Physico-chemical (CTD) and biogeochemical data from the Saguenay Fjord and the St. Lawrence Estuary during the NSERC-Hypoxia 2021 cruise

The overarching objective of the Hypoxia 2021 — C2021-06 cruise is to provide a new and informed assessment of the relationship between the reactivity of natural organic matter and the benthic ecosystem functioning in estuarine environments, with a focus on the hypoxic conditions in the deep waters. For this purpose, the cruise had assembled a team of researchers from three Québec institutions, ISMER-UQAR, McGill University and Concordia University, whose work is largely focused on the fate of the organic matter in natural environments as well as the benthic ecological processes it sustains. This initiative, supported by NSERC's Shiptime Program (NSERC — Shiptime 556538-2021), took place in August 2021 from the Estuary to the Gulf of St. Lawrence and via the Saguenay Fjord.

This dataset presents the vertical profiles of practical salinity, temperature, dissolved oxygen, fluorescence, transmissivity, and density of a dozen stations, from the surface to 350 m deep. Although the probes were calibrated by the manufacturer during the year, discrete salinity samples were taken throughout the water column and analyzed on a Guildline Autosal 8400 salinometer calibrated with standard IAPSO (International Association for the Physical Sciences of the Oceans) seawater and CTD profiles reprocessed after the mission. Similarly, dissolved oxygen concentrations were determined by Winkler chemical titration (Grasshoff et al., 1999) on about forty discrete water samples collected directly from Niskin bottles. The relative standard deviation, based on repeated analyses of samples taken from the same Niskin bottle, was less than 1%. These measurements were also used to calibrate the SBE-43 oxygen probe mounted on the rosette.

The team on board consisted of 12 people, professors, young researchers and students. A biogeochemical database on discrete water samples is associated with this physicochemical dataset.

本数据集所属的Hypoxia 2021 — C2021-06航次，其核心目标是为河口环境中天然有机物（natural organic matter）反应性与底栖生态系统（benthic ecosystem）功能间的关联提供全新且基于详实观测的评估，重点关注深水层的低氧（hypoxia）环境。为达成该目标，本航次组建了来自魁北克省3家机构的科研团队：ISMER-UQAR、麦吉尔大学（McGill University）与康考迪亚大学（Concordia University），团队的研究方向主要集中于天然环境中有机物的归趋，以及其支撑的底栖生态过程。本项目由加拿大自然科学与工程研究委员会（Natural Sciences and Engineering Research Council of Canada，NSERC）的航次时间项目（Shiptime Program，项目编号NSERC — Shiptime 556538-2021）资助，于2021年8月在圣劳伦斯河口至圣劳伦斯海湾以及萨格奈峡湾海域开展。

本数据集包含12个站位从表层至350米水深的实用盐度（practical salinity）、温度、溶解氧（dissolved oxygen）、荧光（fluorescence）、透射率（transmissivity）及密度（density）的垂直剖面数据。尽管相关探头已于本年度由厂商完成校准，研究团队仍在整个水层采集了离散盐度水样，并使用采用IAPSO（国际海洋物理科学协会，International Association for the Physical Sciences of the Oceans）标准海水校准的Guildline Autosal 8400型盐度计进行分析，同时对航次后重新处理的CTD（温盐深剖面仪，Conductivity-Temperature-Depth）剖面数据进行校正。同理，研究团队直接从尼斯金采水器（Niskin bottles）中采集了约40个离散水样，采用温克勒（Winkler）化学滴定法（Grasshoff等，1999）测定溶解氧浓度。基于对同一尼斯金采水器中水样的重复分析计算，其相对标准偏差小于1%。上述测定结果同样用于校准安装在采水器架（rosette）上的SBE-43型溶解氧探头。

本航次的在船科研团队共计12人，涵盖教授、青年科研人员及学生。本理化数据集同步关联了一套离散水样的生物地球化学数据库。