kohfeld dust

The role of dust in climate cycles: 

The role of dust in climate cycles Karen E. Kohfeld Max Planck Institute for Biogeochemistry, Jena, Germany SeaWIFS

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Key Questions What processes control contributions and properties of natural dust emissions? What are the spatial patterns of dust properties, and how does mineral dust in the atmosphere change through time? How does atmospheric dust interact (directly and indirectly) with the earth system?

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The global mean radiative forcing of the climate system for the year 2000, relative to 1750 (Intergovernmental Panel on Climate Change, 2001)

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(Engelstaedter et al. submitted) Where is Dust Emitted and Transported? (International Station Meteorological Climate Summary (ISMCS) version 4.0) Dust Storm Frequencies, 1970-1990s, (Visibility < 1km) days/yr 0 1 2 5 10 20 50 100 200 365 Total Ozone Mapping Satellite TOMS Aerosol Absorbing Index (1985-1990) (Figure courtesy of I. Tegen)

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Where is Dust Deposited? Dust Indicators and Records of Terrestrial and MArine Paleoenvironments (DIRTMAP) marine sediment ice core (K. E. Kohfeld, Coordinator)

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DIRTMAP Late Holocene Accumulation Rates (Kohfeld et al.,in prep) Where is Dust Deposited? Mass Accumulation Rate = Dust Fraction * Density * Sed Rate

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What Controls Changes in Dust Emissions? Wind Speed Vegetation Cover Sediment Availability Precipitation - Evaporation Climate Factors Land Surface / Geomorphological Features

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What Controls Dust Emissions? (Engelstaedter et al. submitted)

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Simulated Preferential Sources (Topographic Depressions Not Covered by Lakes or Forests) (Tegen et al. in press)

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surface winds (u3 dependence) Simulating the Dust Cycle soil moisture (surface layer undersaturated) low vegetation cover topographic preferential sources (depressions with fine particle accumulation) Sources Atmospheric Transport Wet and Dry Deposition

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Modern Observed and Simulated Emissions and Deposition (Engelstaedter et al, submitted, Tegen et al. in press)

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Glacial-Interglacial Changes in Dust Deposition Ding et al., 1994; Hovan et al., 1991; Petit et al. 1990,2001; Kohfeld and Harrison, 2001

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Ratio in LGM/Holocene Accumulation Rates

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surface wind-dependent source, circulation, deposition (Joussaume, 1990) (Genthon, 1992) Simulating the Glacial Dust Cycle + soil moisture (Joussaume, 1990) (Genthon and Armengaud, 1995) (Andersen et al., 1998) (Reader et al., 1999) ++ changed vegetation cover (Mahowald et al., 1999) (Lunt and Valdes, in press) +++ topographic preferential sources (Werner et al., in press) Comparison with Paleodata

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Modern Dust Flux = 1060 Mt/yr LGM Dust Flux =2383 Mt/yr LGM vegetation/ice cover Modern vegetation/ice cover Change in Sources and Emissions (Werner et al, in press)

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g/m2/y Ratio Changes in Dust Deposition LGM and Modern Climates (Werner et al., in press, Kohfeld et al., in prep) 2.9 2.7 2.1 2.2 4.3 2.7 20 140 800 90 6 0.1 (Mt/y)

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What is radiative impact of glacial dust? Top Of Atmosphere Forcing, LGM-Modern (Claquin et al., in press, simulation of Mahowald et al. 1999) Comparison with Changes in Other Forcings (W/m2) DUST ALBEDO (ICE) CO2 HIGH 45-90N TROPICS 15N-15S +0.3 to -0.9 -1.8 -1.8 -18.8 -2.1 to -3.3

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What is the Ocean Fertilization Impact of Glacial Dust? Total Atm CO2 drawdown = 15 ppm Change in Carbon Export (gC/m2/y) Bopp et al. subm. (15 ppm) Watson et al. 2000 (40 ppm) Archer et al., 2000 (8 ppm) (Bopp et al., submitted, simulation of Mahowald et al., 1999)

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Future Challenges: 1. Climate impact at the LGM AND modern refining radiative properties incorporating feedbacks (e.g. ocean) 2. Changing role in glacial-interglacial cycles glacial transitions? high resolution changes 3. Application to FUTURE climates anthropogenic changes? climate impact? 4. Improve Data: age models! temporal and spatial coverage resolution

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Special Thanks To: Members of the Paleodata community, especially: N. American Data: E.A. Bettis, III, D. Muhs, H. Roberts, A. Wintle Siberian Data: J. Chlachula Alaskan Data D. Muhs, T. Ager, E.A. Bettis, III, J. McGeehin, J.M. Been, J.E. Begét, M.J. Pavich, T.W. Stafford, Jr., and D. Pinney www.bgc-jena.mpg.de/bgc_prentice