Fe_profile

Dataset description

dissolved iron, total iron, and nutrients from water column samples

Acquisition description

Sampling and Analytical Methodology
Water-column samples for trace metal analysis were collected in modified
5-L teflon-lined, external-closure Niskin-X samplers (General Oceanics Inc.)
suspended from a non-metal line.  In addition, a limited number of deeper
water-column samples were collected by Mak Saito in 10-L teflon-lined
GoFlo samplers (General Oceanics Inc.).  All samples were filtered as soon
as possible after collection using a 0.2 µm Supor Acropak filter cartridge
(Pall Corp.), except for the Go-Flo samples which were filtered by Mak Saito
through 0.4 µm polycarbonate membranes.  The filtered seawater samples were
acidified to pH 1.7 with Seastar Baseline ultrapure hydrochloric acid,
stored for at least 24 hours, then dissolved iron (dFe) was determined by
flow injection analysis modified after the method of Measures et al. [1995]
with analytical figures of merit as detailed by Sedwick et al. [2005, 2008].

The efficacy of our sample collection, sample processing and analytical
methods for dissolved iron in seawater have been verified in the SAFe
intercomparison exercise [Johnson et al., 2007].  Our laboratory values
for SAFe seawater reference materials are as follows:

SAFe surface seawater S1: dFe = 0.11 ± 0.01 nM (n = 15) vs consensus value
of 0.097 ± 0.043 nM
SAFE deep seawater D2: dFe = 0.97 ± 0.06 nM (n = 14) vs consensus value of
0.91 ± 0.17 nM.

In addition, unfiltered splits of all samples were acidified to pH 1.7 with
Seastar Baseline ultrapure hydrochloric acid, stored for at least 6 months,
and then total-dissolvable iron (TDFe) was determined by flow injection
analysis using the same method as used for dFe. Total-dissolvable iron is
therefore equal to the concentration of dissolved iron plus acid-labile
particulate iron [see Sedwick et al., 2005].  Dissolved macronutrients were
measured at sea in 0.2-µm filtered using JGOFS-standard autoanalyzer methods.

References
Johnson, K. S., et al. (2007), The SAFe iron intercomparison cruise: An
international collaboration, Eos, Trans. Am. Geophys. Un., 88, 131-132.

Sedwick, P. N., T. M. Church, A. R. Bowie, C. M. Marsay, S. J. Ussher,
K. M. Achilles, P. J. Lethaby, R. J. Johnson, M. M. Sarin, and D. J.
McGillicuddy (2005), Iron in the Sargasso Sea (Bermuda Atlantic Time-series
Study region) during summer: Eolian imprint, spatiotemporal variability,
and ecological implications, Global Biogeochemical Cycles, 19,
doi:10.1029/2004GB002445.

Sedwick, P. N., A. R. Bowie, and T. W. Trull (2008), Dissolved iron in the
Australian sector of the Southern Ocean (CLIVAR-SR3 section): meridional
and seasonal trends, Deep-Sea Research I, doi:10.1016/j.dsr.2008.03.011.

Processing description

Data Processing
An acid blank (to account for iron present in acid added to samples)
has been subtracted from raw dFe and TDFe concentrations.  For the
CORSACS-1 cruise, this blank was determined as 0.007 nM; for the
CORSACS-2 samples, the blank was below the limit of quantification
(i.e., negligible).

1. Niskin:

2. Go-flo Bottle:

This document is created from the content of the BCO-DMO metadata database.    2010-03-15  06:56:47