Highly variable iron content modulates iceberg-ocean fertilisation and potential carbon export

Mark Hopwood (1) , Dustin Carroll (2, 3) , Juan Höfer (4) , Eric Achterberg (1) , Lorenz Meire (5, 6) , Frédéric A.C. Le Moigne (7) , Lennart Bach (8) , Charlotte Eich (5) , David Sutherland (9, 3) , Humberto González (3)

1 GEOMAR - Helmholtz Centre for Ocean Research [Kiel]
2 San José State University - Moss Landing Marine Laboratories [CA, USA]
3 IDEAL - Centro FONDAP de Investigación en Dinámica de Ecosistemas Marinos de Altas Latitudes
4 ECAM - Escuela de Ciencias Aplicadas del Mar
5 NIOZ - Royal Netherlands Institute for Sea Research
6 Greenland Climate Research Centre
7 MIO - Institut méditerranéen d'océanologie
8 IMAS - Institute for Marine and Antarctic Studies [Hobart]
9 University of Oregon [Eugene]

Marine phytoplankton growth at high latitudes is extensively limited by iron availability. Icebergs are a vector transporting the bioessential micronutrient iron into polar oceans. Therefore, increasing iceberg fluxes due to global warming have the potential to increase marine productivity and carbon export, creating a negative climate feedback. However, the magnitude of the iceberg iron flux, the subsequent fertilization effect and the resultant carbon export have not been quantified. Using a global analysis of iceberg samples, we reveal that iceberg iron concentrations vary over 6 orders of magnitude. Our results demonstrate that, whilst icebergs are the largest source of iron to the polar oceans, the heterogeneous iron distribution within ice moderates iron delivery to offshore waters and likely also affects the subsequent ocean iron enrichment. Future marine productivity may therefore be not only sensitive to increasing total iceberg fluxes, but also to changing iceberg properties, internal sediment distribution and melt dynamics.

Domaines: Océan, Atmosphère

Mark Hopwood, Dustin Carroll, Juan Höfer, Eric Achterberg, Lorenz Meire, et al.. Highly variable iron content modulates iceberg-ocean fertilisation and potential carbon export. Nature Communications, 2019, 10 (1), ⟨10.1038/s41467-019-13231-0⟩. ⟨hal-02960690⟩