Laboratory and Field Performance of a 6000 DBAR-rated CTD: the RBR_argo| Deep6K

The Deep Argo program's initiative to explore the deepest regions of the world's oceans up to 6000 m necessitates the deployment of robust, precise, and stable measurements of pressure, temperature, and salinity. This study evaluates the performance of the RBR argooideep6k CTD, designed by RBR for deep-ocean applications, characterized through laboratory experiments and validated in-situ. The main challenges addressed are the errors generated by the compressibility of conductivity cell at high pressure, as well as its thermal inertia during profiling, affecting conductivity measurements. The results indicate that the compressibility calibration derived in the calibration facilities by the manufacturer performs as expected when deployed in the ocean. It also demonstrates that the corrective algorithm developed to address thermal inertia errors greatly improves the quality of salinity data, particularly when experiencing large tem-perature gradients. Finally, the stability of the RBRargo| deep6k CTD in the field is shown using the data from pilot deployments of RBRargo ideep6k CTD on Deep Argo floats.