Brief description
Sampling was conducted according to GEOTRACES protocols. Samples for trace element analyses, including dissolved iron (dFe), were filtered through acid-cleaned 0.2 um cartridge filters (Pall Acropak) under constant airflow from several ISO class 5 HEPA units. All plastic ware was acid-cleaned prior to use, following GEOTRACES protocols. Samples were collected into low-density polyethylene (LDPE) bottles, acidified immediately to pH 1.7 with Seastar Baseline hydrochloric acid (HCl), double-bagged and stored at room temperature until analysis on shore.Samples for dFe analysis were pre-concentrated offline (factor 40) on a SeaFAST S2 pico (ESI, Elemental Scientific, USA) flow injection system with a Nobias Chelate-PA1 column. Samples were eluted from the column in 10% distilled nitric acid (HNO3), with calibration based on the method of standard additions in seawater (made using multi-element standards in a 10% HNO3 matrix, rather than an HCl matrix). Pre-concentrated samples were analysed using Sector Field Inductively Coupled Plasma Mass Spectrometry (SF-ICP-MS, Thermo Fisher Scientific, Inc.). Data were blank-corrected by subtracting an average acidified milli-Q blank that was treated similarly to the samples.
The dFe detection limit for a given analysis run on the SeaFAST/SF-ICP-MS was calculated as 3 x standard deviation of the milli-Q blank on that run. Detection limits ranged from 0.016 to 0.067 nmol kg-1, with a median of 0.026 nmol kg-1 (n=12). GEOTRACES reference materials were analyzed along with samples and results were in good agreement with consensus values: SAFe D1 was measured at 0.69 +/- 0.05 nmol kg-1 (n=7; consensus value = 0.67 +/- 0.04 nmol kg-1) and GD was measured at 1.02 +/- 0.01 nmol kg-1 (n=6; consensus value = 1.00 +/- 0.1 nmol kg-1).
Comments regarding the data spreadsheet:
NaN = no sample
dFe QC flags: 1 = high confidence in data quality
2 = detection limit
3 = low confidence in data quality
detection limits: dFe data that were below the daily detection limit were replaced with the respective detection limit. They are flagged with the number 2 in the dFe QC flag column.
Lineage
Progress Code: completed
Statement: No problems with analysis, but there were a lot of problems with GO-FLO bottles during sampling, i.e. bottles either not closing or leaking on arrival on deck. As a result, there is a large number of missing samples (NaN), and we also took some salinity samples for additional data quality control as follows:
A subset of salinity samples (n=124) was taken from GO-FLO bottles to check whether bottles had closed at the expected depths and/or whether there were problems with leaking. Salinity samples were compared to CTD salinities, and samples where measured salinity did not match the respective CTD salinity (n=9) were flagged as suspect and are not included in the data sheet. Note that salinity checks were predominantly performed on GO-FLO bottles that were suspicious (e.g. leaking), so they do not represent a random set of samples.
A subset of salinity samples (n=124) was taken from GO-FLO bottles to check whether bottles had closed at the expected depths and/or whether there were problems with leaking. Salinity samples were compared to CTD salinities, and samples where measured salinity did not match the respective CTD salinity (n=9) were flagged as suspect and are not included in the data sheet. Note that salinity checks were predominantly performed on GO-FLO bottles that were suspicious (e.g. leaking), so they do not represent a random set of samples.
Notes
PurposeSupply dissolved iron data for the K-axis region. Complimentary to other K-axis data.
Data time period: 2017-01-10 to 2018-02-28
text: westlimit=70; southlimit=-66; eastlimit=95; northlimit=-57
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