14 July, 2003

So how about the CTDs of oceanography?

CTD is the name of the instrument that measures the Conductivity, Temperature, and Depth (or more accurately pressure) of the sea-water that we are studying. The CTD sensor is mounted to the rosette water sampler and lowered through the water while continuously measuring various properties of the water. This information is instantly transmitted through an electronic cable to the surface which gives the scientists a read-out of the water's characteristics. This allows them to distinguish various boundaries within the water column and helps the scientists determine the depths that the water bottles on the rosette will open and sample from.

Some of the characteristics that the scientists use from the CTD are salinity (saltiness), temperature (near freezing here), oxygen (dissolved in the water), chlorophyll (the phytoplankton or "green bugs and plants"), and transmissivity (parcticles, or in a sense, water clarity). Even to a non-oceanographer such as me, it's pretty exciting watching the read-outs as the CTD descends from the surface and creates a profile of the water structure or layers. The resulting display shows where the maximums and minimums of each property occur, and demonstrate just how non-homogeneous the sea-water is from top to bottom.

Over the last couple of days, for example, we have been observing very low salinities near the surface. Jim Swift, the Chief Scientist, speculates that this may be water from the outlet of the Mackenzie River which is located in Canada to the east of our present position. The chlorophyll maximum occurs around the 25 meter mark. This may indicate a boundary layer of nutrients utilized by the phytoplankton. Below that the temperature and oxygen data show layers of water that originate from the Chukchi Sea and the Atlantic Ocean. And very deep is water that may be over 700 years old which some believe represents a relic from the Little Ice Age.

It's no wonder then that our project's name is the Collaborative Research: CTD/Hydrographic and Underway Service Measurements for the Shelf-Basin Interactions Phase II Field Project.

Raytheon technician Jenny White readies the next CTD cast.

Jim Swift and Jeremy Mathis monitor a CTD/rosette cast.

The CTD sensor attached to the bottom of the rosette water sampler.