Iron causes reduction in atmospheric carbon dioxide

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The image, taken by the NASA Space Flight Center in December of 2006, shows dust and other important aerosols being transported to the Southern Ocean. Dust is represented with orange to red colors, sea salt with blue, organic and black carbon with green to yellow, and sulfates with ash brown to white.

The longstanding hypothesis that during the last ice age, dust carried iron to Antarctica which drove plankton growth and lead to the removal of carbon dioxide has been confirmed by researchers from Princeton University and the Swiss Federal Institute of Technology in Zurich.   The research published in Science, states that iron fertilization was the cause of plankton to thrive in a region of the Southern Ocean, which ultimately lead to the removal of carbon dioxide from the atmosphere.

John Martin proposed the hypothesis that iron influenced the storage of carbon dioxide in the ice ages in 1990.  He was the first to discover that iron limits plankton growth in regions of the modern ocean.

Martinez-Garcia and his colleagues were able to confirm Marin’s hypothesis.  Previous studies that aimed to test Martin’s hypothesis established correlations of cold climate, high dust, and productivity.  However, it was not clear that the productivity was due to iron fertilization.

The researchers of this study proposed a new method, which analyzed fossils found in deep sediment of the Subantartic region.  The goal of this study was to reconstruct past changes in the measurements of dust-borne iron and productivity.  If the previous hypothesis was correct, then nitrogen would have been completely consumed by the plankton, leading lower concentrations of nitrogen in the surface waters.  In contrast, if the increases of productivity were a response to a northward shift in ocean conditions, there would have been a rise in nitrogen concentration.

The researchers were able to measure the nitrogen levels that were preserved in the shells of the fossils.  They found that the nitrogen levels indeed declined during the cold periods when iron deposition and productivity rose.  The results suggest that this iron fertilization of the Southern Ocean plankton can explain about half of the carbon dioxide decline during the ice ages.

It has been suggested that iron fertilization is one way to draw down the rising carbon dioxide in the atmosphere, which is associated with the burning of fossil fuels.  A better understanding of this phenomenon could lead to an improved prediction of the affects of climate change to the earth.

It was also noted in the study that the amount of carbon dioxide currently being pushed into the atmosphere is probably a lot more significant than the amount that is removed through iron fertilization.

 

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Journal Reference:

A. Martinez-Garcia, D. M. Sigman, H. Ren, R. F. Anderson, M. Straub, D. A. Hodell, S. L. Jaccard, T. I. Eglinton, G. H. Haug. Iron Fertilization of the Subantarctic Ocean During the Last Ice Age. Science, 2014; 343 (6177): 1347 DOI: 10.1126/science.1246848

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