Icebergs; a huge but highly variable source of iron to the ocean

Icebergs have been speculated to constitute one of the largest fluxes of iron (Fe) into the polar oceans since the 1930s and thus recent increases in ice discharge around the world could potentially change Fe availability in the ocean. But how much Fe is in an iceberg? As part of an international collaboration involving several cruises over the past 5 years including the GEOTRACES Fram Strait GN05 section Hopwood et al., (2019, see reference below) report the concentrations of Fe in ice from over 10 glaciated regions around the world. The global mean iceberg Fe content is found to be similar to, or slightly higher than, limited earlier estimates. However, a critical insight is the highly uneven distribution of this Fe with the ‘dirtiest’ 4% of samples collected accounting for over 90% of the cumulative Fe. Investigating how these ‘dirty’ layers are formed and their fate in the ocean is therefore essential to determining the significance of icebergs for marine primary production.

19 Hopwood

Figure: Ice from around the world is found to have a highly variable total dissolvable Fe content ranging from 2 nM to 2 mM.


Mark J. Hopwood, Dustin Carroll, Juan Höfer, Eric P. Achterberg, Lorenz Meire, Frédéric A. C. Le Moigne, Lennart T. Bach, Charlotte Eich, David A. Sutherland & Humberto E. González, (2019) High variability is evident even within individual geographic regions. Reference: Highly variable iron content modulates iceberg-ocean fertilisation and potential carbon export, Nature Communications, 10, 5261 DOI:

Latest highlights

Science Highlights

Deep sea lithogenic weathering a source of iron colloids for the ocean

Homoky and co-workers determined the isotope composition of dissolved iron profiles in shallow surface sediments of the South Atlantic Uruguayan margin…


Science Highlights

Adding external sources allow a better simulation of the oceanic rare earth elements cycles

Oka and colleagues demonstrate that the global distribution of REE can be reproduced by considering the internal cycle associated with reversible scavenging and external REEs inputs around continental regions.


Science Highlights

First direct measurements of luxury iron uptake in natural phytoplankton communities: surprising results!

This study demonstrates the importance of biology and ecology to understanding iron biogeochemistry.


Science Highlights

Air-sea gas disequilibrium drove deoxygenation of the deep ice-age ocean

This study provides one of the first mechanistic explanations for Last Glacial Maximum deep ocean deoxygenation.