Deep-water oceanographic measurements in the Discovery Gap (Northeast Atlantic) in 2021 and 2022

Comprehensive investigations of oceanographic and hydrochemical parameters were undertaken in the Discovery Gap, a deep-water passage within the Azores–Gibraltar Fracture Zone in the Northeast Atlantic, during two research cruises in 2021 and 2022. To broaden the spatial coverage of the study, supplementary measurements were performed in 2022 in the Madeira and Iberian basins, located south and north of the study region, respectively — along the pathway of Antarctic Bottom Water (AABW) spreading. This study aims to evaluate temporal variations in the physical and chemical properties of AABW within the Discovery Gap and adjacent Atlantic basins. A total of 20 oceanographic stations were occupied: 9 in 2021 and 11 in 2022. In 2021, water sampling employed an SBE 32SC rosette with an SBE 19plus V2 SeaCAT CTD, while in 2022 a General Oceanics GO1018 carousel equipped with an Idronaut Ocean Seven 320plus CTD was used. The temperature sensors of the SBE 19plusV2 and Idronaut Ocean Seven 320plus provided accuracies of 0.005 °C and 0.001 °C, respectively. Water samples for dissolved oxygen and silicate analyses were collected with 5-L Niskin bottles (General Oceanics). To characterize the near-bottom oceanographuc structure, samples were obtained from depths extending from the seafloor to 3800 m, across 6–8 m discrete depths, selected from CTD profiles. Dissolved oxygen content was measured onboard by Winkler titration with a precision of ±0.02 mL L⁻¹ or ±0.85 μmol kg⁻¹. Dissolved silicate concentrations were quantified spectrophotometrically using a KFK-3KM spectrophotometer, with an analytical precision estimated at ±2.5%.

本研究于2021年与2022年两次科考航次期间，在东北大西洋亚速尔-直布罗陀断裂带内的深水通道——发现海隙（Discovery Gap）中，开展了海洋学与水化学参数的系统性调查。为拓展研究的空间覆盖范围，本研究于2022年在研究区域南北两侧的马德拉海盆与伊比利亚海盆——即南极底层水（Antarctic Bottom Water, AABW）的扩散通道沿线——开展了补充观测。本研究旨在解析发现海隙及毗邻大西洋海盆内南极底层水的物理与化学性质的时间变化特征。本次调查共布设20个海洋学站位：2021年9个，2022年11个。2021年采样采用搭载SBE 19plus V2 SeaCAT温盐深仪（CTD）的SBE 32SC型采水架，2022年则使用配备Idronaut Ocean Seven 320plus温盐深仪的General Oceanics GO1018型旋转采水器。SBE 19plus V2与Idronaut Ocean Seven 320plus的温度传感器测量精度分别为0.005 °C与0.001 °C。溶解氧与硅酸盐分析所需的水样采用5升Niskin采水瓶（General Oceanics）采集。为刻画近底海洋学结构，研究人员从温盐深剖面中选取海底至3800米水深范围内、间隔6-8米的离散层位采集水样。溶解氧含量采用温克勒滴定法在船上现场测定，测量精度为±0.02 mL L⁻¹或±0.85 μmol kg⁻¹。硅酸盐溶解浓度采用KFK-3KM分光光度计通过分光光度法定量分析，分析精度约为±2.5%。