Download Marine nutrient cycles IV: Iron

Railsback's Some Fundamentals of Mineralogy and Geochemistry
Marine nutrient cycles IV: Iron
Wind-borne particulate flux of Fe3+
Riverine
particulate
& colloidal
flux of Fe3+
Oxidation in
weathering
Long-term
geologic
cycling with
vast geologic
reservoir
of iron
Particulate and
sorbed Fe3+
Vast
majority
of oceanic
iron takes
this route
and is irrelevant to
biological
processes
Photochemical Dissolved
reduction
Fe2+
by siderophores
Phyto(Fe-binding
plankton
ligands) produced
by bacteria
Re-oxidation
Legend:
Oxidized Fe (Fe3+)
Reduced Fe (Fe2+)
Sources: Barbeau (2006) etc.
This is one of a series of
pages presenting simple
schematic cycles of
nutrients in the oceans.
The other pages are
concerned with nitrogen,
phosphorous, and silicon.
Critical thoughts:
Fe is useful to photosynthesizers only as Fe2+,
which is very scarce in the ocean.
Fe3+ is insoluble and settles readily in or on solids.
The wind-borne flux of Fe is enhanced by barren
land areas (e.g., deserts and peri-glacial
environments) susceptible to erosion by wind.
Differences from other cycles:
Unlike N, P, and Si, Fe is not recycled at depth and
so is not resupplied to surface waters by upwelling.
Reduction, rather than oxidation, is required to
make Fe available to photosynthesizers.
Recycling of Fe from organisms is trivial compared
to oceanic content of Fe. LBR SFMGNutrientCycles06 3/2009