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AMT15 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 55 CTD casts and from the ship's non-toxic supply. Water-column sampling during AMT15 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 approximately every 3 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.

Size-fractionation of chlorophyll was carried out at 2 depths on 21 pre-dawn casts. Methodology for size-fractionation was not detailed in the AMT15 cruise report but from the data file size-fractionated chlorophyll distribution was determined by serial filtration onto 2 and 0.2 µm filters. The filters were treated identically to the GF/F used for total chlorophyll and were soaked in acetone prior to reading on the bench fluorometer.

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 SOC050049. Sample metadata provided (CTD cast, date, time, lat/lon and depth) were checked against information held in the database. There were 3 discrepancies: the cast labelled 41 in the originator's file was in fact cast 42 as the sample depths provided did not match cast 41 but did match those sampled on 42; on cast 18 one sample was provided with a depth of 98 m, the metadata held at BODC indicate sample collection from 88 m; one sample for each of cast 19 and 22 were labelled 'C MAX' with no depth, these data were loaded in sequence with the depths present for each cast (126m and 112m respectively).

One cast was labelled 96/97 by the data originator. These casts were carried out pre-dawn at the same location and the bottles sampled at similar depths. Since the casts cannot be distinguished the data has been loaded against cast 96.

Parameter codes defined in BODC parameter dictionary were assigned to the variable. The units supplied in the spreadsheet were mg m ^-3 , which match the Parameter Dictionary units so no unit conversions were necessary.

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

A parameter mapping table is provided below;

Data Quality Report

BODC were not advised of any data quality checks made by the data originator prior to submission of the dataset.

Problem Report

Not relevant to this dataset.