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δ 56 Fe – Motivation

δ 56 Fe – Motivation . To understand processes and cycling of Fe in the ocean in a way that is not always possible with Fe concentration alone. To fingerprint the different sources of Fe and constrain their various importance, their impact on the ocean, and how Fe is cycled through the ocean.

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δ 56 Fe – Motivation

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  1. δ56Fe – Motivation To understand processes and cycling of Fe in the ocean in a way that is not always possible with Fe concentration alone. To fingerprint the different sources of Fe and constrain their various importance, their impact on the ocean, and how Fe is cycled through the ocean. GA10 Samples & Planned Work We have deep water profiles from the trace metal casts For JC068 we have stations 8, 11, 12, 13, 16, 18 and 21For D357 we have stations 3, 6, 11/4.5 and 8/0.5 No isotope measurements yet, but as soon as we have Fe concentration (hopefully complete Fe isotope measurements early next year) Tim Conway and Seth John Marine Trace Element Lab, University of South Carolina

  2. δ56Fe – What do we know? Fe sources appear to have distinctive signatures : Aerosol Dust is slightly +ve – from 0.1 to perhaps 0.5 ‰ ? Crustal Fe 0.07 ‰ (Poitrasson, 2006), rivers (-0.6 to 0.3 ‰; Radic et al., 2011) Fe(II) from reducing sediments is very –ve (as much as -3 ‰; John and Adkins) Hydrothermal complicated? Biological fractionation is currently relatively unconstrained (heavy?) δ56Fe (‰) Dust Sediments Dust Hydrothermal Venting?? Sediments Sediments Biological remineralization C.S. Ocean D.Eq. Pacifc E.North Atlantic B.San Pedro Basin A.Santa Monica Basin (John et al., 2012; Lacan et al., 2008; Radic et al, 2011; John and Adkins, 2012)

  3. Method for dissolved δ56Fe, δ114Cdand δ66Zn We have developed a new method to measure δ56Fe, δ114Cdand δ66Znsimultaneously in small volumes of seawater (1-2 L). Metals are extracted onto Nobias PA-1 chelating resin, eluted, then purified using AGMP-1 ion-exchange resin. This generates low blank, high extraction efficiency and effective purificationof each element from salts/interference (e.g. Ni, Cr). Analysis is by Neptune MC ICP-MS using a Jet interface (HR for Fe, Zn; LR for Cd). 57Fe-58Fe, 110Cd-111Cd, 64Zn-66Zn double spikes allow correction for IMB. Procedural Blank Extraction Efficiency Column Purification ng Fe Zn Fe Cd Fe Cu Zn Zn Salts Cd Cd

  4. Fe Isotopes from GA-03 (Eastern North Atlantic) [Fe] (nM) δ56Fe (‰) [Fe] (nM) δ56Fe (‰) IRMM-14 Fe IRMM-14 Fe 1 2 1 2 Depth (m) 3 St. 9 3 St. 10 Both stations exhibit similar patterns Several hypothesized features visible: 1. Dust input (+0.5-0.8 ‰) 2. Biological uptake of heavy Fe 3. Deep sedimentary input of light Fe Tim Conway and Seth John Marine Trace Element Lab, University of South Carolina

  5. Cd Isotopes from GA-03 (Eastern North Atlantic) [Cd] (pM) δ114Cd(‰) [Cd] (pM) δ114Cd(‰) NIST 3108 Cd NIST 3108 Cd 1 1 Depth (m) 2 St. 9 2 St. 10 Cd Isotope and concentration profiles reflect nutrient uptake and remineralisation: Low concentration and high δ114Cd at surface Deep water δ114Cd stable at 0.3 - 0.4 ‰ Tim Conway and Seth John Marine Trace Element Lab, University of South Carolina

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