Marine iron cycleMarine iron cycleNutrient dynamics in the deep blue sea – David M. Nutrient dynamics in the deep blue sea – David M.

KarlKarl

What controls dissolved iron concentrations in the What controls dissolved iron concentrations in the world ocean? – Kenneth S. Johnson e.a.world ocean? – Kenneth S. Johnson e.a.

A mesoscale phytoplankton bloom in the polar A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization – Southern Ocean stimulated by iron fertilization –

Philip W. Boyd e.a.Philip W. Boyd e.a.

ContentContent

HistoryHistory Iron profilesIron profiles Iron spread in oceansIron spread in oceans The role of iron in controlling The role of iron in controlling

oceanic productivityoceanic productivity MeasurementsMeasurements ConclusionsConclusions

HistoryHistory

First measuring of iron in oceansFirst measuring of iron in oceans In 1988 Martin and Fitzwater first In 1988 Martin and Fitzwater first

consider that iron is limited the primary consider that iron is limited the primary production in HNLC-areas:production in HNLC-areas: Sub artic Pacific oceanSub artic Pacific ocean Equatorial up welling zone of the Eastern Equatorial up welling zone of the Eastern

Pacific OceanPacific Ocean Ice-free Southern oceanIce-free Southern ocean

Afterwards many scientist focus their Afterwards many scientist focus their resresearchearch on the iron-cycle on the iron-cycle

Dissolved iron (1)Dissolved iron (1)

Iron profiles have uniform shapeIron profiles have uniform shape Concentrations at surface <0.2 nmol Concentrations at surface <0.2 nmol

kgkg-1-1

Average concentration:Average concentration: At surface 0.07 nmol kgAt surface 0.07 nmol kg-1-1

Below 500 m. 0.76 nmol kgBelow 500 m. 0.76 nmol kg-1-1

Total average: 0,38 nmol kgTotal average: 0,38 nmol kg-1-1 NONO inter-ocean fractionation inter-ocean fractionation

Dissolved iron (2)Dissolved iron (2)

Why nutrient like profiles?Why nutrient like profiles?

Mechanisms to maintain constant iron Mechanisms to maintain constant iron concentrations in the deep-sea:concentrations in the deep-sea:

Binding by organic ligandsBinding by organic ligands Equilibrium between dissolved and Equilibrium between dissolved and

suspended particulate ironsuspended particulate iron

Particulate iron (1)Particulate iron (1)

Concentrations are <1 nmol kgConcentrations are <1 nmol kg-1-1 Concentrations increase with Concentrations increase with

depth: in deep water depth: in deep water concentrations between 0.2 and concentrations between 0.2 and 0.8 nmol kg0.8 nmol kg-1-1

Particulate iron (2)Particulate iron (2)

Offshore gradients (1)Offshore gradients (1)

Most of the supply in ocean Most of the supply in ocean derived from wet deposition of derived from wet deposition of dust originating from continental dust originating from continental sourcessources

Aeolian supply:Aeolian supply: Seasonally phasedSeasonally phased Interannually variableInterannually variable Climate sensitiveClimate sensitive

Offshore gradients (2)Offshore gradients (2)

Horizontal variability: Horizontal variability: high concentrations near shorehigh concentrations near shore Low concentrations in the open oceanLow concentrations in the open ocean

Offshore gradients (3)Offshore gradients (3)

CorrelationCorrelation

Correlation Correlation between between

integrated iron integrated iron concentration concentration and iron flux and iron flux

from the from the atmosphere atmosphere

RR22 = 0,34 = 0,34

Primary production (1)Primary production (1)

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

Usable energyUsable energy Life’s essential building blocksLife’s essential building blocks Essential major elements: C, N and PEssential major elements: C, N and P Essential minor elements: Fe and ZnEssential minor elements: Fe and Zn And for many marine organisms: And for many marine organisms:

essential trace organics such as B-essential trace organics such as B-complex vitaminscomplex vitamins

Primary production (2)Primary production (2)

NN22 fixing fixing

Fe is extremely insoluble in Fe is extremely insoluble in oxygenated seawater, so the bio oxygenated seawater, so the bio availability of Fe is controlled by availability of Fe is controlled by presence of organic ligands that presence of organic ligands that enhance Fe solubilityenhance Fe solubility

NN22 fixing micro-organisms needs Fe fixing micro-organisms needs Fe for Nfor N22 reduction reduction

NN22 fixation continuous until, for fixation continuous until, for example, Fe limits further growthexample, Fe limits further growth

NN22 fixation controls by Fe fixation controls by Fe

MeasurementsMeasurements

ConclusionsConclusions

Although Fe is a minor nutrient it is Although Fe is a minor nutrient it is an important nutrient in the an important nutrient in the primary production processprimary production process

Fe plays an important role by NFe plays an important role by N22 fixingfixing

There still a lot research to do There still a lot research to do