Transcript Powerpoint presentation

The export response to ocean iron fertilizationhow to measure it and why it matters
Ken Buesseler
Woods Hole Oceanographic Institution
with help from
Michiel Rutgers van der Loeff et al.
Nicolas Savoye et al.
Matt Charette & others
Two processes needed
to impact atmospheric
CO2 via iron additions
1. Stimulate growth
- relatively well known
2. Enhance C flux to
deep-sea
- the only way to alter
climate is to isolate C
below the depth of
annual/decadal mixing
- little known, hard to
measure, key to C
credits
Discover magazine, 2003
Ocean Iron Fertilization
Key Questions
1. Will it Work?
- in terms of the efficacy of C sequestration on
time-scales of decades
(Buesseler & Boyd, Science, 2003)
- focus of this talk
2. What are the ecological consequences?
- intended and unintended
Outline
• The biological pump
- how does the natural system work?
- how do we measure particle flux?
- thorium-234
• What C flux was measured in past Fe expts?
- summary of five 234Th studies
• Other issues- scaling, verification, other methods to
access C sequestration
• Dialog is lacking
Woods Hole meeting, Sept. 26/27, 2007
The “Biological Pump”
Combined
biological
processes which
transfer organic
matter and
associated
elements to
depth
- pathway for rapid
C sequestration
Quickly remove
C from surface
ocean & atm.
- turn off bio pump
and 200 ppmv
increase atm. CO2
What fraction of primary production leaves upper ocean?
Export ratio = Particle export/primary production
(e-ratio = traps @ 150m/NPP w/14C)
Bermuda Atlantic Time-Series (BATS)
20%
80
Ranges between 2-20%
at one site
trap flux
at 150m
2%
0
No simple relationship
between production and
export
1000
primary production
(all units mg C m-2 d-1) Michaels and Knap, 1996
1995 Gordon Research Conferenceintroduced “ThE” ratio
Global range is large!
1-2% to 50%
For Fe expt’sKnowing biomass
response does not
constrain C out of the
surface
Some regional patterns
emerge using 234Th
approach for POC flux
Need to be carefulTime/space scales
& methods
POC Export:Production- timing is important
Primary Production
POC Export
export/production ratio
 varies within bloom
 varies between food webs
Time lag between onset of primary production
and POC export
For Fe fertilization- how long did we observe?
If we keep adding Fe, no/different export response
Other implications of POC vs PIC pump on C sequestration
a)
The tissue pump
b)The hard-shell pump
(calcifiers)
CO2
CO2
CO2+H2O -> CH2O+O2
photosynthesis
Ca2++2HCO3--> CaCO3+H2O+CO2
Particulate Organic
Carbon
(POC) Flux
calcification
Particulate
Inorganic Carbon
(Calcite)
(PIC) Flux
What fraction of sinking C gets to the deep-sea?
POC flux generally
decreases with depth
How well do we know this
variability and controls?
For Fe fertilization and C
sequestration, need to know
depth of winter mixing
“Martin OOC curve”
Martin et al., 1987
F = F100 (z/100)b
F100 = 1.53 (mol m-2 y-1)
b = 0.86
So if e-ratio = 10%,
Cseq-ratio = 2-5%
C flux @ depth of winter mix/prim. prod
What is range attenuation in mesopelagic?
Open = d#1
Closed = d#2
Flux 500/150m = 20% at ALOHA and 50% at K2
Faster remineralization
at ALOHA (b=1.3) vs. K2 (b=0.5) vs. Martin et al. (b=0.87)
Fz=F150(z/150)-b
Buesseler et al., Science April 2007
How would you measure C sequestration?
-Methods to estimate C fluxes at depth
-Budgets
For C (& nutrients) works best in mixed layer
big uncertainties to constrain
Radionuclides- 234Th & 228Th
-Sediment traps
New designs for improved performance
-Optical methods
Particle #, optical traps
On what time scales?
i.e. how deep?
POC flux below the depth of winter mixing (annual)
or below depth of tritium penetration (decades)
Thorium-234 approach for estimating particle export
[234Th]
*
half-life = 24.1 days
*
depth
(m)
source =
* *
*
238U
238U
parent is conservative
sinks = attachment to sinking
particles and decay
*
Calculate 234Th flux from the measured
d234Th/dt = (238U -
where l = decay rate; PTh =
diffusion
• low
234Th
234Th
234Th)
234Th
activities
* l - PTh + V
export flux; V = sum of advection &
= high flux
• need to consider non-steady state and physical transport
Thorium-234 approach for estimating POC export
(& PON, biogenic Si, PAH’s, PCB’s, metals)
POC export =
234Th
flux • [POC/234Th ]sinking particles
POC/234Th highest in surface water
POC/234Th high in blooms
(esp. diatoms/high latitudes)
issues remaining regarding best methods to collect
particles
See references by:
Buesseler, Bacon, Benitez-Nelson, Cai, Charette, Cochran, Coppola, Dunne,
Guo, Gustafsson, Hall, Langone, Miller, Moran, Murray, Pates, Roy-Barman,
Rutgers vd Loeff, Santschi, Sarin, Shimmield, Smith, Wei & more …..
JGOFS North Atlantic Bloom Experiment
Th (dpm l-1)
234
6
Nitrate
2
5
4
234
Th
3
1
2
Silicate
1
0
0
April 25
May 5
May 15
Nitrate or Silicate (M l-1)
3
May 25
Storm
from 2.2 to <1 dpm/L during
NABE
100
- this allowed for calculation of particle export
POC Export (mM m-2d-1)
234Th decreased
50
Primary Production (mM m-2d-1)
Total
Prim. Prod.
avg. upper 35m
75
POC export at 35m
25
What would
this look like for Fe fertilization
event?
25
50
0
0
April 25
May 5
May 15
May 25
FeEx-II
MLZ (m)
25
2
12
14
1.5
1.0
1.0
>1um
10
234
Th
0.5
5
>1um POC
0.0
0
>1um POC
-1
(uM l )
Total 234Th
10
NO3
5
50
100
75
50
25
0
MLZ
Prim. Prod.
POC flux
+ Fe + Fe
+ Fe
200
150
100
50
0
Prim. Prod. int.
-2
(mM C m d-1)
POC flux @25m
-2
(mM m d-1)
0-25m avg
234
234
>1um
Th Total
Th
-1
-1
NO3 (um l ) (dpm l-1)
(dpm l )
0
2.0
Day (day 1 = 1st Fe)
4
6
8
10
adapted from Bidigare et al., 1999, Paleoceanography
Surface 234Th- decrease
after 8.5 days
Flux poorly constrained
by datasingle surface point, day
12
Export follows drop of
Fv/Fm, deepening of
MLZ, drop PProd;
decrease in diatom
pigments
SOIREE
Charette & Buesseler, 2000
2.5
In-patch
Ingrowth Curve
Dissolved
Particulate
1.5
Total
238
1.0
U
Dissolved
234
Th (dpm l-1)
2.0
Particulate
0.5
0.0
Total
+Fe
0
+Fe
+Fe
+Fe
5
10
Days from Initial Infusion
Control
Station
15
Increasing 234Th though out upper 100m, both IN and OUT
Net flux approx. zero from 234Th
Traps consistent with no or low flux
Fv/Fm remained high; 13C enriched >20um diatoms not in traps;
Patch seen 30-45 days later via satellite
234
Th depletion EisenEx 0-150m
Rutgers vd Loeff et al.
cumulative depletion (Bq m -2)
800
600
400
200
0
?
-200
-5
0
5
10
15
20
25
Time since release (days)
Vertical profiles show initial condition of no/low flux
See development of 234Th depletion over 21 days
but same IN (filled symbols above) vs OUT
est C loss- 210 to 480 mM m-2
(vs. C budget loss 1000)
SOFeX- Buesseler et al. (2004, 2005)
No large decrease in surface 234Th
after 28 days in response to Fe, but…….
SOFeX- Buesseler et al. (2004, 2005)
Thorium-234 (dpm L-1)
Thorium-234 (dpm L-1)
1.4 1.6 1.8 2.0 2.2 2.4 2.6
1.4 1.6 1.8 2.0 2.2 2.4 2.6
0
5.8
10.8
15.5
17.6
21.6
21.7
21.8
23.6
23.8
26.0
27.4
238
U
20
Depth (m)
40
60
80
100
120
140
IN
6.8
8.6
12.6
19.6
24.7
24.9
26.6
238
U
OUT
Detailed times series: IN shows decrease > OUT
& loss of subsurface remineralization “excess” Th,
i.e. more efficient transport to depth
100m 234Th flux
100m POC flux
4000
25
Out
In
POC Flux (mM C m-2 d-1)
Thorium-234 Flux (dpm m-2 d-1)
5000
3000
2000
1000
0
Out
In
20
15
10
5
0
Start
End
Start
End AESOPS
Both Th & C fluxes increase IN vs OUT
Final C flux is similar to other S. Ocean blooms in this region
C flux matches C budget - 7 mM m2 d-2 avg. over 30d, 50m
(but large uncertainties in C budget- +/- 100%)
Eifex- Savoye et al. unpub
EIFEx integrated total 234Th- IN
0-100m
0-200m
2.4
234Th (dpm/l)
0-50m
Longest observations to
date w/many high
resolution profiles
2.2
2.0
1.8
1.6
0
7000
234Th flux (dpm/m2/d)
6000
5
10
15
20
25
30
35
40
in patch flux @ 100m
out patch flux @ 100m
5000
4000
3000
2000
1000
0
-1000
-2000
IN flux decreases, then
increases (and in fact
decreases again day 32)
day -1 - day 9 day 9 - day 15 day 15 - day
23
day 23 - day
28
day 28 - day
36
Hard to compare OUT
data (not a single water
mass, so different Th
model used)
Is this response due to Fe or natural conditions?
i.e. can we really compare IN vs OUT control?
What is proper integration depth?
MLZ? subsurface impacts?
Th:U during Fe fertilization (0-150m avg.)
Th:U during Fe fertilization (0-100m avg.)
1.0
Th:
0.8
234
0.8
234
Th:
238
U
238
U
1.0
0.6
0.6
SOIREE
SOIREE OUT
0
7
14
21
28
7
14
Rutgers vd Loeff et al
0.4
0
EISENEx IN 0-150m
EISENEx OUT 0-150m
35
21
28
35
Days since Fe
Th:U during Fe fertilization (0-200m avg.)
Charette & BuesselerDays since Fe
Th:U during Fe fertilization (0-50m avg.)
1.0
U
0.8
238
0.8
234
234
Th:
Th:
238
U
1.0
0.6
0.6
SOFeX IN 0-50m
SOFeX OUT 0-50m
0.4
EIFeX IN 0-200m
EIFeX OUT 0-200m
0.4
0
7
Buesseler et al
14
21
Days since Fe
28
35
0
Savoye et al
7
14
21
Days since Fe
28
35
Does iron fertilization enhance shallow carbon export
(based upon 5 expts. with 234Th results)?
FeExII
- significant POC flux (12 days; limited surface data only)
SOIREE - little/no POC flux (13 days & satellite 55 days)
EisenEx - ~20 mM/m2/d not insignficant, but
- lack of in/out differences (thorium-234; v.d. Loeff et al. unpub.)
SOFeX - enhanced POC export “in” vs “out” (subtle changes; 28 days)
- did not see crash of Fe induced (or natural) bloom
- maintained high photosynthetic efficiency
- low loss terms imply efficient recycling of iron
EIFeX - no C/Th data yet, but based upon 234Th
- catch large, but short duration export event day 28 to 32
- may have caught decrease expert early & end of export day 36
What fraction of Fe added leads to C export below 500m?
Cmax:Fe
500,000
10-50% loss; bioavailability
scavenging; dilution
Cuptake:Fe
50,000–250,000
e-ratios 2% - 50%
foodweb; diatoms
Cexport-eu:Fe
1,000-25,000 5,000-125,000
Teff 20-50%
remineralization
Cexport-500m:Fe
200-12,500 1,000-62,500
Est. SOFeX = 1000
Scaling- will it “work”?
If one “SOFeX S-patch” leads to 2000 tons C lost
at 100 m, and 1000 tons C below depths that are
ventilated on >decadal time scales, how does this
scale wrt efficacy of ocean fertilization’s impact
atmospheric CO2?
Human impact atmospheric CO2 = 6.5 x 109 tons/yr
Cexport-500m : Fe = 1000
-to remove 10% need 0.65 x 106 “SOFeX’s”
In other units1 SOFeX’s = 103 km2
so 0.65 x 106 “SOFeX’s” = 0.65 x 109 km2
= 5x higher than area So Ocean (south 50˚S)
note area entire ocean = 0.36 x 109 km2
What would be needed to increase impact of ocean
fertilization?
Higher yield per ton FeCexport-500m:Fe of 50,000 possible?
Need high efficiency biological pump
100m C flux/uptake efficiencies as high as 50%
Midwater transfer of 50% into deep ocean
- select for blooms of large diatoms?
Need enough nutrients
not just Fe, or N or P, but
Si would become limiting in So. Ocean blooms
How can we constrain biological pump & ocean C
sequestration?
Important for issues related to verification &
“additionality”
New technologies available for ocean C flux studies
Fleets of NBST’s
- already deployed n=7 & other traps in
VERTIGO study
- traps needed for transfer efficiency to deep sea
234Th surveys
- 1000’s of samples possible
- works best for upper ocean budgets
C-ARGO explorers
- optical particle methods; O2 sensors
How to solve hydrodynamic issues
Valdes and Price
2000
Lampitt et al.
• NBST solves flow/hydrodynamic problems
Carbon Explorer
Lagrangian float (souped up)
Fast Profiling
(diurnal profiles to 1000m)
Long Lived ~1 year
New: Real Time Bi-directional
Satellite Telemetry
Temperature, Salinity
Particulate Organic Carbon
Particulate Carbon Flux Index
Scattering
Unique
Ability
to
Observe
Biology
(Particulate Inorganic Carbon)
$25k per explorer = 1 ship day
Jim Bishop (UCB; LBNL)
+Fe
POC
(M)
8
4
SOFeX
“North Patch” (55 S)
High NO3 : Low Si
(22 M : 2.5 M)
2
1
0.5
ctrl
CARBON FLUX INDEX in RED
Three profiles
per day
MLD 0.05
Bishop et al. Science, 304, 417-420, 2004
Key unknowns:
- extrapolation of results/scaling
- verification of carbon sequestration
- ecological consequences
Knowns:
- ocean fertilization partial solution & not permanent
similar to many other sequestration options
- low “cost” option buys time
is it worth it?
- Oceans already taking up 100 Gt fossil fuel C
- changes are taking place wrt ocean temperature,
circulation, stratification, pH and ecology
What is needed?
Experimental data is sparse & expensive
- scaling issues
- C flux monitoring & biogeochemistry
- ecological consequences
- modeling: downstream impacts; permanence
Dialog is lacking
- not just ocean fertilization, but wrt other
C sequestration & reduction options
- truth in advertising
Our goal is to present the state of the science and discuss
remaining uncertainties regarding the impacts and efficacy
of ocean iron fertilization and issues that arise with the
commercialization of this process
http://www.whoi.edu/conference/OceanIronFertilization
Sept. 26 & 27, 2007
Per invite only (n=60) experts in science, economists, legal,
policy, commercial aspects
(US & international academia; World bank, NRDC,
Commercial interests, NSF, EPA, State Dept., NIST,
EcoSecurities, etc.)
Program: Plenary (n=11), panel (n=2), Q&A
Output- talks (video; slides) on line; 4-5 Oceanus articles;
synthesis paper; media invited
Use sediment traps to capture sinking particles
A. moored deep traps
B. drifting/tethered
shallow traps
C. neutrally buoyant free
vehicles
Marine sediment trapsthe big 3 concerns w/quantity & quality of flux
1. hydrodynamics- flow in/out/across trap and mooring motions
(particles sink 10-100x slower than horizontal currents)
2. swimmers- zooplankton feeders add/remove flux
3. sample preservation- break down of particles after collection
Ref’s- US JGOFS 1989 Knauer and Asper
Gardner, 2000
Buesseler et al. JMR, 2007 (SCOR WG #116)
Are swimmers important
(wrt C flux)?
Can we keep them out?
ALOHA Deployment #1
6
trap net
small swimmers (<350 m)
large swimmers (>350 m)
4
3
2
1
0
< 350 m > 350 m
PC flux (mM m-2 d-1)
5
150
300
500
Trap Depth (m)
Swimmer C is high- equivalent to trap flux &
changes with depth
Peterson et al., L&O
methods 2005
ssolved Si
80
b) % total organic carbon as DOC
0
100
(1)
20
40
60
80
100
How big an issue is sample preservation?
c) % total N as DON
0
20
40
60
80
d) % total P as DIP/TDP
100
0
0
0
0
500
500
500
1000
1000
1000
1500
1500
1500
20
40
(2)
(3)
2000
2000
2000
60
80
100
(3)
(4)
(5)
(6)
(4)
(5)
2500
2500
2500
(7)
(6)
(7)
3000
(8)
3000
(12)
(8)
(9)
3500
(13)
(7)
3000
(14)
3500
4000
(15)
4000
(11)
(12)
4500
(15)
4000
Antia,
2005
4500
(17)
(16)
4500
(10)
(18)
(19a)
(14)
(10)
(8)
(11)
(8)
3500
(7)
(19b)
(20a)
(20b)
Measuring post deployment concentrations of DOC in solution
vs. original concentrations as an estimate of solubilization
More commonly done in deep traps (12 mo deploy; sealed; Hg
preservatives)
(one problem is the potential swimmer contribution to DOC)
** Variable losses & element specific
& likely time dependent
D
100
100
120
C/Th variability is small at depth
(esp. on large particles)
- tight constraint on POC flux
120
start
t=10 20 end
140
POC flux (mmol m-2 d-1)
0
5
10
25
>53 m
>53 m
>1-53 m
Average >53 m
>1-53 m
Average >53 m
30
25
20
20
15
15
10
10
5
5
Depth (m)
POC/Th (mol dpm-1)
30
0
5
10
15
20
25
30
0
5
10
15
20
25
25
20
D) 50-100m OUT
>53 m
>53 m
>1-53 m
Average >53 m
>1-53 m
Average >53 m
40
60
60
80
80
100
100
120
120
140
140
Days post iron
0
5
10
15
20
25
30
0.5
1.0
1.5
2.0
60
60
80
80
100
100
120
120
140
140
0
30
0.0
40
5
25
2.0
40
20
20
1.5
25
5
15
1.0
20
10
10
0.5
bSi flux (mmol m-2 d-1)
30
10
5
20
0
15
0
15
35
15
0
10
D) OUT
bSi flux (mmol m-2 d-1)
Depth (m)
POC/Th (mol dpm-1)
C) 50-100m IN
5
40
0.0
30
0
C) IN
30
35
15
0
0
0
POC flux (mmol m-2 d-1)
0
35
B) 0-50m OUT
A) 0-50 m IN
end
140
20
35
start
0
E) IN
Days post iron
Calculate POC, bSi fluxes
POC flux/Primary Prod = 5-10% (low for So Ocean)
bSi flux/Si uptake = 6% (low for So Ocean)
F) OUT
20
Thorium-234 (dpm L1)
Thorium-234 (dpm L1)
2.4
Thorium-234 (dpm L1)
2.4
Thorium-234 (dpm L1)
2.4
2.2
2.0
1.8
0-25m
Thorium-234 flux (dpm m-2 d-1)
2.2
t-post Fe vs 0-25
Plot 1 Regr
Plot 1 Conf1
2.0
0
1000
2000
Thorium-234 flux (dpm m-2 d-1)
3000
0
1000
2000
3000
0
0
t-post Fe vs 0-25
Col 17 vs Col 18
A) IN
20
1.8
B) OUT
20
Depth (m)
0-50m
2.2
2.0
1.8
0-75m
40
40
60
60
80
80
100
100
120
120
start
2.2
t=10 20 end
start
end
140
140
2.0
POC flux (mmol m-2 d-1)
1.8
0-100m
0
2.4
2.2
2.0
1.8
0-125m
0
5
10
15
Days post iron
20
25
30
POC flux (mmol m-2 d-1)
Flux IN>OUT
Particle flux continues
to increase
C) IN
D) OUT
below “in shadow” of SOFeX
- changes in quality of material
leaving mixed layer and/or changes in
subsurface remineralization
Depth (m)
Thorium-234 (dpm L1)
2.4
Advantage of Lagrangian study- changes
w/in patch allow better calculation of
export flux
- estimate dTh/dt & physical transport
terms
5
10
15
0
5
10
15
0
0
20
20
40
40
60
60
80
80
100
100
120
120
Rutgers vd Loeff et al.
EisenEx cumulative NSS carbon export
600
mmol C
500
400
300
200
100
0
0
5
10
15
days
est C loss- 210 to 480 mM m-2
(vs. C budget loss 1000)
20
25
Final thoughts234Th provides indication of flux conditions prior to arrival
Lagrangian sampling ideal for NSS tracer application
New small volume methods (4L) allow for 4D sampling
SF6 constrains mixing/dilution & unlike stable elemental
budgets, main factor in 234Th balance is production & decay
Can extrapolate to C flux (& other elements) on particles for
mass balances
Within patch variability in 234Th will confound issues of
spatial vs. temporal variations- impt. for NSS models
Would be better with lagrangian control
See flux impacts in ML and subsurface
Can augment with traps & other flux indicators
234Th best applied in ML and upper 200-300m
Have yet to see huge export response- small % of PProd
2000
Days after infusion
- how you treat daily changes in dTh/dt impact calculated export
difficulty in separating spatial from temporal changes
- looks like large increase near end, followed by decrease
- at times of highest fluxes 200m>100m
so impact of Fe on particle export extends below patch
day 32 – day 36
-2000
day 30 – day 32
0
day 28 – day 30
day -1 day 4 - day 9 - day 11 day 15 day 20 day 23 day 28 day 30 day 32
-5000 - day 4 day 9 day 11 - day - day - day - day - day - day - day
in patch flux @15100m 20
23
28
30
32
36
-10000
in patch flux @ 200m
4000
day 23 –day 28
0
6000
day 15 – day 23
5000
8000
day 9 – day 15
10000
10000
day -1 –day 9
15000
export flux (dpm/m2/d)
234Th flux (dpm/m2/d)
20000
234Th
25000
@100m
Eifex- Savoye et al. unpub
Th:U during Fe fertilization (0-100m avg. or est)
0.8
Response variedTh:U increase (zero flux)
for SOIREE, later
EISENEx?
234
Th:
238
U
1.0
Fe added during many
different states of particle
flux
- prior to Fe, conditions
included no/low/high export
0.6
0.4
Th:U flat (constant flux)
for EIFeX first 3-4 weeks?
0.2
0
7
14
21
28
35
Days since Fe
FeExII
SOIREE
EISENEx
SOFeX
EIFeX
Sources: Bidigare et al; Charette & Buesseler
Buesseler et al; Rutgers vd Loeff et al; Savoye et al.
including unpublished data
Th:U decrease (increasing
flux)
for SOFeX; early
EISENEx; late FeExII;
after day 28 EIFeX
initial
conditions
234Th trends
comments on Fe impact
on flux
FeExII
surface
drops day 12 &
data Th:U = rebounds? n<10
0.6
surface data only not
ideal for flux estimate
SOIREE
0-100m avg increasing;
Th:U 0.6
IN=OUT, n≈20
approx zero flux during
13 day expt.
EISENEx
profiles
Th:U = 1
decreasing;
IN=OUT, n>100
late experiment flux
decrease?
SOFeX
profiles
Th:U = 0.9
decreasing IN;
“constant” OUT,
n≈200
Modest flux increase in
ML & impact on flux
below patch; didn’t
reach end of bloom
EIFeX
profiles
Th:U = 0.8
late day 28
activity decrease;
OUT variability,
n>200
May see early decrease
in flux, short high
intensity increase &
final decrease
Nature Feature of the Week- Oct. 2000
Just Add Iron
ABCnews.com, Amanda Onion 10/11/00
How algae may slow warming
By Gareth Cook, Boston Globe Staff, 10/12/2000
Helping ocean algae could beat
greenhouse effect
LONDON (Reuters), WIRE:10/11/2000
Global Warming
NPR Morning Edition- John Nielsen, 10/11/00
Iron-Fed Plankton Absorbs Greenhouse
Gases
By ANDREW C. REVKIN, NY Times, 0/12/00
Iron May Increase Gas - Eating Algae
By THE ASSOCIATED PRESS, 10/11/00
SO
F
SO eX ou
Fe t s
X i tar
ns t
SO
tar
Fe
t
SO X ou
Fe t e
X i nd
ne
nd
AE
AE SOP
SO S l
PS ow
hig
h
NA
B
NA E l
BE ow
hig
h
EQ
EQ PAC
PA lo
Ch w
Ara
igh
b
Ara ian
bia Se
n S a lo
ea w
hig
h
Thorium-234 Flux (dpm m-2 d-1)
6000
5000
4000
3000
2000
1000
0
By 18
end of SOFeX, Th
flux16 is typical of
14 blooms
other
POC Flux (mM C m-2 d-1)
100m flux
100m flux
12
10
8
6
4
2
0
Carbon flux =
234Th
particles
flux  [C/234Th]sinking
POC/234Th
•
Empirical approach
Must use site and
depth appropriate
ratio
•
• change C/Thsink impacts flux & ratios
EIFEx- Savoye et al.
IN
1.5
2.0
2.5
1.0
0
0
100
100
200
200
300
300
400
400
500
600
700
800
900
1000
424 day -1
466 day 4
238U
508 day 9
511 day 11
513 day 15
543 day 20
544 day 23
553 day 28
570 day 30
580 day 32
593 day 36
Depth (m)
Depth (m)
1.0
OUT
234Th, 238U (dpm/l)
234Th, 238U (dpm/l)
1.5
2.0
500
600
700
800
900
1000
424 day
509 day
238U
514 day
546 day
587 day
day 5
-1
10
16
25
34
2.5
SOIREE- Nodder et al
SOIREE fluxes - with Matt's POC data
180
Flux (mg m-2 d-1)
160
140
120
100
80
60
40
20
0
-
-
-
-
-
IN
IN
OUT
T=0-3
T=6-9
T=11-13
T=11-13
Days since first iron infusion
Mass (x 0.1)
POC
PSi
Th (x 0.1)
Thorium-234
(everything you need to know on one slide)
Th half-life = 24.1 days
source: produced from dissolved 238U in sea water
sinks: attachment to sinking particles & radioactive decay
234
1) Calculate export flux from 234Th activity balance
low 234Th = high flux
d234Th /dt = (238U - 234Th) l - PTh + V
where:
238U & 234Th are parent & daughter activities
d234Th/dt = non-steady state term
l = 234Th decay constant
PTh = net removal flux of particulate 234Th
V= sum of advective and diffusive fluxes
2) Calculate export flux of POC from POC/234Th ratio
POC flux = PTh  POC/234Th
where: POC/234Th is measured ratio on particles
TWO BIG QUESTIONS:
1) How well can we calculate 234Th export flux?
2) How well can we constrain POC/234Th ratio of sinking particles?
What is impact of the biological pump on C
sequestration potential as a result of Fe
addition?
Example from “SOIREE”
So. Ocean Feb. 1999
Low
C uptake* 400 tons
(1.3 tons Fe added)
C flux @100m*: 1% 2100
50% 200
C flux @500m*: 10% 0.4-1.6
(100m/500m) 40% 20-80
High
3000
tons
* Observed
from DIC &
C stocks
30
1500
* Range of
export ratios
3-12
150-600
* Range of
deep ocean flux
data
The effectiveness of Fe on C sequestration is controlled
by the type of plankton community that responds
Carbon Explorers can sample diurnal processes for a year
Hours
Measure Carbon Flux
Profile POC
Carbon
Flux
Typical Mission Profile
Carbon
Flux
First Explorers gave fundamental and new
insights to the Ocean Carbon Cycle
First 6 Robot Carbon Explorers
•
First obs. of natural iron fertilization of
marine biomass by Asian dust (Bishop et al.,
Science 298, 817-821,2002)
First obs. of purposeful iron-stimulation of
carbon biomass and carbon sedimentation in
Southern Ocean (Bishop et al. Science, 304,
417-420, 2004).
“Being there matters”