Iron Fertilization during the Last Glacial Maximum

It has been thought that changes in the biological pump, such as iron fertilization, caused atmospheric carbon dioxide drawdown of 80-100 parts per million during the Last Glacial Maximum (LGM) (Kohfeld et al, 2005). Kohfeld et al (2005) analysed sediment records to see whether there is link between atmospheric dust deposition and CO₂ concentrations. Atmospheric dust deposition in the oceans increases the nutrient content of the oceans, and therefore more phytoplankton can grow. They expected to find increased CO₂ uptake by the oceans because of the increased dust deposition during the LGM.

The figure shown above shows the changes in CO₂ uptake for (A) stage 5a-d (80,000 to 110,000 years ago) minus Late Holocene (0-5000 years ago), (B) LGM (18,000 to 22,000 years ago) minus stage 5a-d, and (C) LGM minus Late Holcene. The dark and pale blue circles represent lower or slightly lower uptake of CO₂. The dark or pale red circles represent higher or slightly higher uptake of CO₂. White circles represent no change and grey circles represent ambiguous data. The size of the circle represents the confidence interval (Kohfeld et al, 2005). Their results showed that the CO₂ uptake by the Southern Ocean was lower during the LGM, particularly during a period of increased dust deposition (Kohfeld et al, 2005). Kohfeld et al (2005) concluded that iron fertilization from dust deposition could not be the only cause of CO₂ drawdown. 

Kohfeld, K. E., C. Le Quere, S. P. Harrison, and R. F. Anderson (2005) 'Role of Marine Biology in Glacial-Interglacial CO₂ Cycles' Science, 308, 5718, pp.74-78

DOI: 10.1126/science.1105375