Ocean Oxygen

By Amanda Fay

As week two comes to a close on the ship we are all settling into our sampling practices, meal, and sleep schedules (listed from most to least important of course).  Discussions at meal times range from inquiries on if everyone’s analysis machinery is working appropriately to lamenting the lack of sea life we have seen thus far on the cruise (read: none. Absolutely none). 

For those scientists who have been onboard for both I08S and continuing on I09N, this week marked their halfway point for their (extra long) cruise. One such scientist is Joseph Gum who is conducting our oxygen analysis onboard.  The oxygen sampler is a tireless workhouse.  Because of the longer analysis times of some parameters being measured onboard, these groups must sample from fewer bottles (depths) every other station so as to not fall behind on analyses and keep up with our packed schedule.  Oxygen, however, is always sampled from the full 36 bottles at every station.  Thankfully Joseph is up to the task.

Sampling from a Niskin bottle.

Since the 1960s, oxygen analysis has been done using the Winkler titration method, a tried and true analysis process that provides an accurate reading of the amount of oxygen in a sample of seawater. Sampling for oxygen requires precision: the specific volume of each beaker goes into the calculation as well as the sampling temperature, which must be read as the water is coming out of the Niskin, to account for thermal expansion.  At sampling, the addition of two compounds fixes the oxygen in the sample to a solid. When ready to titrate, the addition of an acid breaks up the oxygen and prepares it to be measured. 

Joseph adds reagents to "fix" the oxygen in the sample.

Joseph, working in the hydrolab in his white lab coat, is able to titrate all 36 samples during our transit time between stations. Joseph, and the other scientists in the hydrolab, keep their spirits high by listening to standup comedy podcasts and maintain their fitness by doing tricep dips while their samples run.

Titrating to determine the oxygen concentration of seawater.

(Photo credits - Amanda Fay)