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.

www.globalcarbonproject.org

Dissolved Iron (nmol kg-1)

0.0 0.5 1.0 1.50

1000

2000

3000

4000

Open ocean iron measurements made by John Martin’s group.

Adding iron to bottles of surface seawater makes plants grow.

The Vostok ice core record (Petit et al., 1999).

High dust = low CO2 = low temperature.

Can we link these processes quantitatively?

0 100 200 300 400

Tem

pera

ture

(°C

)

-8

-4

0

40 100 200 300 400

CO

2 (p

pmV

)

160

200

240

280

320

Age (kyr)

0 100 200 300 400

Dus

t (pp

m)

0

1

2

The “Iron Hypothesis”, John Martin, MLML

Adding iron to bottles of surface seawater makes plants grow.

Published by AAAS

P. W. Boyd et al., Science 315, 612 -617 (2007)

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)

SOFeX South Patch In Stations

Chlorophyll (mg m-3)

0 1 2 3 4 5

Dep

th (

m)

0

20

40

60

80

100

120

140

160

180

200

Figure 4.SOFeX Chl and PP

data from Duke - MBARI - VIMS

Day 6 (25r)Day 11 (19-33m) Day 12 (29r)Day 15 (23-44m)Day 21 (43-66m)

Pre fertilization (14-20r)

R. Barber et al.

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).

High dust = low CO2 = low temperature.

Can we link these processes quantitatively?

0 100 200 300 400

Tem

pera

ture

(°C

)

-8

-4

0

40 100 200 300 400

CO

2 (p

pmV

)

160

200

240

280

320

Age (kyr)

0 100 200 300 400

Dus

t (pp

m)

0

1

2

Global mean profiles of nitrate and pCO2 (pre-industrial)

Global mean nitrate = 23.4 uMLine if no biology or ironBiological

pump

From Gruber and Sarmiento (2002) >80% due to biology

Parekh et al. (2006)

280

480

Model

Archer et al. (2000)

Watson et al. (2000)

Bopp et al. (2003)

Parekh et al. (2006)

Pred. Atm.

CO2

5 ppm

35 ppm

15 ppm

25 ppm

Coupled atm./ocean simulations of iron fertilized, glacial cycle.

Interglacial-glacial CO2 = ~100 ppm

Fossil Fuel CO2 = ~300 ppm in 100 yr

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 ofiron 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 ofknowledge, 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”