December 29

We have turned more south and are now south of our planned course (which is good). Winds and seas are forecast to be calmer (10 to 15kt, less than 10 ft) for the next two days. Winds are now out of the north and are expected to shift to be from the south later today. Seas should be 5 to 10 ft. Most of us have gotten used to these conditions, so it is no big deal.  Most of us have now adjusted to the motion and hopefully the bouts of motion sickness are over.  The ride should be much smoother than it has been for the past couple of days. 

(The cruise track is the heavy red line - just crossing the SubAntarctic Front (green dashed line) and going west across the South Pacific.)

We have started getting ready for sampling once we get to the Ross Sea.  Our group is doing the hydrographic measurements and the primary instrument we use is one that measures conductivity-temperature-depth (CTD). The conductivity measurement is converted to salinity (salt content of the water) which is the more traditional way to measure seawater properties. 

The sensors that measure conductivity, temperature and depth are mounted at the center of a cylindrical cage called a Rosette. In the picture below you can see the sensors at the bottom at the height of the two round bars. The wire that is used to lower the CTD into the water (just visible at the top of the picture) contains conducting cables that transmit the data to a computer on the ship.  Around the outside of the Rosette are 24 Niskin bottles, which are used to collect water.  Each bottle collects several liters of water.  The bottles are closed a different depths by commands sent from the computer.  The water in the bottles is analyzed after it comes back to the ship to measure nutrients (nitrate, phosphate, silicate) and other properties.  The size of the CTD/Rosette can be estimated by comparison with Pierre - it is a large instrument. 

Pierre is standing next to the CTD/Rosette in the Baltic Room, which is about mid-ship. This is a special room in the ship with a large hatch to the outside. The CTD/Rosette is large and it requires a winch and crane to move it to the side of the ship and then lower it into the water.  The Baltic Room provides an enclosed space to deploy the CTD/Rosette and then take water samples when the instrument comes back on board the ship.  Doing CTD/Rosette deployment and recovery on an open deck would be difficult and the water in the bottles would freeze before the samples could be taken.  Also, the sensors on the CTD would freeze up if exposed on the deck. 

When we are ready to use the CTD, the large hatch opens (orange area behind Pierre) and a crane lifts the CTD/Rosette out and over the water. The entrances to the Baltic Room are water-tight doors which mostly prevent waves and water from entering the Baltic Room (which sometimes happens during deployment/recovery) and causing problems.  The winch lets out wire to lower the CTD/Rosette to the desired depth.  The CTD operator in the dry lab on the ship monitors various measurements as the instrument is lowered and makes decisions about where to close the Niskin bottles. 

We are planning a test cast with the CTD/Rosette in a day or so if the weather is good.  We are also planning to test some of the other instruments that will be used by other groups on the ship. I will post pictures from these tests.  

I have been doing some reading to pass the time.  Just finished Cleopatra by Stacy Schiff.  This book is a fast read and tells an entertaining story of a life as well as describing a time in history. A good thing about a cruise is that there is time to read books that are not technical or job related.