AMT13 extracted chlorophyll-a (total and size-fractionated) measured fluormetrically from CTD bottle and underway samples
Data Acquisition and Analysis
Total chlorophyll was analysed on samples collected from both the CTD rosette sampler and from a small number of underway samples collected from the ship's non-toxic water supply. Water-column sampling during AMT13 concentrated around 5 or 6 light depths from the predawn CTD cast (~0200 - 0400h local time), with a reduced set of 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 and these samples were filtered on 25 mm GFF filters. Filters were extracted in 90% acetone for 10-24 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 for samples collected on the pre-dawn cast. Size-fractionated chlorophyll distribution was determined by serial filtration onto 10, 5, 2 and 0.2 µm polycarbonate membrane filters (Poretics, UK). The filters were treated identically to the GF/F used for total chlorophyll and were soaked in 10-ml 90% acetone (HPLC grade) for 10-24 hours 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 were accessioned under BODC archive SOC040010. Sample metadata provided (CTD cast, date, time, lat/lon and depth) were checked against information held in the database. There were no discrepancies noted.
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;
| Originator's Parameter | Units | Description | BODC Parameter Code | Units | Comments |
|---|---|---|---|---|---|
| Chlorophyll-a | mg m -3 | Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate >GF/F phase] by filtration, acetone extraction and fluorometry | CPHLFLP1 | mg m -3 | n/a |
| 0.2-2µm | mg m -3 | Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate 0.2-2µm phase] by filtration, acetone extraction and fluorometry | SCHLFLPF | mg m -3 | n/a |
| 2-5µm | mg m -3 | Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate 2-5µm phase] by filtration, acetone extraction and fluorometry | SCHLFLPC | mg m -3 | n/a |
| >5µm | mg m -3 | Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate >5µm phase] by filtration, acetone extraction and fluorometry | SCHLFLPA | mg m -3 | n/a |
| 5-10µm | mg m -3 | Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate 5-10µm phase] by filtration, acetone extraction and fluorometry | SCHLFLPX | mg m -3 | n/a |
| >10µm | mg m -3 | Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate >10µm phase] by filtration, acetone extraction and fluorometry | SCHLFLPO | mg m -3 | n/a |
| Total | mg m -3 | Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate >0.2µm phase] by filtration, acetone extraction, fluorometry and summation of size-fractionated values | CPHLFLP4 | mg m -3 | n/a |
Data Quality Report
The data originator removed any suspect data before submission to BODC.
Problem Report
Not relevant to this dataset.
