Constraints on the Cycling of Iron Isotopes From a Global Ocean Model

Konig, D, Conway, TM, Ellwood, MJ, Homoky, WB and Tagliabue, A ORCID: 0000-0002-3572-3634 (2021) Constraints on the Cycling of Iron Isotopes From a Global Ocean Model GLOBAL BIOGEOCHEMICAL CYCLES, 35 (9). e2021GB006968-. ISSN 0886-6236, 1944-9224

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Abstract

Although iron (Fe) is a key regulator of primary production over much of the ocean, many components of the marine iron cycle are poorly constrained, which undermines our understanding of climate change impacts. In recent years, a growing number of studies (often part of GEOTRACES) have used Fe isotopic signatures (δ⁵⁶Fe) to disentangle different aspects of the marine Fe cycle. Characteristic δ⁵⁶Fe endmembers of external sources and assumed isotopic fractionation during biological Fe uptake or recycling have been used to estimate relative source contributions and investigate internal transformations, respectively. However, different external sources and fractionation processes often overlap and act simultaneously, complicating the interpretation of oceanic Fe isotope observations. Here we investigate the driving forces behind the marine dissolved Fe isotopic signature (δ⁵⁶Fe<inf>diss</inf>) distribution by incorporating Fe isotopes into the global ocean biogeochemical model PISCES. We find that distinct external source endmembers acting alongside fractionation during organic complexation and phytoplankton uptake are required to reproduce δ⁵⁶Fe<inf>diss</inf> observations along GEOTRACES transects. δ⁵⁶Fe<inf>diss</inf> distributions through the water column result from regional imbalances of remineralization and abiotic removal processes. They modify δ⁵⁶Fe<inf>diss</inf> directly and transfer surface ocean signals to the interior with opposing effects. Although attributing crustal compositions to sedimentary Fe sources in regions with low organic carbon fluxes improves our isotope model, δ⁵⁶Fe<inf>diss</inf> signals from hydrothermal or sediment sources cannot be reproduced accurately by simply adjusting δ⁵⁶Fe endmember values. This highlights that additional processes must govern the exchange and/or speciation of Fe supplied by these sources to the ocean.

Item Type:	Article
Uncontrolled Keywords:	biogeochemistry, iron isotopes, ocean, model
Divisions:	Faculty of Science & Engineering > School of Environmental Sciences
Depositing User:	Symplectic Admin
Date Deposited:	20 Dec 2021 16:20
Last Modified:	16 Jun 2026 10:48
DOI:	10.1029/2021GB006968
Open Access URL:	https://agupubs.onlinelibrary.wiley.com/doi/10.102...
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3145709
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