Does the Southern Ocean hold the key to halting climate change?
Oceanic iron fertilization is regarded by many as a possible solution to modern climate change. Recent findings presented by Raymond Pollard and colleagues, in the journal Nature, has called this into question; the carbon capturing ability of oceans may be some 15-50 times less effective than previously thought…
John Martin, the late originator of the iron fertilisation idea, once jokingly said “give me half a tanker of iron, and I’ll give you an ice age”; he adamantly believed iron could be used to cool the Earth. Since those words in the 1980s vast areas of the world’s oceans have been classified as lacking adequate iron to fuel plankton growth, so-called high nutrient-low chlorophyll (HNLC) waters. The iron fertilisation theory suggests that artificial addition of iron into these areas could create blooms of algae that would remove excess CO2 from the atmosphere because during photosynthesis this compound is used and integrated into the animals themselves. This CO2 also becomes a part of those that graze from the plankton thus filtering through the food web. Eventually the waste products and dead parts of these “carbon collectors” falls to the seafloor as marine snow and becomes ‘locked’ in the sediments. So this theory if viable in practice, would lead to blooms of phytoplankton and atmospheric carbon removed into ocean floors.
The Southern Ocean is an area that lacks bio-available iron, creating an ecosystem where rates of photosynthesis and carbon export are low. As this ocean covers a large area and has abundant nutrients it is viewed by some as a particularly important potential CO2 sink. A number of recent artificial iron enrichment experiments have been carried out in the Southern Ocean but despite these tests the ability of this ocean to lock carbon away remained poorly understood until the work by Pollard’s team. An alternative to artificial experiments is to study the role of iron in natural areas and the recently conducted research programme, known as CROZEX, during the austral summer of 2004/05 near the Crozet Islands was one such opportunity. The productivity near the two islands is highly affected by the oceanic currents that flow past it and as a result HNLC areas exist, some of which undergo iron fertilisation during the light-limited winter (areas with abundant iron), and others that do not (these areas lack iron).
The CROZEX research team found that plankton blooms at the two regions were markedly different; the one observed in the iron abundant region lasting longer, of a greater magnitude and compromising of different species of phytoplankton to the iron limited area. As a consequence the amount of carbon falling from the surface waters to the seabed was 2 to 3 times higher in the enriched area. Whilst these results support the original hypothesis of John Martin and gave carbon sequestration some 18 times greater than that found during an artificial experiment (SERIES) it was also 77 times less than another bloom that occurred from natural iron fertilisation. Applied on a global scale the findings are short of other geo-engineering estimates by 15 to 50 times.
So the work by Raymond Pollard and others has significant implications for the earlier proposals of climate change mitigation by iron fertilisation, leading some to call this form of geo-engineering “dead in the water”. Certainly more research is required, especially into the indirect effects of fertilisation – how will ecosystems react to phytoplankton blooms in previously barren environments? With commercial groups, governments, lawyers, and environmentalists ready to ‘jump’ on to the idea a clear set of regulations and directions is needed to safeguard the future; the last thing we need is an iron experiment after the carbon experiment.
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