Oxygen…it’s not just for breathing anymore
Posted by sogasex on March 7, 2008
By Roberta Hamme, University of Victoria
Most of us don’t think about oxygen much. It’s always there for us at an almost steady 21% of our atmosphere. But I think about oxygen a lot, because it gives me clues to the ocean. Since plants produce oxygen during photosynthesis, the amount of oxygen in the ocean is one way of measuring how productive plankton in different areas are. Of course, there are some complications. Aren’t there always? One of the biggest challenges to using oxygen to look at photosynthesis is that physical processes, like changing temperatures, also affect oxygen. We can overcome this challenge by comparing oxygen to another gas that is like oxygen in its physical properties but has no biological role. Lucky for me, nature has provided the perfect gas for this purpose, argon, found naturally in our atmosphere at about 1%.
On this cruise, I’m collaborating with Michael Bender at Princeton University to continuously measure the oxygen/argon ratio in surface seawater. The ship pumps seawater continuously to the main lab, where I flow it past a membrane to extract the gases. Then, I use Michael’s small mass spectrometer to detect the amounts of oxygen, argon, and other gases in my sample. Right now we are surveying the surrounding area to find the perfect place to do our experiment. We need a place that is both productive and physically stable (no big currents!). My measurements of productivity from the oxygen/argon ratio in seawater will help us decide on the right spot to spend the next few weeks studying.
Our equipment combines a sophisticated mass spectrometer with a water reservoir made from a trashcan purchased in port.
Here you can see our survey pattern and the results of my measurements. Red areas are the most productive.