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

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

Ocean iron fertilisation [Wingenter et al., PNAS, 2004] CO 2 uptake VOC emission

Aerosol iron solubility Dust SourcesHuman Emissions Insoluble Iron Acidic Gases Soluble Iron Combustion Sources

Soluble iron emission Dust Combustion

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. (1)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.

Iron internally mixed alkaline dust Iron, Alkaline minerals Acidic Gases Alkaline Gases Dust SourcesHuman Emissions Soluble Iron

Alkaline dust Surface air Free troposphere

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

Comparison of iron fractional solubility (%) Model Observation Fine modeCoarse mode

Iron externally mixed alkaline dust Acidic Gases Alkaline Gases Dust SourcesHuman Emissions Soluble Iron Insoluble Iron

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

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

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

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

 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. Take home messages