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.
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