CTD and LADCP measurements in the Vema Channel during cruise 79 of the R/V Akademik Mstislav Keldysh in 2020
Description
A detailed CTD/LADCP survey in the Vema Channel was carried out during cruise 79 of the R/V “Akademik Mstislav Keldysh” in January-April, 2020. The main objective of this survey was to measure bottom gravity currents of Antarctic Bottom Water and estimate its transport to the Brazil Basin. The stations were located along the entire channel from 32°S to 26S. A total of 25 full water depth stations (down to the bottom) were performed in the Vema Channel. The rosette system Sea-Bird Electronics SBE32SC included SBE19 Conductivity-Temperature-Depth (CTD) probe 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 to 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 channel. 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 January 1 to April 6, 2020.