1. Nutrient dynamics in the deep blue sea – David M. Karl
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 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