Overview of Dust in the Earth System

Transcription

1 AAAS Symposium 1 Overview of Dust in the Earth System Dr. Karen E. Kohfeld School of Resource and Environmental Management, Simon Fraser University, CANADA

2 What is dust? Soil mineral fragments Quartz, feldspars, carbonate, gypsum clay minerals Kaolinite, illite, montmorillonite, chlorite, iron oxides Size range ~0.1 ~100 μm AAAS Symposium Dust 2 storm approaching Stratford, Texas. (Credit: NOAA Photo Library, Historic NWS collection)

3 Dust through the ice ages Antarctic Ice AAAS Symposium 3 Data: Jouzel et el.,2007; Siegenthaler et al., 2005; Lambert et al., 2008; Figure: Kohfeld and Ridgwell (2009).

4 Recent changes Last 10,000 years Porphyry Lake Western Interior USA Last two centuries Antarctic Peninsula Log age (yr before present) AAAS Symposium 4 (Neff et al., 2008; McConnell et al., 2007)

5 Role of dust in the earth system temperature, precipitation 2 CO fertilization land (surface properties and dust availability) wind speed precipitation anthropogenic land-use change aeolian P supply to terrestrial ecosystems LAND air (atmospheric aerosol loading) AIR CLIMATE climate optical properties sinking dust particles ocean CO sequestration 2 cloud cover, sea-ice, SSTs, ocean circulation N O and CH 2 4 ecosystem composition and CaCO production 3 aeolian iron supply to the open ocean ocean anoxia sea (marine productivity) SEA halocarbon, alkylnitrate, & DMS emissions to atmosphere AAAS Symposium 5 Modified from Jickells et al. (2005)

6 AAAS Symposium 6 LAND dust emissions

7 Dust Emission hot spots today Globally, almost 2 billion tonnes are removed from surface and transported by wind within the atmosphere Hot spots associated with lake, fluvial, and dune deposits. >60% found in North Africa, Middle East. AAAS Symposium 7 Engelstaedter and Washington (2007)

8 AAAS Symposium 8 Controls on Dust Emissions LAND SURFACE Soil moisture & properties, availability VEGETATION COVER Temperature, precipitation, CO 2 SURFACE WINDS LAND USE Cultivation Rangeland Infrastructure

9 AAAS Symposium 9 Dust Emissions, Last Ice Age (20 ka) Emissions controls different during Last Ice Age: Temperature Precipitation Glaciogenic dust CO 2 Surface winds Vegetation Availability: Glacial grinding

10 Last Ice Age Global datasets and models suggest that Ice Age deposition rates were ~3 times greater than today (globally). LGM Source areas Dust Source areas expanded due to changes in vegetation cover, winds, and glacial sources. Inferred glaciogenic sources increase ice age emission by just over 55%. AAAS Symposium 10 Mahowald et al. (2006)

11 AAAS Symposium 11 Future Changes? Natural climate changes (and resultant changes in land surface) Changes in land use Human induced changes in climate Klein Goldewijk, 2001

12 AAAS Symposium 12 Dust emissions in future? Global changes in dust emissions are model dependent MODEL YEAR CHANGE SOURCE NCAR CSM to 60% Mahowald and Luo (2003) HADCM % Tegen et al. (2004) ECHAM % Tegen et al. (2004) HADAM % Woodward et al. (2005)

13 AAAS Symposium 13 AIR radiative forcing Dust over white clouds: Warming Dust over dark ocean: Cooling

14 Ice age Top of Atmosphere Radiative Forcing Important spatial differences, but both simulations show: Globally averaged Cooling of about 1 W m 2 Largest impact observed in tropics Wm 2 Claquin et al. (2003) Average Surface T cooled by 0.85 C Due to dust AAAS Symposium 14 Mahowald et al. (2006) Wm 2

15 Direct Radiative Forcing by Total (Natural + Anthropogenic) Mineral Dust IPCC, 2001: IPCC 2007: 1.2 Wm 2 to +0.8 Wm Wm 2 to +0.5 Wm 2 Uncertainty range remains at 2 Wm 2 Main reasons for large uncertainty range: 1. Dust optical properties uncertain 2. Dust distribution: Uncertainties in emission location and fluxes, vertical transport, deposition AAAS Symposium 15 (global annual mean, re computed for natural and anthropogenic dust sources)

16 AAAS Symposium 16 Radiative Impact of dust in the Future? Similar, small change predicted, entirely different reasons, large (and differing!) regional effects Δ (W m 2 ) Process less negative TOA forcing, due to reduced dust emissions X increase in positive TOA forcing, due to increased dust emissions Study Mahowald et al. (2006) Woodward et al. (2005)

17 AAAS Symposium 17 SEA dust as a nutrient

18 Dust as a nutrient Iron fertilization in Southern Ocean Source of Fe, Si, P, N 141 E Surface Ocean Nitrate chl a (mg m ) (NASA SeaWiFS project) AAAS Symposium Conkright et al. (2004)

19 A driver of lower atmospheric pco 2, Last Ice Age Enhanced Ice Age Dust Deposition Mahowald et al. (2006) Increased Carbon Export, Lower Atm CO 2 Paleoceanographic Export Production Data LGM increase LGM decrease no change gc/m2/y AAAS Symposium Bopp et al. (2003); Kohfeld and Ridgwell (2009)

20 A moderate driver of ice age CO 2 change Iron fertilization from dust AAAS Symposium 20 Kohfeld and Ridgwell (2009)

21 Dust as an ocean fertilizer in the future? Sensitivity Study using ocean Iron cycle model 50% decrease +14 ppm 5 fold increase 8 ppm AAAS Symposium 21 (modified from Parekh et al., 2006)

22 Still open questions Iron in dust: Solubility varies by orders of magnitude (but not in models yet!) Chemical interactions with combustion products will change iron solubility? Fe cycle in ocean models Complexation with ligands poorly understood surface vs subsurface Fe contributions not well constrained Regional ecosystem impacts could be very important AAAS Symposium 22 Variable Iron Solubility Schroth et al. (2009)

23 AAAS Symposium 23 Summary Dust has varied in the past and will vary in the future! And will contribute to changes in radiative forcing and ocean biogeochemistry Knowledge of past changes in dust provided some first order answers to questions about dust cycle, but many challenges remain: emissions, transport, dust removal Spatial (and temporal) gaps in data Radiative properties of dust Chemical characteristics of dust Impacts on biogeochemistry The future is wide open: Natural climate variability and associated land surface changes Human induced changes in climate Human induced changes in the land surface

24 AAAS Symposium 24 Thanks! Organizers: Art Bettis, Paul Bertsch, Nick Lancaster, Ester Sztein Funding: Canadian NSERC Discovery, Canada Research Chair, and Canadian Fund for Infrastructure Programmes, Simon Fraser University Contributions: N. Mahowald (Cornell U.); I. Tegen (Leibniz Laboratory for Tropospheric Research); A. Ridgwell (Bristol U.); G. Winckler (LDEO)

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26 AAAS Symposium 26 Extra slides

27 The last 20 Ma Asia 2.5 Terrigenous Accumulation Rate (g/m2/y) Dust Accumulation in the Central North Pacific Ocean for the last 20 Million Years ODP Hole A ODP Site Age (1000 years) AAAS Symposium 27 (Rea et al., 1998; An et al.; 2001)

28 Modeled response of desert area to future climate change % Change in Desert Area with Time also model dependent AAAS Symposium 28 (Mahowald, 2007)

29 Global Emissions / Transport Globally, almost 2 billion tonnes are removed from surface and transported by wind within the atmosphere AAAS Symposium 29 Kohfeld and Tegen (2007) (adapted from Livingstone and Warren, 1996)

30 Anthropogenic perturbations of land surface AAAS Symposium 30 (IPCC, 2007, Ch 2)

31 Global dust deposition today AAAS Symposium 31 g/m 2 /year Jickells et al. (2005)

32 IPCC AR4: Radiative Forcing of Anthropogenic Mineral Dust Backscattering by aerosols partly offsets greenhouse gas warming Soil dust aerosols major part of atmospheric aerosol load Direct radiative effect of dust is negative Aerosol forcing remains large uncertainty AAAS Symposium 32 IPCC, 2007, Ch 2

33 AAAS Symposium 33 Direct radiative forcing of anthropogenic mineral dust IPCC, 2001: 0.6 Wm 2 to +0.4 Wm 2 Assumption: Maximally 50% from anthropogenic sources IPCC 2007: 0.3 Wm 2 to +0.1 Wm 2 Assumption: Maximally 20% from anthopogenic sources