CTD deployment
An intensive physics survey has begun onboard. The team are planning 9 deployments of the CTD (Conductivity Temperature Device) per day for the next 4-5days! The CTD is used to profile the water column and sample water at different depths. This is one of the most basic and yet fundamental tools oceanographers have to monitor the physical properties of the ocean. Almost every single research cruise will use a CTD at some point and the data are essential for monitoring the status of the water masses in the survey area. At the PAP site the water column is ~ 4800 km deep and one profile even in the upper 0-2000m can take a few hours as it has to travel down and back up at a safe speed (~ ½ m/sec). A quick calculation – a 2000m profile could take as long as 2-2.5 hours – with 9 deployments per day that’s a lot of sampling time!
What is a CTD?
A CTD is a sensor which measures the Conductivity and Temperature of the water. It is an essential piece of oceanographic equipment and provides a profile of physical data through the water column. The CTD is attached to a metal frame called a rosette, or carousel along with numerous water sampling bottles. These bottles open (‘fire’) at different depths to sample surface, intermediate and deep water. The CTD is deployed off the side of a vessel, and provides information about the composition of the water column.
CTD preparation on deck
What does it measure and how?
The salinity of seawater is difficult to measure directly. It is therefore determined by simultaneously measuring the temperature and the electrical conductivity of a sample volume. Since the ionic constituents of seawater are in nearly the same relative proportion everywhere, knowledge of the conductivity and temperature is sufficient to calculate the salt content and density, which is of importance for ocean dynamics.