Iron studies during JGOFS Philip Boydijgofs.whoi.edu/Final_OSC/Boyd.pdf · Iron studies during...
Transcript of Iron studies during JGOFS Philip Boydijgofs.whoi.edu/Final_OSC/Boyd.pdf · Iron studies during...
1
Iron studies during JGOFS
Philip Boyd
• Fe and JGOFS - historical perspective
• Fe limitation and the Biota
• Biogeochemical cycling of Fe
• Reappraisal - Fe supply and the global C cycle?
IRON and CLIMATE
Marine biota play a key role in climateby regulating atmospheric CO2 levels
One means of regulation is via the BIOLOGICAL PUMP
The PUMP works mostefficiently when all of the available nutrientsare utilised
2
0.5
1.0
1.5
Fe (
mol/kg ice)
180
200
220
240
260
280
300
[CO
2] (
ppm
v)
20 40 60 80 100 120 140 160
Age (1000 yr)
Iron
CO2
The Vostok ice core provided tantalising evidence of the impact of changes in Fe supply on atmosphericCO2 (Martin, 1990)
Historicalperspective
• S. Ocean Paradox - Gran, Hart
• Trace metal chemistry and contamination (Patterson, Bruland, Martin) - improved techniques
• Shipboard Fe enrichments - Martin, de Baar
• The link to climate - Fe Hypothesis - Martin
• In situ Fe enrichments - SF6 - Watson, Duce, Liss, Martin
0.5
1.0
1.5
Fe (
mol/kg ice)
180
200
220
240
260
280
300
[CO
2] (
ppm
v)
20 40 60 80 100 120 140 160
Age (1000 yr)
Iron
CO2
3
Mahowald et al.,JGR 104,15895-15916 (1999)(g m-2 yr-1) N. Mahowald et al. (1999)
JGOFS Sites in relation to (modelled) dust deposition
Time-series
Field studies/surveys
JGOFS STUDIES IN HNLC POLAR WATERS
There were also major studies conducted in tropical (EQPAC) and subpolar (N PACIFIC) HNLC waters
4
Fe limitation and the biota
1) Shipboard Fe enrichments
2) Oceanic surveys - spatial relationships
3) Molecular and other proxies of Fe stress
4) In situ mesoscale Fe additions
Shipboard FeEnrichments
S. Ocean - Martin, de Baar…...EqPac - Coale, Price…..NE Pacific - Martin, Coale…….
5
Oceanic surveys - spatial relationships
de Baar et al. (1995) - Polar Front (Atlantic sector)Iron, chlorophyll and CO2 drawdown
500
1000
1500
2000
2500
Fla
vodo
xin
(R.U
.)
1 2
[Fe] (nmol L-1)
Sep 95May 95
Molecular and other proxies of Fe Stress
LaRoche et al. (1996)NE Pacific Flv can substitute for Fd to alleviateiron stress by reducing the cell’sFe requirements
Other proxiesFRRF - biophysical (Falkowski….)Nutrient uptake kinetics (Coale, Timmermans….)
6
In situ Fe enrichments - (10 km length-scale)
IronEx I - subducted after 3-4 days, increase in Fv/Fm
IronEx II - chlorophyll 0.3 to > 3 mg m-3, CO2 and DMS
Behrenfeld et al. (1996)
Fe limitation and mesoscale Fe enrichments in the S. Ocean
Largest inventory of unused nutrientsDeep-water formationOther limiting factors? Mixed layers, Si, Krill?
SOIREE Summer, Pacific sectorEisenex - Spring, Atlantic sectorSOFEX - Summer - Pacific sector
7
In situ experiments have yielded similar trends
Cellular chlorophyll
Cell size
Increased growth rate, C fixation, Fv/Fm………..
Altered Si:C uptake ratio’sFloristic shifts
DMSP C fixation
Fe-
bin
din
g li
gan
ds
(nM
)
0.0
0.5
1.0
1.5
2.0
2.5
3.0L1L2
A
B
Days0 2 4 6 8 10 12 14 16 18
0
2
4
6
8
10
12
Fe
FeBut there havealso been differenttrends betweentropical and polar HNLC in situexperiments
Iron-binding ligandsand their production
8
Fv/Fm
Fe uptake kineticsMesozoo #
Microzoo grazing
Nutrients
Zn, Mn, Cd
Algal sinking rates
Fe stress markers
Bacterial #
POC, PON
DOC
Optics
DMSPp
Bact prod
Phyto #
tau
1ry prod
EXPORT (Th/U, traps)
VERTICAL
PROFILES
Diffusivity
BIOGENIC GASES
OpalFe remineralizationSi production
Pigments
FeL
Redox spps
DICPFe
DFe
C and Nisotopes
Particlesize spectra
Algal respiration
Nitrous oxide
CH4
Fe`, FeLKd
In situ experimentspermit the concurrentexamination of many parameters
permittingthe construction ofFe budgets
and validation datafor models
19 pM
Dissolved FeParticulate Fe
(inorganic and detrital)
SOIREE FeSOIREE Feenriched patchenriched patch(140(140ooE, 61E, 61ooS)S)
OUTpatch
INpatch
Upper mixedUpper mixedlayer 65 mlayer 65 m
Atmospheric flux
Sinking biogenic Fe(from sediment trap data,
mostly diatom aggregates)
Patch areaPatch area56 to 200 km56 to 200 km22
Upwelling
?
0.004 pM d-1 185 pM d-1
?
Sinking non-biogenic Fe
72 pM d-1
Biogenic Fe
Diffusive flux(pre-infusion)
Eddy diffusion(post-infusion)
Four Fe infusions over 13 d(ferrous sulphate solution)
Horizontaldispersion
180 pM d-1
1073 pM 1110 pM
negligible0.1 pM d-1 0.85 pM d-1 0.72 pM d-1
58 pM
11.9 7.3
11.9 3.3
Producers Micro-zooplankton
Meso-zooplankton
?
Sinking mesozooplankton biogenic Fe
(predicted from biogenic budget)
0.79 pM d-1
6.5
25.2 pM
Fe budget from SOIREE (Bowie et al. 2001)
9
0
100
200
300
400
500
600
0 100 200 300
time from initial release (hour)
fmol
SF
6 l-1
field
model
Dissolved Fe
0
1
2
3
4
0 10 20 30 40 50 60
days from initial iron release
µm
ol m
-3
field
model
pCO2
250
300
350
400
0 10 20 30 40 50 60
µat
m
online CO2model (OUT)model (IN)
Chlorophyll a
0
1
2
3
4
5
1 11 21 31 41 51
µg
Chl
a l-1
> 20µm
< 20µm
total
Numerical modelling of SOIREE (Hannon et al., 2001)
Biogeochemical cycling of Fe
What are the relative contributions of
Atmospheric inputs
Upwelling Martin Dust deposition is dominantin the NE Pacific
de Baar; MeasuresUpwelling is the dominant driver in the S. Ocean
10
Remote-sensing (TOMS, SeaWiFs) has enabled us to monitor episodic dust events from source to sink
Other iron supply mechanisms
Ice melt (Sedwick, DiTullio)Offshore transport of Fe in eddies (Crawford, Whitney)Coastal ocean - geomorphology (Bruland, Hutchins)
Upwelling - Cromwell undercurrent (Coale, Chavez)
11
THE ‘FERROUS’ WHEEL (Kirchman, 1997)
Evidence that the microbial loop rapidly recycles Fe
Heterotrophic bacteriaHeterotrophic nanoflagellatesViruses ??
DFe (nM)
0.00 0.05 0.10 0.15 0.20 0.25 0.30D
epth
(m
)0
50
100
150
200
250
Spring 61SSummer 61S
(Measures & Vink, 2001)Dissolved Fe profiles:little decrease in DFe duringthe ‘growth season’
Relatively flat profile compared to macro-nutrients
0.5
1.0
1.5
Fe (
mol/kg ice)
180
200
220
240
260
280
300
[CO
2] (
ppm
v)
20 40 60 80 100 120 140 160
Age (1000 yr)
Iron
CO2
IRON AND THE OCEANICC CYCLE
What has been learnt during JGOFS
The Fe Hypothesis
Tenet 1 - Fe would increase phytoplankton growth
Tenet 2 - Fe would increase Csequestration ? Modelling - yes, Field data ??
12
0180
xCO
(pp
mv
)2
Age (kyr )BP
200
220
240
260
280
0.0
0.5
1.0
1.5
100 200 300 400
Dus
t (p
pm)
180
xCO
(pp
mv)
2
200
220
240
260
280
0.0
0.5
1.0
1.5
Dus
t (pp
m)
Age (kyr )BP
10 20 30 130 140 150 240 250 260 330 340
Watson et al.(2000)
SOIREECO2 drawdownSi:C uptake ratio’s
Glacialspredicted timing andmagnitudes matchrecords well
Glacial terminationsFe supply - 50%of 80 ppm CO2 change
Modeling
In situ experiments display increases in chlorophyll, but not always increases in export - WHY?
Fig.CourtesyK. Buesseler
13
A
Days
0 2 4 6 8 10 120.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7Fe watersHNLC waters
B
0 2 4 6 8 10 12
Fv/
Fm
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Eisenex(Gervais et al. 2002)
Days0 5 10 15 20
Fv/
Fm
0.20
0.25
0.30
0.35
0.40
0.45
0.50
IronEx II
SOIREE
SOFEX
Eisenex
Time-series of Photosynthetic competence provides some clues
Why the exceptional longevity of SOIREE?
INHNLC watershi Silow Felow diatomslow Chl
Fe Patch increased from 50 to 1100 km2
OUTlow Sihi Fe*hi chlahi diatoms
Stretching via horizontal flows
Mixing of water by horizontal diffusion
SOIREE vs. polar blooms
Days0 10 20 30 40 50 60
Ch
loro
ph
yll (
mg
m-3
)
0.0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
SOIREE APFZ bloom (Abbott et al., 200)BSi max flux (Honjo et al., 2000)
Few data available on the temporal evolution of polar blooms
Mooring data in the vicinity of the APFZ (60S, 170W) from 10 bio-opticalarrays provides excellent coverage
14
DOES ‘DILUTION’ OF CELLS PREVENT AGGREGATION
The Future
• Improved global/seasonal coverage of DFe profiles
• Better understanding of Fe biogeochemistry - Fe:C ratios, scavenging, remineralisation length scales
• More data to explore the links between Fe supply, bloom termination and export (and C sequestration)
• Use of SF6 approach for other manipulations - DISCO, FeCycle
• The Fe-phytoplankton link is an example of what can be achieved for other key groups - N Fixers, Calcifiers...
15
Conclusions
• During JGOFS in situ mesoscale expts have confirmed the key role that iron plays in the ocean C Cycle
• Expts have placed JGOFS field studies into context - IronEx II and EQPAC
• Iron supply results in similar trends in tropical - polar HNLC waters
• Some divergences remain - Fe-L production