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Iron : Chemistry, sources and sinks.

Iron : Chemistry, sources and sinks. « Iron hypothesis ». (Martin et al. 1990). (Petit et al. 1990). Iron is the limiting factor in the surface water of S.O.  HNLC conditions. Enhanced iron supply during glacial time  increase in productivity.

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Iron : Chemistry, sources and sinks.

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  1. Iron : Chemistry, sources and sinks.

  2. « Iron hypothesis » (Martin et al. 1990) (Petit et al. 1990) • Iron is the limiting factor in the surface water of S.O.  HNLC conditions • Enhanced iron supply during glacial time  increase in productivity • This explains drawdown of atmospheric CO2 during glacial times.

  3. A switch from Si(OH)4 to NO3- depletion in the glacial Southern Ocean (Pondaven et al. 2002) • Phytoplankton in the Antarctic deplete silicic acid Si(OH)4 to a far greater extent than they do nitrate NO3-. • 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.

  4. Upwelling Winter mixing Atmospheric Vertical diffusion « New Iron » in present Southern Ocean: ? ? ? ? Kerguelen plateau Open ocean

  5. St 19 St 27 St 28 Atlantic ocean Laes et al. GRL (2003). Chlorophyll (mg m-3) Continental margins are an important source of iron: Southern Ocean : Blain et al. 2000

  6. Iron chemistry : • Iron distribution and speciation : 3 size fractions + Fe(II)/fe(III)+ ligands 0.1 nm 1 nm 10 nm 0.1 µm 1 µm 10 µm 100 µm Colloidal Fe Soluble Fe Particulate Fe Dissolved Fe Particulate Fe Fe(III) ’ Fe(OH)2+ Fe(OH)3 Fe(OH)4- Fe Humic Fe Colloid Alumino-silicate clays intracellular and extracellular Detritus FeL Fe(II) ’ Fe2+ FeCO3

  7. Sediment : LGE and LSCE 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

  8. IRON TEAM: • 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

  9. But more sophisticated the front tower seems the most appropriate place: feasibility? Front tower Meteo-platform Small front tower

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