Iron fertilization: the
biogeochemical basis for carbon
sequestration
Ken Johnson
MBARI
The biogeochemical basis for regulation of carbon
sequestration by iron:
• History
• Iron and it’s link to carbon sequestration in the
unperturbed ocean
• Iron fertilization experiments
• Global models
• Paleoceanographic evidence
• The potential for geo-engineering
Conflicting evidence makes the potential for significant
carbon sequestration unclear. But it can’t be dismissed.
-1
Dissolved Iron (nmol kg )
Open ocean iron
measurements
made by John
Martin’s group.
0.0
0
1000
2000
3000
4000
0.5
1.0
1.5
Adding iron to bottles of surface seawater makes plants grow.
The Vostok ice core
record (Petit et al., 1999).
CO2 (ppmV)
320
280
240
200
160
0
100
200
300
400
0
100
200
300
400
0
100
200
300
400
Can we link these
processes quantitatively?
0
-4
-8
2
Dust (ppm)
High dust = low CO2 = low
temperature.
Temperature (°C)
4
1
0
Age (kyr)
The “Iron Hypothesis”, John Martin, MLML
Adding iron to bottles of surface seawater makes plants grow.
Fig. 1. Annual surface mixed-layer nitrate concentrations in units of {micro}mol liter-1 (48), with
approximate site locations of FeAXs (white crosses), FeNXs (red crosses), and a joint Fe and P
enrichment study of the subtropical LNLC Atlantic Ocean (FeeP; green cross)
P. W. Boyd et al., Science 315, 612 -617 (2007)
Published by AAAS
SOFeX South Patch In Stations
0
20
40
Depth (m)
60
Pre fertilization (14-20r)
Day 6 (25r)
Day 11 (19-33m)
Day 12 (29r)
Day 15 (23-44m)
Day 21 (43-66m)
80
100
120
140
160
R. Barber et al.
180
200
0
SOFeX Chl and PP
data from
Duke - MBARI - VIMS
1
2
3
4
5
Chlorophyll (mg m-3)
Figure 4.
Kerguelen
Island
natural Fe
experiment
(Blain et al.,
Nature,
2007)
The Kerguelen “natural” experiment gives much higher C/Fe
export ratios (~200,000:1) than do “un-natural” iron addition
experiments (4,300:1).
Blain et al., 2007
The “Biological Pump” can move more CO2 into the ocean if
plants could utilize the unused stocks of nitrate in surface waters of
the ocean.
• Does the “biological pump” get stronger in glacial periods?
Ocean Biogeochemistry
The Vostok ice core
record (Petit et al., 1999).
CO2 (ppmV)
320
280
240
200
160
0
100
200
300
400
0
100
200
300
400
0
100
200
300
400
Can we link these
processes quantitatively?
0
-4
-8
2
Dust (ppm)
High dust = low CO2 = low
temperature.
Temperature (°C)
4
1
0
Age (kyr)
Global mean
profiles of
nitrate and
pCO2 (preindustrial)
Biological
pump
Global mean
nitrate =
23.4 uM
Line if no
biology or
iron
From Gruber and Sarmiento (2002) >80% due to biology
480
280
Parekh et al. (2006)
Coupled atm./ocean
simulations of iron
fertilized, glacial cycle.
Model
Pred. Atm.
CO2
Archer et
al. (2000)
5 ppm
Watson et
al. (2000)
35 ppm
Bopp et al.
15 ppm
(2003)
Parekh et
al. (2006)
25 ppm
Fossil Fuel
CO2 = ~300
ppm in 100 yr
Interglacialglacial CO2
= ~100 ppm
However, some
simulations of iron
fertilization produce
massive phytoplankton
blooms!
Z. Neufeld et al., Ocean
fertilization experiments
may inititate a large
scale phytoplankton
bloom. Geophysical
Research Letters, 29,
2002.
Paleo-estimates of
ocean C
production.
Export production
change:
Last Glacial Max –
Holocene
Red = positive
difference; Blue =
negative difference
SOLAS (Suface Ocean/Lower Atmosphere Study), Scientific Steering
Committee Position statement on large-scale ocean fertilisation
Large-scale fertilisation of the ocean is being actively promoted by various
commercial organisations as a strategy to reduce atmospheric CO2 levels.
However the current scientific evidence indicates that this will not
significantly increase carbon transfer into the deep ocean or lower
atmospheric CO2. Furthermore there may be negative impacts of
iron fertilization including dissolved oxygen depletion, altered trace gas
emissions that affect climate and air quality, changes in biodiversity, and
decreased productivity in other oceanic regions. It is then critical and
essential that robust and independent scientific verification is undertaken
before large-scale fertilisation is considered. Given our present lack of
knowledge, the judgement of the SOLAS SSC is that ocean fertilisation will
be ineffective and potentially deleterious, and should not be used as a
strategy for offsetting CO2 emissions
Volaire’s “Candide” Chapter 2
illustration by Brueghel – “All is
for the best in the best of all
possible worlds”