Search the data

Labile Iron (II) (size-fractionated) and dissolved Iron (dFe) fractions from CTD bottles and surface underway samples collected during the 2004 AMT15 cruise

Originator's Protocol for Data Acquisition and Analysis

This data originates from analyses on samples collected from the ship's non-toxic supply and from titanium CTD casts during the cruise. Samples were collected between 20 September 2004 and 25 October 2004.

For the CTD casts, samples were collected using 10 L Ocean Test trace metal bottles. The samples were filtered using a 0.2 µm pore size, 25mm PTFE membrane (GD/X, WhatmanTM).

For the surface underway supply, samples were pumped from a trace metal towfish at 5 m depth using a diaphragm pump (Sandpiper II) into a clean container via a 1/2" i.d. polyethylene tube. Prior to use, the equipment was cleaned with 5% HCL (ARISTAR, BDH) solution. The underway seawater supply was split by a Y-piece to separate the unfiltered and filtered seawater. The filtered seawater was passed through a Sartobran 300 Cartridge (Sartorius, 0.2 µm pore size). The filtrates were stored for 6 months at pH 1.9 before analysis.

The analytical proceedure for quantifying dissolved Fe (II) and dissolved iron concentration was flow injection chemiluminescence (Bowie et al., 1998; 2002). The flow injection incorporates a 8-HQ preconcentration column and an HCL (0.05 M) carrier was used to elute Fe (II) from the column. The 8-HQ column was rinsed before each elution to remove any unassociated species using a UHP water wash line controlled via the three-way valve.

References Cited

Bowie, A.R., Achterberg, E.P., Mantoura, R.F.C., Worsfold, P.J., 1998. Determination of subnanomolar levels of iron in seawater using flow injection with chemiluminescence detection. Anaytica Chimica Acta 361, 189-200.

Bowie, A.R., Achterberg, E.P., Sedwick, P.N., Ussher, S., Worsfold, P.J., 2002. Real-time monitoring of picomolar concentrations of iron (II) in marine waters using automated flow injection chemiluminescence instrumentation. Environmental Science and Technology 36, 4600-4607.

Instrumentation Description

Not applicable for this data set.

BODC Data Processing Procedures

Data were submitted via email in excel spreadsheets archived under BODC's accession number UPL060020. Initially, cast data from station 32 to 51 (upwelling region) were not provided to BODC by the data originator due to poor analytical precision. After subsequent email correspondence, revised datasets with reanalysed CTD casts for stations 32 to 51 were submitted by the data originator. Data are now considered to be of good quality. The underway data file contained dFe (dissolved iron concentration), TDFe (Total dissolvable iron concentration, unfiltered) and standard deviation data. The final CTD file contained dFe and standard deviation data. The standard deviation data provided by the originator were not loaded to the database but are available in the originators file which can be supplied on request.

Sample metadata (Date, time (GMT), latitude, longitude and depth) were checked against information held in the database and the cruise report. The sampling times had been converted to GMT from local time in the file provided by the data originator.

For the the filtered underway data, the sample taken on 02 October 2004 at 11.45 hours was not loaded because it had no values for Fe concentration. There are 6 samples with repeat measurements (23 September 2004, 10.40 hours; 24 September 2004, 10.50 hours; 25 September 2004, 10.50 hours; 26 September 2004, 10.50 hours; 30 September 2004, 11.50 hours and 23 October 2004, 09.50 hours. Although the repeat samples have the same latitude and longitude, they were loaded separately.

For the CTD data, 9 samples had repeat measurements, (25 September 2004, 11.14 hours, rospos 20; 27 September 2004, 11.05 hours, rospos 16; 06 October 2004,11.04 hours, rospos 4, 7, 12, 16 and 20; 16 October 2004, 10.08 hours, rospos 4; 23 October 2004, 10.04 hours, rospos 20 (x2 repeats)). The mean and standard deviation of these data values were loaded to the database.

There were 3 discrepancies with the CTD data when compared to the CTD logs: CTD095t and CTD101t were provided with depths of 125 m but loaded against 150 m according to the CTD cruise logs. CTD025 was sampled on 27 September 2004 according to the originators file, but was loaded against 28 September 2004 according to the CTD log. There were no discrepancies with the filtered underway or unfiltered underway data.

The data were reformatted and marked up with BODC parameter codes and loaded into BODC's samples database under Oracle Relational Database Management System.

The iron concentraion data were provided in nM/L. These units were consistent with the BODC parameter code units and no conversions were applied.

A parameter mapping table is provided below:

Data Quality Report

BODC was not advised of any quality issues with the data by the data originator. There were no outlying values that were flagged by BODC.

Problem Report

Not relevant to this data set.