to about 15 degrees C, Lauren runs it through the Coulometer. The seawater reacts with phosphoric acid and the released gas flows through the Coulometer, which measures the concentration of dissolved inorganic carbon in the seawater.

But that is not all. We use the same water to take out the carbon that is dissolved in the water and trap it in ampoules (a small airtight glass tube). When we get back to Stanford we will test the gas in the ampoules for the concentration of carbon thirteen (13C), an isotope of carbon. We make these ampoules with fire and ice. First we let the sea water react with phosphoric acid, releasing CO2, which is sent into a coil. The coil is almost completely submersed in liquid nitrogen (aka dry ice). By freezing the CO2 in the liquid nitrogen, we can separate it from the other gas molecules, which freeze at a lower temperature. From there we transfer the CO2 into a long glass tube. To speed up the transfer process, we reheat the CO2 using a hair dryer. We slowly refreeze the gas in the bottom of the glass tube and then very carefully melt the glass with a torch to create a sealed ampoule. If we have done a good job there will be a small ring of frozen gas at the bottom of the ampoule.

This procedure takes about twenty minutes. The Coulometer takes approximately fifteen minutes and filtering generally takes between three and four hours.

If we collect water at ten depths can you calculate how long it took us to process it?