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CTD stands for conductivity, temperature and depth – the primary variables measured when the sensor is lowered into the seawater. The sensor is usually mounted on a rosette with Niskin bottles that can be used to collect seawater from selected depths, and makes continuous measurements during its descend to the seafloor that are subsequently send to a computer on board the ship.


Deploying the CTD attached to a rosette with Niskin bottles from the G.O. Sars



Sampling water from the Niskin bottles.


In previous years, CGB researchers have added additional sensors to the CTD to measure methane (CH4) and carbondioxide (CO2), to search for evidence of hydrothermal activity in the water column. Although the CTD casts represent only a single location, these sensors are highly valuable as they provide much faster information on the potential presence of hydrothermal vents on the seafloor than ROV dives.


Data collected by a CTD showing the characteristic signal of a hydrothermal plume in the seawater. H2 was measured onboard in seawater collected in the Niskin bottles. 


Learn more about CTDs here: