CTD and LADCP measurements in the Azores-Gibraltar Fracture Zone during cruise 59 of the R/V Akademik Ioffe in September-October, 2021 and during cruise 62 of the R/V Akademik Ioffe in July-August, 2022

A detailed CTD/LADCP survey in the Azores-Gibraltar Fracture Zone was carried out during cruise 59 of the R/V Akademik Ioffe in September-October, 2021 and during cruise 62 of the R/V Akademik Ioffe in July-September, 2022. The main objective of these surveys was to measure abyssal currents of bottom water and estimate AABW transport from the Madeira Abyssal Plain to Iberia Abyssal Plain through two passages: the Discovery and Western gaps. The majority of stations were located in both gaps and a few were located in the Madeira and Iberia abyssal plains. A total of 24 and of 27 full water depth stations (down to the bottom) were performed in 2021 and in 2022, respectively. Oceanographic measurements were carried out with a oceanographic complex, which was based on a carousel water sampler and included a Conductivity-Temperature-Depth probe (CTD) and Lowered Acoustic Doppler Current Profiler (LADCP). We used different sets of equipment on the two cruises. During the cruise 59 a SBE 19plusV2 SeaCAT CTD and a Teledyne RDI Workhorse Sentinel 300 kHz LADCP in the down-looking mode, as well as a Teledyne Benthos PSA-916 altimeter were mounted on an SBE 32 SC carousel water sampler. CTD data were collected online with the standard Seasave V7 package and processed with SBE Data Processing software. During the cruise 62 General Oceanics GO1018 carousel water sampler was used as the carrier for an Idronaut Ocean Seven 320plus CTD, a Teledyne RDI Workhorse Monitor 300 kHz LADCP, which was set in the down-looking mode, and a Valeport VA500 altimeter. Data were collected online and processed on the fly with the REDAS5 software. The velocity profiler was set in the narrowband mode, which increases the profiling range in comparison with the broadband mode and allows more reliable processing of the raw data. We set 30 vertical bins of 8 m each with 1.76 m blank distance immediately below the transducer. The LADCP compass was calibrated before the cruise in the down looking mode according to the standard procedure. LDEO LADCP data processing software version IX.14 was used for LADCP data processing. In both cases, before the start of measurements, the times of the computer and instruments were synchronized with the time of GPS satellites (UTC) using the NMEATime utility. The measurements were carried out from the surface to the depths of 5-10 m above the bottom level, the speed of lowering of the instruments was about 1 m/s. Date and time are indicated for the moment when the CTD was near the bottom; the ocean depth was determined based on the CTD pressure and altimeter records. The entire survey was performed from September 24 to October 13, 2021 and from July 29 to August 1 and from August 29 to September 1, 2022.