Science Report:
Since we have been talking a lot about CTD work during this trip, I thought it might be helpful to show you a close -up picture of its various parts. The accompanying figure shows the CTD package without the usual wall of large sampling bottles that cover the outside and hide the sensors on the inside of the frame. The "brain" of the CTD is an electronic package inside a large white pressure case, called the "fish." Circuits inside the fish take the power sent down the cable from the ship and make it usable by a variety of sensors. These circuits also take input from the sensors and send it back up the wire in a way it can be interpreted by computers in the ship's lab. Inside the fish is a sensitive pressure sensor that measures the weight of the water above the package and thus the depth of the CTD below the sea surface-the "D" in CTD.

Outside the fish are several other sensors. A temperature sensor measures the temperature of the seawater with a precision of better than 1/1000 of a degree Celcius-the "T" in CTD. A conductivity sensor measures the electrical conductivity of seawater-the "C" in CTD. Seawater conducts electricity since it is a salt solution, and measuring the conductivity of seawater, together with its temperature and pressure, allows us to calculate its salinity. Also shown in the picture are two light-scattering sensors. These sensors send a flash of light into the seawater and measure the amount of light reflected back to a light detector in the sensor. The amount of reflected light is a measure of the number of tiny particles suspended in the water the CTD is moving through. CTDs are one of the most common instruments used by oceanographers, both to describe the temperature and salinity of ocean water and to carry other sensors for specialized measurements. It's really the workhorse of oceanographic research!