AMT14 extracted chlorophyll-a measured fluormetrically from CTD bottle and underway samples
Data Acquisition and Analysis
Size-fractionated measurements were only performed on samples collected from the CTD rosette sampler. Total chlorophyll was analysed on samples collected from both the CTD rosette sampler and the ship's non-toxic water supply. During AMT14 underway samples were collected every 2 hrs. Water-column sampling during AMT14 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 at 29 stations on a total of 140 samples. Methodology for size-fractionation was not detailed in the AMT14 cruise report but was confirmed to be the same as that used for AMT13 by originator. 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 2 Excel spreadsheets. The CTD (including size-fractionated data) were accessioned under BODC archive SOC040122 and the underway samples under BODC archive SOC040147. Sample metadata provided (CTD cast, date, time, lat/lon and depth) were checked against information held in the database. There were 3 discrepancies noted and these have now been checked with the originator:
- - excessive difference in depth for station AMT14_06 between originator's depths and BODC's CTD depths: closest match to samples attributed to 100 and 150 m were 81.1 and 176.3 m respectively. Originator agreed with correction.
- - the surface sample from station AMT14_10 corresponds to a Niskin bottle reported as having misfired in UKORS' CTD log sheets. This was also observed with Mike Zubkov's AFC data. Following enquiry, originator confirmed that the sample did indeed originate from that particular bottle and that some water had been collected despite the misfiring problem.
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 |
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 following values were reported as suspect by the originator and were flagged 'L' in the database:
- AMT14_38, 46m : value for 0.2-2µm size fraction ("Incorrect measurement")
- AMT14_63, 50m: value for >10µm size-fraction ("too high")
- AMT14_67, 57m: value for 0.2-2µm ("too low, bad measurement")
- AMT14_85, 45m: value for 0.2-2µm ("too low, not extracted properly")
Two values (AMT14_06, 176 m and AMT14_09, 7.6 m) were found suspect during the calibration of the CTD fluorometer and were flagged 'M' in the database.
Problem Report
Not relevant to this dataset.