Publication Date:
2021-10-01
Description:
Dissolved lignin phenols, chromophoric dissolved organic matter (DOM), and in situ fluorescence were determined
in waters of the Laptev Sea and major Arctic basins, and they were compared with dissolved iron (dFe)
distributions to elucidate the sources, molecular characteristics and distributions of iron-binding ligands in the
Arctic Ocean. In the Transpolar Drift region (TPD), concentrations of dFe were positively correlated with concentrations
of lignin phenols and multiple optical proxies of DOM composition and source. Strong relationships
between dFe and visible and ultraviolet wavelength fluorescent DOM indicated that vascular plant and algalderived
DOM contributed to the dFe-ligand pool. These observations are consistent with previous studies suggesting
the association of dFe with humic terrigenous and marine organic ligands. The primary sources of ironbinding
ligands appear to be the riverine discharge of terrigenous DOM, marine organic matter produced on the
shelves, and degradation products of plankton-derived organic matter in the shelf sediments. A stronger relationship
between dFe and visible wavelength CDOM fluorescence than with lignin phenols suggested the presence
of multiple terrigenous ligands, such as aromatic tannins. The aromatic nature of these terrigenous ligands
was indicated by a strong relationship between dFe and the absorption coefficient at 254 nm. A strong negative
correlation between the p-hydroxyl to vanillyl lignin phenols ratio and dissolved iron concentrations indicated
recently-discharged terrigenous DOM (tDOM) was an important source of iron-binding ligands. Given the strong
relationships of marine and terrigenous DOM with dissolved iron, iron-binding functional groups appear to occur
in diverse molecules of multiple sources. Examples of such iron-binding functional groups included catechols and
carboxylates found in lignins and tannins of terrigenous origins and carboxyl-rich alicyclic molecules (CRAM) of
terrigenous and marine origins. The observed dFe distributions in the Arctic Ocean could not be explained by the
presence of a single ligand type, but rather by a potpourri of ligand molecules of varying concentrations and
binding strengths. This molecular diversity of ligands and associated binding strengths ultimately controls the
distribution and transport of dFe in the Arctic Ocean and beyond.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
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isiRev
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