Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Marine Chemistry 173 (2015): 125-135, doi:10.1016/j.marchem.2014.09.002.
Description:
The size partitioning of dissolved iron and organic iron-binding ligands into soluble and
colloidal phases was investigated in the upper 150 m of two stations along the GA03 U.S.
GEOTRACES North Atlantic transect. The size fractionation was completed using cross-flow
filtration methods, followed by analysis by isotope dilution inductively-coupled plasma mass
spectrometry (ID-ICP-MS) for iron and competitive ligand exchange-adsorptive cathodic
stripping voltammetry (CLE-ACSV) for iron-binding ligands. On average, 80% of the 0.1-0.65
nM dissolved iron (〈0.2 μm) was partitioned into the colloidal iron (cFe) size fraction (10 kDa 〈
cFe 〈 0.2 μm), as expected for areas of the ocean underlying a dust plume. The 1.3-2.0 nM
strong organic iron-binding ligands, however, overwhelmingly (75-77%) fell into the soluble
size fraction (〈10 kDa). As a result, modeling the dissolved iron size fractionation at equilibrium
using the observed ligand partitioning did not accurately predict the iron partitioning into
colloidal and soluble pools. This suggests that either a portion of colloidal ligands are missed by
current electrochemical methods because they react with iron more slowly than the equilibration
time of our CLE-ACSV method, or part of the observed colloidal iron is actually inorganic in
composition and thus cannot be predicted by our model of unbound iron-binding ligands. This
potentially contradicts the prevailing view that greater than 99% of dissolved iron in the ocean is
organically complexed. Untangling the chemical form of iron in the upper ocean has important
implications for surface ocean biogeochemistry and may affect iron uptake by phytoplankton.
Description:
J.N. Fitzsimmons was funded by a National
Science Foundation Graduate Research Fellowship (NSF Award #0645960). Research funding
was provided by the National Science Foundation (OCE #0926204 and OCE #0926197) and the
Center for Microbial Oceanography: Research and Education (NSF-OIA Award #EF-0424599)
to E.A. Boyle. R.M. Bundy was partially funded by NSF OCE-0550302 and NSF OCE-1233733
to K.A. Barbeau and an NSF-GK12 graduate fellowship.
Keywords:
Iron
;
Iron ligands
;
CLE-ACSV
;
Colloids
;
Ultrafiltration
;
Trace metals
;
GEOTRACES
;
North Atlantic Ocean
;
Chemical oceanography
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
Permalink
