δ56Fe – Motivation

GA10 Samples & Planned WorkWe 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)

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.

Tim Conway and Seth JohnMarine Trace Element Lab,

University of South Carolina

δ56Fe – What do we know?

0 0.5 10

1000

2000

3000

4000

5000

56 (‰)d Fe-4 -3 -2 -1 0 1

0

200

400

600

δ56Fe (‰)

Dep

th (m

)

-2 -1.5 -1 -0.5 0 0.5 10

200

400

600

800

1000

0 0.5 10

100

200

300

400

500

600

700

800

900

56 (‰)d Fe0 0.5 1

0

1000

2000

3000

4000

5000

56 d Fe(‰)

A. Santa Monica Basin E. North AtlanticD. Eq. PacifcC. S. OceanB. San Pedro Basin

SedimentsSediments

HydrothermalVenting??

DustSediments

Biologicalremineralization

Dust

(John et al., 2012; Lacan et al., 2008; Radic et al, 2011; John and Adkins, 2012)

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 (‰)

Method for dissolved δ56Fe, δ114Cd and δ66Zn We have developed a new method to measure δ56Fe, δ114Cd and δ66Zn simultaneously 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 purification of 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.

0%

20%

40%

60%

80%

100%

0

0.5

1

Fe Zn Cd Fe Zn Cd

Procedural Blank Extraction Efficiency Column Purification

CdFeSalts ZnCu

ng

Fe Isotopes from GA-03 (Eastern North Atlantic)

0.20.40.60.8 1 1.21.41.61.8 20

500

1000

1500

2000

2500

3000

3500

-1 -0.5 0 0.5 1

[Fe] (nM) δ56Fe (‰)

Dep

th (m

)

0 0.5 1 1.5 20

500

1000

1500

2000

2500

3000

-1 -0.5 0 0.5 1

[Fe] (nM) δ56Fe (‰)

Both stations exhibit similar patterns

IRMM-14 Fe

St. 9St. 10

Tim Conway and Seth JohnMarine Trace Element Lab,

University of South Carolina

Several hypothesized features visible:1. Dust input (+0.5-0.8 ‰) 2. Biological uptake of heavy Fe3. Deep sedimentary input of light Fe

12

3

3

2 1

IRMM-14 Fe

Tim Conway and Seth JohnMarine Trace Element Lab,

University of South Carolina

Cd Isotope and concentration profiles reflect nutrient uptake and remineralisation : 1. Low concentration and high δ114Cd at surface2. Deep water δ114Cd stable at 0.3 - 0.4 ‰

0 300 6000

500

1000

1500

2000

2500

3000

3500

0 1 2 3 4 5 6

NIST 3108 Cd[Cd] (pM) δ114Cd (‰)

0 300 6000

500

1000

1500

2000

2500

3000

[Cd] (pM) δ114Cd (‰)

0 1 2 3 4 5 6NIST 3108 Cd

St. 9

St. 10

Dep

th (m

)Cd Isotopes from GA-03 (Eastern North Atlantic)

1 1

2

2