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AMT6 Picophytoplankton and heterotrophic bacteria abundance (AFC) measurements

Originator's Protocol for Data Acquisition and Analysis

This data originates from analyses of bottle samples taken from 39 CTD casts.

Seawater was collected in Niskin bottles from up to 12 depths from 2 to 300 m at 31 stations at intervals of 4 ^o latitude. Additionally 33 samples were collected from the ship's non-toxic supply along the cruise track and 6 surface samples were collected with a bucket. Two or three 0.9 ml subsamples from the same sample were pooled in a polypropylene vial, fixed with 0.1-0.3% (final concentration) glutaraldehyde, frozen and kept either in liquid nitrogen or at -30 ^o C for 1-2 months before they were analysed.

Samples were analysed in a FACSort flow cytometer (Becton Dickinson, Oxford, UK) equipped with a 15 mW laser exciting at 488 nm. Three major gruops of picophytoplankton: Prochlorococcus , Synechococcus and picoeukaryotic cells, were characterised and enumerated using group specific side scatter and orange (585±21 nm) and red (>650 nm) autfluorescence properties. The total concentration of bacteria was measured in samples stained with SYBR Green I. Further details of the methodology can be found in Zubkov et al. (2000).

References Cited

Zubkov M.V., Sleigh M.A., Burkill P.H. and Leakey R.J.G., 2000. Picoplankton community structure on the Atlantic Meridional Transect: A Comparison between Seasons. Progress in Oceanography, 45:369-386.

Instrumentation Description

Not relevant to this data set.

BODC Data Processing Procedures

Data were submitted to BODC in Microsoft Excel spreadsheet format along with the equivalent data from AMT3 and AMT4. The data were saved to the BODC archive with reference SOC030034. The original file received was partly loaded to the database by matching metadata - in three cases there was no metadata in the database or cruise log and the data from the submited file were loaded. Sample metadata were checked against information held in the database - there was one discrepancy aside from the data which could not be matched. Metadata provided in the file upon which matching was based were date, latitude/longitude and bottle firing depth. It was assumed that station JD149 is listed in the data file with the incorrect latitude as there is no cast at 8.1 ^o S. The depths of samples for this station match exactly with the depths for CTD28 and were therefore matched together. The latitude for this sample was changed to 5.8 ^o S accordingly.

Where replicate data were provided for a sample depth, the data were averaged to provide one value for each sample.

Biomass was calculated for each microorganism using the cellular biomass conversion factors (pg C cell ^-1 ) for each type as listed in the originator's file: 0.011507 for heterotrophic bacteria, 0.028638 for Prochlorococcus , 0.09997 for Synechococcus and 1.5 for picoeukaryotes.

Count (cells ml ^-1 ) * biomass conversion factor (pg C cell ^-1 ) = pg C ml ^-1

This was then divided by 1000 to convert to mg C m ^-3

Parameter codes defined in BODC parameter dictionary were assigned to the variables. The data were assigned parameter codes defined in BODC parameter dictionary. Data loaded into BODC's database using established BODC data banking procedures.

A parameter mapping table is provided below;

Data Quality Report

The dataset has been checked by the data originator - any suspect data values were removed from the data set before submission to BODC. Data were checked at BODC when loading. Data values of 0 have been loaded. Empty cells have not been loaded.

Problem Report

Not relevant to this data set.