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timates of gas hydrate reserves greatly surpass total known world petroleum reserves (Juni-
per, 2001 ). Although exploitation of subsea gas hydrates is probably many decades away,
their extraction could involve large-scale disturbance of the seabed and consequent effects
on seep communities (Juniper, 2001 ) .
In addition to being inefficient, ocean fertilization has the potential to exacerbate
chemical change in the oceans. Such chemical changes may have a range of important bio-
logical consequences, including potentially negative impacts. For example, the decay of
excess phytoplankton uses oxygen, and may result in an undersaturation of oxygen in the
water column. This would have substantial impacts on mid-water and deep-sea organisms
and biodiversity. It is also likely that iron fertilization may lead to increases in production
of N 2 O, another greenhouse gas, reducing the overall efficiency of using iron fertilization
to reduce climate impacts (Secretariat of the Convention on Biological Diversity, 2009 ).
For carbon sequestration, available techniques include direct injection of CO 2 into
deep seawater, the storage of CO 2 as a liquid or a hydrate on the seafloor, and the injection
of CO 2 into geological formations below the seafloor (Schubert et al ., 2006 ; Davies et al .,
2007 ; IPCC, 2005 ) . The first two options are controversial because they are unlikely to of-
fer a permanent solution because of oceanic circulation and eventual exchanges with the
atmosphere. Today, only the third option, injection into sub-seabed geological formations,
isallowedunderthe2006amendment oftheLondonConventiononthePreventionofMar-
ine Pollution by Dumping of Wastes and Other Matter, and there are significant research
effortsinthisdirection(Schubert et al ., 2006 ) .Dependingonthevolumesinjected,measur-
able change in ocean chemistry could be expected and marine organisms near the injection
site may be harmed (Secretariat of the Convention on Biological Diversity, 2009 ). The risk
of CO 2 leakage from the deep subsurface and potential effects on deep-sea ecosystems and
biodiversity are unknown, and will need to be assessed before operations proceed (Inagaki
et al ., 2006 ) .
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