Underway seawater analysis

RV Investigator is constantly collecting and analysing seawater while underway.

Measurements we make

Seawater is sampled from RV Investigator's port drop keel and supplied to laboratories for analysis, research and use. Continuous data collection provides important baseline data for scientists to observe changes in oceanographic properties, such as temperature, salinity, acidification, oxygen and chlorophyll levels over time. 

Scientists on board also use this data to make correlations between in-situ measurements and observations of, for example, seabirds and marine mammals.

We also regularly use underway data to make comparisons and calibrations with measurements taken from various deployable equipment such as the CTD or Triaxus.

Key equipment and capabilities

Seawater is first pumped into RV Investigator via the port-side drop keel. The water flows through the ship at consistent flow rates to three laboratories: trace metal clean, general scientific seawater and underway seawater. From there, it gets diverted to various seawater instrumentation, including our fluorometer, pCO2 and thermosalinograph.

Drop keels

RV Investigator has two drop keels that can be lowered 4 m below the hull. They can be used to mount acoustic sensors and acoustic transducers, and the port-side drop keel contains an inlet for the pumped seawater sampling system.


The thermosalinograph (TSG) continuously measures surface temperature and salinity along the track of the ship using the underway seawater supply system. The TSG is located in the underway seawater Laboratory.


The fluorometer provides chlorophyll-a which is an important indicator of active phytoplankton biomass and chlorophyll concentrations, and also provides coloured dissolved organic matter (CDOM). This instrument is located adjacent to the TSG.

pC02 system

The pCO2 system measures surface water CO2 concentration, an important measurement for understanding ocean acidification. This instrument is located adjacent to the TSG in the Underway Seawater Laboratory, and is calibrated against daily against reference gas standards stored in-situ.

Other equipment typically available on RV Investigator includes:
• SST Radiometer – Sea Surface Skin temperature that provides accurate and reliable measurements of the radiative sea surface temperature.


RV Investigator is fitted with three specialised laboratories and various specialised equipment for underway seawater sampling and analysis.

  • Underway Seawater Laboratory
  • CTD Laboratory
  • General Purpose Wet Laboratory - Dirty
  • Clean Wet Laboratory.

The constant supply from the underway seawater supply services the back deck, container spaces, deck Level 2 and the General Purpose Wet Laboratory - Dirty.