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.

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 CO 2 = low temperature. Can we link these processes quantitatively?

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, (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)

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 CO 2 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 CO 2 = low temperature. Can we link these processes quantitatively?

Global mean profiles of nitrate and pCO 2 (pre- industrial) Global mean nitrate = 23.4 uM Line if no biology or iron Biological pump From Gruber and Sarmiento (2002) >80% due to biology

Parekh et al. (2006)

Model Archer et al. (2000) Watson et al. (2000) Bopp et al. (2003) Parekh et al. (2006) Pred. Atm.  CO 2 5 ppm 35 ppm 15 ppm 25 ppm Coupled atm./ocean simulations of iron fertilized, glacial cycle. Interglacial- glacial  CO 2 = ~100 ppm Fossil Fuel  CO 2 = ~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 CO 2 levels. However the current scientific evidence indicates that this will not significantly increase carbon transfer into the deep ocean or lower atmospheric CO 2. 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 CO 2 emissions

Volaire’s “Candide” Chapter 2 illustration by Brueghel – “All is for the best in the best of all possible worlds”