Dissolved Oxygen

SBE43 oxygen sensor (left) is shown on the Shallow Profiler Science Pod, which will profile between 200 m and the surface.

Photo credit: Mitch Eland (UW)

Dissolved oxygen is the most well-known gas in ocean waters: several types of sensors are commercially available. These include membrane Clark-type cells and optode sensors.  The OOI program uses both types of oxygen sensors on different platforms. The oxygen sensors are coupled to CTDs.

Seabird SBE 43 instruments are on the Shallow Profiler Mooring Science Pods. Aanderaa - Optode 4831 instruments are on the stationary 200 m platforms (Platform Interface Assemblies), on the Deep Profiler Moorings and near the seafloor associated seafloor junction boxes coupled to CTD  They are also a component of the Benthic Experiment Packages.  Thus, oxygen measurements are being made throughout the water spanning near coastal to far offshore environments.

The distribution of oxygen in the oceans is dependent on four major processes: (1) gas exchange with the atmosphere at the ocean surface, (2) mixing of waters away from the surface, (3) production of oxygen from phytoplankton photosynthesis in subsurface waters, consumption of oxygen by plants and animals throughout the water column, and oxidation of plant material at intermediate depths by microbial processes, and (4) increased oxygen in deep waters due to the sinking of cold, oxygen-rich water masses. Dissolved oxygen concentrations have been decreasing in the north Pacific for a variety of reasons.