Marine iron cycle

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Marine iron cycle

• Nutrient dynamics in the deep blue sea David M.
  Karl
• What controls dissolved iron concentrations in
  the world ocean? Kenneth S. Johnson e.a.
• A mesoscale phytoplankton bloom in the polar
  Southern Ocean stimulated by iron fertilization
  Philip W. Boyd e.a.

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Content

• History
• Iron profiles
• Iron spread in oceans
• The role of iron in controlling oceanic
  productivity
• Measurements
• Conclusions

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History

• First measuring of iron in oceans
• In 1988 Martin and Fitzwater first consider that
  iron is limited the primary production in
  HNLC-areas
• Sub artic Pacific ocean
• Equatorial up welling zone of the Eastern Pacific
  Ocean
• Ice-free Southern ocean
• Afterwards many scientist focus their research on
  the iron-cycle

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Dissolved iron (1)

• Iron profiles have uniform shape
• Concentrations at surface lt0.2 nmol kg-1
• Average concentration
• At surface 0.07 nmol kg-1
• Below 500 m. 0.76 nmol kg-1
• Total average 0,38 nmol kg-1
• NO inter-ocean fractionation

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Dissolved iron (2)
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Why nutrient like profiles?

• Mechanisms to maintain constant iron
  concentrations in the deep-sea
• Binding by organic ligands
• Equilibrium between dissolved and suspended
  particulate iron

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Particulate iron (1)

• Concentrations are lt1 nmol kg-1
• Concentrations increase with depth in deep water
  concentrations between 0.2 and 0.8 nmol kg-1

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Particulate iron (2)
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Offshore gradients (1)

• Most of the supply in ocean derived from wet
  deposition of dust originating from continental
  sources
• Aeolian supply
• Seasonally phased
• Interannually variable
• Climate sensitive

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Offshore gradients (2)

• Horizontal variability
• high concentrations near shore
• Low concentrations in the open ocean

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Offshore gradients (3)
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Correlation
Correlation between integrated iron concentration
and iron flux from the atmosphere R2 0,34
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Primary production (1)

• Production of organic matter is sustained by a
  continuous supply of
• Usable energy
• Lifes essential building blocks
• Essential major elements C, N and P
• Essential minor elements Fe and Zn
• And for many marine organisms essential trace
  organics such as B-complex vitamins

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Primary production (2)
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N2 fixing

• Fe is extremely insoluble in oxygenated seawater,
  so the bio availability of Fe is controlled by
  presence of organic ligands that enhance Fe
  solubility
• N2 fixing micro-organisms needs Fe for N2
  reduction
• N2 fixation continuous until, for example, Fe
  limits further growth

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N2 fixation controls by Fe
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Measurements
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Conclusions

• Although Fe is a minor nutrient it is an
  important nutrient in the primary production
  process
• Fe plays an important role by N2 fixing
• There still a lot research to do