Two new sensors have been deployed at 26°N in the Atlantic to measure ocean bottom pressure. Ocean pressure has been measured for decades, but typically suffers from ‘drift’ in the measurement – meaning that the measured value becomes more inaccurate over time. This occurs due to the deformation of the sensor itself under the effect of ocean pressure. While the sensors themselves are very accurate (with errors of a fraction of a percent of the depth rating), when they’re used for ocean transport measurements as with the AMOC, the accuracy requirement is even more stringent. An error of 1 cm of liquid water equivalent (the pressure due to just 1 cm higher water above the pressure sensor) equates to roughly 1 Sv error in transport estimated at 26°N – where 1 Sv or 1 Sverdrup is 1,000,000 cubic meters of water per second.

The new sensors deployed at 26ºN are so-called A-Z(ero)-A sensors meaning that they take a calibration measurement within the instrument itself in order to measure the drift in the sensor over time. In this way, we can know and remove the inaccuracy of the measurement.

The two sensors deployed at 26°N will be used by the EPOC project to test a new method for measuring ocean transports. They won’t be recovered for 2 more years (in late 2024 or early 2025), at which point we’ll get to work evaluating just how drift-free the sensor data are!