Today, my research team, the Physical Oceanography Team, conducted a CTD operation for the first time. Usually when a CTD is conducted, each team goes through about 8-10 stations with a transect gap in between of about 30 mins. Therefore, the group is usually on call to help with CTD operations for the whole day.
CTD stands for “Conductivity, Temperature and pressure (Depth)”. It is a sampling system equipped with a rosette of sampling bottles, a Lowered Acoustic Doppler Current Profiler (LADCP), and other sensors. Maximum water depth is determine prior to a CTD cast (when the system is lowered into the water). A technician must also be present to operate the winch that connects to the CTD rosette to the ship and to ensure that all safety and standard operation procedures are being followed while CTD operations are underway.
As the CTD rosette is lowered into the water column, a “profile” of the water column is taken. Conductivity (salinity), temperature, and other water properties are measured as the system descends at depth. A computer screen (onboard the ship) shows measurements in real time as the system is lowered. On the screen there is a chart of the return feed that displays graphs of temperature, dissolved oxygen, fluorescence, and salinity with depth. The graphs of temperature and dissolved oxygen are inversely related because warmer temperature means less oxygen is dissolved. Whereas in cold water, solubility increases, therefore colder water has more dissolved oxygen.
After reviewing these graphs/data, the scientists then determine where they would like to take water samples as the system is brought back up to the surface. The rosette of sampling bottles, which are cocked open when the system is deployed, can be closed at the discrete depths, as determined by the scientists. These water samples can then be used for analyses of water nutrients, dissolved oxygen, methane, chlorophyll and other ocean properties.
CTD operations are fun but also a little tedious, as they take a while and can lead to long nights. Luckily the students on this expedition have amazing leads, including Chief Scientist, Dr. Brice Loose, who makes sure the samples are taken and maintained in a proper manner. I personally like CTD operations because I think I would like to pursue a career in oceanography and know it is worthwhile to learn everything I can about this sampling system.