Measuring respiration in the ocean
Respiration involves oxygen uptake, CO₂ production, and the biological consumption of organic carbon. It is a ubiquitous process in all oceanic regions, and thus a key physiological process in marine organisms. Along with primary productivity, it is essential for assessing the metabolic balance of the ocean.
During the IMAGE expedition, I am measuring community respiration throughout the water column using the Winkler method, which can measure oxygen consumption. This classic technique determines the concentration of dissolved oxygen in seawater through a series of chemical reactions and is widely used in oceanographic studies.
To measure respiration, I carefully transfer seawater collected in a bottle into glass bottles, avoiding the formation of any air bubbles. From those, I measure initial oxygen concentration and oxygen concentration after 24 and 48 hours of incubation at in situ temperature in the dark. Samples are collected from surface waters, the Deep Chlorophyll Maximum (DCM) —where phytoplankton biomass is concentrated— and deeper waters (500 or 300 m, depending on the station).
By comparing the oxygen concentration before and after incubation, we can determine how much oxygen has been consumed by the organisms present in the water. The decrease in dissolved oxygen over time provides an estimate of the community respiration rate.
Together with measurements of the electron transport system (ETS) activity, they will allow us to compare actual respiratory rates with the potential respiratory capacity of the microbial community through the R/ETS ratio.
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