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.

2021年9—10月与2022年7—9月，研究团队依托约夫院士号研究船（R/V Akademik Ioffe）第59航次及第62航次，在亚速尔-直布罗陀断裂带开展了一套完整的导电率-温度-深度（Conductivity-Temperature-Depth, CTD）与下放式声学多普勒海流剖面仪（Lowered Acoustic Doppler Current Profiler, LADCP）调查作业。本次调查的核心目标为测定底层水深渊流，并估算南极底层水（Antarctic Bottom Water, AABW）经迪斯科维尔通道与西通道，从马德拉深渊平原向伊比利亚深渊平原的输运量。多数测站布设于上述两条通道内，少量测站布设于马德拉深渊平原与伊比利亚深渊平原区域。2021年与2022年航次分别完成了24个与27个全水深测站（测量深度可达海底）。本调查采用基于旋转式采水器搭建的海洋综合观测系统开展海洋学测量，该系统包含CTD探头与LADCP设备。两次航次所使用的观测设备组合存在差异：在第59航次中，观测系统搭载于SBE 32 SC型旋转式采水器，配套设备包括SBE 19plusV2型SeaCAT CTD、工作模式为下视模式的Teledyne RDI Workhorse Sentinel 300 kHz LADCP，以及Teledyne Benthos PSA-916型高度计。CTD数据通过标准Seasave V7软件包在线采集，并通过SBE数据处理软件完成后期处理。第62航次则采用General Oceanics GO1018型旋转式采水器作为搭载平台，配套设备包括Idronaut Ocean Seven 320plus型CTD、工作模式为下视模式的Teledyne RDI Workhorse Monitor 300 kHz LADCP，以及Valeport VA500型高度计。本次航次的数据采用REDAS5软件完成在线采集与实时处理。本次海流剖面仪采用窄带模式运行，相较于宽带模式，该模式可提升剖面测量范围，并可提升原始数据处理的可靠性。我们设置了30个垂直分档，每个分档间距为8 m，换能器下方初始盲区距离为1.76 m。LADCP罗盘于航次前按照标准流程在下视模式下完成校准。LADCP数据处理采用拉蒙特-多尔蒂地球观测站（LDEO）的LADCP数据处理软件IX.14版本。两次航次的测量开始前，均通过NMEATime工具软件将计算机与仪器的时间与全球定位系统卫星的协调世界时（UTC）时间完成同步。本次测量的水深覆盖范围为海面至海底上方5—10 m处，仪器下放速度约为1 m/s。数据记录的时间戳对应CTD接近海底的时刻，海洋水深通过CTD的压力数据与高度计记录共同确定。本次完整调查的作业时段分别为2021年9月24日至10月13日，以及2022年7月29日至8月1日、8月29日至9月1日。