Beyond the Black Sea paradigm: The sedimentary fingerprint of an open-marine iron shuttle.

Scholz, Florian, Severmann, Silke, McManus, James and Hensen, Christian (2014) Beyond the Black Sea paradigm: The sedimentary fingerprint of an open-marine iron shuttle. Geochimica et Cosmochimica Acta, 127 . pp. 368-380. DOI 10.1016/j.gca.2013.11.041.

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Abstract

We present iron (Fe) concentration and Fe isotope data for a sediment core transect across the Peru upwelling area, which hosts one of the ocean’s most pronounced oxygen minimum zones (OMZs). The lateral progression of total Fe to aluminum ratios (FeT/Al) across the continental margin indicates that sediments within the OMZ are depleted in Fe whereas sediments below the OMZ are enriched in Fe relative to the lithogenic background. Rates of Fe loss within the OMZ, as inferred from FeT/Al ratios and sedimentation rates, are in agreement with benthic flux data that were calculated from pore water concentration gradients. The mass of Fe lost from sediments within the OMZ is within the same order of magnitude as the mass of Fe accumulating below the OMZ. Taken together, our data are in agreement with a shuttle scenario where Fe is reductively remobilized from sediments within the OMZ, laterally transported within the anoxic water column and re-precipitated within the more oxic water below the OMZ. Sediments within the OMZ have increased 56Fe/54Fe isotope ratios relative to the lithogenic background, which is consistent with the general notion of benthic release of dissolved Fe with a relatively low 56Fe/54Fe isotope ratio. The Fe isotope ratios increase across the margin and the highest values coincide with the greatest Fe enrichment in sediments below the OMZ. The apparent mismatch in isotope composition between the Fe that is released within the OMZ and Fe that is re-precipitated below the OMZ implies that only a fraction of the sediment-derived Fe is retained near-shore whereas another fraction is transported further offshore. We suggest that a similar open-marine shuttle is likely to operate along many ocean margins. The observed sedimentary fingerprint of the open-marine Fe shuttle differs from a related transport mechanism in isolated euxinic basins (e.g., the Black Sea) where the laterally supplied, reactive Fe is quantitatively captured within the basin sediments. We suggest that our findings are useful to identify OMZ-type Fe cycling in the geological record.

Document Type: Article
Funder compliance: info:eu-repo/grantAgreement/EC/FP7/300648
Additional Information: WOS:000329842900022
Keywords: Iron concentration, FE isotope data, Peru upwelling area, OMZ
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 754 > B5
OceanRep > SFB 754
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.gca.2013.11.041
ISSN: 0016-7037
Projects: SFB754, BICYCLE
Expeditions/Models/Experiments:
Date Deposited: 22 Jan 2014 08:37
Last Modified: 19 Jun 2017 11:43
URI: http://oceanrep.geomar.de/id/eprint/23110

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