Iron geochemistry of SEEDSIron geochemistry of SEEDS--I, I, --II and SERIESII and SERIES

S. Takeda1, J. Nishioka2, C.S. Wong3, W.K. Johnson3, M. Kinugasa4, Y. Kondo1, K. Kuma5, S. Nakatsuka4, H. Obata6, E. Roy7, M. Sato1,

N. Sutherland3, Y. Sohrin4, H. Takata5, H. Tani5, A. Tsuda6, M. L. Wells7

1 Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan.2 Institute of Low Temperature Science, Hokkaido University, Japan

3 Climate Chemistry Laboratory, Institute of Ocean Sciences, Canada4 Institute for Chemical Research, Kyoto University, Japan

5 Graduate School of Fisheries Sciences, Hokkaido University, Japan6 Ocean research Institute, University of Tokyo, Japan

7 School of Marine Sciences, University of Maine, U.S.A

Simplified diagram of iron cycling in the surface oceanSimplified diagram of iron cycling in the surface ocean

Physical processesAtmospheric

flux

Upwelling & Diffusive

FluxesSedimentation

Dissolved Fe

Colloidal Fe

Particulat Fe (Inorganic)

(detrial)

Holizontaldispersion

Adsorption/Aggregation

Mixing

Simplified diagram of iron cycling in the surface oceanSimplified diagram of iron cycling in the surface ocean

Fe (II)

Complexed Fe

Oxidation

Upwelling & Diffusive

Fluxes

PhotoreductionComplexation

Sedimentation

Fe (III) Colloidal Fe

Particulat Fe (Inorganic)

(detrial)

Holizontaldispersion

Chemical processes

Atmospheric flux

Precipitation/Dissolution

Dissolved

Simplified diagram of iron cycling in the surface oceanSimplified diagram of iron cycling in the surface ocean

Dissolved Fe(II)

Complexed Fe

Oxidation

Upwelling & Diffusive

Fluxes

Photoreduction

Sedimentation

Dissolved Fe(III)

Colloidal Fe

Particulat Fe (Inorganic)

(detrial)

Holizontaldispersion

Zooplankton

Sedimentation MigrationSedimentation

Dissolved

Atmospheric flux

Biological processes

Phytoplankton

ExcretionDigestionUptake

ReductionAdsorption

Release

Simplified diagram of iron cycling in the surface oceanSimplified diagram of iron cycling in the surface ocean

Dissolved Fe(II)

Complexed Fe

Oxidation

Upwelling & Diffusive

Fluxes

Photoreduction

Sedimentation

Dissolved Fe(III)

Colloidal Fe

Particulat Fe (Inorganic)

(detrial)

Holizontaldispersion

Zooplankton

Sedimentation MigrationSedimentation

Dissolved

Atmospheric flux

Iron enrichment

Phytoplankton

ExcretionDigestionUptake

ReductionAdsorption

Release

FeSO4Infusions

Eddy diffusion

flux

Simplified diagram of iron cycling in the surface oceanSimplified diagram of iron cycling in the surface ocean

Dissolved Fe(II)

Complexed Fe

Oxidation

Upwelling & Diffusive

Fluxes

Photoreduction

Sedimentation

Dissolved Fe(III)

Colloidal Fe

Particulat Fe (Inorganic)

(detrial)

Holizontaldispersion

Zooplankton

Sedimentation MigrationSedimentation

Dissolved

Atmospheric flux

Iron enrichment

Phytoplankton

ExcretionDigestionUptake

ReductionAdsorption

Release

FeSO4Infusions

Eddy diffusion

flux

What have we learned from What have we learned from SEEDSSEEDS--I, SERIES and SEEDSI, SERIES and SEEDS--II?II?

Sampling methodsSampling methods

SEEDSSEEDS--II SERIESSERIES SEEDSSEEDS--IIII

Discrete vertical samplingDiscrete vertical sampling10-L X-Niskin; Kevlar line ● ● ●

12-L X-Niskin; CTD-Carousel; ●Titanium wire

30-L/12-L Go-Flo, Kevlar line ●

Teflon pump/tubing ●

Underway samplingUnderway samplingTowed fish; Teflon pump/tubing ● ● ●

Surface samplingSurface samplingZodiac rubber inflatable raft ● ●

What did we measure?What did we measure?SEEDSSEEDS--II SERIESSERIES SEEDSSEEDS--IIII

Fe (III) Fe (III) Unfiltered pH 3.2 FIA-CL ● ● ●pH 2.2 ICP-MS ●pH 1.7 FIA-CL ●pH 1.7 Microwave, FIA-CL ●

Filtered (0.22 µm, Durapore)pH 3.2 FIA-CL ● ● ●pH 1.7 FIA-CL ●pH 1.7 Microwave, FIA-CL ●

Filtered (0.2 µm, Nuclepore)pH 2.2 ICP-MS ●

Filtered (0.03 µm, Sterapore)pH 3.2 FIA-CL ●

Filtered (200kDa, Sterapore) pH 3.2 FIA-CL ● ●pH 1.7 FIA-CL ●

Shipboard interShipboard inter--comparison study for Fe at comparison study for Fe at OSP between CRIEPI and IOSOSP between CRIEPI and IOS

(Tully Sep. 2002 cruise)

Dissolved Fe

-1000

-800

-600

-400

-200

00 0.2 0.4 0.6

Fe conc. (nM)

Dep

th (m

)

CRIEPIIOS

Total Fe

-1000

-800

-600

-400

-200

00 0.2 0.4 0.6

Fe conc. (nM)

Dep

th (m

)

CRIEPIIOS

y = 1.0153x - 0.0112

R2 = 0.9752

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.2 0.4 0.6

C RIEPI Fe conc. (nM )

IOS Fe conc. (nM

Comparison between CRIEPI and IOS

Vertical distribution of dissolved and total Fe at OSP

(J. Nishioka, unpublished data)

SEEDSSEEDS--II SERIESSERIES SEEDSSEEDS--IIII

Fe (II) Fe (II) FIA-CL ●

Fe(III)Fe(III)--complexingcomplexing organic organic ligandsligandsFiltered (0.22 µm), CLE-ACSV ● ● ●Filtered (200kDa), CLE-ACSV ●

Fe solubilityFe solubilityFiltered (0.22 µm) 59Fe solubility ● ● ●

Particulate FeParticulate FeFiltered (10 & 0.2 µm) Oxalate, GFAAS ●

What did we measure?What did we measure?

Initial conditionsInitial conditionsVertical distribution of size-fractionated iron in the western and the eastern subarctic North Pacific

(Nishioka et al., 2004)

St. KNOT (May 2000) St. P (Sep. 1998)

Iron levels in the dissolved (soluble and colloidal) fraction in the surface mixed layer in the western region was as low as levels in the eastern region.

Labile (pH 3.2) particulate iron was significantly higher in the surface mixed layer in the western region.

Vertical profiles of acid dissolvable (16–20 months at pH 2.2) and dissolved Fe on days 2 and 11 at Out-patch stations during SEEDS-I.

High concentrations of acidHigh concentrations of acid--dissolvable particulate iron dissolvable particulate iron in the western subarctic North Pacificin the western subarctic North Pacific

(Kinugasa et al., 2005)Day 2 Day 11

Total Fe (microwave, pH 1.7) at St. P was <0.5 nM (Wong et al., 2006)

How much iron was added?How much iron was added?- Difference between target and measured Fe concentrations -

FeSOFeSO44..7H7H22OO AreaArea Fe releaseFe release MLDMLD Dissolved Fe increaseDissolved Fe increase

Theoretical Measured(mol) (km2) (µmol m-2) (m) (nM) (nM) .

SEEDSSEEDS--II6260 80 78 10 7.8 2.9±1.4

SERIESSERIES1st 7300-6900 77 90-95 10 9.0 2.8±0.32nd 1960 92 21 20 1.0 +0.2

SEEDSSEEDS--II II 1st 5750 64 90 30 3.0 1.42nd 2840 200 14 30 0.5 +0.4

Size-fractionated iron concentrations in surface mixed layer and at 5 m depth (underway)

SEEDSSEEDS--II

0

1

2

3

4

5

0 2 4 6 8 10 12 14

Fe

(nM

)

<0.22 μm (underway)

<0.22 μm

Unfiltered

<200kDa (Soluble)

Ks for Diatoms0.95 nM(Noiri et al., 2005)

SERIESSERIESIRON 10 m Time Series

4.50

2nd Fe addition

KAIYO-MARU period

J.P TULLY period

Total labile Fe

Dissolved FeSoluble Fe

< 200kDa < 0.22µm UF

< 0.03µm < 0.22µm UFTully

Kaiyo4.00

3.50

3.00

Fe (

nM)

2.50

2.00

Ks for Diatoms0.95 nM(Noiri et al., 2005)

1.50

1.00

0.50

0.0010-Jul 15-Jul 20-Jul 25-Jul 30-Jul 4-Aug 9-Aug

SEEDSSEEDS--IIIIIRON 5 m Time Series

SEEDSII Fe (5 m)

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25 30 35

Days since beginning of experiment

Fe c

onc. (n

M)

IN Dissolved Fe (< 0.22mm)

IN Total labile Fe

Fe addition

(<0.22µm)

Ks for Diatoms0.95 nM(Noiri et al., 2005)

HalfHalf--life (tlife (t1/21/2) of dissolved Fe) of dissolved Fe

t1/2 = ln(1/2)/k where k = ln(Ct/Ct0)/(t-t0)

SEEDS-I 43-69 hSERIES (1st) 19-69 hSEEDS-II (1st) <26 h*

(2nd) 61 h*

IronEx-I 28-40 hSOIREE 1st 14-34 h

(Gordon et al., 1998)

(Bowie et al., 2001)

(Tsumune et al., 2005)

(Wong et al., 2006)

(J. Nishioka, unpubl.)

Half life of total dissolvable Fe is roughly the same between first and second release. This is similar to SEEDS-I and SERIES (but does not take into account dilution).

SEEDSSEEDS--IIIntegrated iron in the surface mixed layer (0-10 m)

Day 2 Day 9(Peak of phytoplankton bloom)

Day 13(End of experiment)

Soluble Fe

Colloidal FeLabile Particulate Fe

4%11%

85%

9%3%

88%

10%

42%

48%

31.6 μmol/m2

21.3 μmol/m2

13.4 μmol/m2

Soluble Fe

Colloidal Fe

Labile Particulate Fe

2.4 μmol/m2

Uptake by phytoplankton(Tsumune et al., 2005)

SERIESSERIESIntegrated iron (0-40m) in μmol m-2 during first 12 days of the experiment. Soluble (Δ), dissolved (●), labile (○), labile plus non-labile dissolved ( ), and total iron ( )

(Wong et al., 2006)

Integrated iron in the surface mixed layerSEEDSSEEDS--IIII

Day 1 Day 5

Day 8

51.9 μmol/m

2

23.8μmol/m

2

37.6μmol/m

2

50.6μmol/m

2

5.0μmol/m

2

Dissolved Fe

Particulate Fe

ParticulateFe

Colloidai Fe

Soluble Fe

ParticulateFe

Soluble Fe

Colloidai Fe

ParticulateFe

Day 23

～

1～4.2μmol/m

2

Uptake by phytoplankton

(J. Nishioka, unpublished data)Day 7

Large portion of 0.22 µm filtered ('dissolved') Fe is fine colloids.

Uptake of soluble Fe was insufficient to support the observed phytoplankton diatom growth, indicating that part of another Fe fraction, such as colloidal Fe, became bio-available Fe.

Rapid removal of added Fe into colloids next into larger particles.

The colloidal Fe is being transformed into particulate Fe, either by formation of aggregated oxyhydroxides, or through biological uptake by mixotrophic phytoplankton, or simply adsorption of colloidal Fe to the plankton cell surfaces.

The conversion of dissolved Fe to particulate form will ultimately reduce the bio-availability of Fe newly introduced into the photiczone.

0 0.1 0.2 0.3 0.4

Particulate

Fe concentration (nM)

Surface water

Surface water + Rain water(ca.5ml/L)

Surface water

Surface water

Surface water + Aerosol

Surface water + Deep water(3:1)

Colloidal

Soluble(<200kDa)l

What is the differences between artificial and natural What is the differences between artificial and natural iron enrichments? iron enrichments?

Changes in size-fractionated Fe concentrations after the addition of rain water, aerosol, or deep water to oceanic surface water (St.P)

(J. Nishioka, unpublished data)

Integrated iron in the surface mixed layerSEEDSSEEDS--IIII

Day 5

Day 8 Day 23

51.9 μmol/m

2

23.8μmol/m

2

37.6μmol/m

2

50.6μmol/m

2

Day 1

5.0μmol/m

2

Dissolved Fe

Particulate Fe

ParticulateFe

Colloidai Fe

Soluble Fe

ParticulateFe

Soluble Fe

Colloidai Fe

ParticulateFe

～

1～4.2μmol/m

2

Uptake by phytoplankton

24 h after the 2nd release Fe(II) was ~ 20% of dissolved Fe, which indicates that most of the soluble Fe was Fe(II).

Fe(II) species remained a significant fraction of dissolved Fe at the surface throughout the experiment. (M.L. Wells, unpublished data)Day 7

0

1

2

3

0 5 10 15

Day

(nM

)

Dissolved FeLigand

SERIES

10

11

12

13

0 5 10 15

Day

Log

K'

Conditional stability constant

10

11

12

13

0 2 4 6 8 10 12

Day

Log

K'

InOut

Conditional stability constant

0

1

2

3

0 5 10

Day

(nM

)

Dissolved FeLigand (In)Ligand (Out)

SEEDS-I

SEEDS

Changes in organic Fe(III)Changes in organic Fe(III)--complexing ligandscomplexing ligandsSEEDSSEEDS--I and SERIESI and SERIES

(S. Takeda, unpublished data) (R.T. Powell, personal communication)

D-FeLigand

0

1

2

3● Ligand▲ Dissolved Fe

0 5 10 15 20 25 30Days since 1st infusion

Con

cent

ratio

n (n

M)

Changes in organic Fe(III)Changes in organic Fe(III)--complexing ligandscomplexing ligandsSEEDSSEEDS--IIII

■ <200 kDa■ 200 kDa – 0.02 µm

Day 4 Day 7

73% 74%

(Y. Kondo, unpublished data)

Changes in organic Fe(III)Changes in organic Fe(III)--complexing ligandscomplexing ligandsSEEDSSEEDS--IIII

70

60

50

40

30

20

10

00 1 2 3 4 5 6

[LT] (nM),Chlorophyll a (mg/m3)

Dep

th (m

)

[LT]Chl-a

Day 7 (Y. Kondo, unpublished data)

Possible sources Possible sinks

D-FeLigand

0

1

2

3● Ligand▲ Dissolved Fe

0 5 10 15 20 25 30

Con

cent

ratio

n (n

M)

Phytoplankton(Boye & van den Berg, 2000)

Grazing(Sato et al., submitted)

Bacteria(Reid & Butler, 1993; Martinez et al., 2001)

Cell lysis(Poorvin et al., 2004)

Changes in organic Fe(III)Changes in organic Fe(III)--complexing ligandscomplexing ligandsSEEDSSEEDS--IIII

Horizontal and vertical dilutionPhotochemical degradation(Powell & Wilson-Finelli, 2003)

Decomposition by ectoenzyme

D-FeLigand

1

2

3

Con

cent

ratio

n (n

M)SEEDSSEEDS--IIII ● Ligand

▲ Dissolved Fe

IN

Control Fe 0.5 nM Fe 1 nM Fe 2 nM Fe 5 nM

■ >10 µm ■ <10 µm

Day 17 IN - 4 days incubation

Initial

0 5 10 15 20 25 30Days since 1st infusion

5

0

10

Chl

orop

hyll

a(μ

g/L)

SummarySummary

Prior to the iron infusion, dissolved (<0.2 µm) iron concentrations in the surface seawater were extremely low both in the western and eastern experimental sites, although high concentrations of acid dissolvable particulate iron were observed at the SEEDS site.

Additions of an acidified ferrous sulfate solution resulted in increases of the dissolved iron concentration to nanomolar levels and a large portion of the dissolved iron was observed in the colloidal fraction.

Most of the soluble (<200 kDa or <0.03 µm) iron was in the Fe(II) form at the surface. However, we have only limited information about the kinetics of Fe(II) behavior.

The dissolved iron concentrations decreased rapidly in the SF6-labelled patch via aggregation of colloidal iron and dilution of the patch. he half-life of dissolved iron in the surface mixed layer was estimated to be 20-70 hours.

Transformation of dissolved (mainly colloidal) iron to labile particulate (>0.2 µm) iron by aggregation and/or physical adsorption to suspended particles as well as biological utilization seemed to be a key process determining the fate of added iron.

The iron infusions enhanced production of Fe(III)-complexing organicligands and most of the dissolved iron was estimated to be complexedwith these ligands.

SummarySummary

During SEEDS-I, -II and SERIES, changes in concentration of iron showed similar patterns in spite of large differences in biological response between them.

It strongly suggest that an importance process determining biological availability of iron is its dynamics in surface water such as formation and (photo)chemical reactivity of organic iron complexes and colloidal iron, oxidation and reduction kinetics of iron, aggregation, and dissolution rate of particulate iron.