Phytoplankton pigment concentrations of seawater sampled during the Antarctic Circumnavigation Expedition (ACE) during the Austral Summer of 2016/2017.

***** Dataset abstract *****

This dataset contains phytoplankton pigment concentrations sampled during the Antarctic Circumnavigation Expedition (ACE) Leg 1-3 and analysed using high performance liquid chromatography. Water samples were collected from the underway seawater supply every 3 hours and at multiple depths from select CTD (conductivity, temperature and depth) rosette deployments. Pigment concentrations have been quality controlled. This circumpolar dataset contains the main pigment concentrations of phytoplankton and can be used to infer phytoplankton biomass and class composition.

***** Original data collection *****

Samples for phytoplankton pigments were collected from the underway seawater supply every 3 hours and from certain depths within the upper 200 m during select CTD (conductivity, temperature and depth) rosette casts. Up to 2 L of seawater was filtered onto 0.7 micrometre pore size 25 millimetre diameter glass fibre filters under low vacuum pressure. Samples were stored at -80 degrees Celsius before analysis by Céline Dimier from the SAPIGH (Service d'Analyses de Pigments par HPLC) analytical platform of the Insitut de la Mer de Villefranche (CNRS and Sorbonne Université).

External pure pigment standards (provided by DHI Water & Environment, Denmark) were used to calibrate the high performance liquid chromatographic analysis of samples (detailed below). Solutions of pigment standards were prepared with concentrations verified using spectrophotometry before the standard solutions were analysed via the method described below, producing a calibration concentration curve and spectral library for matching pigment peaks from unknown samples. The methodology below produced a total chlorophyll a injection precision of 0.33% and accuracy (SeaWiFS HPLC Analysis Round-Robin Experiment 6) of 3.72%. The retention time precision was 0.10%, calibration precision 0.4% and calibration accuracy 0.3%.

***** Data processing *****

Seawater samples were extracted in a solution of 1:1 (v/v) 100 % methanol with vitamin E acetate internal standard and buffer solution (tetra- butylammonium acetate or TBAA 28 mM) for 2 hours at -20 degrees Celsius, sonicated and clarified through glass fibre filtration (as above) before separation and quantification of pigments via high performance liquid chromatography (HPLC) using a HPLC Agilent Technologies 1200 instrument system with a C8 guard as the analytical column and LC Chemstation software as per Van Heukelem and Thomas (2001) and Ras et al. (2007). Identified pigments include carotenoids, chlorophyll c and chlorophyll b at 450 nm; chlorophyll a and derivatives at 676 nm; and bacteriochlorophyll a at 770 nm. The method detects 25 separate phytoplankton pigments and a full list of pigments is provided in the file data_file_header.txt. Pigment peaks were identified based on retention time and concentrations (in mg/m^3) were calculated from the peak areas with an internal standard correction (Vitamin E acetate) and external calibration (see Calibration section). The lower limit of detection (LOD) is calculated in nanograms per injection and as the concentrations corresponding to a signal:noise ratio of 3 and for a filtered volume of 2 L. For chlorophyll a this is 0.0001 mg/m^3. A full list of LOD for each pigment is available in the file ‘ace_phytoplankton_pigments_lod.csv’.

Latitude and longitude have been extracted from the ACE gps one-minute resolution dataset for underway samples (Thomas and Pina Estany 2019: doi.org/10.5281/zenodo.3483166), matched by DateTime. Latitude, longitude and datetime of sampling for the CTD bottle samples were extracted from the CTD bottle file ace_ctd_BOTTLE20200406CURRSGCM_hy1.csv (Henry et al. 2020 doi.org/10.5281/zenodo.3813646), matched by station number, cast number and bottle number.

***** Quality checking *****

Undetected pigments or pigment concentrations which were lower than the limit of detection (LOD) are reported as a fill value of ‘NaN’ and assigned Flag 4. Each pigment peak was inspected, and quality control flags applied based on comparison and similarity with the spectral library derived from the pure standards calibration. Four samples were identified as either bad samples or without sufficient information after quality control checks and have been assigned bad data Flag 5.

Quality flags for each pigment concentration
Flag ‘1’ = ‘good’
Flag ‘2’ = ‘acceptable’
Flag ‘3’ = ‘questionable’
Flag ‘4’ = ‘below limit of detection’
Quality flags for accepting/rejecting sample (column accept_reject)
Flag ‘5’ = ‘accept’
Flag ‘6’ = ‘reject’

***** Standards *****

The collection and analysis of these water samples conforms to the international standards for biogeochemical sampling and analysis for ocean colour validation as determined in Mueller et al. (2003). In addition, the analysis facility regularly participates in international laboratory intercomparison exercises, SeaWiFS HPLC Analysis Round-Robin Experiments Sea-HARRE (Hooker et al. 2012), including the most recent exercise Sea-HARRE 6 (report is in-prep).

***** Dataset contents *****

- ace_phytoplankton_pigments_20200511CURRSGCMR.csv, data file, comma-separated values
- ace_phytoplankton_pigments_lod.csv, metadata, comma-separated values
- ace_phytoplankton_pigment_concentrations_change_log.txt, metadata, text
- data_file_header.txt, metadata, text
- README.txt, metadata, text

Pigment concentration values below the limit of detection are reported with fill value ‘NaN’. Any null values are reported with fill value ‘NaN’.

***** Dataset contact *****

David Antoine, Curtin University, Australia. ORCID: 0000-0002-9082-2395. Email: david.antoine@curtin.edu.au
Charlotte Robinson, Curtin University, Australia. ORCID: 0000-0001-8519-5641. Email: charlotte.robinson@curtin.edu.au, charlotte.mary.robinson@gmail.com

***** Dataset citation *****

Please cite this dataset as: 
Antoine, D., Thomalla, S., Berliner, D., Little,  H., Moutier, W., Olivier, A., Robinson, C., Ryan-Keogh, T. and Schuback, N. (2020) Phytoplankton pigment concentrations of seawater sampled during the Antarctic Circumnavigation Expedition (ACE) during the Austral Summer of 2016/2017. (Version 1.1) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.3816726