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AMT16 extracted chlorophyll-a measured fluormetrically from CTD bottle and underway samples

Data Acquisition and Analysis

This data originates from analyses on samples collected from CTD rosette bottles for 64 CTD casts and from the ship's non-toxic supply. Water-column sampling during AMT16 concentrated around collection of the main core measurements from 5 or 6 light depths from the predawn CTD cast (~0200 - 0400h local time), with a reduced set of measurements and depths from the late morning 'optics' cast (1100h local time).

Water samples from the 5-6 main light depths were collected from CTD bottles and underway samples from the ship's non-toxic supply every 4-5 hours. These samples were filtered on 25 mm GFF filters. Filters were extracted in 90% acetone for 24 hrs and total chlorophyll-a measured with a TD-700 Turner Designs fluorometer following the procedure of Welschmeyer (1994) which minimises interference by chlorophyll-b. The fluorometer was calibrated with dilutions of a solution of pure chlorophyll-a (Sigma, UK) in 90% acetone, the concentration of which was determined spectrophotometrically after the cruise.

References Cited

Welschmeyer N.A., 1994. Fluorometric analysis of chlorophyll-a in the presence of chlorophyll-b and phaeopigments. Limnology and Oceanography, 39, 1985-1992.

Instrumentation Description

Not relevant to this dataset.

BODC Data Processing Procedures

Data were submitted to BODC in an Excel spreadsheet and accessioned under BODC archive SOC050136. Sample metadata provided (CTD cast, date, time, lat/lon and depth) were checked against information held in the database. There were 2 discrepancies: cast 2 had two samples with very different values from 20 m, the data originator was contacted and confirmed there was a typing error and the second values should be from 30m; cast 43 had sample depths provided that did not match the depths at which the bottles were fired returned from the CTD files (21, 57 and 120m in originators file loaded to 42, 68 and 112m bottle firing depths respectively). There were also 2 samples from 50 m on cast 2 and the data originator confirmed this was correct, these data were averaged and entered into the database at 50 m.

Parameter codes defined in BODC parameter dictionary were assigned to the variable. The units supplied in the spreadsheet were mg l ^-1 , however comparison with data values reported from onboard calibration in the Cruise Report and sensor range of fluorometer (from manufacturer's website) suggests this is an error and the data should be labelled mg m ^-3 (equivalent to µg l ^-1 ).

Data loaded into BODC's database without any changes applied.

A parameter mapping table is provided below;

Data Quality Report

The data originator indicated 4 values where it was felt these data might be lower than they should be. These have been flagged 'L'.

Problem Report

Not relevant to this dataset.