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. Content.

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Marine iron cycle

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Marine iron cycle

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.


Content

Content

  • History

  • Iron profiles

  • Iron spread in oceans

  • The role of iron in controlling oceanic productivity

  • Measurements

  • Conclusions


History

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


Dissolved iron 1

Dissolved iron (1)

  • Iron profiles have uniform shape

  • Concentrations at surface <0.2 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


Dissolved iron 2

Dissolved iron (2)


Why nutrient like profiles

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


Particulate iron 1

Particulate iron (1)

  • Concentrations are <1 nmol kg-1

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


Particulate iron 2

Particulate iron (2)


Offshore gradients 1

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


Offshore gradients 2

Offshore gradients (2)

  • Horizontal variability:

    • high concentrations near shore

    • Low concentrations in the open ocean


Offshore gradients 3

Offshore gradients (3)


Correlation

Correlation

Correlation between integrated iron concentration and iron flux from the atmosphere

R2 = 0,34


Primary production 1

Primary production (1)

Production of organic matter is sustained by a continuous supply of:

  • Usable energy

  • Life’s 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


Primary production 2

Primary production (2)


N 2 fixing

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


N 2 fixation controls by fe

N2 fixation controls by Fe


Measurements

Measurements


Conclusions

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


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