Physical and biogeochemical oceanography data from Conductivity, Temperature, Depth (CTD) rosette deployments during the Antarctic Circumnavigation Expedition (ACE).

Dataset abstract

This data set contains measurements from various sensors mounted on the Conductivity, Temperature, Depth (CTD) rosette that was deployed in the Southern Ocean during the Antarctic Circumnavigation Expedition (ACE). 63 CTD casts were carried out during three legs in the period 21st December 2016 to 16th March 2017, including one test cast and one failed cast, for which no data is available. Data include temperature, salinity, pressure, dissolved oxygen, oxygen saturation, chlorophyll-a concentration, backscatter, and photosynthetically active radiation (PAR) and reported are also the computed variables density, depth, and sound velocity. All data has been quality controlled and post-cruise calibrated, except for the oxygen data. Data is provided at 1 dbar pressure intervals for the up- and down-casts separately and as a merged bottle file when Niskin bottles were closed. This circumpolar data set provides insights into the circumpolar hydrography and biogeochemistry of the Southern Ocean during one austral summer season.

Dataset contents

For transparency, the raw files and files produced at the intermediate stages of data processing have been provided, in addition to the final processed files.

Raw data files:

ace_ctd_raw_files.zip - includes raw files direct from instrument and XMLCON configuration files

Intermediate files:

files output at each stage of the SeaBird processing

Processed data files:

ace_ctd_CTD20200406CURRSGCMR - one final set of files for the complete sensor data;

ace_ctd_BOTTLE20200406CURRSGCMR_hy1.csv - a merged bottle file extracted from the sensor data is also provided

Metadata:

range of files describing the CTD deployments, sensors, water sampling; quality-checking and processing of the files.

Dataset license

This physical and biogeochemical oceanography dataset is made available under the Creative Commons Attribution 4.0 International License (CC BY 4.0) whose full text can be found at https://creativecommons.org/licenses/by/4.0/

Change log

v1.1
Quick summary of issues addressed in CTD DOI Update
- Resolved discrepancies between upcast and downcast MLD estimates
- ‘Bad’ datapoints in file dACE201601_002_ct1.csv which were not flagged with ‘4’ Bad measurement
- CTDFLUOR1, CTDFLUOR1Q, CTDFLUOR2, CTDFLUOR2Q ‘dark’ correction was not applied consistently in first processing and should have been applied to all fluorescence variables
- CTDFLUOR1Q, CTDFLUOR2Q quenching correction needed to be recalculated and reapplied after update to MLD and dark correction
- Limit the number of decimal places for fluorescence, PAR and backscattering variables according to the instrument sensitivity limits (which is 4 decimal places except for backscattering which is 6)
- Changed file names described in data_file_header.txt

Additional details on ‘Issues’ and resolutions
Mixed layer depth estimates
- Large discrepancy in MLD estimates from upcast and downcasts at the same station was due to differences in the ‘reference’ depth i.e. depth other than 10 m was used when there were no datapoints at 10 m.
- Note: influence of time between casts was also checked and was not the driver of the discrepancies.
- Issue was resolved by setting the MLD for any cast where the reference depth was not 10 m to NaN.

Bad data flagging
- 22 ‘bad’ datapoints for variables salinity, density, temperature and sound at the end of the downcast file dACE201601_002_ct1 were missed during the visual inspection of the first CTD processing and hence were not flagged as bad.
- The bad datapoints are now flagged as ‘4’ bad measurement

Fluorescence
- In the first processing, dark correction was only applied to the files where quenching correction was needed, and only to the quenched corrected fluorescence variable, but should have been applied to all fluorescence variables in all files. This has been corrected
- In the first processing, the upcast MLD was used as the MLD estimate in quenching correction for both the upcast and downcast file. This has been changed so that the MLD from the same cast is used i.e. downcast estimate for the downcast file and upcast estimate for the upcasts file, unless the MLD estimate is NaN (because the reference depth was not 10 m), in that case the either the downcast or upcast estimate is used - whichever exists.

Decimal places
- The number of decimal places for the fluorescence, PAR and backscattering variables far exceeded the sensitivity limits of the respective sensors - for the fluorescence and backscattering variables this was due to the additional calculations and corrections applied. For the PAR variable it was the output from the Seabird processing.

Updated files list
The following files have been updated:
Folder: ace_bottle_BOTTLE20200406CURRSGCMR (all files within)
Folder: ace_ctd_CTD20200406CURRSGCMR (all files within)
ace_ctd_mld_CURRSSRGCMR20200405.csv
ace_ctd_visual_inspection_v2.csv
README.txt
data_file_header.txt
ace_physical_biogeochemical_oceanography_ctd_change_log.txt (new file)

v1.0 - Initial release of physical and biogeochemical oceanography data set.

数据集摘要

本数据集包含安装于温盐深（Conductivity, Temperature, Depth, CTD）采水架上的各类传感器的测量数据，该采水架曾在南极环球探险队（Antarctic Circumnavigation Expedition, ACE）期间部署于南大洋。2016年12月21日至2017年3月16日期间，科考队分3个航段完成了63次CTD站位观测，其中包含1次试测站位与1次失败站位（无可用数据）。观测数据涵盖温度、盐度、压力、溶解氧、氧饱和度、叶绿素a浓度、后向散射系数以及光合有效辐射（Photosynthetically Active Radiation, PAR），同时还包含计算得到的密度、深度与声速变量。除溶解氧数据外，所有数据均已完成航次后质量控制与校准。数据以1分巴（dbar）的压力间隔分别提供上行剖面与下行剖面数据，同时在尼斯金采水器闭合时提供合并后的采水瓶文件。本次环南极数据集可为2016/2017南半球夏季期间南大洋的环南极水文与生物地球化学特征提供研究依据。

数据集内容

为保证透明度，本数据集除提供最终处理后的文件外，还包含原始数据文件与数据处理中间阶段生成的文件。

原始数据文件：

ace_ctd_raw_files.zip —— 包含仪器直接导出的原始文件与XMLCON配置文件

中间处理文件：

SeaBird处理流程各阶段输出的文件

处理后数据文件：

ace_ctd_CTD20200406CURRSGCMR —— 覆盖完整传感器数据的最终数据集文件集合；
ace_ctd_BOTTLE20200406CURRSGCMR_hy1.csv —— 从传感器数据中提取得到的合并采水瓶文件，亦随数据集一并提供

元数据：

涵盖描述CTD部署情况、传感器参数、水样采集、数据质量检查与处理流程的各类文件。

数据集许可协议

本物理海洋与生物地球化学海洋学数据集采用知识共享署名4.0国际许可协议（Creative Commons Attribution 4.0 International License, CC BY 4.0）进行授权，协议全文可访问https://creativecommons.org/licenses/by/4.0/查阅。

更新日志

v1.1
本版本针对CTD DOI更新中涉及的问题进行了快速修复：
- 修正了上行剖面与下行剖面混合层深度（Mixed Layer Depth, MLD）估算结果不一致的问题
- 修复了dACE201601_002_ct1.csv文件中未被标记为“4（不良测量）”的22处不良数据点
- 首次处理时未统一对CTDFLUOR1、CTDFLUOR1Q、CTDFLUOR2、CTDFLUOR2Q变量施加“暗背景”校正，该校正应适用于所有荧光变量，现已完成修正
- 在更新混合层深度与暗背景校正后，需重新计算并重新施加CTDFLUOR1Q、CTDFLUOR2Q的猝灭校正
- 根据仪器灵敏度限制调整了荧光、光合有效辐射与后向散射变量的小数位数：除后向散射变量保留6位小数外，其余变量均保留4位小数
- 更新了data_file_header.txt中描述的文件名

关于“问题与解决方案”的补充细节：
混合层深度估算
- 同一站位上行与下行剖面的MLD估算结果存在较大差异，原因在于参考深度选取不一致：当10米深度无有效数据时，未统一采用10米作为参考深度。
- 注：已核查站位间的时间间隔对结果的影响，确认其并非导致差异的诱因。
- 本问题已通过如下方式解决：将所有参考深度非10米的站位的MLD值设为NaN（非数字）。

不良数据标记
- 在首次CTD处理的人工目视检查中，遗漏了dACE201601_002_ct1.csv下行剖面文件末尾处的22处针对盐度、密度、温度与声速变量的不良数据点，未将其标记为不良测量。
- 现已将上述不良数据点标记为“4（不良测量）”。

荧光变量校正
- 首次处理时，仅对需要施加猝灭校正的文件以及经猝灭校正后的荧光变量施加了暗背景校正，但该校正应适用于所有文件中的所有荧光变量，现已完成修正。
- 首次处理时，在对上行与下行剖面文件进行猝灭校正时，均采用了上行剖面的MLD估算值。现已修改为采用对应剖面自身的MLD估算值：即下行剖面文件采用下行剖面的MLD估算值，上行剖面文件采用上行剖面的MLD估算值；若对应剖面的MLD估算值为NaN（因参考深度非10米），则采用存在的另一剖面的MLD估算值。

小数位数调整
- 荧光、光合有效辐射与后向散射变量的小数位数远超对应传感器的灵敏度限制：荧光与后向散射变量的小数位数过多源于后续附加的计算与校正操作，光合有效辐射变量的小数位数过多则源于SeaBird处理流程的输出结果。

更新后的文件列表
已更新的文件如下：
文件夹：ace_bottle_BOTTLE20200406CURRSGCMR（内含所有文件）
文件夹：ace_ctd_CTD20200406CURRSGCMR（内含所有文件）
ace_ctd_mld_CURRSSRGCMR20200405.csv
ace_ctd_visual_inspection_v2.csv
README.txt
data_file_header.txt
ace_physical_biogeochemical_oceanography_ctd_change_log.txt（新增文件）

v1.0 —— 本物理海洋与生物地球化学海洋学数据集的首次发布。