Fluxes of bio-available iron to the ocean ○ Akinori Ito Research Institute for Global Change, JAMSTEC Yan Feng

1. Fluxes of bio-available iron to the ocean ○ Akinori Ito Research Institute for Global Change, JAMSTEC Yan Feng Scripps Institution of Oceanography, University of California

2. Oceanic emission of carbon-containing aerosols Modeled Chlorophylls Observed Chlorophylls (7.3 Tg OC a-1) (6.2 Tg OC a-1) [Ito and Kawamiya, GBC, 2010] High nitrate, low chlorophyll (HNLC) regions Southeast of New Zealand in the southwest Pacific sector of the Southern Ocean

3. Ocean iron fertilisation VOC emission CO2 uptake [Wingenter et al., PNAS, 2004]

4. Aerosol iron solubility Soluble Iron Acidic Gases Insoluble Iron Combustion Sources Dust Sources Human Emissions

5. Soluble iron emission Dust Combustion

6. Aerosol chemistry transport model [Ito and Feng, ACPD, 2010] • Meskhidze et al. (2005) and Solmon et al. (2009) predicted a significant deposition of soluble iron for smaller amounts of dust outflow during the transpacific transport. • Iron internally mixed alkaline dust (Exp1) • McNaughton et al. (2008) and Fairlie et al. (2009) have argued that dust does not acidify in the free troposphere except for submicron particles, because the consumption of calcite alkalinity by uptake of acid gases is slow. • (2) Iron externally mixed alkaline dust (Exp2) • Sullivan et al. (2007) found that the submicron dust particles, which were likely associated with aluminosilicate- and iron-rich dust, could become very acidic due to mixing with sulphuric acid during the early stage of the transport.

7. Iron internally mixed alkaline dust Soluble Iron Alkaline Gases Acidic Gases Iron, Alkaline minerals Dust Sources Human Emissions

8. Alkaline dust Surface air Free troposphere

9. Dissolved iron fraction (DIF) in dust Fine mode Coarse mode Cruise measurement (Chen & Siefert, 2003)

10. Comparison of iron fractional solubility (%) Fine mode Coarse mode Model Observation

11. Iron externally mixed alkaline dust Soluble Iron Alkaline Gases Acidic Gases Insoluble Iron Dust Sources Human Emissions

12. DIF in the fine particles Exp1 Iron internally mixed alkaline dust (Exp1) Exp2 Iron externally mixed alkaline dust (Exp2) Cruise measurement (Chen & Siefert, 2003)

13. Comparison of iron fractional solubility (%) Fine mode Coarse mode Iron externally mixed alkaline dust Iron internally mixed alkaline dust Observation

14. Aerosol supply of soluble iron Exp1 Iron internally mixed alkaline dust (Exp1) High Nitrate Low Chlorophyll (HNLC) Improved Model

15. Aerosol supply of soluble iron Combustion High Nitrate Low Chlorophyll (HNLC) Dust

16. Take home messages • Key flux is the amount of the soluble or bio-available iron as for the biogeochemical response to the atmospheric deposition. • We propose that smaller dust particles may yield increased amounts of soluble iron relative to larger particles due to possible variations in mixing state of alkaline dust as a non-linear function of iron-containing aerosol particle size. • The acid mobilization of iron could be important process for input of bioavailable iron to the eastern North Pacific Ocean. • As global warming has been predicted to intensify stratification and reduce vertical mixing, air pollution might have a large impact on the marine phytoplankton production in the upper ocean. It may further influence the negative feedback of climate change through the ocean uptake of carbon dioxide as well as via aerosol-cloud interaction.