| Summary: | The Iron Hypothesis put forward by J. H. Martin (1990) is behind the development of artificial iron fertilisation as a geoengineering method which could be used to draw down anthropogenic carbon dioxide (CO2) levels. The Southern Ocean, which is rich in macronutrients but iron limited, is a focus for experiments on iron fertilisation. The past experiments (1999 to 2009) have shown that iron increases phytoplankton bloom productivity, and utilised surface water CO2, which would promote draw down of atmospheric CO2. What has not been proven to a climatically relevant extent is the export of carbon to the deep ocean, and over what time scale it could be stored for. These are key components of a CO2 removal method. Also poorly monitored as a result of increased productivity, were side effects such as ecosystem community structures, local food web impacts or the production of other greenhouse gases such as nitrous oxide (N2O). Future experiments should be conducted to understand these side effects and increase monitoring and validation of carbon export, if iron fertilisation is to be considered a legitimate method for CO2 removal.
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