Aeolian Iron Input and Ocean NitrogenCarbon Cycle

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Aeolian Iron Input and Ocean Nitrogen/Carbon
Cycle Yuan Gao Dept. of Earth and Environmental
Sciences Rutgers University Newark, NJ
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Current Project Natural Iron Fertilization in
the Ocean and Its Impacts on Ocean Nitrogen
Fixation and Carbon cycles Investigators Yuan
Gao (Rutgers) Paul Falkowski (Rutgers) Yoram
Kaufman (NASA/GSFC) Daniel Sigman
(Princeton) Michael Follows (MIT) Sponsor NASA
Ocean Biology and Biogeochemistry Program
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• Project Components
• Quantifying the variability of dust source
  functions and aeolian Fe bioavailability
• Quantifying nitrogen fixation and its
  relationship with Fe supply
• Quantifying the feedbacks between aeolian iron
  supply, nitrogen fixation and carbon
  sequestration through biogeochemical modeling.

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LAND (dust source functions)
N Cycle
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Temporal and spatial distributions of aeolian
Fe. (Gao, Y., Y. Kaufman, D. Tanré, D. Kolber,
and P. Falkowski, GRL, 2001)
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• Simulations using a GFDL SKYHI transport model
• Iron input to the ocean is largely carried out by
  wet deposition through precipitation scavenging
• (2) Annual input of dissolved Fe by
  precipitation
• 0.5 to 4x1012 g yr-1, highlighting the role of
  precipitation on natural iron fertilization in
  the ocean.

(Gao, Y., S. Fan, and J. Sarmiento, JGR, 2003)
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Quantifying aeolian Fe input to the ocean 1.
Variability associated with aeolian Fe solubility
and speciation bioavailability 2.
Variability associated with aeolian Fe source
functions dust source characterization.
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Dust Particles over the North Pacific
(Gao and Anderson, JGR, in revision)
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• Figure 2. (a) Grain of calcite in an aerosol
  sample near Xian with a small grain of calcium
  sulfate on it. (b) Grain of clay with two patches
  of aggregated calcium sulfate.
• Gao, Y and J. Anderson, JGR,
  2001.

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Fe solubility build up the acid coating to
dissolve Fe
Key processes (1) acid coating (2) Fe dissolving
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• TO address aeolian Fe solubility and speciation
• Model simulations of dissolved Fe deposition to
  the global ocean, using GFDL MOZART-2,
• 2. Heterogeneous chemistry of Fe-containing
  minerals, focusing surface chemistry,
• 3. Improvement of the in situ Fe measurements
  through the use of nano-technology,

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MOZART-2 Fe solubility (experiment 1)
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• To address aeolian Fe source functions
• Particle Size Distribution of dust in
  entrainment and effects on dust loading and
  deposition,
• Role of land use changes (desertification) on
  dust emissions, using modeling/remote sensing,
• 3. Dust source development and associated
  paleoclimate records.

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MOZART-2 Global Transport model
Table 1 Dust size distribution in entrainment
Sd1 wind-carrying dust in dAlmeida, 1987 Sd2
background dust in dAlmeida, 1987 Sd3
wind-carrying dust in dAlmeida et al., 1991
Sd4 background dust in dAlmeida et al., 1991.
Dvg mass median diameter sg,n standard
deviation of the log-normal size distribution
mn mass fraction of each mode mi mass
fraction of each size bin. Dust size bins in
radius (µm) 0.1, 1.0, 1.8, 3.0, 6.0, 10.0.
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Table 2 Dust annual budget and loading
The numbers in parentheses correspond to
particles with r lt 1µm Sd1 to Sd4 corresponds to
Experiment1 to Experiment4 respectively.
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Loess Plateau
Luochan Loess Profile (Dust accumulation record
of 2.5 million years)
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N fixation signal - low ?15N

• Measurements from N. Atlantic
• Low ?15N consistent with remineralization of
  newly fixed nitrogen
• (Daniel Sigmans work at Princeton)

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• Numerical Model
• Sub-surface DINxs maximum only possible with
  preferential remineralization of organic P
• Depth of maximum depends on relative
  remineralization rate and NP of exported organic
  material

DINxs and SigmaT same remin rate for organic N, P
DINxs and SigmaT faster remin rate for organic P
From Mick Follows of MIT
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• Ongoing work
• Overlay nitrogen isotope fractionation
• address observed nitrogen isotope signatures
• Coupling of explicit iron cycle model (Parekh et
  al., 2005 Dutkiewicz et al., 2005)
• sensitivity of N2 fixation and geochemical
  signatures to dust deposition
• Explicit denitrification and coupling of oxygen
  cycle
• explore relationships of O2, Fe and N cycles

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ACKNOWLEDGEMENT Drs. Larry Horowitz,
GFDL/NOAA Paul Ginoux, GFDL/NOAA Song-miao
Fan, GFDL/NOAA Helen Yang, Rutgers
University Profs Zhisheng An, Chinese Academy
of Sci. Min Hu, Peking University, China
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Si-Al particles
Composition (atomic fraction)
Element
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Table2 Dust flux to the HNLC regions (Tg/yr)