Resupply of mesopelagic dissolved iron controlled by particulate iron composition

Type Article
Date 2019-12
Language English
Author(s) Bressac M.1, 2, Guieu C.2, 3, Ellwood M. J.4, Tagliabue A.5, Wagener T.6, Laurenceau-Cornec E. C.1, Whitby Hannah7, Sarthou Geraldine9, Boyd P. W.1, 8
Affiliation(s) 1 : Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
2 : Sorbonne Université, CNRS, Laboratoire d’Océanographie de Villefranche, LOV, Villefranche-sur-Mer, France
3 : The Center for Prototype Climate Modeling, New York University in Abu Dhabi, Abu Dhabi, United Arab Emirates
4 : Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory, Australia
5 : Department of Earth Ocean and Ecological Sciences, School of Environmental Sciences, University of Liverpool, Liverpool, UK
6 : Aix Marseille Université, CNRS, IRD, Université de Toulon, MIO UM 110, Marseille, France
7 : UMR 6539/LEMAR/IUEM, CNRS, UBO, IRD, Ifremer, Technopôle Brest Iroise, Plouzané, France
8 : Antarctic Climate and Ecosystems Collaborative Research Center, University of Tasmania, Hobart, Tasmania, Australia
9 : UMR 6539/LEMAR/IUEM, CNRS, UBO, IRD, Ifremer, Technopôle Brest Iroise, Plouzané, France
Source Nature Geoscience (1752-0894) (Springer Science and Business Media LLC), 2019-12 , Vol. 12 , N. 12 , P. 995-1000
DOI 10.1038/s41561-019-0476-6
WOS© Times Cited 14
Abstract

The dissolved iron supply controls half of the oceans’ primary productivity. Resupply by the remineralization of sinking particles, and subsequent vertical mixing, largely sustains this productivity. However, our understanding of the drivers of dissolved iron resupply, and their influence on its vertical distribution across the oceans, is still limited due to sparse observations. There is a lack of empirical evidence as to what controls the subsurface iron remineralization due to difficulties in studying mesopelagic biogeochemistry. Here we present estimates of particulate transformations to dissolved iron, concurrent oxygen consumption and iron-binding ligand replenishment based on in situ mesopelagic experiments. Dissolved iron regeneration efficiencies (that is, replenishment over oxygen consumption) were 10- to 100-fold higher in low-dust subantarctic waters relative to higher-dust Mediterranean sites. Regeneration efficiencies are heavily influenced by particle composition. Their make-up dictates ligand release, controls scavenging, modulates ballasting and may lead to the differential remineralization of biogenic versus lithogenic iron. At high-dust sites, these processes together increase the iron remineralization length scale. Modelling reveals that in oceanic regions near deserts, enhanced lithogenic fluxes deepen the ferricline, which alter the vertical patterns of dissolved iron replenishment, and set its redistribution at the global scale. Such wide-ranging regeneration efficiencies drive different vertical patterns in dissolved iron replenishment across oceanic provinces.

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