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
Oceanic emission of carbon-containing aerosols
Modeled Chlorophylls
(7.3 Tg OC a-1)
Observed Chlorophylls
(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
Ocean iron fertilisation
VOC emission
CO2 uptake
[Wingenter et al., PNAS, 2004]
Aerosol iron solubility
Soluble Iron
Acidic Gases
Insoluble Iron
Combustion Sources
Dust Sources
Human Emissions
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 ironrich dust, could become very acidic due to mixing with
sulphuric acid during the early stage of the transport.
Iron internally mixed alkaline dust
Soluble Iron
Alkaline Gases
Acidic Gases
Iron, Alkaline minerals
Dust Sources
Human Emissions
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 (%)
Fine mode
Coarse mode
Model
Observation
Iron externally mixed alkaline dust
Soluble Iron
Alkaline Gases
Acidic Gases
Insoluble Iron
Dust Sources
Human Emissions
DIF in the fine particles
Exp1
Exp2
Iron internally mixed
alkaline dust (Exp1)
Iron externally mixed
alkaline dust (Exp2)
Cruise measurement
(Chen & Siefert, 2003)
Comparison of iron fractional solubility (%)
Fine mode
Coarse mode
Iron externally mixed
alkaline dust
Iron internally mixed
alkaline dust
Observation
Aerosol supply of soluble iron
Exp1
Improved Model
Iron internally mixed
alkaline dust (Exp1)
High Nitrate
Low Chlorophyll
(HNLC)
Aerosol supply of soluble iron
Combustion
Dust
High Nitrate
Low Chlorophyll
(HNLC)
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.