Iron isotope fractionation in a sulfide-bearing subterranean estuary and its potential influence on oceanic Fe isotope flux - INSU - Institut national des sciences de l'Univers Accéder directement au contenu
Article Dans Une Revue Chemical Geology Année : 2012

Iron isotope fractionation in a sulfide-bearing subterranean estuary and its potential influence on oceanic Fe isotope flux

Résumé

We trace pathways of Fe reactions in the Indian River Lagoon (Florida, USA) subterranean estuary using Fe isotopes to provide new constraints on Fe-isotopic fractionation in a sulfide-bearing subterranean estuary. Porewater δ 56Fe values increase from -1.16‰ at 115cm depth to +0.2‰ at 7cm depth due to isotope fractionation in three distinct lithostratigraphic zones. The deepest zone contains orange sands with elevated Fe-oxide contents (0.2wt.%) that dissolve through diagenetic Fe-oxide reduction and elevate Fe concentrations in porewaters (100 to 300μM/l). This reaction causes porewater δ 56Fe values to be ~1‰ lighter than the sediment δ 56Fe values. An intermediate zone contains white Fe-poor sands, with Fe-oxide contents <0.1wt.% and dissolved Fe concentrations <20μM/l. This zone is a sink for dissolved Fe through adsorption of isotopically heavy dissolved Fe(II) onto mineral surfaces. This adsorption results in porewater δ 56Fe values that are as much as 1.8‰ lighter than sediment δ 56Fe values. The uppermost zone contains organic carbon and Fe-sulfide rich black sediments with low dissolved Fe (<1μM/l) and elevated porewater sulfide (up to 600μM/l) concentrations. Precipitation of isotopically light Fe-sulfides increases the porewater δ 56Fe values as much as 0.68‰ more than corresponding sediment δ 56Fe values. The near-surface Fe-sulfide precipitation delivers to the lagoon dissolved Fe with slightly positive δ 56Fe values, averaging about +0.24‰, via submarine groundwater discharge (SGD). Iron-sulfide precipitation in sulfide-containing subterranean estuaries thus may result in a previously unidentified source of isotopically heavy Fe to the coastal oceans.

Dates et versions

insu-00683059 , version 1 (27-03-2012)

Identifiants

Citer

Moutusi Roy, Olivier J. Rouxel, Jonathan B. Martin, Jaye E. Cable. Iron isotope fractionation in a sulfide-bearing subterranean estuary and its potential influence on oceanic Fe isotope flux. Chemical Geology, 2012, 300-301, pp.133-142. ⟨10.1016/j.chemgeo.2012.01.022⟩. ⟨insu-00683059⟩
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