Natural Fe-binding organic ligands in Fram Strait and over the Northeast Greenland shelf.

Ardiningsih, Indah, Krisch, Stephan , Lodeiro, Pablo , Reichart, Gert-Jan, Achterberg, Eric P. , Gledhill, Martha , Middag, Rob and Gerringa, Loes J.A. (2020) Natural Fe-binding organic ligands in Fram Strait and over the Northeast Greenland shelf. Marine Chemistry, 224 (Article number 103815). DOI 10.1016/j.marchem.2020.103815.

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Abstract

Highlights

• Fe-binding ligands associated with primary productivity together with ligands from the Arctic Ocean are the main sources of Fe-binding ligands in surface waters of Fram Strait.
• Fe-binding ligands are present in a high concentrations in front of the glacier terminus, but the ligands have a relatively low binding capacity, thus less reactive.
• Low binding strength coupled with low competing strength of ligands result in a higher inorganic Fe concentration, causing Fe to precipitate or scavenged.

Abstract

There is a paucity of data on Fe-binding ligands in the Arctic Ocean. Here we investigate the distribution and chemical properties of natural Fe-binding ligands in Fram Strait and over the northeast Greenland shelf, shedding light on their potential sources and transport. Our results indicate that the main sources of organic ligands to surface waters of Fram Strait included primary productivity and supply from the Arctic Ocean. We calculated the mean total Fe-binding ligand concentration, [Lt], in Polar Surface Water from the western Fram Strait to be 1.65 ± 0.4 nM eq. Fe. This value is in between reported values for the Arctic and North Atlantic Oceans, confirming reports of north to south decreases in [Lt] from the Arctic Ocean. The differences between ligand sources in different biogeochemical provinces, resulted in distinctive ligand properties and distributions that are reflected in [Lt], binding strength (log KFe'L′) and competing strength (log αFe'L) of ligands. Higher [Lt] was present near the Nioghalvfjerdsfjorden (79 N) Glacier terminus and in the Westwind Trough (median of [Lt] = 2.17 nM eq. Fe; log KFe'L′ = 12.3; log αFe'L = 3.4) than in the Norske Trough (median of [Lt] = 1.89 nM eq. Fe; log KFe'L′= 12.8; log αFe'L = 3.8) and in Fram Strait (median of [Lt] = 1.38 nM eq. Fe; log KFe'L′ = 13; log αFe'L= 3.9). However, organic ligands near the 79 N Glacier terminus and in the Westwind Trough were weaker, and therefore less reactive than organic ligands in the Norske Trough and in Fram Strait. Our findings reveal the fundamental mechanism that underpin transport of dissolved-Fe (DFe) from the 79 N Glacier to Fram Strait, less reactive ligands will reduce Fe solubility. Accordingly, a portion of the glacial DFe will not be transported over the shelf into the ocean. The lower ligand binding strength in the outflow results in a higher inorganic Fe concentration, [Fe´], which is more prone to precipitation and/or scavenging than Fe complexed with stronger ligands. Ongoing changes in the Arctic and sub-Arctic Oceans will influence both terrestrially derived and in-situ produced Fe-binding ligands, and therefore will have consequences for Fe solubility and availability to microbial populations and Fe cycling in Fram Strait.

Document Type: Article
Keywords: Fe-binding ligands, Iron speciation, Fram Strait, PS100, RV Polarstern
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
NIOZ
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.marchem.2020.103815
ISSN: 0304-4203
Projects: GEOTRACES
Date Deposited: 04 May 2020 10:52
Last Modified: 09 Jul 2020 12:02
URI: http://oceanrep.geomar.de/id/eprint/49596

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