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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.

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Marine iron cycle

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  1. 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.

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

  3. 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

  4. 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

  5. Dissolved iron (2)

  6. 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

  7. 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

  8. Particulate iron (2)

  9. 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

  10. Offshore gradients (2) • Horizontal variability: • high concentrations near shore • Low concentrations in the open ocean

  11. Offshore gradients (3)

  12. Correlation Correlation between integrated iron concentration and iron flux from the atmosphere R2 = 0,34

  13. 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

  14. Primary production (2)

  15. 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

  16. N2 fixation controls by Fe

  17. Measurements

  18. 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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