CTD and LADCP measurements in the Vema Fracture Zone during cruise 52 of the R/V Akademik Boris Petrov in November-December, 2022
Description
A detailed CTD/LADCP survey in the Vema Fracture Zone was carried out during cruise 52 of the R/V “Akademik Boris Petrov” in November-December, 2022. The main objective of this survey was to measure abyssal currents of Antarctic Bottom Water and estimate its transport to the East Atlantic. The stations were located along the entire fracture zone from 39 to 46 W. A total of 46 full water depth stations (down to the bottom) were performed in the Vema Fracture Zone. The rosette system General Oceanics GO1018 included Daowan1616 Conductivity-Temperature-Depth (CTD) probe (manufactured in 2022) and Lowered Acoustic Doppler Current Profiler (LADCP; 300 kHz Teledyne RD Instruments WorkHorse Monitor with an external battery package). 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 the standard procedure. The raw data were processed using the LDEO Software version IX_14. We stopped the casts at a distance of 5 m above the bottom using the altimeter (model Valeport VA500) and pinger of the Benthos Co. The combined use of a pinger and an altimeter allowed us to safely approach the bottom even in conditions of rough bottom topography. A 6000-m sea cable allowed measurements at any point of the fracture. 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. Each station took approximately 4 hours (the descent and ascent rates of the CTD and LADCP profilers were approximately 1 m/s); the entire survey was performed from November 6 to December 8, 2022 with an interval for a port call. CTD-station 52025 was performed under low battery. Thus caused many wrong peaks at low temperatures. These peaks were excluded from the data.