Cooperative Institute for Research in Environmental Sciences

Ocean Interactions
Ocean and Atmosphere connecting Scientists, Teachers & Students

Oxygen

This is Dr. Jan Kaiser, formerly of the Max Planck Institute in Mainz Germany, and now working as a postdoctoral scholar at Princeton University. Jan is working to make measurements of dissolved oxygen in the water. The dissolved oxygen measurement provides an indication of the growth of the biomass in the water (or, the net productivity).

Jan uses a mass spectrometer to measure the ratio of oxygen (O2) molecules to argon (Ar) molecules. One can measure the oxygen concentration directly, but there are a number of mechanisms by which it is absorbed into the ocean. For example, whitecapping of the waves acts to dissolve oxygen in the seawater (this is a lot like the the 'reverse' of the situation wherein carbonation escapes from an opened soda).

Since argon is a Noble gas, it is a very stable molecule. This characteristic of argon means that it doesn't readily combine with the biomass, and it is only dissolved in the water by physical means (like the whitecapping above). By measuring the O2/Ar ratio, and from an independent measurement of oxygen using an 'optode' (an optical instrument which works by estimating the decay of light from a surface oxygenated compound), Jan is able to estimate the concentration of oxygen which is attributed exclusively to biological productivity (growth of phytoplankton and algae).

The growth of the biomass helps to exchange gases between the air and sea. Most important of these gases is carbon dioxide (CO2), which is a so-called greenhouse gas. With concerns about possible global warming due to build up of greenhouse gases, scientists would like to understand better the processes which affect the carbon dioxide exchange between the ocean and atmosphere. Biological production is one way in which CO2 is exchanged, so if we know the 'net growth' of biomass, then we may be able to quantify how much CO2 is absorbed in the water by phytoplankton, etc. The work that Jan is doing will hopefully yield knowledge to help us better understand the complex Earth System climate puzzle.