9 February, 2001

CTD - Conductivity, Temperature, Depth

The CTD is a very elaborate water collection device that has the potential to sample sea water at 24 different depths. The CTD is also the first experiment we conduct when we arrive at a station (Why would we collect water before sediment? *). As we send the CTD to the bottom of the ocean, information is being sent back to us constantly. For example, the temperature of the water is measured 24 times a second, which with the CTD traveling at a speed of 30 to 50 meters a minute means a reading every 2 cm! What is so important about water temperature? The water here in Antarctica is the coldest and saltiest anywhere in the world. If cold surface water is denser than the water below what does it do ? Right! Sink! The same is true for salt water, and as such the water from here is where most of the world's ocean bottom water comes from. You might not know this, but water has structure; just as there is specific architecture in buildings, so it is with water. When we talk of the "water column" we are talking of its architecture. Its architecture is defined mostly by mass, density, and composition. Temperature and salinity alone can actually make a fingerprint of sorts. Water can only change its temperature and salinity at the surface. Once the water sinks it cannot change anymore, so a fingerprint of the water is made. Over time, as the water slowly travels the ocean floor it maintains its fingerprint so that one day, 500 to a 1000 later years, perchance, someone may take a sample off the coast of California and they could actually trace the water back by its fingerprint, to the approximate time it first sank here in Antarctica. Several scientists on board are using the water samples for several different things. I am looking at the diatoms in the surface water, as well as at its photosynthetic maximum, which can be up to tens of meters below the surface. Others are interested in the temperature of the water at the bottom. Dr Dunbar is testing so many things that I will have to save his work for another journal entry.

(The reason for doing the CTD first is so that we don't have any sediment mixing with the water and changing our sample)