During oceanographic campaigns, vertical profiles are measured at regular intervals using a tool historically used in oceanography: the bathysonde.
The bathysonde is a strange white carousel equipped with a multitude of measuring instruments. It is attached to the ship and operated by an electric cable activated by a dedicated electric winch, which is deployed like a giant fixed-station arm to lower the bathysonde into the water.
The bathysonde is used to acquire physical and chemical data at a fixed point called a station, and along the water column – typically from the surface to a depth of 6,000 meters. The bathysonde is generally equipped with two main components: a CTD probe and a rosette.
© SAGA project
The CTD probe (an acronym for Conductivity-Temperature-Depth) enables highly accurate measurement of conductivity (from which salinity is deduced), temperature and pressure (from which depth is deduced). Other sensors can be installed on a CTD probe, such as dissolved oxygen sensors in the ocean or fluorescence sensors for measuring chlorophyll, etc.

Sonde CTD type SBE911+V2 © SEABIRD
The rosette is the crown of bottles that surrounds the probe. The bottles enable seawater to be sampled at various depths to measure its physical and biogeochemical characteristics: temperature, salinity, pH, oxygen content, nutrient salts, etc….During the ascent phase of the bathysonde from the seabed to the surface, the oceanographers trigger the closing of the bottles at various depths to collect samples all along the water column. Analyses will be carried out by the teams of chemists either on board, or back in the laboratory after the samples have been preserved.

© SAGA project
Today, the Rosette CTD is the result of constantly evolving technology. It has evolved with advances in electronics, which increasingly enable continuous measurements. It is therefore an invaluable tool for marine scientists, who work a little harder every day to unravel the mysteries of the sea.
Re-live a bathysonde ascent during the SAGA10W campaign!