Iron : Chemistry, sources and sinks.

Iron is the limiting factor in the surface water of S.O. HNLC conditions

« Iron hypothesis » (Martin et al. 1990)

(Petit et al. 1990)

Enhanced iron supply during glacial time increase in productivity

This explains drawdown of atmospheric CO2 during glacial times.

Phytoplankton in the Antarctic deplete silicic acid Si(OH)4 to a far greater extent than they do nitrate NO3-.

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Nitr

ate

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Sili

cic

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)

a

PF WICPOOZ SIZPFZ

A17 A15 A12

(Pondaven et al. 2002)

This pattern can be reverse by the addition of iron which dramatically lower Si(OH)4:NO3- uptake ratios.

Higher iron supply during glacial time would thus drive the Antarctic toward NO3- depletion with

excess Si(OH)4 remaining in surface waters.

A switch from Si(OH)4 to NO3- depletion

in the glacial Southern Ocean

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ter m

ixin

gUpw

ellin

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ffusio

nAtm

osph

eric

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« New Iron » in present Southern Ocean:

Open ocean Kerguelen plateau

? ? ? ?

Continental margins are an important source of iron:

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Chlorophyll (mg m-3)

Southern Ocean :

Blain et al. 2000

St 28

St 19

St 27

Atlantic ocean

Laes et al. GRL (2003).

70 75 80 85 90 95 100 105 110 115 120 125 130 135 140-1000

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Distance km

Dep

th m

Fe(III) ’Fe(OH)2

+

Fe(OH)3

Fe(OH)4-

0.1 nm 1 nm 10 nm 0.1 µm 1 µm 10 µm 100 µm

Soluble Fe

Dissolved Fe

Colloidal Fe Particulate Fe

Particulate Fe

Fe Humic

Fe Colloid

Fe(II) ’Fe2+

FeCO3

Alumino-silicate clays

intracellular and

extracellular

Detritus

FeL

Iron distribution and speciation : 3 size fractions + Fe(II)/fe(III)+ ligands

Iron chemistry :

IRON TEAM:

• Water Column : international team. LEMAR, LOB, NIOZ and ARC

• long experience in iron work • have already work together at sea• SAFE cruise in October 2004.

•On the Marion Dufresne:

•sampling and onboard analysis.•To collect samples for other trace metal determination•To provide clean seawater for OBEX

• Sediment : LGE and LSCE

• Atmosphere : LOV and LISA

To determine the particles abundance of the area

To determine the size distribution in order to attempt a IRON FLUX calculation.

To determine the mineralogical composition.

To determine some geochemical tracers (Al, Pb, …) and elements of biogeochemical interest such as Fe and P.

To quantify dissolved iron originating from these particles in the surface seawater

IRON TEAM:

Front tower

Small front tower

Meteo-platform

the front tower seems the most appropriate place: feasibility?

But more sophisticated