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Water Sampling with a CTD

Conductivity Temperature Depth


C, T, and D, rosette, Niskin bottles: I needed a vocabulary lesson before I could write about the large device the team has been putting into the ocean to collect water samples at each of our stations.


The CTD; conductivity, temperature, and depth device pictured above is a round steel framed rosette, housing 24 Niskin bottles and a several sensors. The CTD readers are found at the bottom, below the Niskin bottle.  The C for Conductivity is often just said to represent salinity. There are also oxygen sensors that tell us how much dissolved oxygen is present. The Niskin bottles are named after the scientist Shale Niskin who worked to advance sea water collection techniques and patented the design in 1966. This particular CTD runs profiles of the water column (surface to bottom) and along the way, collects water samples (at specific predetermined depths) using the rosette of Niskin bottles. 

Day shift preparing CTD

Several researchers on board are collecting water samples collected by the CTD to study the chemistry of the water. Researchers need to know the current water properties to be able to compare them to the theoretical water properties of the past. The samples will be analyzed for dissolved inorganic carbon (DIC), mostly CO2 , a process that has been analyzed in the ocean for decades. The DIC data can help us learn about the global carbon system, and add to the data of DIC trends over time.  

The purple cap bottles will be used to track δ13C (delta-13 Carbon), a stable carbon isotope found less often when human produced, fossil fuel burning, carbon dioxide is present. Tracking of Carbon-13 in conjunction with DIC data can show the increase from anthropogenic sources of carbon into the water. Want to learn more about the difference in carbon types? Look up the Suess Effect. 

The last CTD sample goes into the white capped small bottles. This water will be analyzed for Oxygen-18 isotope that is present in the formation of the water molecule.  By tracking water molecule masses researchers can determine where the water came from.  For example glacial ice is known to have very little δ18O.  The oxygen isotope in the water will also be compared to the oxygen isotopes of the forams (Foraminifera).  

Oxygen isotopes as a climate indicator Photo from: Earth Labs

During this trip the CTD has been deployed in waters from 100 meters to over 3,000 meters and Niskin bottles have brought back waters for further analysis in seven different locations.

Latitude 39 degrees 35.231′ N
Longitude 71 degrees 39.095′ W
Day 12
Water Depth 1339 meters
Weather Conditions light cloud cover 71 Fahrenheit
Wave and Sea Conditions calm seas 68 Fahrenheit