Deepsea Hydrothermal Sediments: Ironoxides at MORs

1
Deep-sea Hydrothermal Sediments Iron-oxides at
MORs
Form by 1) oxidation of Fe2 in reduced, low
S2- vent fluids to Fe3 which precipitates as
Fe-oxide sediment 2) weathering of MOR
Fe-sulfides. Fe-oxides concentrate seawater DIP
by adsorption of PO4 onto high surface area
precipitates and by co-precipitation

A natural concentrator of dissolved PO4
Should scavenge and record seawater PO4 d18Op
2
d18Op of Phosphate Reservoirs in Hydrothermal
Systems


-PO4 in oceanic crust
-seawater PO4 -vent fluids ?
25-26
4 to 8
4-6 increasing biological turnover
24-25
3
Hydrothermal Fe-oxides Microbial filaments
sheaths


J.Alt, 1988
Blake and Coomber, 2003
9N EPR
Delta O-18 of PO4 adsorbed to Fe-Oxides has a
microbial signature and records ambient water
delta O-18 and temperature not ambient seawater
DIP (Blake et al., 2001 Blake and Coomber, 2003
Blake and Moyer, in-prep)
4
2 Catalysts for PO4-water exchange in
hydrothermal systems
enzymes
heat time
???
113-120C ?
gt400C
0
Where is the cutoff?
Hyperthermophilic microbes within and macrobiota
living on vent chimney walls should imprint a
biological delta O-18 signature in PO4. Samples
collected during R/V Atlantis Voyage 11, Leg 9
(2004) are being analyzed to address this
question.