In order to measure the oxygen levels, we lower down an instrument called CTD (as seen in the picture).
The CTD measures conductivity (salinity), temperature and depth (pressure). It has grey plastic bottles attached to it, with which we can take water samples at different depths and analyze for oxygen content in the lab.
By adding chemicals to the water samples, we bind the oxygen so that we later can calculate the concentration through the titration technique.
This blogpost is one of a series written originally for our Insta-takeover of @PortalenIGLO, by the awesome night watch team Elina, Helene, Julie, and Sonja. Check out the twitter accounts of Elina and Sonja for updates on what they are doing when they are not at sea with us!