Dissolved Oxygen

Dissolved Oxygen

What is Dissolved Oxygen?

Dissolved Oxygen (DO) is the measurement of the amount of oxygen gas dissolved in seawater. Oxygen is one of the important elements for life, and the chemical reactions of both photosynthesis and respiration affect the balance of oxygen in the oceans.

How is DO monitored in the open ocean?

For years oceanographers have used water sampling on shipboard surveys to measure dissolved oxygen. A long-standing effort off California, the CalCOFI program, is a more than 50-year time series of oceanographic parameters such as temperature, salinity, and oxygen gathered from shipboard measurements. During a survey, water samples are taken at stations along a transect, at each station water samples are collected from throughout the water column at standard depths. The water samples are then tested in a lab for oxygen concentration with a modified chemical titration. Hydrographic surveys carried out by MBARI follow a similar protocol.

Dissolved oxygen can also be monitored real-time on moorings, shore stations and gliders with sensors such as optodes or electrodes. These sensors are calibrated before deployment to water samples of known dissolved oxygen, calibration values are applied to the raw readings of the sensor to generate these sensor based measurements of dissolved oxygen concentration.