Patrick Robinson at the Eastern Weddell Sea, Antarctica-- The main purpose of this RRS Shackleton expedition is to study the oceanography of the Weddell Sea.  To do this, researchers from the British Antarctic Survey deploy instruments on mooring lines (see previous blog posting), but also complete point samples by lowering instruments deep into the ocean from the ship.  The CTD (conductivity, temperature, depth) recorder as well as current profilers are the basic tools of oceanographers and provide information about a profile of the water column.

British Antarctic Survey researcher Keith Makinson using the winch to lower the CTD through the water. Photo: Patrick Robinson.

To complete a CTD cast, the ship travels to a predefined location and lowers the CTD into the water at a controlled rate using a winch.  The instruments sample the water all the way to the bottom and send the data back to computers on the ship.  As the CTD is raised back to the ship, several water samples are collected to calibrate the salinity measurements.  A CTD cast may take several hours to complete and during the cruise, more than 100 casts will be done.

The CTD about to be lowered into the water. Photo: Patrick Robinson

Below is a photo of the large CTD unit as well as the miniature CTD tags that will be deployed on Weddell seals.  We attached the tags to
the larger CTD unit to verify the calibration of the tags before deployment.

The CTD control center.  This is where the data are logged and water samples triggered. Photo: Patrick Robinson