1. Australian Antarctic Data Centre
2. Discover and Manage Data
3. Records
4. AAS_4512_TEMPO_Phytoplankton_Pigments

Description

This dataset describes phytoplankton distribution and abundance and abundance during the TEMPO Voyage (Trends in Euphausiids off Mawson, Predators, and Oceanography), conducted on RV Investigator from February to March 2021 (IN2021_V01, CSIRO Marine National Facility). The primary goal of TEMPO was to collect data to estimate krill biomass with a view to updating the precautionary catch limit within CCAMLR’s Division 58.4.2-East. It also aimed to increase our understanding of krill habitat to ensure sustainable management, with part focus on phytoplankton populations given they are the main food source for krill. Six north-south transects were conducted from west to east (55-80°E) with each extending from 62 or 63°S to the sea-ice edge. Some transects coincided with the eastern transects of a previous voyage undertaken in 2006 (BROKE-WEST, Nicol, Raymond and Meiners 2010), providing a valuable comparison.

Purpose

This dataset provides the distribution and abundance of phytoplankton taxa throughout the survey region, as determined through analysis of pigment signatures. It also provides integrated chlorophyll a measurements. The aims were to elucidate the drivers that influence phytoplankton populations, and to examine phytoplankton-krill relationships.

Pigments samples (1 L) were taken from Niskin bottles, filtered onto 13 mm GF/F filters in a darkened laboratory, then the filters placed in liquid nitrogen for later analysis. Six depths were sampled at each station and always included the near-surface (5-10 m) and the depth of the deep chlorophyll maximum (DCM), as determined using real-time fluorescence data during downward CTD casts. In total 51 stations were sampled. Pigments were later analysed ashore using high performance liquid chromatography (HPLC) according to the method of Wright et al. (2010). Chemotaxonomic analysis was undertaken using the software program CHEMTAX (Mackey et al. 1996; Wright et al. 1996) with 7 phytoplankton taxa chosen for analysis based on previous experience (Wright and van den Enden 2000; Wright et al. 2010), including greens, cryptophytes, diatoms 1, diatoms 2, dinoflagellates 1, haptophytes 8 high-iron, and haptophytes 8 low-iron. Hierarchical clustering was undertaken on samples prior to analysis in CHEMTAX to reduce potential errors associated with changes in pigment:chlorophyll a ratios under varying environmental conditions such as light and nutrient availability (Wright et al. 2010). The R-Studio packages cluster and dynamicTreeCut were utilised for clustering, with the dynamic tree cutting method enabling the detection of clusters dependent on their shape rather than the use of a fixed height cut-off (Langfelder et al. 2007; Hayward et al. 2023). The analysis resulted in 8 clusters sharing similar pigments. To cross-check CHEMTAX outputs, light microscopy was undertaken on phytoplankton samples that had been fixed in lugols iodine (1 L), taken at the same sites and depths. Initial pigment:chlorophyll a ratios that were utilised in CHEMTAX are shown in Table 1, and an example of optimised ratios shown for Cluster 1.

Quality

There are two columns of data for integrated chlorophyll a and they differ. The first integration (column title: Chlorophyll a integrated using 6 sample depths) was based on the 6 depths that were sampled for HPLC pigments. As only 6 points were used for the column-integration the resolution was low. The second integration (column title: Chlorophyll a integrated calibrated fluorometer - high resolution 1 m bins) was based on high resolution fluorescence profiles from the CTD. To calibrate the fluorometer, HPLC chlorophyll a concentrations were compared against fluorescence measurements from the same depths, and a linear regression established (fluorescence = 3.8633 * Chl a – 0.2033, R2 = 0.91). This integration is more accurate given that fluorometer measurements were taken at 1 m intervals throughout the water column, providing high resolution.

Access

These data are publicly available for download from the provided URL.

Temporal Coverages

• Start date: 2021-02-13 - Stop date: 2024-03-12

Spatial Coverages

Science Keywords

• EARTH SCIENCE > BIOSPHERE > ECOSYSTEMS > AQUATIC ECOSYSTEMS > PLANKTON
• EARTH SCIENCE > OCEANS > OCEAN CHEMISTRY > PIGMENTS
• EARTH SCIENCE > OCEANS > OCEAN CHEMISTRY > CHLOROPHYLL

Use Constraints

This data set conforms to the CCBY Attribution License (http://creativecommons.org/licenses/by/4.0/).

Please follow instructions listed in the citation reference provided at http://data.aad.gov.au/aadc/metadata/citation.cfm?entry_id=AAS_4512_TEMPO_Phytoplankton_Pigments when using these data.